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Dose Response of Two Synthetic Human Growth Hormone-Releasing Factors on Growth Hormone Release in Heifers and Pigs^1,2,

Agriculture Canada Lennoxville, Quebec J1M 1Z3

Abstract

This study was undertaken to evaulate the biological potency of two synthetic human growth hormone-releasing factors, hGRF (1–44)NH₂ and hGRF (1–29)NH₂, on growth hormone (GH) release in young dairy heifers (n = 10) and pigs (n = 10). In each species, the GH response to an iv injection (0, .067, .2, .6 and 1.8 nmol·kg^–1 body weight) of each peptide was evaluated in a double 5 x 5 Latin square design. In each square, there were five animals injected with either hGRF (1–44)NH₂ or hGRF (1–29)NH₂. Main effects were doses (n = 5) of hGRF and days (n = 5) of injection. In both species, data indicated that hGRF (1–44)NH₂ and hGRF (1–29)NH₂ equally stimulate GH secretion at all doses. In dairy heifers, average peak concentrations (81.7, 94.7, 84.5 and 93.7 ng·ml^–1 vs 91.5, 81.0, 94.3 and 91.6 ng·ml^–1) and area under the GH response curve (3,661, 4,541, 7,196 and 6,788 ng·ml^–1 ·min vs 3,000, 3,982, 5,639 and 6,724 ng·ml^–1 ·min) were not different (P>.05) between hGRF(1–44)NH₂ and hGRF(1–29)NH₂ at .067, .2, .6 and 1.8 nmol·kg^–1, respectively. Similarly, in pigs, average peak concentrations (35.6, 38.6, 76.5 and 73.8 ng·ml^–1 vs 28.7, 30.0, 41.3 and 80.8 ng·ml^–1) and area under the GH curve (1,576, 1,567, 3,299 and 3,622 ng·ml^–1 ·min vs 1,115, 1,658, 1,482 and 2,528 ng·ml^–1 ·min) were not different (P>.05) between both peptides. A biphasic release of GH after hGRF (1–44)NH₂ and hGRH (1–29)NH₂ injection was observed at the highest dose in heifers. The GH response to hGRF injection was much more variable in pigs as compared with dairy heifers. In conclusion, hGRF (1–44)NH₂ and its (1–29)NH₂ fragment are equipotent in stimulating GH release in dairy heifers and pigs.

¹ Lennoxville Res. Sta. contribution no. 189.

² This work was supported by Sanofi Recherche, Montpellier, France and Agriculture Canada. We thank Gratia Bertrand, Jasmin Brochu, Michelle Guillette, Marjolaine St. Louis and Lisette St. James for their technical assistance; L. Côté for secretarial assistance as well as Andre Belleau and Maryse Dumas for statistical analysis.

³ Please address reprint requests to Dr. D. Petitclerc, Lennoxville Research Station, 2000 Road 108 East, P.O. Box 90, Lennoxville (Quebec), Canada J1M 1Z3.

⁴ Agriculture Canada, Lennoxville, Quebec J1M 1Z3.

⁵ Sherbrooke Univ., Sherbrooke, Quebec J1K 2R1.

⁶ Montreal Univ., Montreal, Quebec H2L 4M1.