CHANGES IN SOMATOTROPIC AXIS RESPONSE AND BODY-COMPOSITION DURING GROWTH-HORMONE ADMINISTRATION IN PROGRESSIVE CACHECTIC PARASITISM

A multistage protozoan parasitic disease was used as a cachexia model to study the effects of daily administration of bovine growth hormone (GH) on endocrine and body composition changes of young calves from th e onset of the acute phase response (APR). Male calves averaging 127.5 +/- 2.0 kg body weight were assigned to control, ad libitum fed, noni nfected (C); ad libitum fed, infected (250,000 oocysts Sarcocystis cru zi, per os, I); noninfected, pair-fed (PF) to matched I-treatment calv es and these respective same treatments in calves injected daily with GH (USDA-bGH-B1), 12.5 mg/calf/day, im) designated as C-GH, I-GH and P FGH. GH injections were initiated on Day 20 postinfection (PI), 3 to 4 d before the onset of clinical signs of APR, and continued to Day 56 PI, at which time animals were euthanized for tissue collections. Abru pt increases in rectal temperature commensurate with-up to 70% reducti on in voluntary feed intake were observed in I and I-GH beginning 23-2 5 d PI. For the trial period between Days 20 and 56 PI, average daily carcass protein gains were 123, 52, 109, 124, 48, and 67 g/d and avera ge daily carcass fat gains were 85, 11, 43, 71, -23, and 29 g/d for C, I, PF, C-GH, I-GH, and PFGH, respectively. Effects of GH were signifi cant for fat accretion and plasma urea depression. Rectus femoris was highly refractory to catabolic effects of infection while psoas major was significantly catabolized during infection. Plasma concentrations of insulin-like growth factor-I (IGF-) I increased significantly in al l GH-treated calves between Day 20 and 23 PI. Plasma IGF-I declined we ll below Day 20 values in all infected calves from the onset of the AP R through the end of the study. The decrease in plasma IGF-I concentra tions in I and I-G was highly correlated with the magnitude of the fev er response. Hepatic mRNA for GH receptor and IGF-I was decreased in i nfected calves. Hepatic microsomal membrane binding of I-125-GH did no t differ between groups. The data suggest that effects of GH and paras itism on tissue metabolism during disease may vary among different spe cific tissue pools. The data demonstrate that daily GH administration in young calves does not prevent lean tissue losses and may accelerate fat depletion associated with cachectic parasitism. Furthermore, the onset of APR overrode the capacity for GH to maintain elevated plasma concentrations of IGF-I, an effect not readily explained through chang es in GH-receptor binding. (C) Elsevier Science Inc. 1998.