Abstract
Abstract
The effects of central nervous system administration of morphine on secretion of luteinizing hormone (LH), follicle-stimulating hormone, and prolactin were investigated in ovariectomized gilts stereotaxically implanted with lateral ventricular cannulas. In Experiment 1, mean serum LH and follicle-stimulating hormone concentrations and serum LH pulse frequency were unaffected by artificial cerebrospinal fluid administration (P > 0.1), but decreased (P < 0.01) in 8 of 11 gilts when 500 μg of morphine were given 3 hr later. Serum LH pulse amplitude was unaffected (P > 0.1) by cerebrospinal fluid or morphine injection. In Experiment 2, luteinizing hormone concentrations decreased (P < 0.0001) and prolactin concentrations increased (P < 0.0001), but follicle-stimulating hormone concentrations did not change (P > 0.1) after 500 μg of morphine. Gonadotropin responses to 10 μg of gonadotropin-releasing hormone, given 2 hr after intraventricular injection, were similar (P > 0.1) for morphine- and cerebrospinal fluid-treated gilts. These results indicate that morphine inhibits LH secretion at the level of the central nervous system, and are consistent with the concept that endogenous opioid peptides participate in the regulation of gonadotropin and prolactin release in pigs.
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