Verhandelingen - Koninklijke Academie voor Geneeskunde van België vol:54 issue:4 pages:299-326; discussion 326-7
The present survey focuses on some unique features of the testis as an androgen target tissue. Within the testis androgens act in a paracrine rather than in an endocrine fashion. All the available evidence suggests that the concentration of androgens that surrounds testicular target cells is much higher than that observed in peripheral target tissues, but the exact concentration remains unknown. The concentration of androgens required to maintain spermatogenesis considerably exceeds that observed in the peripheral circulation although it is probably lower than that which exists within the testis. The effects of androgens on spermatogenesis are indirect and are mediated by somatic cells. Sertoli cells are the most likely mediators of the effects of androgens on germ cell development. These cells contain androgen receptors which are upregulated by FSH and by androgens and they respond to androgens in vitro. They are not the only androgen-responsive cells in the testis, however, and some effects of androgens on Sertoli cells (epithelial cells) are indirect and are actually mediated by paracrine factors produced by underlying peritubular cells (mesenchymal cells). Androgen-regulated mesenchymal-epithelial interactions may not be limited to the testis but may be a more general feature of androgen action in several target tissues and our data suggest that the mediators involved may be very similar or identical. A final interesting aspect of androgen action in the testis is that the compartment which responds to androgens (the tubular compartment) may locally modulate the activity of the compartment which is responsible for androgen production (the interstitial compartment). A complex network of paracrine mediators is responsible for these interactions.