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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-NH2 10), 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.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate effects of endotoxemia on serum somatotropin (ST) and insulin-like growth factor I (IGF-I) concentrations in finishing pigs.

Animals

Eight female pigs (98 ± 2 kg) randomly assigned to IV administration (time 0) of saline solution (n = 4) or Escherichia coli lipopolysaccharide (LPS; 5 μg/kg of body weight; n = 4).

Procedure

Serum ST concentration was determined in serum samples obtained at 20-minute intervals for 6 hours after treatment. Serum IGF-I concentration was determined in samples collected at 1-hour intervals for 6 hours and at 12, 15, 18, 24, 48, 72, and 96 hours after treatment.

Results

One distinct pulse of ST (peak 10.5 ± 0.5 ng/ml) was observed at 40 minutes in each pig after administration of LPS. Control pigs had 2.25 ± 0.48 ST pulses during the 6 hours of frequent sample collection; however, magnitude of the ST pulses was similar between gilts given LPS and control gilts. A temporal association between ST pulses and saline administration was not evident. Serum IGF-I concentration was similar between gilts of the LPS and control groups prior to treatment. The IGF-I concentration was lower (P < 0.01) in gilts of the LPS group (44 ± 5 ng/ml) than in gilts of the control group (157 ± 4 ng/ml) at 24 hours. The difference in IGF-I concentrations between groups was evident for 96 hours.

Conclusions

Immediate release of ST was attributed to stress associated with acute endotoxemia and stimulation of the pituitary gland; immune stimulation by LPS may have contributed to the changes in IGF-I concentration. Because feed consumption was similar between the 2 groups of pigs, suppression of IGF-I concentration for 96 hours after administration of LPS was attributable to factors in addition to transient feed restriction. Thus, acute endotoxemia altered the positive association between ST and IGF-I, and provided evidence for a potential mechanism of impaired growth in endotoxemic animals. (Am J Vet Res 1997;58:1010–1013)

Free access
in American Journal of Veterinary Research