152 KINETIC HORMONES — II 



In the female placental mammal at least three pairs of hormones 

 are involved, the two members of each pair acting alternately to 

 control the changes associated with the alternation of oestrus and 

 dioestrus phases. The latter group are also active during pregnancy. 

 In the oestrus phase the endocrinokinetic hormone is ICSH and 

 the morphogenetic hypophysial hormone is FSH, as in the male; 

 but the gonadial hormone is an oestrogen. In the dioestrus phase 

 these are replaced respectively by LSH, LH and progesterone, 

 for which there are no counterparts in the male. Their detailed 

 actions, interactions and variations will be discussed in relation to 

 reproduction (Part II, § 4). Oxytocin from the neurohypophysis 

 also plays a part in the reproductive processes in the female ; but 

 its main actions have already been mentioned, being concerned 

 with muscular contraction in parturition (§ 3.113) and with the 

 action of the myoepithelial cells in bringing about ''milk let-down" 

 from the mammary glands (§ 3.114). Prolactin that stimulates 

 the secretion of the mammary glands seems to be identical with 

 LSH, although its action here is so different (§ 4.13). Even this 

 list of seven or eight hormones involved in the reproductive 

 activities of the female takes no account of the hormones which 

 must actively adjust the maternal metabolism to meet the demands 

 of gestation and lactation. 



4.3 General considerations 



As the account of the kinetic hormones is now as complete as 

 space allows, it will be well to review their general characteristics 

 and the means by which their own secretion is induced, before 

 passing on to a consideration of the metabolic hormones, which 

 fall into so different a category (§5). 



4.31 characteristics of kinetic hormones 



The kinetic hormones controlling the reactions of muscles and 

 glands in vertebrates have much in common with each other and 

 they may even be identical, whereas those controlling the pigment- 

 ary effectors are usually distinct and differ from the former in 

 various ways which may in part be due to the nature of the 

 effectors concerned. Gastrin, progesterone and adrenaline are 



