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Analogs of Growth Hormone-Releasing Hormone Induce Release of Growth Hormone in the Bovine^1,2,

Washington State University^,5, Pullman 99164-6332

Abstract

Biological potencies of three 29 amino acid growth hormone-releasing hormone analogs (GHRH[1-29]) were determined in the bovine and compared to synthetic human GHRH (44 amino acids; hGHRH[1-44]NH₂) for their ability to increase serum growth hormone (GH) concentrations. Four prepubertal Holstein heifers (179 ± 10 kg) received hGHRH(1-44)NH₂ or analogs (D-Ala², Nle²⁷, Agm²⁹ GHRH[1-29], [JG-73]; D-N-MeAla², Nle²⁷, Agm²⁹ GHRH[1-29], [JG-75]; and desamino-Tyr¹, D-Ala², Nle²⁷, Agm²⁹ GHRH[1-29], [JG-77]) at the following doses: 0, 6.25, 25, 100 and 400 µg/animal. All treatment-dose combinations were administered to each heifer with at least a 1-d interval between treatments. Sixteen blood samples were collected via jugular cannulas 20 min before and up to 6 h after treatment injection. There was a linear dose-dependent GH release in response to hGHRH(1-44)NH₂ and the three analogs. Growth hormone peak amplitudes for the three analogs were similar to those observed after administration of the hGHRH(1-44)NH₂ (P > .05). However, when total area under the GH response curves for each treatment was averaged over all the doses, JG-73 stimulated greater GH release than hGHRH(1-44)NH₂ (P < .05). Heifers injected with the 400-µg dose of hGHRH(1-44)NH₂ or the three analogs showed a primary release of GH followed by a secondary release 1 h later. At all other doses, only a primary GH release was observed. In conclusion, JG-73, a GHRH analog, was found to be 4.65 times more potent on a weight basis and 3.3 times more potent on a molar basis, whereas JG-75 and JG-77 were as potent as synthetic hGHRH(1-44)NH₂ in stimulating the release of GH in heifers.

¹ Scientific paper no. 7847. College of Agric. and Home Econ. Res. Center, Washington State Univ., Pullman 99164. This research was supported by W. R. Grace & Co., Columbia, MD.

² Appreciation is expressed to the National Hormone and Pituitary Program, Baltimore, MD for supplying oGH antibody and to R. G. Eggert, American Cyanamid Co., for the recombinant bGH used for iodination and standards.

³ Endocrine, Polypeptide and Cancer Inst., Veterans Admin. Medical Center, Tulane Univ. School of Medicine, New Orleans, LA 70146.

⁴ Reprint requests: Dr. J. J. Reeves, Dept. Anim. Sci., Washington State Univ., Pullman 99164-6332.

⁵ Dept. of Anim. Sci.