Influence of nutrition and bovine growth hormone (GH) on hepatic GH binding, insulin-like growth factor-I and growth of lambs

Abstract

The effect on young lambs of 0.25 mg recombinant bovine GH (bGH)/kg per day on plasma concentrations of insulin-like growth factor-I (IGF-I), glucose, specific hepatic GH binding and body composition changes was examined at two levels of nutrition (lucerne pellets; 3 and 1.7% of body weight/day). Lambs on low levels of nutrition had low plasma IGF-I (P less than 0.001). Plasma concentrations of IGF-I were increased by bGH treatment at both levels of nutrition, with the high nutrition group showing the greatest IGF-I response after 3 and 40 days of bGH treatment. Plasma glucose, after 40 days, was higher overall (P less than 0.05) in lambs on high nutrition. bGH treatment increased plasma glucose, with the response being greater in the well-fed lambs. Specific binding of GH to liver membranes was highest in lambs on high nutrition and on bGH treatment; no significant interaction between nutrition and bGH treatment was detected, indicating that specific binding of GH was increased proportionally by bGH at both nutritional levels. The major change in body composition was the reduced level of fatness in lambs treated with bGH. There was no significant effect of bGH on body weight although bGH treatment tended to increase weight gain of well-fed lambs and decreased weight loss of poorly nourished lambs. The results show that, although there was a significant (P less than 0.05) bGH/nutrition interaction for IGF-I there was no such interaction for body weight/components or specific GH binding to the liver. The results indicate that an increase in plasma IGF-I does not necessarily result in increases in growth or changes in carcass composition.

The responseof plasma leptin and feed intake to growth hormone administration in Holstein calves with different planes of nutrition

“…As in low feeding, chronic dietary restriction led to a decline in IGF-1 level in rat liver (Breese et al 1991;Donovan et al 1991) associated with the down-regulation that decreased hepatic-binding sites for GH through malnutrition in rat (Bornfeldt et al 1989) and sheep (Bass et al 1991). The increase in circulating IGF-1 level during the 10 d of bGH treatment in the normal and refeeding periods was consistent with the results of other studies.…”

“…Although various tissues synthesize IGF-1, blood IGFs are derived mainly from the liver and are nutrition-dependent. The rate of IGF-1 production may be influenced by the concentration and affinity of hepatic GH receptors in steer (Breier et al 1988) and sheep (Bass et al 1991). The physiological significance of the high-affinity site is that responses to exogenous bGH were only observed in well-fed steers with high-affinity binding sites (Breier et al 1988).…”

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

“…However, in agreement with our results, differences were not apparent when steers were only moderately underfed (Breier et al, 1986). Similarly, no differences in plasma IGF-I concentrations were reported when castrated male lambs were fed for 40 days at a level of 3 or 1.7% of body weight/day (Bass et al, 1991). It is possible that the experimental factors used in this study, the level of nutrition, age of animals and duration of experimental feeding were insufficient to affect plasma IGF-I concentrations.…”

Dairy cows experience selective reduction of the hepatic growth hormone receptor during the periparturient period

“…Factors responsible for reduced abundance of the GHR protein and GHR1A transcript remain uncertain in dairy cows, but could include the energy deficit and the hypoinsulinemia that develops around the time of parturition (Bell 1995, Block et al 2001. Consistent with this idea, undernutrition results in decreased hepatic GH binding in growing ruminants (Breier et al 1988, Bass et al 1991. Moreover, physiological elevation of plasma insulin in early lactating dairy cows increases hepatic GHR1A abundance (Rhoads et al 2002, Butler et al 2003.…”