Regulation of testicular prolactin and luteinizing hormone receptors in golden hamsters

Iodinated ovine PRL (oPRL) was used to detect the presence of PRL receptors in hamster testes. Binding to these receptors was specific for PRL and was saturable and incompletely reversible. Testicular PRL receptors possessed a single class of independent, high affinity binding sites (Ka = 2.4 × 1010 m−1). The ability of PRL to regulate testicular PRL and LH receptors was measured in experiments wherein mature hamsters were injected daily for 10 days with 600 μg bromocriptine, 600 μg bromocriptine plus 250 μg oPRL, or injection vehicles. Bromocriptine injections, which caused significant reductions in serum PRL, produced commensurate decreases in concentrations (femtomoles per mg protein) of testicular LH and PRL receptors, without affecting binding of PRL to adrenal or liver tissue preparations. Decreases in testicular PRL binding were not always statistically significant, but were consistently measured. The administration of oPRL with bromocriptine significantly increased both concentration and total con...