142 KINETIC HORMONES — II 



1953). The growth-promoting action of TSH is only restored to 

 any appreciable extent if the reimplantation of the hypophysis 

 brings it into contact with the median eminence of the brain, in the 

 position from which it was originally removed. This may be com- 

 pared with the similar effect of CRF upon the growth-promoting 

 actions of other hypophysial hormones (§ 4.323). 



4.222 Parathyroid glands 



Earlier work suggested that activity of the parathyroid glands 

 could be stimulated by thyroxine from the thyroids. It is now 

 established that this is not an endocrinokinetic action, but an 

 indirect effect, in that thyroxine tends to low^er the calcium and 

 increase the phosphate content of the blood and these changes 

 both stimulate the parathyroid glands directly (§ 5.521). 



4.223 Gliicagoji-secreting cells of the pancreas stimulated by STH 



Ayes. The growth hormone or somatotrophin, STH, has only 

 been shown to induce an increase in blood-sugar in the chick, 

 Gallus; but it seems probable that this is an indirect action brought 

 about through its endocrinokinetic stimulation of glucagon 

 secretion, as in some mammals (§ 5.211). 



Mammalia. The stimulation of glucagon secretion from a 

 cells in the islets of Langerhans (§ 2.222) is not yet fully under- 

 stood, nor is glucagon widely distributed in mammals (§ 5.2). 

 Though some may be active in all mammals, it is only in some 

 carnivores (cat and dog, but not ferret) that it has been found to 

 be the main factor in raising the level of blood-sugars, in response 

 to stimulation by hypoglycaemia (Saka, 1952) or by somato- 

 trophin or growth hormone, STH*, from the adenohypophysis 

 (Young, 1945). The evidence for the endocrinokinetic action of 

 STH has been somewhat obscured by the fact that its administra- 

 tion to hypophysectomized dogs and cats gives difTerent results 

 at difTerent ages. In young animals the resulting release of sugar 

 can all be consumed in growth, and the stimulation of the latter 

 is the only observable result; but in older animals, when growth 

 has ceased, the stimulation of glucagon secretion and the conse- 

 quent release of sugar into the blood is not masked, and hyper- 



* Glucagonotrophin would be more descriptive in this context. 



