CONTROL OF LEYDIG-CELL DIFFERENTIATED FUN CTIONS

Endocrine and exocrine functions of the testis are the result of the s pecific tissular organization involving the interstitial compartment c ontaining the steroidogenic Leydig cells and, separated by the blood-t esticular barrier, the tubules containing Sertoli cells supporting spe rmatogenesis both anatomically and functionnally. Although the endocri ne control of the tests, in particular of Leydig cells, is well establ ished, new data accumulated in the last few years indicate that a loca l control is required for a normal production of androgens, mainly tes tosterone, by Leydig cells. In the present paper, we review the endocr ine, paracrine and autoregulation of Leydig cells differentiated funct ions. Luteinizing hormone (LH) or its homologue human chorionic gonado tropic (hCG) have two effects, acute stimulation of testosterone produ ction and long-term effects in the expression of genes coding for LH r eceptor the steroidogenic enzymes. The effects of gonadotropin on Leyd ig cell differentiated functions, are subtly regulated by locally acti ng factors produced by somatic testicular ells and germ cells. In vitr o studies have shown that several growth factors, cytokines and neurop eptides fullfilled the criteria to establish that they may play a para crine/autocrine action. However, the potential physiological. signific ance remains to be established since evidence from in vivo experiments supporting the presumed action of a given factor are, in any cases, l acking. It is hoped that transgenic animals overexpressing a factor or its receptor driven by tissue-specific promoter, or targeted disrupti on of such proteins, may provide a new approach to define their physio logical role in vivo.