246 



HYPOPHYSIS AND GOXADOTROPHIC HORMONES 



LH, like FSH, is a glycoprotein. The bio- 

 logic activity of LH is far more resistant 

 to glycolytic enzymes than is that of FSH ; 

 its resistance to proteolytic enzymes, how- 

 ever, is much less. 



The available preparations of LH seem 

 to be more satisfactory than those of FSH 

 in point of comprising a hormone as a chem- 

 ical entity. However, LH, as indicated by 

 the recent work of Squire and Li (1959), 

 may in turn reveal its biologic activity in 

 some small part of a protein complex. 



2. Physiologic Effects in Females 



The many early studies based on the ac- 

 tion of LH extracts injected into intact im- 

 mature rats are uninformative, since the 

 participation of endogenous gonadotrophins 

 cannot be excluded nor safely discounted. 

 Histologically, the action of LH has been 

 detected with certainty in long-term hy- 

 pophysectomized immature female animals 

 by repair of the atrophic ovarian inter- 

 stitial cells (Simpson, Li and Evans, 1942a, 

 b». 



The ovarian manifestations of the action 

 of LH administered to intact immature fe- 

 male animals are notably inconspicuous. 

 There is no increase in ovarian weight and 

 no evidence that LH promotes the secretion 

 of gonadal hormones. The interstitial cells 

 appear a little more swollen than in un- 

 treated animals, and in guinea pigs in par- 

 ticular so-called pseudolutein bodies may 

 appear. Conversely, the effect of LH on 

 ovaries of adult rats are evident macro- 

 scopically. There occur an excessive number 

 of ovulated follicles, many hemorrhagic fol- 

 lich's, and widespread luteinization of me- 

 dium to large unruptured follicles, the 

 ovaries being generally enlarged due to tlie 

 synergism of the administered LH with en- 

 dogenous FSH. 



In hypophysectomized immature female 

 rats under treatment with FSH, the notable 

 effect of introducing LH is to impose an 

 intensification of the enlargement of the 

 ovaries and to promote a sudden growth of 

 the reproductive tract (Greep, van Dyke 

 and Chow, 1942». That this latter effect is 

 due to tlie initiation of estrogen secretion 

 is uneciuivocal. The cells of the theca in- 

 ktcrna which remain atrophic under FSH 

 stimulation swell and ar(|uire the cytologic 



and histochemical criteria of actively se- 

 creting cells only if LH, among the pitui- 

 tary gonadotrophins, is administered. 



The importance of LH in bringing about 

 the secretion of the ovarian hormone estra- 

 diol-17/3 has been mentioned. The facts that 

 the thecal cells are maintained in a stimu- 

 lated condition and that continuous uterine 

 growth occurs during the follicular phase 

 of a reproductive cycle suggest that LH is 

 secreted during this time. Other lines of evi- 

 dence likewise indicate that LH not only 

 may be secreted throughout each estrous or 

 menstrual cycle, but that it may play a 

 dominant role in sexual periodicity. As early 

 as 1937 Dempsey expressed the view that, 

 as a step in accounting for the estrous cycle, 

 it is necessary to assume that fluctuations 

 occur in the secretion of LH, thus bringing 

 about ovulation and corpus luteum forma- 

 tion. Indeed, McArthur, Ingersoll and 

 Worcester (1958) reported a marked eleva- 

 tion in the urinary excretion of LH by 

 women at the midpoint of the normal ovula- 

 tory menstrual cycle. This view is further 

 supported by the fact of persistent estrus in 

 rats and guinea pigs (for reviews of litera- 

 ture on spontaneously occurring or induced 

 persistent estrus, see Noumura, 1958 and 

 chapter by Everett) in which the causative 

 factor appears to involve an inability to 

 elicit a discharge of LH by reflex neuro- 

 genic mechanisms. 



Although meager study has been made of 

 the ovulating property of pure LH, it is 

 known to have this function (Greep, Chow 

 and van Dyke, 1942; Hisaw, 1947). There 

 seems little reason to suppose that the pure 

 hormone would behave differently in this 

 trespect from preparations having some FSH 

 contamination. From information availa- 

 ble, ovulation may, with reasonable assur- 

 ance, be ascribed to a sudden elevation in 

 the secretion of LH. Once ovulation has 

 taken place, the conversion of the follicle 

 into a luteinized body — a corpus luteum — is 

 unquestionably attributable to LH action. 



3. Phi/sioloiiic Action in Males 



The pi'imary cITcct of LH on the male 

 gonad is to promote the maturation, main- 

 tenance or i-epair of the interstitial tissue 

 leading to the elaboration of androgenic 

 hoi'mone iC.i'eep. Fevold and Hisaw, 1936; 



