The Biological Actions of ‘Testicular LHRH’

Abstract

Although it is now established that LHRH and its agonistic analogues can exert direct effects on the gonads of several mammalian and non-mammalian species (Hsueh & Jones, 1981; Sharpe & Harmer, 1983), the physiological significance of these actions has not been resolved. In the rat testis, LHRH has direct effects only on the Leydig cells and these effects are believed to reflect the actions of an LHRH-like peptide which is secreted within the testis by the Sertoli cells (Sharpe et al. 1982a; Bhasin et al. 1983; Nagendranath et al. 1983; Sharpe & Harmar, 1983). In view of the critical dependence of normal Sertoli cell function on testosterone produced by the Leydig cells, such a line of communication has obvious physiological significance (see also Sharpe, 1983, 1984). Unfortunately, purification of ‘testicular LHRH’ has made poor progress (Bhasin et al. 1983; Sharpe & Harmar, 1983), so that the only line of investigation that has been possible is to explore the effects of synthetic LHRH and its analogues on the testis, and from the results obtained to infer the likely actions of the endogenous peptide. This paper summarizes our recent findings in this area which have been obtained using two different approaches: 1) by examining the effects of an LHRH agonist on Leydig cell function in vitro and in vivo, and 2) by examining the effects of an LHRH antagonist on Leydig cell function in vivo, as this compound should block any actions of endogenous ‘testicular LHRH’.