Estradiol Enhances the Action of Neuropeptide Y on in vivo Luteinizing Hormone-Releasing Hormone Release in the Ovariectomized Rhesus Monkey

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Abstract
The effect of estrogen on the responsiveness of the luteinizing hormone-releasing hormone (LHRH) neurosecretory system to neuropeptide Y (NPY) stimulation was examined using a push-pull perfusion method in conscious monkeys. NPY, at doses of 10(-6) to 10(-12) M, was infused into the stalk-median eminence (S-ME) of ovariectomized monkeys with or without estrogen, while perfusates were continuously collected. LHRH in perfusates was measured by RIA. The results indicate that in both estrogen-primed and unprimed monkeys, NPY infusion into the S-ME elicited LHRH release in a dose-dependent manner (p < 0.01). Moreover, estrogen priming enhanced the responsiveness of LHRH release to NPY infusion: (1) the minimum NPY dose necessary to elicit a significant LHRH response was reduced, (2) the peak LHRH response to NPY at a dose of 10(-6) to 10(-10) M was increased, and (3) the total release of LHRH in response to NPY at doses of 10(-6) to 10(-12) M was increased. These results suggest that NPY stimulates LHRH release in the S-ME in the presence or absence of estrogen and that estrogen enhances the responsiveness of the LHRH neurosecretory system to NPY stimulation in the rhesus monkey.

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