Lovell T M, Gladwell R T, Groome N P, Knight P G
School of Animal and Microbial Sciences, University of Reading, Whiteknights, UK.
Reproduction. 2002 Nov;124(5):649-57.
Previous work has shown that activin A is expressed selectively within the theca rather than the granulosa layer of preovulatory chicken follicles. In the present study, this finding was verified and the potential paracrine actions of activin A on basal and gonadotrophin-induced secretion of inhibin A, inhibin B and progesterone by granulosa cells from the three largest preovulatory follicles (F1-F3) were investigated. Treatment with activin A (0, 0.25, 2.5 and 25 ng ml(-1)) alone increased inhibin A secretion markedly in a follicle- and time-dependent manner, with the greatest response (up to 15-fold increase; P < 0.0001) in F1 follicles after 3 days of treatment. In contrast, activin A alone had no effect on progesterone output at any time. Cells from F3 follicles were more responsive to FSH than were F1 cells in terms of both inhibin A (P < 0.02) and progesterone (P < 0.01) secretion. Furthermore, activin A greatly enhanced FSH-induced secretion of both inhibin A (up to tenfold; P < 0.0001) and progesterone (up to sixfold; P < 0.0001). In terms of LH-induced inhibin A and progesterone secretion, cells from F1, F2 and F3 follicles showed similar responses. Co-treatment with activin A enhanced LH-induced secretion of inhibin A markedly (up to ninefold; P < 0.0001) but had only a marginal effect on LH-induced progesterone secretion (up to twofold; P < 0.001). The presence of activin receptor subtypes IA, IB, IIA and IIB in cultured granulosa cells from F1, F2 and F3 follicles was demonstrated using immunocytochemistry. These findings support the hypothesis that activin A secreted by the theca layers of avian preovulatory follicles exerts a local paracrine action on granulosa cells to modulate 'basal' inhibin A secretion and to upregulate gonadotrophin-induced secretion of both inhibin A and progesterone. However, the extent to which this local role of activin A contributes to the generation of the preovulatory LH-progesterone surge remains to be established.
先前的研究表明，激活素A在排卵前鸡卵泡的卵泡膜而非颗粒层中选择性表达。在本研究中，这一发现得到了验证，并研究了激活素A对来自三个最大排卵前卵泡（F1-F3）的颗粒细胞基础分泌以及促性腺激素诱导的抑制素A、抑制素B和孕酮分泌的潜在旁分泌作用。单独用激活素A（0、0.25、2.5和25 ng ml⁻¹）处理，以卵泡和时间依赖性方式显著增加抑制素A的分泌，处理3天后，F1卵泡中的反应最大（增加高达15倍；P < 0.0001）。相比之下，单独的激活素A在任何时候对孕酮产量都没有影响。就抑制素A（P < 0.02）和孕酮（P < 0.01）分泌而言，F3卵泡的细胞比F1细胞对促卵泡激素（FSH）更敏感。此外，激活素A极大地增强了FSH诱导的抑制素A（增加高达10倍；P < 0.0001）和孕酮（增加高达6倍；P < 0.0001）的分泌。就促黄体生成素（LH）诱导的抑制素A和孕酮分泌而言，F1、F2和F3卵泡的细胞表现出相似的反应。与激活素A共同处理显著增强了LH诱导的抑制素A分泌（增加高达9倍；P < 0.0001），但对LH诱导的孕酮分泌只有轻微影响（增加高达2倍；P < 0.001）。使用免疫细胞化学方法证明了来自F1、F2和F3卵泡的培养颗粒细胞中存在激活素受体亚型IA、IB、IIA和IIB。这些发现支持这样的假设，即鸟类排卵前卵泡的卵泡膜层分泌的激活素A对颗粒细胞发挥局部旁分泌作用，以调节“基础状态”下抑制素A的分泌，并上调促性腺激素诱导的抑制素A和孕酮的分泌。然而，激活素A的这种局部作用在多大程度上促成排卵前LH-孕酮峰的产生仍有待确定。
