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Metabolic Actions of Growth Hormone in Pigs^{1 ,2,}

Iowa State University³, Ames 50011

Abstract

The objectives of this study were to determine whether growth hormone (GH) from porcine and rat origin stimulates growth and anabolism in immature pigs. Twenty male pigs, averaging 37 kg body weight, were subjected to hypophysectomy or sham operation by a supraorbital approach. Porcine GH (pGH) or rat GH (rGH) was injected IM in a daily dosage of 1 mg for 40 days after hypophysectomy; sham-operated and hypophysectomized controls were given saline injections. Body weights were obtained daily, and sequential blood samples from these animals were analyzed for protein, albumin, urea N, -amino N, Na, Ca, K, Fe, aldolase and free fatty acids. Immature-hypophysectomized pigs were acutely sensitive to anabolic effects of low daily dosages of both pGH and rGH. Daily gains during the first 12 days were .554, .488 and .226 kg for hypophysectomized pigs given pGH, rGH and saline, respectively, and .386 kg for sham-operated controls. Thereafter, growth response was less pronounced, but body weight increases remained higher throughout 40 days as compared with those of saline-injected, hypophysectomized controls. pGH given to hypophysectomized pigs increased concentrations of protein and albumin and decreased urea N, whereas levels of -amino N were unchanged in peripheralserum. Serum levels of Na, Ca and K remained similar in hypophysectomized pigs given pGH or saline; Fe concentrations were unaltered by treatment. These metabolic responses were less pronounced in hypophysectomized pigs given rGH. Aldolase concentrations in hypophysectomized pigs given pGH, rGH or saline were not reduced significantly by comparison with die concentrations in sham-operated controls. Free fatty acid levels in hypophysectomized pigs given pGH were increased compared with those in saline-injected controls. These results indicated that low daily levels of either pGH or rGH induced significant increases in body weight and protein anabolism in immature hypophysectomized pigs, but that these responses were transitory. Young, hypophysectomized pigs respond to GH at low treatment levels that are ineffective in intact animals.

¹ Journal Paper No. J-9052 of the Iowa Agr. and Home Econ. Exp. Sta., Ames, Projects 1994 and 2093.

² We thank Dr. W. P. Switzer, Dr. D. O. Farrington and Dr. K. S. Preston of the Veterinary Medical Research Institute for monitoring the health status of the experimental animals; Dr. R. M. Melampy for advice; Dr. D. F. Cox of the Dept. of Statist, for advice on statistical analyses, and Messrs. M. E. Shell and D. L. Plath for technical assistance. Purified rGH (NIAMD-Rat GH-B-3) was kindly provided by Dr. A. F. Parlow, Rat Hormone Distribution Program, NIH.

³ Dept. of Anim. Sci.