122 



KINETIC HORMONES — II 



Cold-blooded Vertebrata. There is as yet no certain evidence 

 of the natural action of gastrin in any class of cold-blooded verte- 

 brates. Frogs have been found to respond to injection of 

 mammalian gastrin by an increased gastric secretion; however, 

 the natural physiological stimulus seems to be brought about by 

 the sympathetic nerves. In Elasmobranchs, on the other hand, it 

 has been claimed that both adrenaline and sympathetic stimulation 

 serve only to inhibit the flow^ of the gastric secretion, while 

 histamine or acetylcholine, but not vagal stimulation, increases it 

 (Prosser, 1950). This rather contradictory state of affairs clearly 

 merits further investigation. 



Volume 



Distention of balloon 



in main stomach pouch 



with 150 cm^of air 



Distention 

 '' stopped 



*!::=&: 



- 20 



- 1-5 



I'O 



0-5 



c— iO 



5 



Fig. 4-3. Result of an experiment on a dog, with two isolated 

 stomach pouches, as in Fig. 4-2. Time in hours is plotted as 

 abscissae, and output of acid from the fundic pouch as ordinates ; 

 the output is stimulated by gastrin, and is shown by weight of 

 HCl (below) and by the changes in volume of the pouch (above). 

 The acid increases markedly in response to the mechanical stimulus 

 of a balloon inserted into the pyloric pouch and inflated with air 

 at the point indicated. When distention in the pyloric pouch stops, 

 the secretion in the fundic pouch falls off rapidly with the fall in 

 GASTRIN production (from Grossman, Robertson and Ivy, 1948). 



AvES. Birds are among the few forms, other than mammals, in 

 which positive evidence has been found for injected gastrin 

 stimulating the acid gastric secretion in the proventriculus 

 (Keeton et al., 1920). Its physiological action has not been shown. 



Bicarbonate secretion by the pancreas 



Mammalia. Secretin was discovered in 1902 by Bayliss and 

 Starling; but it was many years before its action was fully proved. 



