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Stimulation of In Vitro Muscle Cell Proliferation by Sera from Swine Injected with Porcine Growth Hormone¹

University of Minnesota, St. Paul 55108

Abstract

The proliferation-promoting activity of sera obtained from pigs before and after porcine growth hormone injections was tested in a muscle cell culture bioassay. For 3 d, purified porcine growth hormone (pGH) was administered by intramuscular injection to crossbred barrows. Two levels of pGH were administered: 18 µg pGH·kg^–1 body weight·d^–1 (low dose) or 143 µg pGH·kg^–1 body weight·d^–1 (high dose). Multiple blood samples were withdrawn from jugular catheters for 3 d prior to the injection, during the injection period and for 6 d after the last injection. Although serum pGH levels in low-dose pigs were raised from two to three times pre-injection levels, there was no significant change in serum proliferation-promoting activity or somatomedin-C (SraC), insulin or cortisol levels during or after administration of pGH. In contrast, the proliferation-promoting activity of sera obtained during and after the high-dose pGH injections was higher (P<.005) than the pre-injection levels. Serum pGH levels were increased approximately 30-fold by 4 h after each injection, and increases in SmC levels were observed 10 to 16 h after the pGH injection. During the injection period SmC levels increased from 1.7 to 4 times pre-injection levels. Insulin and Cortisol levels did not change significantly during the 3-d treatment period. We believe that this muscle cell culture bioassay system will be a useful addition to traditional radioimmunoassays and whole animal studies in elucidating the mode of action of pGH in pituitary-intact swine.

¹ Published as paper no. 15161 of the scientific journal series of the Minnesota Agr. Exp. Sta. on research conducted under Minnesota Agr. Exp. Sta. Project No. 0302-4816-83. This work was supported by Monsanto Co., Minnesota Agr. Exp. Sta. and a grant from the Natl. Pork Producers Council.

² Monsanto Co., 700 Chesterfield Village Parkway, Chesterfield, MO 63198.

³ Dept. of Anim. Sci.

⁴ To whom all correspondence and requests for reprints should be addressed.