2G0 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



ing season and those obtained in the non- 

 breeding season. Kammhide, Welsh, Nal- 

 bandov and Norton ( 1952 ) , using the same 

 assay as Warwick- — the chick testis — found 

 the potency highest during anestrum and 

 lowest during estrus. Although the reproduc- 

 tive tract of the anestrous ewe was found to 

 be atrophic, the ovaries contained a few 

 sizeable follicles (Hammond, 1945; Nalban- 

 dov, 1953a, b) and ovulation was induced 

 by exogenous gonadotroi)hins. Granting that 

 LH is a requisite for the secretion of estro- 

 gen as well as for ovulation, Kammlade, 

 Welsh, Nalbandov and Norton (1952) and 

 Nalbandov ( 1953b j speculated that anes- 

 trum in the ewe may perhaps be attributed 

 to an imbalance of the gonadotrophins 

 characterized by increased pituitary FSH 

 potency and a deficiency in circulating LH. 

 They surmised that the follicular develop- 

 ment was brought about by the action of 

 virtually "pure" endogenous FSH. In accord 

 with this view Dutt ( 1953 1 and Robinson 

 (1952, 1954) reported that ovulation, fol- 

 lowed in some instances by pregnancy 

 (Robinson, 1950), can be induced in the 

 anestrous ewe by the administration of 

 progesterone, thereby suggesting that LH 

 is "stored." Progesterone, as noted else- 

 where, can be used to induce or hasten 

 ovulation in hens, estrous rabbits, the per- 

 sistent-estrous rat, and in monkeys during 

 the anovulatory summer months. According 

 to current opinion, these effects are attribut- 

 able to excitation of neurohumoral mecha- 

 nisms which promote the release of LH, 

 Missing for the purpose of the present con- 

 sideration is knowledge of whether or not 

 the pituitary of the anestrous ewe contains 

 LH. Unfortunately the methods used in 

 studying the ewe pituitary have not been 

 informative in regard to the separate gon- 

 udotrophic activities. 



Especially noteworthy are the data of 

 Simpson, van Wagenen and Carter (1956) 

 concerning the fluctuation in pituitary gon- 

 adotrophic potency in adult female monkeys 

 killed at different stages in the menstrual 

 cycle. The low titer of FSH (in unit and to- 

 tal potency) at the beginning of tlie cycle 

 quadrupled near the end of the follicular 

 phase and decreased during the luteal phase. 

 The unit and total potency of LH was high- 

 est on (lavs 9 to 11. TheFSH to LH ratio 



was roughly 1:3 at the beginning and end 

 of the cycle and 1 : 10 through the preovula- 

 tory and ovulatory stages. This is mainly 

 because the LH increased relatively much 

 more during that time than did FSH. At 

 the time of greatest concentration, the mini- 

 mal effective dose for both FSH and LH 

 effects was 1/10 that of pooled sheep pitui- 

 tary powder. The two hormones were, how- 

 ever, present in the same relative propor- 

 tions as in sheep pituitaries. 



b. Pregnancy. Marked differences exist in 

 the gonadotrophic functions of the hypophy- 

 sis during pregnancy. In a number of ani- 

 mals, of which the monkey, guinea pig, rat, 

 and mouse are examples, the gonadotrophic 

 functions of the pituitary are assumed by 

 the placenta to the extent that the hypophy- 

 sis can be ablated without interrupting 

 pregnancy (for review see Smith, 1954). 

 There are authenticated instances in which 

 the ovaries involute especially during the 

 later stages of gestation. Contrariwise, in 

 many animals growth of ovarian follicles 

 continues throughout gestation and, in 

 some, heat ensues immediately following 

 parturition (for review see Williams, Gar- 

 rigus, Norton and Nalbandov, 1956, and 

 chapter by Young on the mammalian 

 ovary). There are many reports of mating 

 and of spontaneous or artificially in- 

 duced ovulation during pregnancy. It is, 

 therefore, not unexi)ected that marked 

 variation between species has been noted 

 with respect to the gonadotrophic ac- 

 tivity of the hypophysis during preg- 

 nancy; it has been reported to increase, 

 decrease, or to show little or no change 

 (reviewed by Cowie and Folley, 1955). 

 Within species, the results have not al- 

 ways been consistent; such discrepancies 

 are probably related to the different pro- 

 cedures that have been used for collecting, 

 storing, and assaying the glands. In a nota- 

 ble example, the pituitaries of pregnant cat- 

 tle were observed to show a steady increase 

 in gonadotrophic content over those of non- 

 l)rcgnant animals (Bates, Riddle and Lahr, 

 1935), but in a later study (Nalbandov and 

 Casida, 1940) the potency was found to 

 decline steadily throughout ])regnancy. Sim- 

 ihiily. Robinson and Nalbandov (1951) 

 found that the gonadotrojihic potency of the 

 pregnant sow decreases throughout gesta- 



