Effects of chronic gonadotropin-releasing hormone agonist treatment on serum luteinizing hormone and testosterone concentrations in boars

Glen W. Almond From the Department of Food Animal and Equine Medicine, College of Veterinary Medicine, (Almond, Smith, Richards), and Department of Animal Science, College of Agriculture and Life Sciences (Esbenshade), North Carolina State University, Raleigh, NC 27606.

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Ken L. Esbenshade From the Department of Food Animal and Equine Medicine, College of Veterinary Medicine, (Almond, Smith, Richards), and Department of Animal Science, College of Agriculture and Life Sciences (Esbenshade), North Carolina State University, Raleigh, NC 27606.

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Craig A. Smith From the Department of Food Animal and Equine Medicine, College of Veterinary Medicine, (Almond, Smith, Richards), and Department of Animal Science, College of Agriculture and Life Sciences (Esbenshade), North Carolina State University, Raleigh, NC 27606.

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R. Gregg Richards From the Department of Food Animal and Equine Medicine, College of Veterinary Medicine, (Almond, Smith, Richards), and Department of Animal Science, College of Agriculture and Life Sciences (Esbenshade), North Carolina State University, Raleigh, NC 27606.

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Summary

Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH210), and serum luteinizing hormone (lh) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days – 2 and –1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days –1, 0, 4, and 8. Serum testosterone and (lh concentrations were determined by radioimmunoassay. Maximal (lh (7 ± 1 ng/ml) and testosterone (26 ± 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, (lh and testosterone concentrations decreased to pretreatment values (0.3 ± 0.1 ng/ml and 1.8 ± 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile (lh release were observed between the groups. Testosterone and lh concentrations in samples collected at 6- and 12-hour intervals and pulsatile (lh release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum lh and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in lh and testosterone concentrations in mature boars.

Summary

Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH210), and serum luteinizing hormone (lh) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days – 2 and –1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days –1, 0, 4, and 8. Serum testosterone and (lh concentrations were determined by radioimmunoassay. Maximal (lh (7 ± 1 ng/ml) and testosterone (26 ± 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, (lh and testosterone concentrations decreased to pretreatment values (0.3 ± 0.1 ng/ml and 1.8 ± 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile (lh release were observed between the groups. Testosterone and lh concentrations in samples collected at 6- and 12-hour intervals and pulsatile (lh release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum lh and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in lh and testosterone concentrations in mature boars.

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