Determination of Luteinizing Hormone (LH) Response to Different Doses of Lecirelin Acetate (a GnRH Analogue) in Tuj Ewe-Lambs

Abstract

The aim of the present study was to determine the LH response to different levels of lecirelin acetate (a GnRH agonist) in Tuj ewe-lambs. Twenty lambs, aged 5-months-old, were randomly allocated into four groups of five. Lecirelin acetate was intravenously administered to lambs from groups 1,2, 3, and 4 at 0.1, 0.2, 0.5 and 1.0 μg per kg BW, respectively (Administration I). Blood samples were collected from the jugular vein 30 minutes before and at 30 min intervals for 300 minutes after the administration to determine the plasma LH concentrations. The administration was repeated 72 h later, to determine the replenishment of pituitary stores of LH in the same lambs (Administration II). Following both administrations, LH response was dosedependent and the doses of 0.5 and 1.0 μg per kg resulted in a significantly greater response than the dose of 0.1 and 0.2 μg/kg (P lower than 0.05). On the other hand, LH release characteristics for all dosage groups were similar between the first and second administrations (P greater than 0.05). These data suggest that (1) LH stores were replenished within 72 hours after lecirelin acetate administration and that (2) highest LH responses were obtained at 0.5 and 1.0 μg per kg dose levels in Tuj ewe-lambs.