principles. laboratory [Stehle & Fraser, 1935] and contains 200 pressor units and (Received 20 November 1940)

Transcription

1 .#Lil-RAFY J. Physiol. (I94I) IOO, V>6x :577.I52 I THE RATIO BETWEEN ANTIDIURETIC AND PRESSOR ACTIVITIES OF POSTERIOR PITUITARY EXTRACT SUBJECTED TO MILD HYDROLYSIS BY A. M. FRASER From the Department of Pharmacology, McGill University, Montreal (Received 2 November 194) HELLER [1939] has recently studied the effect of hydrogen-ion concentration on the stability of the antidiuretic and pressor activities of posterior pituitary extracts. He found that treating extracts at ph values ranging between -57 and 1J invariably destroyed more pressor than antidiuretic activity. On this work Heller bases his suggestion that the antidiuretic and pressor actions are due to two chemically different principles. These experiments of Heller are especially interesting because they provide the only noteworthy evidence in the literature that these actions are produced by different substances. Stehle [1934] and others had presented convincing evidence that pressor and antidiuretic actions of pituitary extract are caused by a single principle. The work presented here, while confirming the results of Heller, supplies reason to believe that this increased ratio of antidiuretic to pressor action in hydrolysed extract is not real, but only apparent. METHODS Postlobin-V, Stehle's [1933] preparation of the pressor hormone, was used in this work. The actual extract employed was prepared in this laboratory [Stehle & Fraser, 1935] and contains 2 pressor units and 1 oxytocic units per milligram. Clark & Lubs' [1916] series of buffers was used to obtain the desired ph values. The extract was dissolved in the buffer in a concentration of 5 mg./c.c. The solution was sealed in ampoules, heated in a boiling water bath for a given length of time, neutralized to Congo red and again sealed in ampoules and sterilized. PH. C. 16

2 234 A. M. FRASER A pressor assay was then carried out using the same preparation of postlobin-v, but untreated, as standard, and finally the quantities, in pressor units, of standard and treated materials, necessary to produce equal antidiuretic responses were determined by techniques described below. Pressor assay. Chloretonized dogs were employed for this purpose. The standard was dissolved in the same concentration of neutralized buffer as the treated solutions. Antidiuretic assays. Three methods were employed, viz. the riat method, an intravenous dog method and a subcutaneous dog method. The rat method of Burn [1931] was used with slight modifications. Food was removed from the cages at 5 p.m. on the evening before the experiment. The following morning, sixteen rats received 2-5 % of their body weight of water. Three hours later they received 5% of their body weight of water, following which two groups of four rats each were injected subcutaneously with the standard solution and two groups injected with the unknown solution. The standard solution was adjusted to contain the same concentration of neutralized buffer as the unknown solution. Readings of urine output were made at 15 min. intervals, until considerably more than 5 % of the volume of administered water was excreted. Two days later this procedure was repeated, but the two groups which had been given standard solution were now given the unknown preparation and vice versa with the other two groups. The results were now combined, so that the urine output for the whole group of rats was determined for each time interval and for both standard and unknown preparation. By interpolation the time reqnired for the excretion of 5% of the volume of administered water was determined for both standard and unknown. Assays were repeated until one could select a dose of the unknown which gave a 5 % end-point in about the same time as a suitable standard dose. (An attempt was made to relate dosage and antidiuretic response in the group of rats employed. The plan was to plot the relation in the form of a curve and thus enable one to determine the strength of an unknown preparation by comparing its antidiuretic response with that of a standard dose. The attempt was unsuccessful because the response to given doses was found to fluctuate considerably from week to week.) In the intravenous dog method, animals with bladder fistulae were employed. These dogs were trained to lie on a table in which a funnel was placed so that the urine was collected in graduated cylinders as it dropped from the ureteral orifices. The dogs were hydrated by stomach

3 ANTIDIURETIC AND PRESSOR ACTIVITIES 235 tubes some hours before, and again, on beginning the experiment. Intravenous injection of the solution to be assayed was made within 5 min. after the diuresis attained a rate of 2 c.c./min. Readings of urine output were made every minute. The time at which the urine flow returned to 2 c.c./min. was taken as the end-point, and time elapsing between the injection and the end-point was regarded as the antidiuretic period. Only one injection was made in each experiment. The antidiuretic period is fairly constant for a given dose of an extract in the same dog. Unknown extracts are assayed by adjusting the dose so that the antidiuretic period matches that of a suitable dose of a known extract. In the subcutaneous dog method, the animal was prepared as in the intravenous method. On beginning the experiment the administration of water was immediately followed by subcutaneous injection of the extract. The time required for the excretion of 5% of the administered water was taken as the criterion for comparison. For a given dose of extract in the same dog, this time, although somewhat variable, was found constant enough for purposes in this work. RESULTS Several samples of postlobin-v were treated at various ph values and for varying lengths of time. In all cases subsequent assay showed less pressor activity than antidiuretic activity, when the latter was measured by the rat method, but these differences were smaller than those observed by Heller. Two samples were studied in detail and the results are presented below. Preparation I was treated for 1 hr. at ph 1. A pressor assay showed that about 33 % of the pressor activity remained. The results of the antidiuretic assays appear in Table 1. The rat assay indicates that its antidiuretic action is about four times that to be expected from its pressor action. However, in the intravenous dog assay the antidiuretic activity of this preparation corresponds closely to its pressor activity. Preparation II was treated for 45 min. at ph 1. About 1 % of its original pressor activity remaiped. Antidiuretic assays are shown in Table 2. According to the rat method its antidiuretic activity is about three times greater than its pressor activity. But, again, as with Preparation I, the intravenous dog assay indicates approximately equal pressor and antidiuretic action. The subcutaneous dog method, however, although not accurate, yields a result which agrees approximately with that of the rat method. 16-2

4 236 A. M. FRASER TABLE 1 In this table the legend 'dose rat antidiuretic units' means the antidiuretic activity as determined by the rat assay, which is four times as great as the pressor assay indicates it should be. P. I = Preparation I; P-V =Postlobin-V. Rat antidiuretic asmay Exp. 1 Exp. 2 Name of extract P. I P-V P.i P-V Dose pressor units per 1 g. rat Minutes to end-point Dog antidiuretic assay (intravenou8) Wt. dog =9.5 kg. Given 25g. Purina Fox Chow dailv at 11 a.m.; 5 c.c. water daily at 5 p.m.; 3 c.c. water daily at 9.3 a.m. Experiment begun at 9.3 a.m. Exp. Exp. Exp. Exp. Exp. Exp. Exp. Exp. Exp. Exp. Exp. Exp Name of P.I P.I P.I P-V P-V P-V P.I P.I P.I P"-V P-V P-V extract Dose pressor.1.1 ' units Dose rat * antidiuretic units Antidiuretic period in min. DISCUSSION On testing the treated preparations by the rat method, one is led to believe, as was Heller, that here is rather direct evidence that the pressor and antidiuretic actions of posterior pit"uitary extract are due to different substances. However, the subsequent assays by the intravenous dog method seemed to throw doubt on such a conclusion. The results of the two methods of assay lead to speculation as to the cause of their divergence. Species difference was ruled out as the causative factor by the agreement between the results of the subcutaneous dog method and those of.the rat method. Subcutaneous method of administration of the preparations then appeared to be the chief feature necessary for the high antidiuretic value obtained. Strong support is lent to this supposition by the recent work of Noble and his collaborators [Dodds, Noble, Rinderknecht & Williams, 1937; Noble, Rinderknecht & Williams, 1939]. These investigators draw attention to the objections to subcutaneous methods for the antidiuretic assay of impure extracts. They have found that many inorganic and organic substances, when added to posterior pituitary extract, prolong the antidiuresis produced by subcutaneous injection. It seems probable, then, that hydrolytic

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6 238 A. M. FRASBR products contained in these treated preparations likewise prolong the antidiuretic action of the unchanged hormone fraction when subcutaneous injection is employed. SUMMARY AND CONCLUSIONS The work of Heller on pituitary extract was repeated and his results in finding the ratio of antidiuretic to pressor activity increased by mild hydrolysis are confirmed. But when the subcutaneous rat method of assaying antidiuretic activity was replaced by an intravenous dog method, hydrolysis was found to have no effect on the ratio between these activities. A subcutaneous dog method yielded results similar to those obtained with the rat method, proving that the cause of the discrepancy in assay results is not a species difference and suggesting that it may be associated with the route of administration. It is concluded that partial inactivation of pituitary extract by hydrolysis produces no real change in the ratio of antidiuretic and pressor activities. One may continue to assume, therefore, that the pressor hormone is responsible for the antidiuretic action of pituitary extract. REFERENCES Burn, J. H. [1931]. Quart. J. Pharm. 4, 517. Clark, W. M. & Lubs, H. A. [1916]. J. biol. Chem. 25, 479. Dodds, E. C., Noble, R. L., Rinderknecht, H. & Williams, P. C. [1937]. Lancet, 2, 39. Heller, H. [1939]. J. Phy8iol. 96, 337. Noble, R. L., Rinderknecht, H. & Williams, P. C. [1939]. J. Phy8iol. 96, 293. Stehle, R. L. [1933]. J. biol. Chem. 12, 573. Stehle, R. L. [1934]. Arch. exp. Path. Pharmak. 175, 471. Stehle, R. L. & Fraser, A. M. [1935]. J. Pharmacol. 55, 136.