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Determination of the Temporal Relationship Between Porcine Growth Hormone, Serum IGF-1 and Cortisol Concentrations in Pigs¹

The Pennsylvania State University, University Park 16802

Abstract

We found previously that porcine growth hormone (pGH) causes an increase in growth rate with a concurrent improvement in carcass composition in pigs. The somatomedin, insulin-like growth factor 1 (IGF-1), is thought to play a major role in mediating some of the anabolic actions of GH, while the glucocorticoid hormones are potential counter-regulators of these effects. The present study was conducted to determine the temporal and dose-response relationship between GH administration and serum IGF-1 and cortisol concentrations in pigs. Twelve Yorkshire barrows, fitted with femoral artery catheters, were injected (im) with either 0, 10, 100 or 1,000 µg/kg pGH. Blood sampling began 40 min prior to pGH injection and was continued for 37 h. Serum GH, IGF-1 and cortisol concentrations were determined by radioimmunoassay. In control animals, serum GH concentrations ranged from 1.6 to 5.7 ng/ml over 37 h. In the animals treated with increasing doses of pGH, peak serum GH concentrations reached 28, 112 and 286 ng/ml and levels remained elevated for 4, 12 and 24 h, respectively. Serum IGF-1 concentrations were elevated by pGH after a lag time of 4 to 6 h. When the IGF-1 concentrations were integrated over time, the response appeared to be dose-dependent, with an ED₅₀ of 710 µg/kg body weight (BW). Data for serum cortisol concentrations showed a great deal of individual variation. A transient increase in cortisol was observed, but only in the group treated with 1,000 µg pGH/kg BW. Cortisol levels returned to baseline 2 h after pGH injection. Observations from a recent growth trial in pigs suggest that a maximally effective dose of pGH is in the region of 100 to 200 µg·kg BW^–1·d^–1. Since serum IGF-1 concentrations can be elevated by pGH far beyond the effects produced within this dose range, it is concluded that the acute inductive effect of pGH on serum IGF-1 provides neither a sensitive marker, nor represents a rate-limiting step with respect to the anabolic effects achievable in pigs treated chronically with pGH.

¹ Authorized for publication as paper no. 7549 in the Journal Series of the Pennsylvania Agr. Exp. Sta.

² Dept. of Dairy and Anim. Sci.