Differences in the secretion pattern of growth hormone and insulin-like growth factor - I in sheep of two crossbreeds after dietary protein restriction

Abstract

The presented study was designed to evaluate the relationships between cross types of lambs and the pattern of GH and IGF-I secretion under conditions of standard and restricted protein feeding. The experiment was performed on two different cross types of female lambs: [(Merino x Romanov) x Suffolk], n=10, (MxR) and [(Merino x Finn) x Suffolk], n=9, (MxF). Lambs of both cross types were divided into two groups and fed on two isoenergetic diets, but containing different protein levels, for 16 weeks, starting at 6 months of age. At the end of the experimental feeding blood samples were taken over a period of 6 hours at 10-min intervals. The concentrations of GH and IGF-I were estimated by a radioimmunological method, the parameters of GH release pulsatility were calculated using the Pulsar computer program. The basal level of GH rand IGF-I were significantly (P<0.05) higher in MxR compared to MxF lambs. The higher GH level in MxR lambs was associated with significant elevation (P<0.05) of GH pulse amplitude. Long-term feeding on the restricted protein diet in both cross types caused a significant (P<0.05) increase of mean GH concentrations and GH pulse amplitude, higher in MxR lambs, but had no effect on the IGF-I level. In conclusion, the basal secretion of GH and IGF-I could be dependent on the genetic background of the cross-bred lambs. GH secretion can be modulated by the protein level in the diet, with the intensity of the changes depending on the basal GH level.