Effect of naloxone and morphine on LH and prolactin release in androgen-sterilized rats

Many studies suggest that the hypothalamic opiate system modulates the secretion of LH and prolactin (PRL) by its effects on catecholamine release. We previously provided evidence that the LH response to the opiate receptor antagonist naloxone (NAL) may depend upon spontaneous activity in the hypothalamic noradrenergic system at the time the drug is administered. Thus, when NAL is given to rats which have low turnovers of hypothalamic norepinephrine (NE), only small transient rises in LH occur. This is contrasted to the effects of NAL on the LH responses of animals with high rates of NE turnover where marked amplification of phasic LH release is observed. In the present studies, we examined the effects of NAL on LH and morphine on PRL responses in androgen-sterilized rats (ASR). These animals do not respond to the positive feedback actions of estrogen by having LH surges, and hypothalamic NE turnovers do not increase during the afternoon as they do in normal rats. Female rats were given a single injection of testosterone propionate (50 micrograms s.c.) at 5 days of life and ovariectomized (OVX) at 100 days of age. Seven days later (day 0), estrogen capsules were inserted subcutaneously, and on day 2, their responses to NAL or morphine were examined. Comparable estrogen-treated gonadectomized controls also were studied. In control rats, NAL (10 mg/kg s.c.) markedly amplified the phasic secretion of plasma LH. In contrast, NAL had no effect on the basal afternoon secretion of LH in ASR. To determine if neonatal androgen treatment deleteriously affected opiate-tuberoinfundibular dopamine (TIDA)-serotonergic interactions, a second series of studies was performed.(ABSTRACT TRUNCATED AT 250 WORDS)