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Title: EFFECTS OF GNRH ANTAGONIST (SB75) ON GONADOTROPIN AND STEROID SECRETION IN BOARS

Author
item ZANELLA, ERALDO - UNIVERSITY OF NEBRASKA
item Lunstra, Donald
item Wise, Thomas
item KINDER, JAMES - UNIVERSITY OF NEBRASKA
item Ford, Johny

Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/23/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The objective of the first study was to evaluate FSH and LH secretion in boars after treatment with SB75, a GnRH antagonist. Fourteen mature boars were injected once a day with SB75 (10 ug/kg of body weight) for 4 days. Both, LH and T concentrations decreased after 1 h from the first dose of SB75. However, after 12 h of treatment, LH gradually returned to basal concentrations, but T remained suppressed (<2 ng/ml) 24 h after the last dose of SB75. There was a marginal reduction in FSH during SB75 treatment. The prolonged inhibitory effect of SB75 on T secretion in the presence of normal LH concentrations implied direct effects of SB75 at the testis. In the second experiment testicular tissue was incubated in the presence of 3 doses of hCG with SB75 or with Deslorelin, a GnRH agonist. Testosterone (T) and estrone (E1) concentrations increased linearly with time in response to hCG. SB75 suppressed (p<.01) T secretion (77.9 vs. 85.7 +/- 2.02 ng/mg) compared to controls. SB75 diminished the T response to hCG stimulation at all dosages and times, except at the largest dosage at 1 h. SB75 also impaired (p<0.03) the stimulatory effect of hCG on E1 secretion compared to controls, (4.7 vs 5.3 +/- 0.2 ng/mg, respectively), and E1 secretion was reduced at all dosages of hCG. Deslorelin had no effect on the increase of T (p>0.50) or E1 (p>0.26) concentrations, respectively, that resulted from hCG stimulation. These results indicate that SB75 has a direct effect on the testis, decreasing T and E1 secretion; however, Deslorelin had no direct effects on the testis. Thus, the direct effect of SB75 on testicular steroidogenesis may occur independent of GnRH receptor activation in porcine testis.