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Serum LH Levels in Bulls Treated with Synthetic Luteinizing Hormone-Releasing Hormone/Follicle Stimulating Hormone-Releasing Hormone (LH-RH/FSH-RH)^{1, 2, 3,}

Washington State University,^,4 Pullman, Washington 99163 , VA Hospital and Tulane Medical School,^,5 New Orleans, Louisiana 70140

Abstract

PRIOR to commencing studies to evaluate concentrations of bovine serum LH in response to synthetic LH-RH/FSH-RH, a double antibody radioimmunoassay was developed and validated for bovine LH. Synthetic LH-RH/FSH-RH (0.03, 0.3 and 3.0 µg/kilogram) was injected intramuscularly into each of four Hereford bulls to determine concentration of serum LH in response to this decapeptide. The sequence of treatments was initially determined at random with each bull receiving a different treatment at any one injection period. Each bull received each dose at 9-day intervals. The 0.03 µg/kilogram treatment did not induce a significant increase in mean peak serum LH concentration (2.7±0.4 ng/ml) relative to the highest serum LH concentration in the saline treated controls (1.9±0.4 ng/ml), but both the 0.3 and 3.0 µg/kilogram doses significantly increased mean peak serum LH concentrations to 14.8±2.1 and 46.2±7.0 ng/ml, respectively. The duration of the elevation in serum LH after injections of LH-RH/FSH-RH was 55±15, 220±12 and 366±33 min. for the 0.03, 0.3 and 3.0 µg/kilogram doses, respectively. Subcutaneous placement of 1.3 µg LH-RH/FSH-RH per kilogram body weight in either acidified saline, 2% carboxymethylcellulose or a silastic implant elicited a peak serum LH response of 41±10, 55±10 and 4±4 ng/ml, respectively. The duration of LH response was significantly longer for LH-RH/FSH-RH in CMC than for LH-RH/FSH-RH in acidified saline (60±92 vs. 285±40 min., respectively). The subcutaneous LH-RH/FSH-RH silastic implants failed to elicit a significant LH response.

¹ Scientific Paper 3906 College of Agriculture Research Center, Washington State University, Project 1695.

² The authors thank G. Vogel, R. Geiger and F. Enzmann, Farbwerke Hoechst, West Germany for synthetic LH-RH/FSH-RH; L. E. Reichert for LH used for iodination; J. Pierce for Bovine TSH and the Endocrine Study Section NIH for FSH, GH, Prolactin and LH used in this study. The technical assistance of T. W. Beck and G. K. Tarnavsky is greatly acknowledged.

³ This study was supported in part by USPHS Grant from National Institute of Child Health and Human Development AM06192 to JJR.

⁴ Department of Animal Sciences.

⁵ Endocrine and Polypeptide Laboratories, Department of Medicine.