Specific Binding of Prolactin to Seminal Vesicle, Prostate and Testicular Homogenates of Immature, Mature and Aged Rats

Abstract

Ovine prolactin was iodinated by the lactoperoxidase method and purified by gel filtration on Sephadex G-100. The binding ability of the labelled hormone was determined, by incubation with liver homogenate from rabbits in late pregnancy, to be 8-8% total binding/mg protein, of which 86% was specific. The fraction of 125I-labelled ovine prolactin which bound most strongly was subsequently used to study its binding to rat seminal vesicle, prostate and testicular homogenates. The total binding to the seminal vesicle homogenate taken from mature (80-day-old) rats was the highest (11-69%/mg protein), but the greatest degree of binding specificity (82-6%) was to immature (30-day-old) rat prostate. Both total and specific binding to rat testicular homogenate were consistently very low. The binding specificity was demonstrated by displacement studies: while ovine prolactin caused displacement of specific binding, human chorionic gonadotropin, rat thyrotropin and human follicle-stimulating hormone did not cause any significant displacement of bound 125I-labelled ovine prolactin. Affinity constants (Ka) and binding capacities for the seminal vesicle and prostate homogenates were determined by Scatchard analysis and the effect of age on these parameters was studied. There was no difference in Ka between the aged (220-day-old), immature and mature rat tissue homogenates; however, a significant fall in binding capacity was observed in the mature rat prostate, and a further fall in the aged rat prostate. No such change was observed in the binding capacity of the seminal vesicle, as estimated by Scatchard analysis, although total and specific binding to the mature homogenates was higher than that of the other age groups.

Visualization of Gene Expression of Short and Long Forms of Prolactin Receptor in Rat Reproductive Tissues

“…Specific binding sites for prolactin were originally identified in membrane preparations of several tissues: testis, epididymis, seminal vesicle, and prostate of male rats [7,[27][28][29][30][31][32][33][34]. Prolactin binding sites have also been localized in these tissues by autoradiography [14], and mRNAs of both forms of PRL receptor have been detected by PCR and measured by quantitative PCR [35].…”

Effects of pituitary hormones on the prostate

“…These effects are, in part, explained by the stimulating effect PRL has on testicular steroidogenesis [20]. As a specific prolactin receptor (PRL-R) is expressed in the prostate [21][22][23], PRL can bind to this receptor directly with the consequent stimulation of 5␣-reductase activity and increase in receptivity to androgens [24][25][26][27][28].…”

Effect of hypoprolactinaemia and hyperprolactinaemia on LH secretion, endocrine function of testes and structure of seminiferous tubules in boars

“…The physiological role of prolactin in male laboratory mammals includes the regulation of growth and normal func¬ tion of all tissues sensitive to androgens. Prolactin receptors have been found in Leydig cells of the testes, epididymides and accessory glands (Barkey et al, 1977;Bouhdiba et al, 1989). Prolactin, together with LH and growth hormone (GH), con¬ trols the production and maintenance of the LH receptors in the testes (Zipf et al, 1978).…”