ACUTE EFFECTS OF ADMINISTRATION OF PORCINE GROWTH-HORMONE ON CIRCULATING LEVELS OF HORMONES AND METABOLITES IN 20-KILOGRAM, 40-KILOGRAM, AND 60-KILOGRAM GILTS

Three groups of eight gilts weighing 20, 40, or 60 kg were fitted with indwelling venous catheters to determine daily integrated circulating levels (DICL, serum concentration above baseline x time) of insulin, growth hormone (GH), glucagon, glucose, urea, and nonesterified fatty acids (NEFA) in response to acute challenge with porcine pituitary GH (pGH). Pigs were fed a common diet containing 18% CP and 3.5 Mcal of DE/kg between 0800 and 1200 (85% of ad libitum). Blood and urine were collected at 2- or 4-h intervals for 4 d. On d 2, 3, and 4, four pigs in each group were injected i.m. at 0800 with pGH (.1 mg/kg) and four pigs (controls) were injected with buffer. In control pigs DICL of GH was 20.4, 14.1, and 10.2 ng pGH-h-mL-1 in 20-, 40-, and 60-kg pigs, respectively. The DICL of GH in pGH-treated pigs was 4.2-, 7.0-, and 10.7-fold greater in 20-, 40-, and 60-kg pigs, respectively, than in controls. The DICL of insulin in control pigs was 7.9, 9.7, and 9.4 ng.h.mL.1 and was increased (P < .001) in pGH-treated pigs by 118, 213, and 276% in 20-, 40-, and 60-kg pigs, respectively. Although serum levels of glucose were increased (P < .001) by pGH treatment, the acute elevation observed in 60-kg pigs was more consistent relative to 20- and 40-kg pigs. In contrast, the acute reduction in blood urea upon pGH injection was more apparent in 20-kg gilts. Urea excretion was also reduced (P < .002) in PGH-treated compared with control gilts, whereas creatinine excretion was influenced by weight (P < .001) and not by pGH treatment (P < .74). Circulating levels of NEFA were influenced by pGH treatment, but only apparently in 60-kg pigs. Data suggest that administration of pGH alters amino acid metabolism in pigs greater-than-or-equal-to 20 kg, but direct acute effects on lipid metabolism may be limited to larger pigs, which are exposed to a greater effective concentration of injected hormone relative to baseline control levels of circulating GH.