Loss of Estrogen-Induced Daily Surges of Prolactin and Gonadotropins by Suprachiasmatic Nucleus Lesions in Ovariectomized Rats*

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Abstract
The suprachiasmatic nucleus is suggested to be a generator of several circadian rhythms. In the present study, the suprachiasmatic nucleus was examined to determine whether it is involved in the generation of daily PRL and gonadotropin surges which are induced by estrogen administration in ovariectomized female rats. Blood samples were obtained at 3-h intervals for 24 h from individual animals with an indwelling atrial cannula. Subcutaneous injections of 50 μg estradiol benzoate into ovariectomized rats elicited pronounced surges of serum PRL, LH, and FSH, with a peak around 1800 h. Hypothalamic frontal deafferentation by a bayonet-shaped knife, which interrupted frontal afferents to the medial basal hypothalamus at the retrochiasmatic level, abolished the surges of PRL and gonadotropins. In rats with large lesions of the suprachiasmatic nuclei (destruction of more than 50% of the bilateral nuclei), the characteristic PRL surges were eliminated, whereas comparable PRL surges to those in sham-lesioned animals were observed in rats with the small lesions (destruction of adjacent structures or less than 20% of the nuclei). Furthermore, most of animals with large lesions of the suprachiasmatic nuclei exhibited the pulsatile or sporadic release of PRL rather than the consistently low secretion observed in serum LH and FSH of these animals. These results suggest that the suprachiasmatic nuclei play an essential role in the endogenous generation of estrogen-induced daily PRL surges and other circadian rhythms. (Endocrinology106: 1087, 1980)