Evaluation of a gaba receptor antagonist on luteinizing hormone secretion before, during and after fasting in ewe lambs

Abstract

The objective of this study was to assess the effect of a GABA receptor antagonist, (Bicuculline) on the pulsatile LH secretion before, during and after fasting in ewe lambs. Five Suffolk ewe lambs of 20 weeks of age were subjected to fasting for 8 days. A study of LH pulsatility was performed before (day 0), after one and eight days of fasting and 48 hours after the end of fasting. This study consisted in collecting blood samples by means of an indwelling jugular vein catheter at 10 min intervals for 10 hours from 9am inwards hours. Five hours after the start of the pulsatility study, a bolus of Bicuculline (50 ug/kg BW) was given intravenously. Thus, the 10-hours study period was divided in two phases of 5-hours each: before and after bicuculline. Parameters of the LH secretion were determined by the CLUSTER program independently for both phases and compared by paired t-test. Basal parameters of LH secretion on each day of the study were analyzed with ANOVA for repeated measures and comparison of the means with the Newman Keulss test. Body weight was recorded and basal levels of blood glucose, insulin and cortisol were also obtained before, during and after fasting. 
Body weight and basal plasma glucose concentrations decreased significantly after 8 days of fasting, however, insulin and cortisol did not change. Parameters of pulsatile LH secretion did not change with fasting or after 48 hours of refeeding. Bicuculline tended to increase (p<0.06) both mean plasma concentrations and amplitude of LH pulses before fasting (Day 0), but it had no effect on LH secretion on day 1, 8 of fasting or after two days of refeeding. 
Results suggest that GABA may be involved in the control of LH secretion in normally fed ewe lambs, however this control is not apparent during fasting. Fasting has an impact on body weight and plasma glucose concentrations but no effect on basal plasma levels of insulin. Plasma cortisol concentrations did not change suggesting that fasting did not evoke a stress condition.