222 /. /. Christian 



cantly reduced the number of births on Microtus agrestis even though they 

 were maintained on summer food. Chitty and Austin (1957) have called 

 attention to the effects of environmental factors, especially social "stress," 

 on changes is estrous pattern and behavior exhibited by Microtus agrestis. 

 Additional examples of the effects of deleterious environmental factors on 

 reproduction will be given later. 



There is another aspect of the suppression of reproduction which should 

 be mentioned at the present time, although it is not directly pertinent to 

 adrenocortical-gonadal relationships. Inanition, starvation, protein defi- 

 ciency, and probably other dietary inadequacies are capable of depressing 

 or totally inhibiting reproduction, the degree depending on the severity of 

 the inadequacy (Lutwak-]\Iann, 1958), without stimulating increased 

 secretion of ACTH and therefore increased adrenocortical activity (Baker, 

 1952; Christian, 1959b, c; Eisenstein, 1959), and adrenocortical secretion is 

 actuallj^ depressed in rats deficient in pantothenic acid (Eisenstein, 1957). 

 The experimental evidence on which this statement is based has been 

 derived from laboratory mammals and therefore does not necessarily apply 

 to other species or to natural populations, but the burden of proof lies with 

 those who claim otherwise. Recent experiments with house mice have 

 demonstrated rather conclusively that inanition does not stimulate the 

 pituitary-adrenocortical system, although its effect on the reproductive 

 system is striking ( Lutwak-Mann, 1958; Christian, 1959b, c). Further- 

 more, a deficiency of vitamin Be or partial starvation does not increase the 

 secretion of corticoids nor impau- the ability of the adrenal cortex to secrete 

 them, even though they may be a marked cortical hypertrophy (Eisenstein, 

 1959). These results are in agreement with those from a large number of 

 earlier experiments (cf. Baker, 1952; Christian, 1959c) . In addition Srebnik 

 et al. (1958) have shown that a protein deficiency results in a failure in the 

 secretion of gonadotropins, and jVIarrian and Parkes (1929) had shown 

 earlier that anterior pituitary extracts could correct the anestrus produced 

 by a dietary insufficiency of vitamin B with the return of normal estrus and 

 normal changes in the accessory organs of reproduction with the estrous 

 cycle. One might hypothesize that an inadequate diet would impair the 

 ability of the anterior pituitary to synthesize its protein hormones. How- 

 ever, the ability of the pituitary-adrenocortical system of mice to exhibit 

 the usual responses to alarming stimuli, and therefore the ability to elabo- 

 rate adrenocorticotropin, in spite of inanition indicates that this is probably 

 not the case (Christian, 1959c). Therefore, the decreased production of 

 gonadotropins by animals subjected to inanition, starvation, or other 

 dietary inadequacies probably operates through an unknown mechanism, 

 probably at the hypothalamic level, which does not reflect an inability of 

 the anterior pituitary to synthesize protein hormones. 



