THE DIABETOGENIC HORMONE OF THE PITUITARY GLAND

Transcription

1 VOL. XIII, i JANUARY, 96 THE DIABETOGENIC HORMONE OF THE PITUITARY GLAND BY DAVID SLOME. (From the Department of Social Biology, the University of London, and the Buckston Browne Research Farm, Royal College of Surgeons of England.) (Received June 6, 95.) (With Two Text-figures.) NUMEROUS clinical observations have provided indirect evidence that the pituitary gland exercises a significant effect on carbohydrate metabolism. Glycosuria is frequently a part of the acromegalic syndrome (Borchardt, 98; Goetsch, Cushing and Jacobson, 9). Houssay (9) and Eidelsberg (9) have emphasised that cases of acromegaly often manifest the symptoms and signs of diabetes. The participation of the pituitary gland in the control of carbohydrate metabolism has been the subject of a most searching investigation by Houssay and his collaborators (Houssay and Biasotti, 9a, b, c), who have conclusively established that the hyperglycaemia, glycosuria, acidosis and other diabetic manifestations, which follow excision of the pancreas in the toad, do not develop or develop only in a very mild degree if the animal has previously been hypophysectomised. This result was attributed to the secretion of a " diabetogenic " substance by the pituitary gland. Since it is possible in Amphibia to remove the anterior lobe of the pituitary gland alone, Houssay was able to demonstrate unequivocally that this "diabetogenic" substance is elaborated in the anterior lobe alone. Subsequent work by Houssay's school was carried out on dogs; but, as it is not possible in the dog to remove the separate morphological portions of the pituitary gland, the investigation was necessarily confined to indirect confirmation of the basic results obtained in amphibian experiments. Most of the experiments in this communication are based on the South African clawed toad (Xettopus laevis) and were reported at a meeting of the Society of Experimental Biology in December 9. More recently a fresh supply of animals has made it possible to carry the enquiry to a further stage. TECHNIQUE AND METHODS. Hypophysectomy was carried out by the buccal route described by Hogben (9). Using this approach, it is possible in Xenopus to remove () the anterior lobe, () the posterior lobe, and () the entire gland. The clear-cut effects on the chromatic function exhibited by toads after each of these provide independent confirmation of the success of the operation. Pancreatectomy can be performed in a few minutes with the aid of an electric cautery without the loss of a drop of blood. IBB-Xl.li I

2 DAVID SLOME was estimated in o-i c.c. by the micro-colorimetric method described by Folin and Malmross (99). The accuracy of the method was tested by estimating the in a sample of blood and in a similar sample to which a minute known quantity of was added. The added was almost completely recovered. For the withdrawal of blood the frog was pithed and the heart exposed by removal of the sternum and opening of the pericardium. The exterior of the heart was dried with absorbent cottonwool and the frog held in a horizontal position. The pendent heart was opened with scissors and the blood collected in a small crucible. About -5- c.c. of blood was thus obtained. THE NORMAL BLOOD-SUGAR LEVEL. It has now been firmly established that pigmentary effector activity in Amphibia is a delicate indicator of pituitary secretion. Xenopus laevis possesses a very striking capacity for colour change, predominantly determined by light reflected from the surface which occupies the field of vision, influenced only to a slight extent by temperature and ordinarily unaffected by humidity. In a white container the melanophores are fully contracted in light and the animal is pale. In a black container they are expanded and the animal is dark. In darkness the melanophores are partially expanded and the animal assumes an intermediate hue. Total removal of the eyes or section of both optic nerves produces an intermediate condition of the melanophores. Complete hypophysectomy or removal of the posterior lobe alone results in loss of the normal black "background" response. The animals remain permanently an intensely pale colour. Removal of the anterior lobe, which also involves removal of the pars tuberalis, results in a permanent expansion of the melanophores, i.e. the normal response to a white " background " is lost. Colour response in Xenopus laevis and in all probability in other Amphibia is determined by two endocrine agencies. One of these (the " melanophore stimulant") is elaborated in the posterior lobe of the Table I. Normal pale toads Normal dark toads Body weight in gm. Bodyweight in gm i V i' + a 6* r I- 4 S- 7 Average blood sugar 5^4 ± ' 'i! O-O i I9-5 7 Average blood sugar 7'O ±

3 The Diabetogenic Hormone of the Pituitary Gland pituitary gland. The other endocrine agency is directly or indirectly associated with the pars anterior or pars tuberalis of the gland. In these experiments all animals from which the whole gland was removed showed characteristic pallor and all animals from which the anterior lobe (plus pars tuberalis) was removed showed maximum darkening of the skin. The blood sugar of a series of twelve animals on a white background and of a similar series on a black background was first determined. The results are shown in Table I. A further series of blood- determinations were carried out. The mean value for thirty-two normal pale toads was 5-6 mg. per and for twenty-one normal dark toads, 5- mg. per Thus the normal fasting level of the blood of toads kept on a black background is significantly higher than that of toads on a white background. THE EFFECT OF HYPOPHYSECTOMY ON THE BLOOD SUGAR. The blood-sugar level in twelve toads after total hypophysectomy and in a similar number after removal of the anterior lobe alone is set out in Table II. Including a further series of animals the mean value for twenty-two totally hypophysectomised toads was -8 and for forty-one toads after removal of the anterior lobe alone - These values are only slightly below those for the Table II. Total hypophysectomy Removal of anterior lobe* 8 <J io Body weight in gm O-O «7-4 I'O 6 - Average blood -8 ±o-66 ±66 4 S V V + <? Seven months after operation. Body weight 7 7'S ' i8-4-9 Average blood ^5 ± -55 Table III. Mean values of blood. Toad Normal pale Normal dark Total hypophysectomy Removal of anterior lobe Number of individuals

4 4 DAVID SLOME normal pale controls. The blood sugar of well-fed hypophysectomised animals is within normal limits. If, however, the animals are fasting, a fatal hypoglycaemia rapidly develops. EFFECT OF HYPOPHYSECTOMY ON SUGAR TOLERANCE. Zwarenstein and Bosman (9) have demonstrated an increased tolerance for in the hypophysectomised toad. The blood sugar of a series of normal and hypophysectomised animals was determined at regular intervals after the injection into the dorsal lymph sac of c.c. of a per cent, aqueous solution of per gm. of body weight. A series of animals were used to determine each point on the curve. The results shown graphically in Fig. show the manifest increased tolerance of the hypophysectomised animal. B Normal A Hypopliysectoinieed Fig.. Glucose tolerance curve. EFFECTS OF PANCREATECTOMY ON THE NORMAL AND HYPOPHYSECTOMISED TOAD. Excision of the pancreas in the normal toad results in an intense hyperglycaemia. The blood sugar rises rapidly, attaining a level of hours after operation. Most of the animals pass in the urine. Eventually a state of coma develops, frequently with convulsive seizures, and death ensues generally on the third or fourth day after pancreatectomy. A few toads survived until the sixth day. When pancreatectomy is performed on the previously hypophysectomised toad, this immediate rise of blood sugar fails to develop. Twenty-four hours after operation the blood sugar has only risen to an average value of 45 Six days after operation the blood sugar of a series of animals was only 6-5 At this time the normal controls were all dead. Toads with complete removal of pancreas and pituitary were alive 4 days after operation.

5 The Diabetogenic Hormone of the Pituitary Gland 5 Removal of the pancreas from toads from which only the anterior lobe (i.e. pars anterior + pars tuberalis) of the pituitary had previously been ablated is also not followed by the intense diabetes which develops after pancreatectomy. In a series of five such animals the mean blood sugar was 44-4 hours after pancreatectomy. The effect of pancreatectomy on the blood sugar of the hypophysectomised and normal toad is illustrated graphically in Fig.. The removal of the pituitary gland or of the anterior lobe alone therefore prevents or considerably modifies the development of the intense diabetes consequent upon experimental extirpation of the pancreas. - - S 8-6- S. 4- " - p loo- & 8" n r I a Q Normal A HypqphyBectomised i i i i i Hours Fig.. Effect of pancreatectomy. DISCUSSION. The results of this investigation confirm the findings of Houssay and his coworkers. Removal of the pancreas in the hypophysectomised toad is not accompanied by the production of diabetes. This effect is dependent upon the operation of a "diabetogenic" hormone elaborated in the anterior lobe of the pituitary gland. Collateral evidence for the existence of such a "diabetogenic " substance is provided by the experiments of Kepinov and Dutailis (9). These workers demonstrated that there is present in the blood of a diabetic animal a substance capable of producing hyperglycaemia on injection into a normal animal. Since the profound disturbances of metabolism associated with experimental pancreatic diabetes are ameliorated by extirpation of the anterior lobe of the pituitary gland, this hormone must exercise its effect not by controlling the secretion of the islets of Langerhans or neutralising insulin, but by acting at some other point in carbohydrate metabolism. Insulin in the normal animal is necessary for the formation of glycogen in the liver and tissues A

6 6 DAVID SLOME and it accelerates the utilisation of in the tissues. Furthermore it is believed to check the formation of from protein sources in the liver. Pancreatectomy therefore effects a rise of blood by removing this inhibition of formation from protein sources and by preventing the utilisation of by the tissues. The abnormally high blood sugar of the starved diabetic animal is derived from protein and fat sources. Animo-acids derived from endogenous protein are converted quantitatively to. It is at this point that the diabetogenic hormone may exercise its effect. Removal of the anterior lobe of the pituitary effects a considerable reduction of the blood sugar of the starved diabetic toad. Thus a probable hypothesis, as postulated by Houssay, is that the hormone elaborated in the anterior lobe catalyses the formation in the liver of from endogenous protein sources. If this hypothesis is correct, it seems reasonable to assume that the diabetogenic hormone must also control the formation of from exogenous protein. This aspect of the problem will be the subject of another communication. SUMMARY.. The normal fasting level of the blood of toads kept on a black background was significantly higher than that of toads on a white background.. After hypophysectomy the blood sugar was within normal limits.. An increased tolerance for was demonstrated after extirpation of the pituitary gland. 4. The diabetic manifestations which follow pancreatectomy in the normal toad did not develop or developed only to a mild degree if the toad had previously been hypophysectomised. REFERENCES. BORCHARDT, L. (98). Z. klin. Med. 66,. EIDELSBERG, J. (9). Ann. Int. Med. 6,. FOLIN, O. and MALMROSS, H. (99). J. btol. Chem. 8, 5. GOETSCH, E. et al. (9). Johns Hopk. Hosp. Bull., 65. HOGBEN, L. T. (9). Quart, jf. exp. Phytiol., 77. HOUSSAY, B. A. (9). Endocrinology, IS, 5. HOUSSAY, B. A. and BlASOrn, A. (9a). PflUg. Arch. get. Phytiol. 7, 9. (9*)- PftOg- Arch. get. Physiol. 7, 657 (9c). Pfliig. Arch. get. Phytiol. 7, 664. KEPINOV, L. and PETIT DUTAILIS, S. (9). C.R. Soc. Biol., Paris, 8, 66. ZWARENSTEIN, H. and BOSMAN, L. P. (9). Quart. J. exp. Phytiol., 45.