Luteinizing hormone, follicle stimulating hormone and prolactin secretion in ewes and wethers after zeranol or estradiol injection

Journal of Animal Science
T H ElsasserM Roper

Abstract

Plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) were determined over a 24-h period using radioimmunoassay in sheep injected with corn oil (control) or various doses of zeranol or estradiol-17 beta. Injection of .333, 1 or 10 mg of zeranol caused dose-related increases (P less than .01) in plasma PRL (peak levels at 12 to 18 h) and LH (peak levels at 12 to 20 h) in ovariectomized ewes. Similarly, PRL and LH increased following doses of 33 or 100 microgram of estradiol. Before the LH surge, plasma LH levels were significantly depressed (4 to 8 h). Plasma FSH levels were significantly decreased 4 to 8 h after zeranol and estradiol injection. Slight surges of FSH were observed at times similar to those of LH, but the peak level was never greater than control levels. Injection of 1 mg of zeranol or 100 microgram of estradiol into wethers resulted in a 24-h pattern of PRL secretion not significantly different of LH concentration and significantly prolonged inhibition of FSH secretion. These results indicate similarities in the effects of zeranol and estradiol on anterior pituitary hormone secretion within groups of animals of the same sex or reproductive state. Differences in ...Continue Reading

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