162 KINETIC HORMONES — II 



factor, CRF^ from the median eminence of the brain (Nikitovitch- 

 Winer and Everett, 1957). The substance is clearly not a true 

 vascular hormone, since it does not act upon the hypophysis when 

 the latter is out of contact with the brain, but supplied by the 

 same blood. It may perhaps be a neurohormone (§ 1.2), or a short- 

 lived vascular hormone, since some neurosecretory cells of the 

 hypothalamus normally make contact with the portal blood supply 

 of the adenohypophysis in the median eminence (Fig. 2-12). It is 

 claimed that after re-implanting the hypophysis in contact with the 

 median eminence, these cells may again pass their secretion for a 

 short distance in the portal circulation, rather than just allowing 

 it to diffuse between the hypothalamus and the hypophysis. 



One curious result has been reported. Implantation of an 

 adenohypophysis from a male rat, under the median eminence of a 

 hypophysectomized female, is able to maintain her normal oestrus 

 cycle, and even to support pregnancy. This must mean that the 

 implanted hypophysis is secreting the luteinizing hormone, LH, 

 the secretion of which is normally totally inhibited in the male 

 (§ 4.232). It seems necessary to conclude that "the hypothalamus 

 supplies not only a general stimulus to anterior pituitary function, 

 but also sets the pattern of this function''^ (Harris, 1955). 



It would clearly be of interest if this type of experiment, and 

 those on CRF, were to be related more specifically to effects upon 

 the release of endocrinokinetic hormones from the hypophysis. 



4 . 3 24 Hormojial control of endocrine glands 



Four exceptional hormones, among those classed as kinetic, 

 remain to be considered ; they all come from the gonads and are 

 therefore mesodermal in origin. Of these, the vertebrate gonads 

 secrete three : oestrone and testosterone, the two sex hormones 

 which affect the tone and perhaps the activity of somatic muscle 

 (§ 3.12), and progesterone, which is said to stimulate the secretion 

 of oviducal glands in Amphibia and Mammalia (§ 4.12). Unlike 

 any other kinetic hormones, the secretion of these vertebrate 

 hormones is induced by endocrinokinetic hormones from the 

 adenohypophysis (Table 17); such stimulation is characteristic of 

 morphogenetic hormones, and it is noticeable that all the other 



* My italics. P. M. J. 



