Effects of active immunization against estradiol-17 beta on luteinizing hormone and testosterone in male rats.

Abstract

The role of endogenous estradiol-17 beta (E2) in regulating luteinizing hormone (LH) and testosterone secretion was investigated in adult male rats actively immunized against the E2-bovine serum albumin (BSA) conjugate. The antigen was injected intradermally 4 times at 2-week intervals and additional boosters were continued once a month. A pooled antiserum from immunized animals cross-reacted 8% to estrone, 1% to testosterone and 5 alpha-dihydrotestosterone, and less than 1% to estradiol-17 alpha, estriol, dehydroepiandrosterone, corticosterone, cortisol, progesterone and 20 alpha-dihydroprogesterone when compared with E2 (100%). Serum E2 in immunized rats was not adsorbed with dextran-coated charcoal, indicating that most of the serum E2 was bound to the antibody. In serum of immunized rats, LH and testosterone concentrations were significantly higher than those in intact rats. The metabolic clearance rate of testosterone was not changed, but the production rate of testosterone was significantly increased by the immunization. By the implantation of a micropellet of E2 in one testis, testosterone concentrations in the testicular vein blood from either the implanted or intact side were significantly decreased in intact rats, but not in immunized rats. In both groups, there were no significant differences between the testosterone concentration in testicular vein blood in the implanted and intact sides. It is concluded that circulating E2 physiologically participates in maintaining LH-testosterone homeostasis by inhibiting LH secretion in adult male rats.