Estradiol, but not testosterone, heightens cortisol-mediated negative feedback on pulsatile ACTH secretion and ACTH approximate entropy in unstressed older men and women

Abstract

How sex steroids modulate glucocorticoid feedback on the hypothalamic-pituitary-corticotrope (HPC) unit is controversial in humans. We postulated that testosterone (T) in men and estradiol (E2) in women govern unstressed cortisol-mediated negative feedback on ACTH secretion. To test this hypothesis, 24 men and 24 women age 58 ± 2.4 yr were pretreated with leuprolide and either sex steroid (E2 in women, T in men) or placebo addback. Placebo or ketoconazole (KTCZ) was administered overnight to inhibit adrenal steroidogenesis during overnight 14-h intravenous infusions of saline or cortisol in a continuous versus pulsatile manner to test for feedback differences. ACTH was measured every 10 min during the last 8 h of the infusions. The main outcome measures were mean ACTH concentrations, pulsatile ACTH secretion, and ACTH approximate entropy (ApEn). ACTH concentrations were lower in women than men (P < 0.01), and in women in the E2+ compared with E2- group under both continuous (P = 0.01) and pulsatile (P = 0.006) cortisol feedback, despite higher cortisol binding globulin and lower free cortisol levels in women than men (P < 0.01). In the combined groups, under both modes of cortisol addback, ACTH concentrations, pulsatile ACTH secretion, and ACTH secretory-burst mass correlated negatively and univariately with E2 levels (each P < 0.005). E2 also suppressed ACTH ApEn (process randomness) during continuous cortisol feedback (P = 0.004). T had no univariate effect but was a positive correlate of ACTH when assessed jointly with E2 (negative) under cortisol pulses. In conclusion, sex steroids modulate selective gender-related hypothalamic-pituitary adrenal-axis adaptations to cortisol feedback in unstressed humans.

Keywords: adrenocorticotropin; glucocorticoids; pulsatile; regulation; sex steroids.

Fig. 1.

Experimental protocol. Twenty-four healthy older men and 24 comparably aged women received 2 doses of leuprolide im 2 wk apart. Sex-steroid addback (weekly testosterone in men and daily estrogen in women) or placebo was started on the day of the second leuprolide injection (day 1) and continued for 26 days (A). Each participant underwent 4 randomly ordered overnight sampling and infusion sessions during the time window 18–26 days inclusive. Volunteers received placebo (1 session) or ketoconazole (KTCZ) (3 sessions) orally to inhibit cortisol production. Concomitantly, glucocorticoid feedback was imposed by way of a 14-h intravenous infusion of saline or midphysiological dose of cortisol in a continuous or pulsatile fashion (B). To monitor ACTH and cortisol, blood was sampled every 10 min during the last 8 h of each infusion. Time is shown in days (A) or clock hours (B).

Fig. 2.

Eight-hour profiles of mean (± SE) ACTH concentrations sampled every 10 min in men (left) and women (right). Each subpanel shows an individual interventional group (placebo/saline, KTCZ/saline, KTCZ/continuous cortisol, and KTCZ/pulsatile cortisol). Data from sex-steroid addback (closed circles) and placebo (open circles) are displayed for comparison. To convert ACTH from ng/l to pmol/l, divide by 4.5.

Fig. 3.

Effects of gender and sex steroids on mean ACTH concentrations (0400–1200 h) during the last 8 h of the 14-h experimental cortisol-infusion feedback phase in each of the 4 treatment arms. Data are means ± SE (n = 24 men, n = 24 women). Different Roman numerals denote significant effects of cortisol-treatment arm. Unshared (unique) uppercase alphabetic letters identify significant effects of gender on mean ACTH concentrations within each treatment arm. Results are based on ANCOVA (main effects) and Tukey's Honestly Significantly Different post hoc testing (for gender and sex-steroid effects).

Fig. 4.

Mass of ACTH secreted per burst (left) and pulsatile ACTH secretion (right) as a function of treatment group (Roman numerals), gender (capital letters), and T or E₂ addback (lower-case letters). Data are presented as given in the legend of Fig. 3.