Testosterone Secretion in the Rat in Response to Chorionic Gonadotrophin: Alterations with Age

Abstract

It has been reported by others that both prevailing blood concentrations of testosterone and Leydig cell response to gonadotrophin (up to 1 h after injection) are reduced in the aged male rat. Although resting levels of plasma testosterone in our aged (24-26 months old) Sprague-Dawley rat are also depressed compared with young (3-4 months) or mature (12 months) animals of the same strain, subcutaneous injection with human chorionic gonadotrophin for 3 days restores secretory function, producing testosterone levels indistinguishable from those of similarly stimulated younger rats. In short term experiments, old rats did show a diminished testesterone secretory response to human chorionic gonadotrophin 1 h after a single intravenous injection, consistent with previous reports, but restoration of normal stimulated levels was observed by 2 h, and persisted up to 24 h. These findings differ from the demonstrated intrinsic testicular hyporesponsiveness to gonadotrophin of aged men, and probably represented a state of chronic understimulation of the aged rat Leydig cells, due to low prevailing levels of LH.

Impact of Aging on Steroid Hormone Biosynthesis and Secretion

“…Similar to the age-related loss of basal blood testosterone concentrations, the acute response (<1-4h) of the rat testis to gonadotropin (hCG) stimulation in vivo is also impaired in older rats [171][172][173]. Moreover, chronic hCG treatment (3-7 days) was shown to restore plasma testosterone levels of older rats to levels comparable to those of similarly stimulated young mature Wistar [173] or LongEvans [174] rats. In contrast, treating rats for up to three weeks with hCG, Lin et al, [175] were unable to restore testosterone levels in 24-month old Sprague-Dawley rats to values seen in identically treated young mature rats.…”

“…The rat is the most popular laboratory animal to examine the effects of aging on testicular androgen synthesis and secretion. A number of studies carried out during the past few decades have led to a clear demonstration that aging leads to significant reduction in blood testosterone levels in several rat strains [157][158][159][160][161][162][163][164][165][166][167][168][169].…”

Effects of goat social rank on kid gender

“…Gorecki (2003) reported that different sires with different testosterone levels could have different gender ratios in their progeny. In this study, older sires had more female progeny, which could be due to lower testosterone levels compared to younger sires (Harman et al, 1978).…”

Altered Ovarian Regulation of Wound Healing during Aging

“…This observation is also consistent with the earlier reports cited above (13 -17), many of which are from studies on males. Since androgens as well as estrogens have been shown to potentiate wound healing (6-9), and reductions in both androgen levels and androgen sensitivity have been found in aged rats (20)(21)(22)(23) there may also be an endocrine contribution to reduced wound healing in old males. It is not possible to determine from the present data whether estrogen sensitivity is reduced in the senescent group.…”