Altered Testosterone Feedback in Pubertal Male Rats Raised on Reduced Caloric Intake

Abstract

A study was conducted to explore the hypothesis that reduced caloric intake increases the negative feedback efficacy of testosterone on gonadotropin secretion. Daily subcutaneous injections of testosterone propionate in oil were administered to either age-matched (37-day-old) or weight-matched (mean = 178 g) ad libitum-fed (control) or underfed rats that received 60% of normal daily food intake from the age of 20 days. Daily doses of testosterone propionate ranged from 25 to 400 micrograms/100 g body weight. Results indicate that reduced caloric intake increases the suppression of serum LH by testosterone propionate in both age-matched and weight-matched underfed rats. On the other hand, the response of serum FSH concentrations to testosterone propionate was affected by reduced diet only in the weight-matched animals. Results suggest that the increased negative feedback of testosterone on LH secretion is a specific diet-induced effect and not merely the result of reduced growth. The altered response in FSH secretion, however, may represent age-associated changes in sensitivity to testosterone rather than diet-induced effects.

Underfeeding Alters the Effect of Low Levels of Estradiol on Luteinizing Hormone Pulsatility in Ovariectomized Female Rats

“…Direct effects (not dependent on ovarian steroid hormone feedback) of reduced food intake on luteinizing hormone (LH) release have been shown in the prepubertal female rat [24] and in the lamb [25], Altered gonadal steroid feedback may be, at least partly, re sponsible for the effect of underfeeding. Although underfeeding in adult rats does not alter the ability to exhibit a postovariec tomy increase in LH secretion [3], the response to postovariec tomy administration of 17(3-estradiol (E2) is a greater decrease in serum LH concentrations in underfed rats (UR) than in ad libitum fed controls (CR) [4,5], Similar results have been ob tained using different doses of testosterone following castration in adult [6] and immature [7] male rats, and with E2 in ovariec tomized immature female rats [8], It is not clear, however, if the increased efficacy of E2 in the underfed rat is mediated through the central nervous system (CNS), the pituitary, or both. The research presented here attempts to resolve this question through an analysis of the pulsatile pattern of in vivo LH secre tion in chronically underfed rats.…”

“…The present study indicates that the UR were more sensitive to the negative feedback effect of E2 than CR, supporting the theory that underfeeding causes an al teration in LH secretion by a steroid-dependent mechanism [4-6] acting on the CNS to suppress LHRH secretion. Evidence for a steroid dependent mechanism has been suggested by re sults of studies in the adult male rat [6], adult female rat [4,5], immature male rat [7] and immature female rat [8,24]. Studies in the lamb [25] indicate that a similar mechanism may operate in that species to mediate the delayed puberty in underfed animals.…”

Diet-Induced Changes in the Male Reproductive System of Rats

“…The main ANFs in legumes are lectins, trypsin inhibitors, and tannins and they exert their effect by interfering with the digestion and absorption of nutrients [4]. This could have led to underfeeding which leads to alterations in the FSH and LH titers [9], increases the negative feedback efficacy of testosterone on gonadotrophin secretion [6], and affects testosterone-LH feedback [7]. Piacsek et al [6] reported that nutritional changes may induce hormonal alterations at the hypophyseal or pituitary level or at a combination of both sites.…”

“…This could have led to underfeeding which leads to alterations in the FSH and LH titers [9], increases the negative feedback efficacy of testosterone on gonadotrophin secretion [6], and affects testosterone-LH feedback [7]. Piacsek et al [6] reported that nutritional changes may induce hormonal alterations at the hypophyseal or pituitary level or at a combination of both sites. It is proposed that legumes inhibited epididymal function by decreasing androgen titers through its antinutritional factors.…”

“…However, reduced calorie or protein intake decreases basal serum FSH concentration but not serum LH concentration [3]. It is also hypothesized that reduced calorie intake increases the negative feedback efficacy of testosterone on gonadotrophin secretion [6]. The effect of starvation on testosterone-luteinizing hormone feedback in rats is also well documented [7].…”