Differential effects of pancreatic polypeptide on luteinizing hormone release in female rats

Observations that a pancreatic polypeptide-like substance is present in hypothalamus and may coexist with catecholamines prompted evaluation of its possible role in control of luteinizing hormone (LH) secretion. Intracerebroventricular administration of 0.5 or 2 micrograms of human pancreatic polypeptide to ovariectomized, hormonally untreated rats significantly decreased LH levels. However, when administered to ovariectomized rats pretreated with estradiol benzoate and progesterone, the neuropeptide significantly increased circulating LH in a dose-related manner. These results, which are similar to those reported for centrally administered norepinephrine, raise the possibility that pancreatic polypeptide, or a similar peptide, may participate in the physiologic regulation of LH release, either independently or perhaps as a neuromodulator or a cotransmitter with catecholamines.