Temporal Relationship Between hCG Induced Desensitization of LH/hCG Responsive Adenylyl Cyclase and Down regulation of LH/hCG Receptors in the Rat Testis

Abstract

A single s.c. injection of 75IU of human chorionic gonadotropin (hCG) into adult male rats caused a transient desensitization of the LH/hCG responsive adenylyl cyclase (AC) in membrane particles from rat testis. Two hours after the injection of hCG, LH/hCG responsive AC was reduced by 40%, whereas LH binding was still normal. After 24 hr LH/hCG responsive AC was lost, whereas LH binding only showed a marginal decrease. During the next 2-3 days there was a gradual loss of LH/hCG receptors, which reached a nadir at day 4 (14% of control levels). At day 6 and 9 following the hCG injection LH/hCG receptors and LH/hCG responsive AC gradually returned towards normal. Fluoride (F∼) stimulated AC activity showed only minor changes throughout the period investigated. The initial loss of AC responsiveness to hCG was associated with maximal levels of circulating hCG. However, desensitization persisted for several days after hCG was cleared from the circulation. AC desensitization preceded LH receptor downregulation and may support the notion that uncoupling of the catalytic subunit of the AC from Leydig cell LH/hCG receptors is a requirement for subsequent receptor internalization.

Key Words:

• Leydig cells
• LH/hCG receptors
• Desensitization