Serum concentrations of luteinizing hormone, growth hormone, and prolactin in untreated and estradiol-treated ovariectomized ewes after immunoneutralization of hypothalamic neuropeptide Y.

Ovine antiserum against a conjugate of porcine neuropeptide Y (NPY) with bovine thyroglobulin was infused repeatedly into one lateral ventricle of five ovariectomized (ovx) ewes before and after subcutaneous injection of estradiol-17 beta (E beta). Serum concentrations of LH, growth hormone (GH), and prolactin (PRL) were measured at 10-min intervals before E beta and at approximately hourly intervals 8 to 18 h after E beta injection. Control ewes were infused with ovine serum from animals immunized against bovine thyroglobulin. Basal episodic profiles (pre-E beta) of LH, GH, and PRL were similar in ovx ewes infused with control or anti-NPY serum. Injection of E beta induced a surge-like increase of serum LH, which began at 12.6 h after E beta in ewes infused with anti-NPY and at 14.4 h after E beta in ewes infused with control antiserum (P < .05). The magnitude of the E beta-induced surge of LH was not different between treatments. In addition to initiating a surge-like release of LH over the period 12 to 18 h after E beta, serum GH was transiently increased during the period between 10 and 15 h after E beta. In contrast, serum PRL was increased during the entire period between 8 and 18 h after E beta. Based on the effects of immunoneutralization, endogenous NPY in the brain of E beta-treated ovx ewes seems to restrain or delay the onset of the surge-like secretion of LH and probably GnRH, but endogenous NPY does not affect the episodic pulsatile releases of LH characteristic of ovx ewes.(ABSTRACT TRUNCATED AT 250 WORDS)