hCG induced steroidogenic response in Mangalarga young stallions: plasma testosterone and estrone sulphate

Abstract

Leydig cell acute steroidogenic response, in seven young Mangalarga stallions (2.6 - 4.5 ys), was evaluated through human Corionic Gonadotrophin (hCG) stimulation. The animals were treated with 5,000 UI (hCG) Vetecor®, i.v., in bollus, at 8 a.m. Plasma samples were collected by venopuncture at 7 a.m. (basal), 4, 24, 48, and 72 hours after stimulation (from 28 to August 31). Testosterone (T) and estrone sulphate (E1SO4) was measured by radioimmunoassay (RIA), intra-assay variation <= 5%. Data were analysed by Friedman and Wilcoxon Matched-Pairs tests (p <= 0.05). The magnitude of hormonal production after stimulation was analysed by Percentual Variation (delta %). At 48 hours, 57.1% of the animals (n = 4) had maximal response (T) with values 5.7 greater than basal. And although 57.1% of them (n = 4) had maximal response (E1SO4) at 4 hours, the maximal value was 1.6 greater than basal at 24 hours. The hCG may be employed to stimulate the Leydig cell steroidogenic response and 5,000 UI is enough to stimulate testicular steroidogenesis. The estrogen basal concentrations are higher than testosterone basal concentrations. This protocol could be applied to identify fertility problems of endocrine origin in horses of this breed.