Comparison of the effects of deafferentation and ablation of medial basal hypothalamus on thyrotropin and prolactin secretion.

To further delineate the interrelationships of neural control of TSH and prolactin secretion, medial basal hypothalamic deafferentation (MBHD) or medial basal hypothalamic ablation (MBHA) were performed in euthyroid or hypothyroid male rats. MBHD produced a prompt and significant fall in plasma TSH but no change in plasma prolactin. MBHA produced a more marked fall in plasma TSH and a 6-fold rise in plasma prolactin within 3 days postoperatively. Plasma TSH remained at a low level postoperatively, but plasma prolactin gradually declined from its peak 3-5 days postoperatively to approximately the initial basal levels 2 weeks postoperatively. MBHA did not appreciably impair the ability of TRH to stimulate TSH secretion or of perphenazine to stimulate prolactin secretion. Where the same experiments were performed in both euthyroid and hypothyroid rats, there was no qualitative difference between the two, although basal plasma TSH was higher and prolactin lower in the hypothyroid than in the euthyroid animals. Our data support the concept that the medial basal hypothalamus is important in stimulating TSH and inhibiting prolactin secretion. Dormant inhibitory influences on prolactin secretion, but not stimulatory influences on TSH secretion, may be aroused after hypothalamic ablation.