Factors affecting circulating growth hormone binding protein in chickens

Growth hormone binding protein (GHBP) may be an important factor in the regulation of growth as well as an indirect, less invasive way of predicting the status of growth hormone receptors. Several factors (age, nutritional status, sex, and glucocorticoid administration) have been reported to influence circulating growth hormone (GH) levels, growth hormone receptor (GHR) activity and/or GHBP in mammalian species. Therefore, the studies conducted in this research were designed to determine if these factors have any affect on serum GHBP in the young broiler chicken. Serum GHBP activity was expressed as a percent specifically bound ¹²⁵IhGH (%SB), as measured by a dextran-coated charcoal assay. Serum GHBP activity was highest (mean %SB= 14.6 ± 1.2) at hatch aniedecreased linearly (r= -.9516) to 4 wk of age (mean %SB= 4.1 ± 0.6). Sex had no significant affect on serum GHBP activity from hatch to 4 wk of age. Short term nutrient deprivation (24 h fast) of 4 wk old birds had no significant affect on serum GHBP activity, nor did refeeding. Feeding birds nutrient poor diets (low energy, low protein or low energy and low protein) did not significantly affect serum GHBP activity when compared to birds fed a commercial broiler diet. Pulsatile delivery of cortisone acetate (1, 5 and 10 mg/d/b) had no affect on serum GHBP activity at any dose. These results suggest that serum GHBP activity in the chicken is not affected by many factors which do influence GHBP in mammalian species. The lack of response to nutrient deprivation and cortisone acetate may be a factor related to the age of the birds used in these studies

IL-1α and TNF-α Down-Regulate CRH Receptor-2 mRNA Expression in the Mouse Heart

Two receptors (CRH receptor type 1 and CRH receptor type 2) have been identified for the stress-induced neuropeptide, CRH and related peptides, urocortin, and urocortin II. We previously found marked down-regulation of cardiac CRH receptor type 2 expression following administration of bacterial endotoxin, lipopolysaccharide, a model of systemic immune activation, and inflammation. We postulated that inflammatory cytokines may regulate CRH receptor type 2. We show that systemic IL-1α administration significantly down-regulates CRH receptor type 2 mRNA in mouse heart. In addition, TNFα treatment also reduces CRH receptor type 2 mRNA expression, although the effect was not as marked as with IL-1α. However, CRH receptor type 2 mRNA expression is not altered in adult mouse ventricular cardiomyocytes stimulated in vitro with TNFα or IL-1α. Thus, cytokine regulation may be indirect. Exogenous administration of corticosterone in vivo or acute restraint stress also reduces cardiac CRH receptor type 2 mRNA expression, but like cytokines, in vitro corticosterone treatment does not modulate expression in cardiomyocytes. Interestingly, treatment with urocortin significantly decreases CRH receptor type 2 mRNA in cultured cardiomyocytes. We speculate that in vivo, inflammatory mediators such as lipopolysaccharide and/or cytokines may increase urocortin, which in turn down-regulates CRH receptor type 2 expression in the heart. Because CRH and urocortin increase cardiac contractility and coronary blood flow, impaired CRH receptor type 2 function during systemic inflammation may ultimately diminish the adaptive cardiac response to adverse conditions