160 KINETIC HORMONES — II 



for Stimulating its secretion be linked to its metabolic purposes, 

 for which it is certainly under nervous control (§ 5.322). It has 

 been maintained that oxytocin and ADH are always secreted in 

 the same proportions and may either be combined in one molecule 

 or be linked to the same inactive matrix. More recently it has been 

 claimed that the ratio between the two hormones can be appreci- 

 ably changed in the neurohypophysial secretion, since electrical 

 stimulation of the supraoptic nucleus releases a secretion with a 

 ratio of oxytocic to ADH activity of 4:1, whereas suckling releases 

 a secretion with a ratio of 100:1 (Harris, 1955). 



Nothing is known of the way in which the endogenous heart- 

 accelerating hormone from the gland cells of the insect corpora 

 cardiaca (§ 2.113) is stimulated, since its presence does not depend 

 upon either the neurosecretion or the nerves from the brain ; but 

 neither is it known if this substance from the corpora has a true 

 physiological action (§ 3.111). 



4.323 Nervous or other control of ectodermal glands 



There are no kinetic hormones in invertebrates secreted from 

 ectodermal cells other than nerve cells. In vertebrates, they are 

 confined to the adenohypophysis, which is derived from the 

 stomodaeum (§ 2.123). This is the anterior lobe of the pituitary 

 and includes the pars tuberalis, the pars intermedia and the pars 

 distalis. The first is the source of the melanophore concentrating 

 hormone, W, in Amphibia, and the second is the source of 

 the antagonistic dispersing hormone, B. Both are secreted in 

 response to stimulation of the eyes and must have a direct nerve 

 connection with the brain. The pars intermedia has no nerves 

 in mammals (Fig. 2-12); but it appears to secrete intermedin 

 and may affect morphological, rather than physiological, colour 

 changes. 



The kinetic hormones secreted from the pars distalis of the 

 adenohypophysis are all endocrinokinetic, apart from prolactin, 

 LSH, which stimulates the exocrine mammary glands as well as 

 the endocrine corpora lutea. In most mammals the stimulation of 

 these two glands would seem to alternate rather than to be linked, 

 in that the mammary secretion of milk follows at the end of 

 pregnancy, when the secretion of progesterone from the ovary 



