Adrenergic system participation on LH secretion in pre-pubertal Nelore heifers

Abstract

The aim of this study was to evaluate the response of clonidine administration (alfa-adrenoceptor agonist, 10g/kg body weight, i.v. and blood collected every 15 min for 4 h thereafter) on luteinizing hormone (LH) secretion in B. indicus pre-pubertal heifers at 8, 12 e 15 months of age). LH was quantified by RIA, sensitivity (0.05 ng/mL) and coefficient of variation (20.39%). Alfa-adrenoceptor action (clonidine) reduced (P<0,05) basal LH and time to greatest peak occurrence at 15 months-old and increased (P>0,05) peak total area and area of highest peak of LH secretion to 8 months-old. The results suggest reduced hypothalamic sensibility by gonadal steroid in pre-pubertal Nelore heifer maturation sexual and clonidine neurotransmitter participation, either stimulating or inhibiting LH secretion.