Tsubota T, Howell-Skalla L, Nitta H, Osawa Y, Mason J I, Meiers P G, Nelson R A, Bahr J M
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
J Reprod Fertil. 1997 Jan;109(1):21-7. doi: 10.1530/jrf.0.1090021.
American black bears, Ursus americanus, are seasonal breeders with a mating season in late spring to early summer. The objectives of this study were to determine whether there are seasonal changes in spermatogenesis and immunolocalization of testicular steroidogenic enzymes, and to correlate these changes with peripheral steroid concentrations. Three captive mature bears were maintained in open cages during the summer season and provided with chambers for denning during the winter. Testicular biopsies and blood samples were obtained from anaesthetized bears on 12 March, 15 June, 12 October and 15 January. Steroidogenic enzymes were immunolocalized using polyclonal antisera raised against bovine adrenal cholesterol side-chain cleavage cytochrome P450 (P450scc), human placental 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), porcine testicular 17 alpha-hydroxylase cytochrome P450 (P450c17) and human placental aromatase cytochrome P450 (P450arom). Spermatogenesis changed seasonally: spermatogonia and degenerating spermatocytes were observed in October; spermatogonia and primary spermatocytes were present in January; spermatogonia, spermatocytes and round spermatids were present in March; and spermatogonia through spermatozoa were present in June. P450scc and P450c17 were immunolocalized in spermatids and Leydig cells in June, whereas in October these enzymes were present only in Leydig cells. 3 beta HSD was localized in Leydig cells in June and October with more intense staining in June. Localization of P450arom changed seasonally: no immunostaining in October; positive immunostaining in Sertoli cells in January; more extensive immunostaining in Sertoli cells, peritubular-myoid cells and round spermatids in March; and strong immunostaining in Sertoli cells and round and elongating spermatids in June. Serum testosterone and oestradiol concentrations changed seasonally: testosterone and oestrogen were low in October and January, slightly higher in March, and high in June. The present study demonstrates that in the black bear seasonal changes in spermatogenesis are accompanied by changes in the immunolocalization of testicular steroidogenic enzymes that are correlated with changes in serum testosterone and oestradiol concentrations. The presence of P450arom in Sertoli cells at the beginning of testicular recrudescence suggests that aromatase and oestrogen may play a role in re-initiating spermatogenesis.
美洲黑熊（Ursus americanus）是季节性繁殖动物，其交配季节在春末至夏初。本研究的目的是确定精子发生和睾丸类固醇生成酶的免疫定位是否存在季节性变化，并将这些变化与外周类固醇浓度相关联。三只圈养的成年熊在夏季饲养于开放式笼子中，冬季提供洞穴以供其筑窝。于3月12日、6月15日、10月12日和1月15日从麻醉的熊身上获取睾丸活检组织和血样。使用针对牛肾上腺胆固醇侧链裂解细胞色素P450（P450scc）、人胎盘3β - 羟基类固醇脱氢酶（3βHSD）、猪睾丸17α - 羟化酶细胞色素P450（P450c17）和人胎盘芳香化酶细胞色素P450（P450arom）产生的多克隆抗血清对类固醇生成酶进行免疫定位。精子发生呈现季节性变化：10月观察到精原细胞和退化的精母细胞；1月存在精原细胞和初级精母细胞；3月有精原细胞、精母细胞和圆形精子细胞；6月则有从精原细胞到精子的各个阶段。6月时，P450scc和P450c17在精子细胞和睾丸间质细胞中免疫定位，而10月时这些酶仅存在于睾丸间质细胞中。3βHSD在6月和10月定位于睾丸间质细胞，6月染色更强。P450arom的定位呈现季节性变化：10月无免疫染色；1月在支持细胞中有阳性免疫染色；3月在支持细胞、睾丸肌样细胞和圆形精子细胞中有更广泛的免疫染色；6月在支持细胞以及圆形和伸长的精子细胞中有强免疫染色。血清睾酮和雌二醇浓度呈现季节性变化：10月和1月时睾酮和雌激素水平较低，3月略高，6月时较高。本研究表明，在黑熊中，精子发生的季节性变化伴随着睾丸类固醇生成酶免疫定位的变化，且这些变化与血清睾酮和雌二醇浓度的变化相关。睾丸再生开始时支持细胞中存在P450arom，这表明芳香化酶和雌激素可能在重新启动精子发生中发挥作用。
