Receptors for vasoactive intestinal peptide on isolated epithelial cells of rat ventral prostate

Receptors for porcine vasoactive intestinal peptide have been characterized in isolated epithelial cells of rat ventral prostate. The interaction of ¹²⁵I-labelled VIP with cells was rapid, reversible, specific, saturable and dependent on temperature. Degradation of peptide and receptors was minimized at 15°C. At apparent equilibrium, the binding of ¹²⁵I-labelled peptide was competitively inhibited by native VIP in the 1·10⁻¹⁰−10⁻⁷ M range concentration. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a K_d = 4.0 nM and a low binding capacity (0.12 pmol VIP/mg cell protein), and a low-affinity class with a K_d = 17.8 nM and a high binding capacity (1.6 pmol VIP/mg cell protein). Chicken VIP and porcine secretin exhibited a 7-fold higher and a 7-fold lower affinity than porcine VIP for binding sites, respectively. Glucagon, Leu-enkephalin, Met-enkephalin and somatostatin were ineffective. The presence of high-affinity receptors for VIP together with previous reports on the occurrence of VIP-containing neurones innervating the male genitourinary tract strongly suggest that this peptide may be important in the physiological regulation of the functions of prostatic epithelium.