RAT TESTICULAR MYOID CELLS EXPRESS VASOPRESSIN RECEPTORS - RECEPTOR STRUCTURE, SIGNAL-TRANSDUCTION, AND DEVELOPMENTAL REGULATION

Detection of the neurohypophysial hormones vasopressin (AVP) and oxyto cin (OT) in the testis of several species has led to the proposal that these peptides may have a physiological role in the regulation of tes ticular function. Therefore, me investigated whether the contractile m yoid cells of rat seminiferous tubules express functional receptors fo r AVP or OT and, thus, constitute a target for these hormones. This st udy used primary cultures of purified peritubular myoid cells derived from rats both before and after puberty. By several criteria, myoid ce lls prepared from adult rats expressed vasopressin receptors (VPRs). W e detected specific and saturable [H-3]AVP binding to a single populat ion of sites with a K-d of 7.5 mM and a binding capacity of 145 fmol/m g protein. AVP stimulated the accumulation of inositol phosphates in a dose-dependent manner with an EC(50) of 1.7 nM. Cloning and sequencin g of the myoid cell VPR confirmed it to be the V-1a subtype of VPR. VP R expression by myoid cells is under developmental control, as the rec eptors are present in the adult rat, but absent before puberty. In con trast, OT receptors were not expressed at any stage of development. Pe ritubular myoid cells are also responsive to endothelin-1 (ET-1), whic h potently stimulated phosphoinositidase-C. However, unlike AVP, the E T-1 responses were observed both before and after sexual maturity, sug gesting different roles for AVP and ET-1 in the control of myoid cell function. Our data establish that the myoid cells of the adult rat sem iniferous tubule are a target for AVP. This indicates an additional ro le for AVP in the regulation of testicular function and male fertility in the adult rat.