Pulsatile follicle stimulating hormone (FSH) secretion in prepubertal female sheep with and without food restriction

Abstract

Food restriction delays the onset of puberty due to a low secretion of LH and probably the FSH as well. The objective of this work was to assess and to compare the diurnal pulsatile secretion of FSH in normal growing and in growth-retarded ewe lambs due to food restriction. Five Suffolk ewe lambs were fed at 2% of their body weight in two daily rations whereas the other 5 were fed ad-libitum from 20 and until 30 weeks of age and served as a control group. A FSH pulsatile study was conducted, before and after six and ten weeks of food restriction corresponding to 20, 26 and 30 weeks of age respectively. The FSH pulsatile study consisted in collecting blood samples every 10 minutes for 5 hours from 10 AM onwards. In the obtained plasma the FSH was measured by RIA. The characteristics of the pulsatile FSH secretion were assessed using the CLUSTER program. Data obtained from the CLUSTER program were analyzed with analysis of variance for repeated measures. Mean plasma FSH concentrations (ng/mL/5h) increased in almost 50% in control ewe lambs between 20 and 30 weeks of age but without statistical difference. At 30 weeks of age, control lambs had a 50% higher mean plasma FSH concentrations and mean FSH pulse amplitude than food-restricted lambs. FSH pulse frequency did not show any difference between ages within a group or between groups. Results suggest that food restriction has a partial suppressor effect on the FSH secretion. The delay on the onset of puberty due to food-restriction in the ewe lamb could be attributed more to an insufficient LH secretion GnRH-stimulated than to an inadequate FSH secretion.