Dose- and Age-Dependent Effects of Prolactin (PRL) on Luteinizing Hormone- and PRL-Binding Sites in Rat Ley dig Cell Homogenates*

Various doses of ovine PRL (oPRL; NIH-P-S12) were injected into immature (22 days old) and adult (82 days old) Sprague-Dawley rats at 1400 h for 2 days to determine the effects of PRL on hCG- and hPRL-binding sites in Leydig cell homogenates. Since hCG and LH bind to the same receptor site, labeled hCG was used for the assessment of LH-binding sites. From a total of 30–60 immature rats for each treatment group, testes from 6 rats were pooled for homogenization and preparation of 27,000 × g Leydig cell homogenates. From a total of 35 adult rats, testes from single rats were pooled for each 27,000 × g preparation. Binding characteristics for hCG and hPRL were determined for each homogenate pool, viz. 5–10 immature and 5–8 adult pools per treatment group. In immature rats, 1, 2.5, 5, 10, or 20 μg oPRL sc/day for 2 days resulted in an increase in hCG-binding sites to 291, 318, 876, 642, and 591 fmol hCG/mg protein compared to 212 fmol hCG/mg protein in saline injected controls. Receptor affinity remained unch...