§5.522 CONTROL OF SECRETION OF METABOLIC HORMONES 257 



in the blood. Yet the administration of thyrotrophin, TSH 

 (§ 4.221), which might be expected to increase phosphates through 

 its action on the thyroids (§ 5.421), was followed in Xiphophorus 

 by the almost complete destruction of the ultimobranchial body 

 (Rasquin and Rosenbloom, 1954). The indirect relation of the 

 ultimobranchial body to activity of the hypophysis also differs 

 apparently in the eel, Afiguilla, from that in Astyanax and Fundulus 

 (§ 5.411). The situation in the Amphibia also remains obscure. 



It may be noted that the three metabolic hormones which can be 

 controlled directly and be kept in balance by the effects of their 

 own action are all secreted by endodermal endocrine glands. The 

 kinetic hormones controlled in a similar way are all secreted from 

 isolated cells, but they also come from the gut, which is endo- 

 dermal. It is, therefore, interesting that the secretion of the 

 thyroid gland, with its predominantly morphogenetic actions, is 

 not controlled in this way, although it is formed from gut cells. 



5.522 Nervous control of secretory cells of nervous origin 



The metabolic hormones secreted from neurosecretory cells are 

 controlled by nerves in all cases that have been sufficiently fully 

 investigated. Among the Crustacea, the best established case is that 

 of the diabetogenic hormone from the sinus gland, the secretion of 

 which is impeded by sectioiling its nerve supply from the brain 

 (§ 5.211). In the case of the moult-inhibiting hormone, associated 

 with the restraint of protein catabolism and the increase of water 

 diuresis, it is possible (though as yet unproven) that the nervous 

 action is one of inhibition, which allows moulting to occur. The 

 implantation of isolated sinus glands can have at least some of the 

 normal effects of the glands in situ, as though nerve stimulation is 

 not necessary to induce secretion. The effect of nerve section, 

 rather than gland removal, in inducing forced mouhs and the 

 accompanying metabolic changes, has not apparently been 

 investigated. 



Among Insecta, the brain can only inhibit the secretion of the 

 diapause hormone from the suboesophageal ganglia if the nerves 

 connecting them are intact (§ 5.112). In Vertebrata, the secretion 

 of ADH from the neurohypophysis responds to nervous stimuli 

 initiated from osmoreceptors in the hypothalamus, where they 



