The Effect of Thyroidectomy on the Secretion of Prolactin and on Plasma Levels of Thyrotropin, Luteinizing Hormone and Growth Hormone in Lambs1

Plasma levels of prolactin (PRL), thyrotropin (TSH), thyroxine, growth hormone (GH) and luteinizing hormone (LH) were measured in 4 ewes before and 1, 2, 3, 4, 5, 28 and 42 days after thyroidectomy. In addition, the metabolic clearance (MCR) and secretion rates (SR) of PRL were determined before, and, 28 and 42 days after thyroidectomy. Plasma levels of PRL and TSH increased (p > 0.01) with time after thyroidectomy reaching highest levels at 42 days, while plasma thyroxine decreased, reaching non—detectable levels at 42 days. The increased plasma levels of PRL were accompanied by a decrease in the MCR and an increase in SR of PRL. Plasma levels of GH did not change significantly following thyroidectomy while a decrease in LH was noted at 28 and 42 days. These data support the hypothesis that endogenous TRH is stimulatory to the secretion of PRL as well as TSH. Other possible explanations of these results are discussed.(Endocrinology92: 1736, 1973)