Leptin expression in porcine adipose tissue is not increased by endotoxin but is reduced by growth hormone

The physiologic response to infection includes reductions in tissue concent rations of anabolic growth factors as a means of reducing growth and conser ving nutrients for immunologic processes. This repartitioning of nutrients is accompanied by anorexia, which has been linked to increased leptin expre ssion, Furthermore, leptin and growth hormone (GH) concentrations are inver sely related, with leptin being required for normal GH release. The objecti ve of this study was to determine if pretreatment with GH would influence e ndotoxin-induced changes in leptin expression or attenuate endotoxin-induce d reductions in serum insulin-like growth factor-1 (IGF-1) and IGF-1 expres sion in liver and longissimus muscle, In experiment 1, 40 pigs were assigne d to four treatments (n = 10 per treatment) arranged as a 2 x 2 factorial w ith GH (s.c. injection, 2 mg 1 h before challenge and 2 mg 2 h after challe nge) and endotoxin (single i.m. injection, 25 mu g/kg body weight) as main effect variables. Pretreatment with GH resulted in a marked increase (p < 0 .001) in serum GH within 1 h that was sustained throughout the study. Endot oxin challenge reduced (p < 0.003) serum IGF-1 independent of GH (GH x endo toxin, p > 0.682), and reduced (p < 0.05) IGF-1 expression in longissimus m uscle but not liver. Leptin mRNA abundance was reduced 56% (p < 0.005) by G H but was not affected by endotoxin (p > 0.81), In experiment 2, 36 pigs (n = 12 per treatment) were either allowed ad libitum feed consumption with n o injection or deprived of feed and injected twice with either saline or en dotoxin 24 h apart. Feed deprivation reduced leptin expression (p < 0.05), However, endotoxin did not change leptin expression but markedly increased (p < 0.05) serum haptoglobin. These data indicate that changes in IGF-1 sta tus in endotoxin-challenged pigs are independent of serum GH and that lepti n expression is not increased by endotoxin challenge in the pig. These data also indicate a regulatory linkage between GH and leptin in vivo.