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 and 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 (PO.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.

Prepubertal changes in the synthesis, storage and release of growth hormone and luteinising hormone and in the immunoreactivity of oestrogen receptor-α in lamb pituitary cells

“…Generally, the pulsatile measures of GH differ between the sexes, being higher in males than females (Gatford et al, 1997). These values also depend on the breed (Wójcik-Gładysz et al, 2002) and level of nutrition . It has been suggested that the gradual age-related fall in GH release could be related to prepubertal processes leading to attainment of fertility (Suttie et al, 1991).…”