Zanella E L, Lunstra D D, Wise T H, Kinder J E, Ford J J
USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933, USA.
J Anim Sci. 2000 Jun;78(6):1591-7. doi: 10.2527/2000.7861591x.
The hormone GnRH has a stimulatory effect on gonadotropin synthesis and secretion. The objective of the first study was to evaluate concentrations of FSH and LH in plasma of boars after successive treatment with SB75, a GnRH antagonist. Thirteen boars greater than 1 yr of age (eight White Composite [WC] and five Meishan [MS]) were injected once daily with SB75 (10 microg/kg of body weight) for 4 d. Plasma concentrations of LH and testosterone (T) decreased after 1 h from the first dose of SB75. After 12 h of treatment, LH gradually returned to pretreatment concentrations, but T remained suppressed (< 2 ng/mL) until after the last injection of SB75. There was a modest, but significant, reduction in FSH during treatment with SB75. The prolonged inhibitory effect of SB75 on suppression of plasma T concentrations, in the presence of pretreatment concentrations of LH, implied direct effects of SB75 at the testis. In the second experiment, testicular tissue from adult boars was incubated in the presence of three doses of human chorionic gonadotropin (hCG; 0, .5, and 5 IU) with SB75 (250 ng/mL) or with Deslorelin, a GnRH agonist (500 ng/mL). Samples of media were collected every hour for 3 h, and concentrations of T and estrone (E1) were determined by RIA. Concentrations of T and E1 increased with time in response to treatment with hCG. Co-treatment with SB75 decreased media concentrations of T (P < .01) and E1 (P < .03) compared to controls (77.9 vs 85.7 +/- 2.0 and 4.7 vs 5.3 +/- .2 ng/g). In contrast, treatment with Deslorelin had no effect on the amount of T (P > .50) or E1 (P > .26) released with all dosages of hCG. These results indicate that a GnRH antagonist has a direct effect on the testis, decreasing amounts of T and E1 released from the Leydig cells; however, treatment with a GnRH agonist had no direct effect on release of these gonadal steroids. Thus, it remains unresolved whether the site of action of GnRH antagonist on testicular steroidogenesis is through a testicular GnRH receptor or through some other mechanism.
激素促性腺激素释放激素（GnRH）对促性腺激素的合成和分泌具有刺激作用。第一项研究的目的是评估用GnRH拮抗剂SB75连续处理后公猪血浆中促卵泡激素（FSH）和促黄体生成素（LH）的浓度。13头1岁以上的公猪（8头白色杂交猪[WC]和5头梅山猪[MS]）每天注射一次SB75（10微克/千克体重），持续4天。从第一剂SB75注射后1小时起，血浆中LH和睾酮（T）的浓度下降。处理12小时后，LH逐渐恢复到处理前的浓度，但T一直受到抑制（<2纳克/毫升），直到最后一次注射SB75后才恢复。在用SB75处理期间，FSH有适度但显著的降低。在存在处理前浓度LH的情况下，SB75对血浆T浓度抑制的延长作用表明SB75对睾丸有直接作用。在第二项实验中，成年公猪的睾丸组织在三种剂量的人绒毛膜促性腺激素（hCG；0、0.5和5国际单位）存在下，与SB75（250纳克/毫升）或GnRH激动剂地洛瑞林（500纳克/毫升）一起孵育。每小时收集3小时的培养基样本，并通过放射免疫分析法测定T和雌酮（E1）的浓度。随着时间的推移，T和E1的浓度因hCG处理而增加。与对照组相比，与SB75共同处理降低了培养基中T（P<.01）和E1（P<.03）的浓度（分别为77.9对85.7±2.0和4.7对5.3±.2纳克/克）。相反，用地洛瑞林处理对所有剂量hCG释放的T（P>.50）或E1（P>.26）量没有影响。这些结果表明，GnRH拮抗剂对睾丸有直接作用，减少了睾丸间质细胞释放的T和E1量；然而，用GnRH激动剂处理对这些性腺类固醇的释放没有直接作用。因此，GnRH拮抗剂对睾丸类固醇生成的作用位点是通过睾丸GnRH受体还是通过其他机制仍未解决。
