PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



259 



the separate follicle-stimulating and lutein- 

 izing activities of the pars clistalis. 



Bahn, Lorenz, Bennett and Albert 

 (1953b) found a sharp increase in the FSH 

 content of the human hypophysis at the 

 time of the menopause, with no coincident 

 increase in LH. The ratio of FSH to LH 

 was found to be 1:1 in the pituitaries of 

 women of reproductive age and 3:1 in 

 those from women past the menopause. The 

 failure of LH to increase under these con- 

 ditions in man is at variance with the ob- 

 servation by jVIcArthur, Ingersoll and Wor- 

 cester (1958) that appreciably more LH is 

 excreted in the urine after the menopause 

 than during the reproductive years. 



In recent years the Dutch workers, Paesi, 

 de Jongh, Gaarenstroom, and Hoogstra in- 

 troduced modifications in their procedure 

 for studying the gonadotrophic activity of 

 rat pituitaries, which provide in their views 

 an estimate of the relative amounts of FSH 

 and LH (for methods see Hoogstra and 

 Paesi, 1955, 1957). Paesi, de Jongh, Hoogs- 

 tra and Engelbregt (1955) reported that 

 gonadectomy produced within 3 months a 

 5-fold increase in the FSH content of the 

 pituitaries of females, and no conspicuous 

 increase in males; LH increased following 

 gonadectomy in each sex, but more so in 

 males than in females. Their finding that 

 gonadectomy tended to diminish the sex dif- 

 ference in pituitary gonadotrophic content 

 in rats is in keeping with the experience of 

 others. 



4- Reproductive Rhythms 



a. Cijclic Vhanges. In those species in 

 which the reproductive activity is closely 

 tied-in with seasonal alterations in the en- 

 vironment, the expectation is that the peaks 

 in i)ituitary potency would correspond with 

 periods of heightened breeding activity. The 

 few observations available suggest that with 

 certain exceptions this is true. 



Valuable preliminary data based on a 

 year-round collection of adult pheasant 

 pituitary has been summarized by Greeley 

 and Meyer (1953). The dried glands were 

 pooled by months or pairs of months and 

 tested in day-old chicks for testis-stimulat- 

 ing potency. The potency of the glands was 

 at a minimum in July when the testes of the 

 donor birds were undergoing rapid regres- 



sion. Before settling to winter level pitui- 

 tary potency showed a small increase, while 

 the testes were in what several workers 

 have termed a "refractory state" (see Mar- 

 shall, 1955). The major upsurge in pitui- 

 tary gonadotrophin, correlating well wdth 

 weight of donor testes, occurred in January, 

 February, and March, and reached its maxi- 

 mum in April. The close parallel of hy- 

 pophyseal potency and testis development 

 throughout the annual cycle is noteworthy. 

 It indicates that pituitary gonadotrophin 

 content reflected accurately the rate of 

 gonadotrophin release. Benoit's early studies 

 showed that the duck pituitary is weakest 

 in the off-breeding season and gathers gon- 

 adotrophic potency as added illumination 

 brings the animals into sexual competence; 

 also Riley and Fraps (1942b) found a lesser 

 potency in laying than in nonlaying hens. 



Some information has been obtained from 

 mammals. The pituitary of the ground 

 sciuirrel has a much reduced gonadotrophic 

 potency during hibernation (Wells, 1935). 

 A peculiar situation was found to exist with 

 respect to the cottontail rabbit at the time 

 of the breeding season. The pituitary of the 

 male showed an increase in gonadotrophic 

 content, whereas that of the female did not 

 (Elder and Finerty, 1943). Assay of mule 

 deer pituitaries (Grieser and Browman, 

 1956) has indicated that potency in yearling 

 does is lowest in winter months, gradually 

 increases as spring progresses, and reaches a 

 peak by late fall. 



In recent years pituitary gonadotrophic 

 potency has been studied throughout the 

 estrous cycle in the cow, sow, and ewe. The 

 gonadotrophic potency of the cow pitui- 

 tary is at its lowest point during estrus 

 (Paredis, 1950). In like manner, Robinson 

 and Nalbandov (1951) reported that the 

 gonadotrophin content of sow pituitaries 

 collected during estrus was approximately 

 half that of pituitaries taken at midcycle. 

 The potency remained low in glands taken 

 through the first 8 days of the cycle and 

 then climbed sharply. 



Reports on cyclic variations in the gon- 

 adotrophic potency of the ewe pituitary are 

 at variance. According to Robinson (1951), 

 potency is at its peak during estrus; War- 

 wick (1946), however, found no difference 

 between glands collected during the breed- 



