Acetyl-l-carnitine restores the daily pattern of hypothalamic beta-endorphin in rats exposed to continuous light.

With the aim of evaluating the effect of acetyl-l-carnitine (ALC) on the daily pattern of hypothalamic beta-endorphin (beta-EP), we studied the effect of chronic treatment with ALC on hypothalamic beta-EP contents after suppression of the dark-phase of the light-dark cycle in female rats. We evaluated the hypothalamic content of beta-EP immunoreactivity every 3 h for 24 h in: (1) female rats treated with ALC for 15 days; (2) female rats treated with ALC for 15 days and exposed to continuous light for 24 h. The concentration of beta-EP immunoreactivity in tissue extracts was measured by radioimmunoassay. The results demonstrate that concentrations of beta-EP immunoreactivity in the medial basal hypothalamus show a circadian rhythm, with beta-EP immunoreactivity levels being higher during the night than during the rest of the day. Exposure to continuous light for 24 h abolished the nocturnal increase in hypothalamic beta-EP immunoreactivity. Rats treated with ALC showed a daily pattern in the beta-EP content of the medial basal hypothalamus similar to that of control rats. These data emphasize the possible role of ALC in restoring or maintaining the endogenous rhythmicity of central beta-EP.

Norgestimate increases pituitary and hypothalamic concentrations of immunoreactive beta-endorphin.

Progesterone is a potent hormone acting on the female reproductive tract and influencing a series of other functions. Recent studies revealed a correlation between progesterone and brain neurotransmitters and neuropeptides. Our study evaluated the possible effect of norgestimate, a new progestin, on hypothalamic and pituitary beta-endorphin (B-EP) concentration in castrated female rats. Ovariectomy was performed under ethyl ether anesthesia. Treatment was started 3 weeks after surgery. Norgestimate, estradiol benzoate or norgestimate plus estradiol benzoate were administered. The two steroids were dissolved in sesame oil and injected (s.c.) every day for 2 weeks. Pituitary and hypothalamus B-EP concentrations were measured by radioimmunoassay. Our studies showed that norgestimate increases the pituitary and hypothalamic B-EP concentration in female rats, reaching values higher than controls and estrogen-treated rats. Because B-EP has an important role in reproductive function, both modulating gonadotropin secretion and sexual behavior, the present results lead to the hypothesis that norgestimate affecting B-EP concentrations may influence central functions.

Estrogens modulate the circadian rhythm of hypothalamic beta-endorphin contents in female rats.

The aim of the present study was to evaluate the changes in the diurnal rhythm of the hypothalamic beta-endorphin (beta-EP) contents in female rats as a function of circulating estrogens. With this purpose we evaluated the diurnal hypothalamic beta-EP changes (1) during the estrous cycle, and (2) in ovariectomized rats with and without acute and chronic estrogen replacement. Ovariectomized rats were treated either acutely with 10 micrograms of estradiol benzoate (EB) or chronically with 2 micrograms/day of EB for 15 days. beta-EP concentrations were measured in acid extracts of medial basal hypothalamus by a specific radioimmunoassay. During the estrous cycle, hypothalamic beta-EP concentrations showed a significant nocturnal increase, with no difference between the 4 days of the cycle. On the day of estrus, beta-EP concentrations between 12.00 and 18.00 h resulted significantly lower than in the other days of the cycle. After ovariectomy, the night-related changes in hypothalamic beta-EP disappeared. The acute administration of EB induced a significant increase in hypothalamic beta-EP after 21 h (18.00 h). On the other hand, the chronic replacement restored the nocturnal peak of hypothalamic beta-EP (18.00, 21.00, 24.00 h). The present data emphasize the role of central beta-EP in regulating the reproductive functions. Moreover, the effect of estrogen in modulating the circadian changes in hypothalamic beta-EP supports the important role of estrogens in brain function.