*1 p.c. NaOH, 75 p.c. alcohol and 75 p.c. acetone. Further, it has been

Transcription

1 THE SECRETION OF PANCREATIC JUICE. By J. MELLANBY. (From the Physiological Laboratory, St Thomas's Hospital, London.) SINCE 1902 the secretin hypothesis of Bayliss and Starling(l) for the secretion of pancreatic juice has been generally accepted. This hypothesis states that secretin is derived from a precursor (prosecretin) by the action of acid, and prosecretin exists in that situation in which it is in a position to be acted upon by acid chyme and to discharge into the blood the substance which acts as a timely stimulus to the pancreatic cells. As a corollary to this hypothesis the secretion of pancreatic juice has been causally associated with the secretion of hydrochloric acid by the gastric mucosa. In a previous paper by Mellanby and Huggett(2) it has been shown that secretin exists in a preformed condition in the mucous membrane of the small intestine since active solutions of it may be obtained by solvents so diverse as water, 5 p.c. NaCl, *85 p.c. NaCl, *2 p.c. HCI, *1 p.c. NaOH, 75 p.c. alcohol and 75 p.c. acetone. Further, it has been shown that secretin exists in the preformed condition in the mucous membrane of the small intestine in positions far removed from any possible action of acid chyme. It is evident, therefore, that there exists no immediate causal relation between gastric acidity and pancreatic secretion. According to Bayliss and Starling the formation of secretin from prosecretin by the action of acid chyme leads, ipso facto, to its discharge into the blood and thereby acts as a timely stimulus to the pancreatic cells. But since secretin exists in a preformed condition in the intestinal mucosa it is evident, assuming that secretin is immediately responsible for the secretion of pancreatic juice, that some definite event must cause the passage of this secretin from the cells of the intestinal mucosa into the portal blood so as to evoke the secretion. A detailed investigation was made in order to determine whether the entry of acid from the stomach into the duodenum acts as the timely stimulus or whether some other alimentary stimulus causes the absorption of secretin into the blood. Experimental methods. The experiments were carried out on cats -anaesthetised by urethane (1.5 gm. per kilo of body weight). The 28-2

2 420 J. MELLANBY. pancreatic juice was collected from a cannula tied into the pancreatic duct, and the rate of secretion was determined by timing the drops. Intravenous injections were made by means of a cannula tied into the right femoral vein. Previous work. The secretion of pancreatic juice may be evoked by the introduction of numerous substances (apart from the normal foodstuffs) into the stomach or duodenum. Thus Dolinski(3) observed in a dog that a copious secretion was produced on passing 200 c.c. of *5 p.c. HCI into the stomach and that the greater the concentration of acid the greater the secretion of pancreatic juice. Further, he observed that the action of hydrochloric acid was not specific since other acids, such as lactic, phosphoric and acetic acids could produce this effect. Even water in copious quantities was effective and Bekker(4) showed that mineral waters containing a large quantity of CO2 were especially so. The introduction of acid into the stomach is generally recognised as the strongest alimentary stimulus for pancreatic activity; but many other substances have been observed to produce this action, notably fat and alcohol (Dolinski), soaps (Babkin(5)), soap into the duodenum (Fleig(6)), chloral hydrate, mustard oil, croton oil (Wertheimer and Lepage(7)). It is noteworthy that, as Bayliss and Starling showed, secretin introduced directly into the duodenum does not cause a secretion of pancreatic juice. At the beginning of this work the capacities of a large number of substances, including many of those mentioned above, to cause a secretion of pancreatic juice, when introduced directly into the duodenum, were determined. Quantities up to 50 c.c. of each of the following substances were injected into the duodenum immediately below the entrance of the pancreatic duct: secretin at different reactions (ph 6-5, 7 0 and 10.5); secretin in 75 p.c. alcohol; 1 p.c. sodium bicarbonate; fresh pancreatic juice; 10 p.c. glycerol; water; 1 p.c. suspension of mustard; 1 p.c. croton oil in olive oil; and 1 p.c. HCl. The only solution which caused a secretion of pancreatic juice was.1 p.c. HCl. The quantity secreted after the introduction of 50 c.c. of 1 p.c. HCl into the duodenum was ten drops in 10 minutes. Since the intravenous injection of 1 c.c. of an active solution of secretin may stimulate the pancreas to secrete 50 drops of juice in the course of half an hour it is evident that even.1 p.c. HCl cannot be looked upon as an adequate alimentary stimulus for the secretion of pancreatic juice. A series of experiments was also carried out in which extracts of the various parts of the alimentary canal, either alone or in conjunction with one another, were introduced into the

3 THE SECRETION OF PANCREATIC JUICE. 421 duodenum. As a matter of interest the first experiment which gave a clue to the nature of the alimentary stimulus responsible for the secretion of pancreatic juice is detailed below. 10 c.c. of a mixture containing 2 c.c. of ox bile' and 8 c.c. of a *2 p.c. HCI extract of the gastric mucosa of a cat was injected into the duodenum of an anaesthetised cat. After a latent period of 7 minutes pancreatic juice started to drop from the cannula tied into the pancreatic duct. The rate of secretion is shown in the following figures: Pancreatic juice Mins. in drops (6 c.c.) The secretion of pancreatic juice continued for 3 hours. At the end of that time 6*5 c.c. of juice had been collected. It may be observed that within the first hour 4 c.c. of pancreatic juice was secreted, in the second hour 2 c.c. of juice and in the third hour 05 c.c. of juice. As a control experiment 5 c.c. of the above mixture of bile and extract of gastric mucosa was injected directly into the blood stream. No secretion of pancreatic juice was produced, showing that the mixture did not directly stimulate secretion after absorption into the blood. The amount of pancreatic juice secreted, and the rate of secretion indicated that the essential factors which constitute the alimentary stimulus for this secretion were present in this experiment. A number of experiments were carried out to determine whether in the above mixture it was the acid or some other constituent derived from the bile or gastric mucosa that was active. As a result of these experiments it became evident that the essential factor was the introduction of bile into the duodenum, but that the efficiency of bile was intimately related to its reaction. The extract of the gastric mucosa was not essential except in so far as in the above experiment it produced that reaction which was essential to the orderly action of bile. (A) Bile as the alimentary stimulus for pancreatic secretion. The introduction of bile of an adequate reaction into the duodenum produces a copious secretion of pancreatic juice. This statement is exemplified in the following experiment: 1 Ox bile was used in all the experiments done with bile, kince a large quantity can be readily obtained and a series of comparable experiments may be made on one specimen.

4 422 J. MELLANBY. A dilute solution of bile (2 c.c. bile, 8 c.c. *85 p.c. NaCi, 05 c.c.. HCI (N)) was injected into the duodenum of a cat. The reaction of the mixture was approximately neutral (ph 6.9). After a latent period of about 5 minutes the secretion of pancreatic juice started and continued for about 2 hours. At the end of that time 5 c.c. of juice had been collected: Pancreatic juice m. s. in drops The figures illustrate a striking fact which may be observed in a successful experiment, viz. the rapid rate at which pancreatic juice is produced after the initiation of secretion. It may be seen in the above figures that after the initial latent period, juice was secreted at the rate of two drops a minute for the next 30 minutes. Even powerful extracts of secretin introduced directly into the blood rarely provoke in the cat a secretion at a greater rate than three drops a minute and at the end of about 20 minutes the secretion ceases. A series of experiments was now undertaken to determine whether bile contained an unknown substance which produced this secretion or whether the effect was due to one of its well-known constituents. (a) Bile salts. An experiment similar to that described was carried out except that a mixture of bile salts (sodium taurocholate and sodium glycocholate) was substituted for the bile. The following mixture was injected into the duodenum of a cat: 5 c.c. bile salts (5 p.c.), 5 c.c. *85 p.c. NaCl and -05 c.c. HCI (N). After a latent period of only 2 minutes the secretion of pancreatic juice started. Pancreatic juice m. S. in drops (2-9 c.c.) It is clear, therefore, that bile salts, contained in a solution of adequate reaction, injected into the duodenum stimulate the secretion of pancreatic juice. In this case the secretion was preceded by a short

5 THE SECRETION OF PANCREATIC JUICE. latent period (2 minutes) and was completed in a comparatively short period of time (45 minutes). (b) Cholic acid. The phenomenon was further analysed by determining the capacity of cholic acid to initiate the secretion of pancreatic juice. 1 p.c. cholic acid (pure) was dissolved in *85 p.c. NaCl by means of a trace of NaOH (N). After solution the fluid was brought to the acid side of neutrality by the addition of HCI (N). The amount of acid added did not precipitate the cholic acid but made the solution slightly opalescent. 10 c.c. of this 1 p.c. cholic acid solution was injected into the duodenum of a cat, with the following result: Pancreatic juice m. S. in drops (1.7 c.c.) 423 It is evident that pure cholic acid is able to act as an alimentary stimulus for the secretion of pancreatic juice, although its capacity to act thus is less than that of bile salts and these in turn less than that of pure bile. (c) Bile pigments. The injection of 4 c.c. of an alcoholic extract of bile pigment, in a concentration equal to that contained in the original bile, into the duodenum of a cat did not produce a secretion of pancreatic juice. (d) Thefunction of mucin in bile. From the above results it is evident that cholic acid is the essential constituent of bile which acts as the alimentary stimulus for the secretion of pancreatic juice, but that the action of cholic acid is profoundly modified by the state in which it exists in the bile. The combination of cholic acid with glycine and taurine is one of the modifying factors but another factor, at least as important, is the presence of the mucin in the bile. The function of mucin is illustrated by the following experimental results obtained from a cat into the duodenum of which was first injected (i) dilute bile (2 c.c. bile, 8 c.c. *85 p.c. NaCl, -05 c.c. HCI (N)), and later (ii) the same mixture but made with bile from which the mucin had been precipitated. The following figures give the rates and the quantities of juice secreted under the two conditions:

6 424 J. MELLANBY. Pancreatic juice (i) (ii) in drops h. m. h. m (i) The secretion continued for 4 hours. At the end of that time 12 c.c. of pancreatic juice had been produced. (ii) The secretion continued for 2 hours only. At the end of that time 5-4 c.c. of pancreatic juice had been produced. This experiment illustrates the long latent period which may elapse between the introduction of the bile into the duodenum and the initiation of pancreatic secretion. It further emphasises the importance of mucin in the bile in prolonging pancreatic secretion. The results indicate that mucin prevents a too rapid absorption of the bile salts and thereby prolongs the action of the bile as an alimentary stimulus for the secretion of pancreatic juice. As a subsidiary action of mucin it may be observed that the injection of bile salts into the duodenum occasionally causes heemoglobinuria, a result which is probably due to the too rapid absorption of the bile salts causing the haemolysis of red corpuscles. Probably the association of mucin with bile salts in bile prevents this toxic action. In fact mucin carries to a still further stage the effect produced by the combination of cholic acid (the essential stimulus) with glycine and taurine. (e) The influence of the ligature of the bile duct and pylorus on the secretion of pancreatic juice. The secretion of pancreatic juice after the injection of bile into the duodenum continues for a considerable period of time, in the above experiment, for instance, for 4 hours. Experimental results of this nature indicated that the continuance of secretion might be due to the occurrence of secondary events, such as the renewed entrance of bile into the duodenum from the gall bladder or a repeated acid stimulus from the stomach in consequence of the opening of the pyloric sphincter. Experiments were therefore made to test these possibilities. After the ligature of the common bile duct, 10 c.c. of dilute slightly acidified bile (2 c.c. bile, 8 c.c. *85 p.c. NaCl, -05 c.c. HCI (N)) was injected into the duodenum of a cat. A copious secretion of pancreatic juice, (i), was produced during the succeeding 3 hours, and then ceased. After the lapse of an hour the pyloric sphincter was securely tied and an

7 THE SECRETION OF PANCREATIC JUICE. additional 10 c.c. of dilute bile, (ii), similar to the above was injected into the duodenum. The results are given below: Pancreatic juice (i) (ii) in drops m. S. m. s Total juice secreted 11 c.c. 5-3 c.c. Certainly the pancreatic juice was secreted more slowly after tying the pylorus but too much importance must not be attached to this fact since the experiment had lasted 5 hours before secretion (ii) was initiated. The results offer fair evidence that the long continued secretion of pancreatic juice after the introduction of bile into the duodenum is not causally associated with the secondary passage of bile from the cat's own gall bladder into the duodenum or with the entrance of acid chyme from the cat's stomach. At the conclusion of the above experiment 1 c.c. of a solution of secretin was injected into the femoral vein. A copious secretion of pancreatic juice lasting for 20 minutes was elicited, showing that the action of secretin, when introduced directly into the blood stream, is not due to the entrance of bile into the duodenum from the cat's gall bladder-a possible action which required to be controlled by direct experiment. (f ) The minimal quantity of bile. Experiments were carried out to determine whether there was any relation between the quantity of bile injected into the intestine and the amount of pancreatic juice secreted. It was found that cats vary greatly in the amount of secretion produced after the injection of dilute bile into the duodenum. The following experiment indicates that the amount of pancreatic juice secreted in any cat is determined to some degree by the quantity and dilution of the bile which enters the intestine. 10 c.c. of the dilute bile (0.5 c.c. bile, 9-5 c.c. *85 p.c. NaCl, *02 c.c. HCI (N)) was injected into the duodenum of a cat. After the cessation of the flow of pancreatic juice 10 c.c. of a more concentrated solution of bile (5 c.c. bile, 5 c.c. *85 p.c. NaCl, *05 c.c. HCI (N)) was injected into the duodenum. The rates of secretion in the two cases are given below. The figures show that the amount of bile injected into the duodenum determines (a) the latent period, (b) the duration of secretion, and (c) the amount of pancreatic juice secreted. A similar experiment on another 425

8 426 J. MELLANBY. Stronger solution Pancreatic juice Dilute bile of bile in drops minutes minutes Total juice secreted 4-3 c.c. 12 c.c. cat showed that 2 c.c. of bile diluted to 10 c.c. produced a secretion almost identical with that caused by 5 c.c. bile diluted td 10 c.c. It is of interest to observe that the average capacity of a cat's gall bladder is approximately 2 c.c., so that dilution of this bile with the gastric contents would produce conditions of the same order as that observed in the above experiments. The influence of the reaction of bile. (B) Small changes in reaction exert a profound influence on the capacity of bile to act as the alimentary stimulus for the secretion of pancreatic juice. On the other hand, the mechanism appears to be completely free from the control of the autonomic nervous system. The importance of the reaction of bile on its capacity to act as the alimentary stimulus for the secretion of pancreatic juice was demonstrated at an early stage in the investigation. In the experiments previously described the reaction of the dilute bile injected into the duodenum was approximately neutral or just on the acidic side of neutrality. In a number of the earlier experiments, however, it was found that the injection of bile of this reaction led to no secretion of pancreatic juice. In some few cases the absence of secretion was due to the occlusion of the pancreatic duct, and in other cases the duodenum was full of gross parasites. But, excluding all these cases, it was evident that some unknown factor entered into the mechanism. A series of experiments showed that the state of digestive activity of the alimentary canal was the deciding factor. If active gastric digestion was proceeding in the cat the effective alimentary stimulus for calling out a secretion of pancreatic juice was the presence of dilute acidic bile in the duodenum; if, however, the cat was in a fasting condition, the injection of a slightly alkaline bile into the duodenum was essential. A cat fed with minced beef the previous afternoon and given milk at 7 a.m., regularly gave a large and prolonged secretion of pan-

9 THE SECRETION OF PANCREATIC JUICE. creatic juice when dilute acidic bile was injected into its duodenum after midday (urethane having been administered at about 9 a.m.). This is illustrated by the experimental results recorded on p On the other hand, a cat supplied with water only for the previous 24 hours produced no secretion of pancreatic juice when acidic or neutral bile was injected into the duodenum, but gave a copious secretion if a definitely alkaline solution of bile was first injected. The following experimental results illustrate this latter statement: Cat supplied with water only for previous 24 hours. The following mixture was injected into the duodenum: 2 c.c. bile, 7 c.c. *85 p.c. NaCl, 1 c.c. NaHCO3 (1.5 p.c.). The amount of bicarbonate added to the dilute bile corresponds to the quantity which may be assumed to be present in the arterial blood of a cat, calculated from the CO2 content. After a latent period of 26 minutes pancreatic juice was secreted at a fairly rapid rate for the next 2 hours: Pancreatic juice in drops Minutes Total juice 6-7 c.c. 427 The mechanism has been analysed by means of a considerable number of experiments. Briefly stated it has been found that in a fasting cat the optimum reaction for the dilute bile injected into the duodenum is approximately ph 7*8, and in a cat undergoing active gastric digestion, the optimum reaction is approximately ph 6-5. The results emphasise in a marked way the dependence of alimentary processes on reaction. A further series of experiments was carried out to determine how far the reaction of the bile injected into the duodenum influenced its capacity to produce a secretion of pancreatic juice after secretion had been initiated. It was found that in a fed cat, after secretion had been started by an injection of bile of adequate reaction into the duodenum, subsequent injections of bile of considerable degrees of acidity were able to evoke a further secretion of pancreatic juice. This fact is illustrated by the following experiment: 10 c.c. of dilute bile (5 c.c. bile, 5 c.c. NaCl *85 p.c., -05 c.c. HCl (N)), of a reaction ph 7, was injected into the duodenum of a fed cat. At the

10 428 J. MELLANBY. conclusion of the secretion evoked by this bile a similar dilution of bile, to which HCI was added until the reaction was ph 4 5, was now injected into the duodenum. The respective rates of secretion were as follows: Dilute bile (ph 7) Dilute bile (ph 4.5) Pancreatic juice (i) (ii) in drops h. m. h. m Total juice 12 cc. 7 c.c. It may be observed that (a) the second injection of acidic bile stimulated the secretion of a considerable quantity of pancreatic juice, although the total quantity was less than that secreted under the stimulus of the neutral bile, and (b) the initial rate of secretion with the acidic bile was greater than that produced after the injection of the neutral bile. Similar results may be observed with the fasting animal. Although in the cat with the resting alimentary canal, the bile injected into the duodenum which initiates the secretion of pancreatic juice must be on the alkaline side of neutrality, subsequent injections of bile may be definitely acidic and yet cause a renewed secretion of pancreatic juice. This statement is illustrated in the following experimental results. Column 1 shows the rate of secretion of pancreatic juice secreted after the injection of dilute alkaline bile into the duodenum (2 c.c. ox bile, 7 c.c. NaCl, 85 p.c. and 1 c.c. NaHCO3 15 p.c.). Column 2 shows the rate of secretion produced in the same cat by the injection of dilute acidic bile into the duodenum after secretion 1 had ceased (2 c.c. ox bile, 8 c.c. NaCl *85 p.c., 1 c.c. HCl (N)): Pancreatic juice (i) (ii) in drops minutes minutes The similarity between the rates of secretion in the two cases is remarkable and indicates that the activity of the intestinal epithelium in passing secretin into the portal blood is determined by its own

11 THE SECRETION OF PANCREATIC JUICE. mechanism rather than by the relation of the reaction of the intestinal contents to the reaction of the blood. These and many similar experiments indicate that although the bile injected into the alimentary canal must be of an adequate reaction, depending on the state of digestive activity of the animal, to initiate the secretion of pancreatic juice, yet the secretory mechanism having been set in motion, subsequent injections of bile may vary widely in reaction and yet continue to act as adequate stimuli for the secretion of pancreatic juice. (C) The mechanism of the alimentary action of bile. The mechanism whereby the introduction of bile into the duodenum leads to a secretion of pancreatic juice was investigated. The experimental analysis indicated that the absorption of bile salts from the intestine determines the passage of secretin from the cells of the mucous membrane into the blood and thereby to the pancreas. (a) The effects of introducing cholic acid into the duodenum and ileum respectively. Cholic acid was dissolved in dilute NaOH and then made slightly acidic by the addition of HCl. The acidity was such as to render the solution slightly opalescent but not to cause precipitation. Columns (i) and (ii) show respectively the rates of secretion after the injection of 10 c.c. of 1 p.c. cholic acid solution into the duodenum and ileum: Pancreatic juice (i) (ii) in drops m. S. m. s Thus the injection of 10 c.c. of cholic acid (1 p.c.) into the duodenum produced 2 c.c. of pancreatic juice in 1 hour; a similar quantity injected into the ileum of the same animal produced one drop of pancreatic juice. The cholic acid appeared to be absorbed in both cases. Since secretin is present in maximal concentration in the mucous membrane of the duodenum and practically absent from the ileum, the result offers strong evidence in favour of the hypothesis that the absorption of bile acids from the intestine causes the passage of secretin into the portal blood and hence leads to the secretion of pancreatic juice. Confirmatory evidence in favour of this hypothesis was obtained from experiments in which the effects were determined of vagal and sympathetic paralysis

12 430 J. MELLANBY. on the secretion of pancreatic juice produced by (1) the injection of secretin into the blood, and (2) the injection of bile into the duodenum. (b) Paralysis of the vagus. In a previous paper(8) the effect of paralysis of the vagus on the secretion of pancreatic juice produced by the injection of secretin directly into the blood has been dealt with in detail. Briefly stated, paralysis of the vagus by atropine diminishes the enzyme content but increases the rate of secretion of pancreatic juice produced by the injection of secretin into the blood. The following experimental results show the effects produced by atropine injected into the blood stream during the secretion of pancreatic juice subsequent to the injection of bile into the duodenum. 10 c.c. of dilute bile (2 c.c. bile, 8 c.c. *85 p.c. NaCl, -05 c.c. HCI (N)) was injected into the duodenum. After a latent period of 5 minutes pancreatic juice was rapidly secreted. After the secretion of 4 c.c. of juice, 5 mg. of atropine was injected into the femoral vein. As a result of this procedure the rate of secretion was accelerated by one-third: Pancreatic juice in drops m. S. (i) Before injection of atropine (ii) After injection ( The acceleration of the rate of secretion of pancreatic juice produced by atropine persists for.a considerable period of time-in this experiment for more than 30 minutes. The duration of the acceleration indicates that atropine not only dilates the pancreatic ducts by paralysis of the vagal endings in the smooth muscle surrounding them (Anrep(9)) but also affects the glandular tissue of the pancreas. As a confirmatory experiment the relative rates of secretion of pancreatic juice produced by two separate injections of dilute bile into the duodenum, (i) before, and (ii) after the intravenous injection of 10 mg. of atropine were determined: Pancreatic juice (i) (ii) in drops m. S. m. S

13 THE SECRETION OF PANCREATIC JUICE. 431 The acceleration of pancreatic secretion produced after the intravenous injection of atropine by bile in the duodenum is particularly marked in this experiment. A control experiment in which atropine. was injected directly into the intestine showed that the effect was not due to a local action of atropine on the intestinal mucosa facilitating the absorption of the injected bile into the blood stream from the duodenum. (c) Paralysis of the sympathetic. An experiment similar to the above was carried out before and after the paralysis of the secretory fibres of the sympathetic by the intravenous injection of 1 mg. of ergotamine tartrate. 10 c.c. of dilute bile (2 c.c. bile, 8 c.c. NaCl *85 p.c.,.05 c.c. HCI (N)) was injected into the duodenum. Then 20 minutes after the initiation of pancreatic secretion 1 mg. of ergotamine tartrate was injected into the femoral vein: Pancreatic juice in drops m. s (i) Before injection of ergotamine ( j (ii) After injection ( t It is evident that paralysis of the sympathetic secretory fibres by ergotamine tartrate has no effect on the secretion of pancreatic juice produced after the injection of bile into the duodenum. The result is similar to that observed after the intravenous injection of ergotamine tartrate on the secretion of pancreatic juice produced by the intravenous injection of secretin. It is a matter of considerable interest that the capacity of bile to act as an alimentary stimulus for the secretion of pancreatic juice is not diminished by paralysis of the vagus or the motor fibres of the sympathetic. The facts indicate that the absorption of bile salts from the intestine and the passage of secretin from the cells of the mucosa into the portal blood are independent of extraneous nervous influences to at least as great an extent as the action of secretin, injected directly into the blood, on the cells of the pancreas. (D) The cessation of secretion. In the previous pages the factors determining the capacity of bile to act as an adequate alimentary stimulus for the secretion of pancreatic

14 432 J. MELLANBY. juice have been discussed. The processes which determine the duration of pancreatic secretion after the injection of a given quantity of bile into the duodenum have been subjected to experimental analysis. Four possible causes have been investigated, (a) the exhaustion of secretin from the intestinal mucosa, (b) the presence of pancreatic juice in the intestine, (c) the rate of absorption of bile salts, and (d) the limited distribution of secretin. (a) The amount of secretin contained in the intestinal mucosa is so large that there appears to be no diminution in its content after the injection of dilute bile into the intestine and the consequent production of a large quantity of pancreatic juice. Thus the mucous membrane of a cat which had secreted 21 c.c. of pancreatic juice after the injection of dilute bile into the duodenum was extracted with absolute alcohol in the usual way. This secretin extract (1 c.c.) injected into the femoral vein of an experimental cat stimulated the pancreas to secrete 4 c.c. of juice in 25 minutes. In fact a copious pancreatic secretion produced by the injection of bile into the duodenum appeared to be associated with the presence of an unusually large quantity of secretin in the duodenal mucous membrane. (b) The influence of reaction on the capacity of bile to act as an alimentary stimulus for pancreatic secretion indicated that the cumulative action of the alkali contained in the pancreatic juice secreted into the duodenum would automatically stop the stimulating action of the bile. In order to examine this hypothesis, dilute bile was injected into the duodenum of a cat. A copious secretion of pancreatic juice was produced. At the end of 1 hour the total juice secreted from the pancreatic cannula was reinjected into the duodenum and the effect of this procedure on the flow of pancreatic juice was observed. The following figures show the rate of secretion (i) before, and (ii) after the injection into the duodenum of the secreted pancreatic juice: Pancreatic juice in drops Minutes f () 1lOO (ii) The pancreas secreted at a slightly slower rate after the injection of the pancreatic juice into the duodenum, but as the secretion continued for a further period of an hour (at the end of which time the total juice secreted during the experiment amounted to 8-6 c.c.) it is evident that

15 THE SECRETION OF PANCREATIC JUICE. the alimentary mechanism is not stopped by the entrance of the secreted pancreatic juice into the duodenum. (c) The absorption of the bile is not completed in the upper small intestine. After the cessation of pancreatic secretion, produced by the injection of bile into the duodenum, demonstrable quantities of bile salts may be found not only in the ileum but also in the large intestine. Therefore the early absorption of bile salts cannot be responsible for the cessation of pancreatic secretion. (d) It is probable that the action of bile as the alimentary stimulus for the secretion of pancreatic juice is limited by the distribution of secretin in the intestinal mucosa. Thus in the case of the herbivorous animals, e.g. the goat, the distribution of secretin extends to the large intestine, as the following figures show: Small intestine (upper third) units of secretin (middle third) (lower third) Large intestine In the case of the pig the distribution of secretin is limited to the first 10 feet of the small intestine, thus: Distance from pyloric sphincter in feet Units of secretin In the cat practically the whole of the secretin is contained in a few inches of duodenum, the jejunum and ileum containing only small quantities: Duodenum units of secretin Jejunum Ileum , It is evident therefore that wide differences in the distribution of secretin occur in different animals. The extension of secretin into the mucous membrane of the large intestine in the goat would appear to be correlated with the continuous digestion which occurs in herbivorous animals. The experimental analysis of the question indicates that the duration PH. LXI. 29

16 434 J. MELLANBY. of secretion of pancreatic juice after the entry of bile into the duodenum is determined by the distribution of secretin in the intestine rather than by changes of reaction, absence of bile salts or exhaustion of secretin from the cells of the intestinal mucosa. On this hypothesis it is evident that a large secretion of pancreatic juice might be evoked by a diminished peristalsis of the alimentary canal or the entrance of a large quantity of bile into the duodenum. In this connection it is clear that the volume of fluid in which the bile is contained is of some importance. Thus a well-marked secretion of pancreatic juice may be produced after the injection into the duodenum of *5 c.c. of bile diluted to 10 c.c., whereas the same quantity of bile diluted to 4 c.c. produces a small secretion only. This effect of volume on the efficacy of a given quantity of bile injected into the duodenum on the rate of pancreatic secretion has not, however, been worked out in detail. SUMMARY. (1) The introduction of bile of an adequate reaction into the duodenum of a cat causes a copious secretion of pancreatic juice. (2) The active substance present in bile is cholic acid, but the activity of cholic acid is profoundly modified by (a) its association with taurine and glycine, and (b) the presence of mucin in the bile. (3) The optimum reaction of bile as a pancreatic stimulant varies with the state of digestion of the animal. In a fasting cat the optimum reaction is ph 7-8; in a cat in which gastric digestion is actively proceeding the optimum reaction is ph 6-5. (4) Paralysis of the vagus by the intravenous injection of atropine or paralysis of the motor side of the sympathetic system by the intravenous injection of ergotamine does not diminish the capacity of bile to act as an alimentary stimulus for the secretion of pancreatic juice. (5) The duration of pancreatic secretion after the injection of a given quantity of bile into the duodenum is determined mainly by the distribution of secretin in the intestinal mucosa. (6) The immediate stimulus for the secretion of pancreatic juice is secretin. Secretin contained in the cells of the intestinal mucosa is carried into the portal blood associated with the bile salts contained in the fluid absorbed from the intestine. (7) The facts offer an adequate basis for the appreciation of the severe digestive disturbances which occur in catarrhal jaundice. The expenses of this work were defrayed by a grant from the Government Grant Committee of the Royal Society.

17 THE SECRETION OF PANCREATIC JUICE. 435 REFERENCES. 1. Bayliss and Starling. This Journ. 28. p Mellanby and Huggett. Ibid. 61. p Dolinski. Quoted from Babkin-Die iiussere Sekretion der Verdauungsdriisen. Berlin, Bekker. Ibid. 5. Babkin. Ibid. 6. Fleig. C. R. de la Soc. de Biol. 55. p Wertheimer and Lepage. Journ. de Physiol. 3. p Mellanby. This Journ. 60. p Anrep. Ibid. 50. p