Central 5-alpha reduction of testosterone is required for testosterone's inhibition of the hypothalamo-pituitary-adrenal axis response to restraint stress in adult male rats

Abstract

In rodents, the hypothalamo-pituitary-adrenal (HPA) axis is controlled by a precise regulatory mechanism that is influenced by circulating gonadal and adrenal hormones. In males, gonadectomy increases the adrenocorticotropic hormone (ACTH) and corticosterone (CORT) response to stressors, and androgen replacement returns the response to that of the intact male. Testosterone (T) actions in regulating HPA activity may be through aromatization to estradiol, or by 5α-reduction to the more potent androgen, dihydrotestosterone (DHT). To determine if the latter pathway is involved, we assessed the function of the HPA axis response to restraint stress following hormone treatments, or after peripheral or central treatment with the 5α-reductase inhibitor, finasteride. Initially, we examined the timecourse whereby gonadectomy alters the CORT response to restraint stress. Enhanced CORT responses were evident within 48 h following gonadectomy. Correspondingly, treatment of intact male rats with the 5α-reductase inhibitor, finasteride, for 48 h, enhanced the CORT and ACTH response to restraint stress. Peripheral injections of gonadectomized male rats with DHT or T for 48 h reduced the ACTH and CORT response to restraint stress. The effects of T, but not DHT, could be blocked by the third ventricle administration of finasteride prior to stress application. These data indicate that the actions of T in modulating HPA axis activity involve 5α-reductase within the central nervous system. These results further our understanding of how T acts to modulate the neuroendocrine stress responses and indicate that 5α reduction to DHT is a necessary step for T action.

Keywords: 3V; 3β-diol; 5-Alpha reductase; 5-alpha androstane 3β,17βdiol; 5-alpha reductase; 5α-dihydroprogesterone; 5αDHP; 5αR; ACTH; Androgen; BnST; CORT; CRH; CSF; DHT; DHTP; Dihydrotestosterone; E; ER; HPA; HPA axis; Hypothalamus; MPOA; PBS; PVN; Stress; T; TP; Testosterone; Veh; adrenocorticotropic hormone; bed nucleus of the stria terminalis; cerebrospinal fluid; corticosterone; corticotropin releasing hormone; dihydrotestosterone; dihydrotestosterone propionate; estradiol; estrogen receptor; hypothalamo-pituitary-adrenal; icv; immunoreactivity; intracerebroventricular; ir; medial preoptic area; paraventricular nucleus; phosphate-buffered saline; s.c; subcutaneous; testosterone; testosterone propionate; third ventricle; vehicle.

Figure 1

Changes in post-stress plasma corticosterone levels following gonadectomy (GDX) of male rats. Animals were GDX’d or sham GDX’d and subjected to a 20 min. restraint stress 1-7 days later. An additional group was left intact. Each bar represents the mean +/− SEM of 8-14 animals. Two way analysis revealed a significant effect of gonadectomy. Post hoc analysis using Fisher’s protected LSD after one way ANOVA for GDX or sham groups including the intact animals (0 day GDX) showed # = p<0.05 compared to intact control group. * = p<0.05 compared to day 1 GDX group..

Figure 2

Effect of 5alpha reductase inhibition on plasma corticosterone (CORT; upper panel) or adrenocorticotrophin (ACTH; lower panel). Intact male rats were given finasteride (1 or 10 mg/kg bodyweight, SC) for two consecutive days and then subjected to a 20 min restraint stress. Non-stress animals were euthanized directly from their home cage. Each bar represents the mean +/− SEM of 6-8 individuals. Fisher’s protected LSD showed *= significantly different from non-stress group of same treatment. # = significantly different from stress/vehicle group.

Figure 3

Effect of testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) treatment of gonadectomized male rats on plasma corticosterone (left panel) and ACTH (right panel) following a 20 min restraint stress. Non-stressed animals were euthanized immediately after removal from their home cage. Each bar represents the mean +/− SEM of 7-8 animals per group. Significant differences by Fisher’s protected LSD are shown by lower case letters that are different from each other (p<0.05).

Figure 4

Effect of 3^rd ventricle infusion of finasteride on testosterone propionate (TP) or dihydrotestosterone propionate (DHTP) effects on plasma corticosterone or ACTH. Upper panel shows plasma corticosterone levels in non-stress or stress (20′ restraint) conditions. Lower panel shows plasma ACTH levels in non-stress or stress (20′ restraint) conditions. Each bar represents the mean +/− SEM of 5-7 animals per group. Posthoc analysis using Fisher’s protected LSD shows: * = stressed groups that are significantly different from vehicle / stress group. # = finasteride groups that are significantly elevated compared to the similar vehicle control group. @ = groups showing significant elevation in CORT or ACTH compared to non-stress groups.