The long-term effect of protein malnutrition on concentrations of growth hormone and insulin-like growth factor-I in female lambs

The present study was designed to set up the influence of long-term protein restriction in the diet of growing female lambs on the level of growth hor mone (GH) and insulin-like growth factor-I (IGF-I) in blood plasma and to c arry out adaptations for the method of estimation of blood plasma IGF-I in the sheep. The experiment was undertaken on eight, six-month-old female lam bs. For the period of 12 weeks they were subjected to an isocaloric diet co ntaining either a low (8%) or a high (18%) amount of protein. Blood collect ions were performed at the end of experimental feeding for 6 hrs at 10 min intervals. The results obtained by radioimmunoassay showed that the mean co ncentration of GH was significantly higher (P < 0.05) in the group fed the low protein diet (8.0 +/- 3.9 vs. 4.2 +/- 1.6 ng/ml) and this difference wa s associated with a significant elevation (P < 0.05) of the pulse amplitude (8.0 +/- 4.4 vs 2.7 +/- 1.4 ng/ml). The level of IGF-I did not differ sign ificantly between the two groups of sheep (56.4 +/- 3.9 ng/ml vs. 52.2 +/- 5.3 ng/ml). The results indicate, that long-term restrictions of dietary pr otein in growing lambs augment the GH secretion but have no effect on the I GF-I levels.