1204 



HORMONAL REGULATION 



(1925), Slonaker (1924), Stone (1932a, 

 1939a), Grunt and Young (1952a), and 

 Larsson (1956, 1958a) are indicative of 

 changes in the running activity of male and 

 female rats and in the mating behavior of 

 male rats and guinea pigs, these changes 

 could be attributed to a reduction in the 

 quantity of endogenous hormones, or to a 

 decrease in the sensitivity of the tissues to 

 such hormones. Indirect evidence supports 

 the former rather than the latter hypothesis, 

 although until the point has been checked 

 experimentally the possibility that both 

 changes occur may not be excluded. 



Hooker (1937) concluded from assays of 

 bull testis extract that after 5 years of age 

 the hormone content gradually decreases. 

 Determination of the male hormone in 

 urine from men of different ages led Kocha- 

 kian (1937) to conclude that the amount 

 excreted by men 50 to 76 years of age is 

 only about 1/6 that excreted by men 22 to 

 29 years of age. According to I3ingemanse, 

 Borchardt and Laqueur (1937), old men 

 excrete less capon comb-growth-promoting 

 substance than middle-aged men. Schou 

 (1951), after making serial determinations 

 over 10 years, stated that there is a steady 

 decrease in the excretion of androgenic sub- 

 stance between the 39th and 62nd years, 

 with advancing age the production of 11- 

 desoxy-17 ketosteroid precursors is mark- 

 edly reduced. Some of the decline is attrib- 

 uted to a decrease in androgen precursor 

 from the testes (Pincus, 1956). In women 

 a secretory decline in ovarian estrogen is 

 gradual, with a sharp drop in the 7th to 9tli 

 decades. 



The results from two experiments invoh'- 

 ing the injection of gonadal hormones into 

 old rats are consistent with the suggestion 

 that the decrease in the intensity of repro- 

 ductive behavior in old animals is attril)uta- 

 ble to a decreased production of hormones, 

 but, unfortunately, they do not eliminate 

 the possibility that the amount of injected 

 hormone simply compensated for a decrease 

 in responsiveness. Hoskins and Bevin (19401 

 showed that the running activity of old 

 male rats was increased by injections of 

 estriol glucuronide. (It will be recalled that 

 under experimental conditions estrogens 

 seem to be more effective than androgens in 



the stimulation of running activity in the 

 male rat.) Minnick, Warden and Arieti 

 (1946) injected 8 28-month-old male rats 

 with 1.25 mg. of testosterone propionate 

 for 15 days and 9 with a preparation from 

 pregnant mare serum. In both groups the 

 average copulatory scores increased ap- 

 proximately 10-fold after only 8 days of 

 treatment. 



It is obvious from this miscellaneous in- 

 formation that alterations in sexual be- 

 havior as animals mature and age may be 

 assumed. How much should be attributed to 

 changes in the quantity of gonadal hor- 

 mones and how much to changes in the 

 reactivity of the tissues mediating such be- 

 havior can only be conjectured. 



D. PROBLEM OF THE MECHANISM AND SITE 

 OF ACTION OF GONADAL HORMONES 



Little to nothing is known about the 

 mechanism whereby gonadal hormones 

 stimulate mating behavior. At the molecu- 

 lar level the likelihood that such informa- 

 tion will be revealed in the near future is 

 not great. Beyond the statement that gon- 

 adal hormones bring about their many ef- 

 fects by regulating the activity of tissue 

 enzymes, this basic endocrinologic problem 

 has not been answered (Dempsey, 1948; 

 Pincus, 1952; Zuckerman, 1952; Szego and 

 Roberts, 1953; Kochakian, 1959; chapter 

 by Villee), even by those who have ex- 

 amined the tissues which, by virtue of their 

 accessibility and structure, are best adapted 

 to histochemical and cytochemical proce- 

 dures. Furthermore, the neural tissues me- 

 diating mating behavior have not been 

 identified in the sense that attention can 

 be directed to cells in which change or 

 changes in response to hormonal stimula- 

 tion could be correlated with the expression 

 of sexual behavior. We suggest, however, 

 that when the mechanism of hormone action 

 has been worked out for the more accessible 

 tissues, such as the uterine epithelium (Rosa 

 and Velardo, 1959) or myometrium (Csapo, 

 1955, 1959a, b), much of the knowledge will 

 be applicable to the tissues mediating mat- 

 ing behavior. The response is to the same 

 hormones, many of the same problems of 

 reactivity exist, and a number of the same 

 rules apply. With respect to the latter, the 



