Modification of Serum Luteinizing Hormone and Prolactin Concentrations by Corticotropin and Adrenalectomy in Ovariectomized Rats

The effects of ACTH and adrenalectomy (ADX) on serum concentrations of LH and prolactin were examined in ovariectomized (OVX) rats. In the first study ACTH (4 IU) was administered daily for one week. ACTH prevented an increase in serum LH in response to OVX and stimulated serum prolactin. ACTH also reduced serum LH in OVX+ADX rats and increased prolactin concentration. ADX was utilized in the second experiment to enhance secretion of endogenous ACTH. Two weeks after ADX serum prolactin was elevated above intact values. ADX also enhanced serum prolactin in OVX rats to the level found in intact animals. ADX markedly reduced the LH response to OVX but ADX alone had no effect on serum LH concentration. All of these findings indicate that ACTH acts directly to reduce serum LH concentration and to enhance serum prolactin. The influence of adrenal corticoids on serum concentrations of LH and prolactin as reported by other investigators appears to be mediated via their negative feedback effects on ACTH release. Whether ACTH has its action on adenohypophyseal cells or on hypothalamic sites has yet to be determined.