Hormonal regulation of prolactin receptors in male rat target tissues: the effect of hypothyroidism and adrenalectomy.

The effects of hypothyroidism and adrenalectomy (ADX) on PRL receptors as well as the subcellular distribution of PRL-binding sites in adult male rat target tissues were investigated. In ventral prostate, kidney, and adrenal, PRL-binding activity was enriched in the 15,000 X g pellet (mitochondrial/Golgi fraction). The zona fasiculata/reticularis plus medulla of the adrenal had higher PRL-binding activity than the zona glomerulosa (plus capsule). Propylthiouracil-induced hypothyroidism significantly decreased PRL binding to kidney (65%) and testis (50%), and 16-h replacement with T4 restored PRL binding to control levels. T4 was, however, without effect on renal PRL binding in hypothyroid castrated rats, indicating that androgen may be required for this response. The increase in PRL binding to ventral prostate and adrenal due to hypothyroidism was not reversed within 16 h of T4 injection, whereas T3 injection decreased PRL binding to ventral prostate within 12 h. ADX increased PRL binding to rat testis (38%) and kidney (18%), and 5-day replacement with dexamethasone decreased PRL binding to levels lower than those in control rats. ADX had no effect, and dexamethasone treatment decreased (16-20%) PRL binding to ventral prostate and hCG binding to rat testis. The modulation of PRL receptors by hypothyroidism and ADX suggests that thyroid and adrenal hormones play a role in the regulation of PRL receptors.