Nagata S, Miyake Y I, Nambo Y, Nagamine N, Watanabe G, Tsunoda N, Taniyama H, Hondo E, Yamada J, Taya K
Laboratory of Racing Chemistry, Tokyo, Japan.
Equine Vet J. 1998 Mar;30(2):98-103. doi: 10.1111/j.2042-3306.1998.tb04467.x.
To examine the physiological role of inhibin in the stallion, a heterologous radioimmunoassay (RIA) based on a bovine RIA was validated and used to measure immunoreactive (ir)-inhibin concentrations in plasma and testicular homogenates. The bioactivity of equine testicular inhibin was also examined using an assay for suppression of FSH secretion from rat anterior pituitary cells. In addition, to identify the cell responsible for secreting testicular inhibin, the localisation of inhibin in the testis was investigated by an immunohistochemical method using a polyclonal antibody against (Tyr30)-porcine inhibin alpha(1-30) NH2. In the RIA, parallel dose response curves were obtained for the bovine inhibin standard and serial dilutions of stallion plasma and equine testicular homogenates. Parallel FSH inhibition curves were also observed for the bovine inhibin standard and serial dilutions of equine testicular homogenates in the bioassay. The inhibition of FSH secretion from rat pituitary cells by equine testicular homogenates was neutralised by an antiserum against bovine inhibin in vitro. Plasma concentrations of ir-inhibin, testosterone and oestradiol-17beta in stallions decreased abruptly after bilateral gonadectomy and FSH and LH concentrations in the plasma subsequently increased. Therefore, circulating inhibin in the stallion appeared to be largely of testicular origin. The histochemical results showed for the first time that strong immunopositive staining for inhibin occurred in the Leydig cells of the testes. Sertoli cells were also stained by the inhibin antibody but the reaction was weaker than that in Leydig cells. These results indicate clearly that both Leydig and Sertoli cells are potential sources of testicular inhibin in the stallion. A clear increase in plasma ir-inhibin concentrations was observed during the natural breeding season. Similar seasonal changes in the plasma concentrations of testicular steroid hormones and pituitary gonadotrophins occurred throughout the year. In conclusion, the testes appear to be the main source of inhibin, and testicular inhibin is secreted by Leydig and Sertoli cells in stallions. The positive correlations between plasma ir-inhibin and testicular activity during both the breeding and nonbreeding seasons indicate that plasma ir-inhibin is a useful indicator of reproductive activity in the stallion.
为研究抑制素在种马中的生理作用，基于牛放射免疫分析（RIA）的异源放射免疫分析得到验证，并用于测定血浆和睾丸匀浆中免疫反应性（ir）抑制素的浓度。还利用一种抑制大鼠垂体前叶细胞促卵泡激素（FSH）分泌的分析方法检测了马睾丸抑制素的生物活性。此外，为确定负责分泌睾丸抑制素的细胞，使用抗（Tyr30）-猪抑制素α(1-30) NH2的多克隆抗体，通过免疫组织化学方法研究了抑制素在睾丸中的定位。在放射免疫分析中，牛抑制素标准品以及种马血浆和马睾丸匀浆的系列稀释液得到了平行的剂量反应曲线。在生物分析中，牛抑制素标准品以及马睾丸匀浆的系列稀释液也观察到了平行的FSH抑制曲线。在体外，马睾丸匀浆对大鼠垂体细胞FSH分泌的抑制作用被抗牛抑制素抗血清中和。双侧性腺切除后，种马血浆中ir抑制素、睾酮和雌二醇-17β的浓度急剧下降，随后血浆中FSH和LH的浓度升高。因此，种马体内循环的抑制素似乎很大程度上来源于睾丸。组织化学结果首次表明，睾丸间质细胞对抑制素呈现强烈的免疫阳性染色。支持细胞也被抑制素抗体染色，但反应比间质细胞弱。这些结果清楚地表明，间质细胞和支持细胞都是种马睾丸抑制素的潜在来源。在自然繁殖季节观察到血浆ir抑制素浓度明显升高。全年睾丸类固醇激素和垂体促性腺激素的血浆浓度都出现类似的季节性变化。总之，睾丸似乎是抑制素的主要来源，种马睾丸抑制素由间质细胞和支持细胞分泌。繁殖季节和非繁殖季节血浆ir抑制素与睾丸活性之间的正相关表明，血浆ir抑制素是种马生殖活动的有用指标。
