Spare Gonadotrophin Receptors in Rat Testis

Abstract

GONADOTROPHIN receptor sites with high specificity and affinity for luteinizing hormone (LH) and human chorionic gonadotrophin (HCG) have been demonstrated in particulate and soluble interstitial cell fractions of rat testis^1–4. Such hormone binding sites have been used in radioligand receptor assays for LH and HCG^1,2, and in studies on the structural determinants of gonadotrophin binding to target tissue^5–7. Other parameters of gonadotrophin action have been examined during incubation of intact rat testes with HCG by radioimmunoassay of the cyclic AMP and testosterone produced during trophic hormone stimulation in vitro^8–11. Decapsulated intact rat testes are highly sensitive to gonadotrophic stimulation in vitro, responding to HCG concentrations as low as 0.1 ng ml⁻¹ (10⁻¹² M) with synthesis and release of testosterone and to higher concentrations with synthesis and release of cyclic AMP¹⁰. Release of cyclic AMP during incubation with HCG has been shown to reflect cyclic AMP synthesis by simultaneous measurement of ¹⁴C-adenine incorporation and radioimmunoassay of cyclic AMP^9,10.