Neuroendocrine Regulation of Luteinizing Hormone ıcretion in Beef Calves1

Abstract

Hypothalamic regulation of luteinizing hormone (LH) secretion was investigated in 5-month-old beef calves by comparing the effects of hypophysial stalk transection and sham operation during prepuberal development. LH is released episodically in these sham-operated heifer calves. LH in peripheral blood serum reaches average peak concentrations of 4.4 ng/ml (range 1.6–12.6 ng/ml) within 20 min and requires about 80 min to return to average basal levels of 0.3 ng/ml (range 0.20–0.48 ng/ml). During an 8 h period the mean number of LH peaks is 3.4 (range 1–6) in control calves. After hypophysial stalk transection, a complete inhibition of the episodic release of LH occurs; peripheral serum LH remains consistently at basal or nondetectable (<0.2 ng/ml) concentrations in these calves. These results indicate that episodic release of LH depends upon hypothalamic stimulation during prepuberal development in cattle.