Effects of Hypophysectomy on LH Receptor Binding and Leydig Cell Sensitivity and Responsiveness to hCG/LH in the Immature (30 Day) Rat

Abstract

The sensitivity (dose of hormone eliciting half maximal response) and the magnitude of the maximal response of Leydig cell suspensions prepared from immature intact and immature eight day hypophysectomized rats to hCG and dibutyryl‐cyclic‐3'5‐adenosine monophosphate (dBC) were assessed in vitro in the presence or absence of the phosphodiesterase inhibitor, methylisobutyl‐xanthine (MIX). In separate studies LH/hCG binding to dispersed Leydig cells from intact and hypophysectomized rats of the same age was evaluated by Scatchard analysis and autoradiography.Hypophysectomy was associated with a 3–4 fold increase in the sensitivity of response, but an 80 % reduction in the maximum steroidogenic response to both hCG and dBC (when expressed per million 3β‐hydroxy‐steroid‐dehydrogenase (3β‐HSD) positive cells. Addition of MIX resulted in a greater increase in the sensitivity of response from intact Leydig cells than from cells from hypophysectomized rats, suggesting that hypophysectomy is associated with a decrease in the activity of the phosphodiesterase. Scatchard analysis of [125I]hLH binding to Leydig cells indicated no major decrease in the average number of LH/hCG receptors per cell after 8 days of hypophysectomy. Grain counts after autoradiography of the radiolabelled LH/hCG receptor confirmed this finding.