202 



HYPOPHYSIS AND GOXADOTROPHIC HORMONES 



tion is significant in view of the fact that 

 the peripheral gonadotrophs ordinarily are 

 more strongly granulated than the central 

 ones. The observation suggests at least that 

 a discharge of stored FSH precedes the dis- 

 charge of LH on the occasion of the first 

 ovulation. 



B. SEXUAL MATURATION IX OTHER AXIMALS 



Characteristic globular basophil cells 

 first appear in the red eft stage of Triturus 

 viridescens simultaneously with the differ- 

 entiation of the male and female gonads and 

 are presumed to be gonadotrophic (Cope- 

 land, 1943). In the opossum (Didelphys 

 virginiana) some interesting observations 

 have been made by Wheeler (1943). A 

 vesiculation of the basophil cells and an ac- 

 cumulation of hyaline material occurs in 

 adult animals after castration, producing 

 cells similar to the castration cells of the 

 rat. Wheeler observed that at 100 days of 

 age there occurs a vesiculation of basophils 

 similar to that produced in adult animals 

 by castration. The assumption is that during 

 sexual maturation the hypophysis is called 

 on to secrete gonadotrophic hormones in 

 large amounts and that before full differ- 

 entiation of the gonads, a temporary endo- 

 crine situation exists similar to that pro- 

 duced by castration. 



C. SEASONAL BREEDIXG 



In seasonally breeding animals an initia- 

 tion of the breeding phase has been observed 

 to be accompanied by basophil changes. 

 In the wild cotton-tail rabbit Elder and 

 Finerty (1943) found an increase in gonado- 

 trophic potency in the male hypophysis in 

 the spring, the maximal level being six times 

 that of the level during the winter. This 

 change was accompanied by an increase in 

 the percentage of basophil cells from 4.4 to 

 13.8. In Necturus, Aplington (1942) related 

 the seasonal activity of the testes to an 

 increased activity in the number of granular 

 basophil cells. A similar increased basophil 

 granule content in Anolis rarolinensis during 

 the spring was observed by Poris (1941). 



D. INDUCED SEXUAL MATURATION IN 

 THE FEMALE RAT 



An important series of observations luis 

 l)ecii made concerning the eft'ect of estrogen 



injections on immature female rats ap- 

 proaching the age of sexual maturation. In 

 the immature female rat gonadotrophin 

 secretion is inhibited by minute amounts of 

 estrogen and as long as this relationship ex- 

 ists, no high estrogen levels can be naturally 

 produced in the animal. With the approach 

 of maturation this inhibiting action of estro- 

 gen on gonadotrophin must diminish. Indeed 

 it is found that a condition is reached as the 

 time of the first ovulation approaches when 

 estrogen, instead of inhibiting gonado- 

 trophin secretion, triggers the sudden release 

 of these substances. The physiologic ob- 

 servations of Hohlweg and Chamorro 

 (1937) indicate that a release of gonado- 

 trophic hormones occurred between the sec- 

 ond and fourth day after the injection of 

 estrogen into the immature female rat ap- 

 proaching the expected time of first ovula- 

 tion. The effect of the release of gonado- 

 trophic hormones may be shown by the 

 l)roduction of ovulation and corpora lutea 

 or by follicular enlargement only, the actual 

 response being different in different strains 

 of rats. The liberation of the gonado- 

 trophins after estrogen administration re- 

 sults in a marked drop in the hypophyseal 

 gonadotrophin content which occurrs ap- 

 jn'oximately between 3 and 4 days after 

 estrogen administration (Bradbury, 1947). 

 Purves and Griesbach (unpublished) have 

 studied the responses of the gonadotrophs 

 of the immature female rat after single 

 estrogen injections and found that regard- 

 less of dose in the range from 1 to 100 jug. 

 of estradiol benzoate, there was no change 

 in the hypophysis in the first 2 days. As 

 previously mentioned, in these immature fe- 

 male rats both FSH and LH cells are very 

 numerous and the content of glycoprotein 

 is high. Four days after estrogen admin- 

 istration, the gonadotrophs of the pars an- 

 tei'ioi- ai'e almost free of glyco]irotein and 

 can he recogniz(>d only with difficulty as 

 large pale cells. It is important to note that 

 at this adolescent stage there is no differ- 

 ential effect of estrogen on peripheral and 

 central gonadotroi)hs or on the secretion of 

 FSH 01' LH. The effect is rather that of the 

 triggered discharge of the total gonado- 

 troi)hin content of the hypophysis. 



At the time of glycoprotein discharge 

 from tlic liypophysis of innnature female 



