Beard A J, Castillo R J, McLeod B J, Glencross R G, Knight P G
Department of Biochemistry & Physiology, School of Animal and Microbial Science, University of Reading.
J Endocrinol. 1990 Apr;125(1):21-30. doi: 10.1677/joe.0.1250021.
Chronically ovariectomized prepubertal heifers were used for a comparison of the effects of highly purified bovine inhibin (Mr 32,000) and steroid-free bovine follicular fluid (bFF) on the secretion of FSH and LH. In view of the limited availability of highly purified inhibin, an initial study was undertaken to establish the optimal method for administration of bFF inhibin activity. In comparison with the FSH response to a single large i.v. bolus injection of bFF (50 ml; 3250 mg protein), a far more effective suppression of plasma FSH concentrations was achieved when considerably less bFF (6.3 ml; 410 mg protein) was administered gradually over an extended time-period (2 days) either as a continuous i.v. infusion or as a series of 2-hourly i.v. injections. Following a single i.v. bolus injection of bFF, immunoreactive inhibin was cleared rapidly from the circulation (half-life 51 +/- 8 (S.E.M.) min, n = 5), presumably accounting for its limited ability to suppress FSH secretion when administered in this manner. In a second experiment, treatment of ovariectomized heifers (three per group) with highly purified Mr 32,000 bovine inhibin at a dose rate of 15 micrograms/2 h for 2 days significantly (P less than 0.05) suppressed plasma FSH concentrations, which reached their minimum values (40% suppression) during day 2 of treatment. At a lower dose rate (5 micrograms/2 h), inhibin did not significantly affect plasma FSH levels. Administration of bFF was also associated with a dose-dependent suppression of FSH secretion. For each of three dose rates tested (three heifers per group), plasma FSH concentrations were maximally suppressed during day 2 of treatment (65 mg/2 h, 86% suppression, P less than 0.001; 21.7 mg/2 h, 66% suppression, P less than 0.001; 7.2 mg/2 h, 15% suppression, P greater than 0.05). Neither highly purified inhibin nor bFF significantly affected mean plasma LH concentrations, LH pulse frequency or LH pulse amplitude. Thus we have shown for the first time that highly purified Mr 32,000 bovine inhibin does possess in-vivo biological activity in cattle, promoting a selective suppression of plasma FSH concentrations qualitatively similar to that evoked by steroid-free bFF.(ABSTRACT TRUNCATED AT 250 WORDS)
长期卵巢切除的青春期前小母牛被用于比较高纯度牛抑制素（分子量32,000）和无类固醇牛卵泡液（bFF）对促卵泡素（FSH）和促黄体素（LH）分泌的影响。鉴于高纯度抑制素的可得性有限，开展了一项初步研究以确定给予bFF抑制素活性的最佳方法。与单次大剂量静脉推注bFF（50 ml；3250 mg蛋白质）后FSH的反应相比，当以持续静脉输注或每2小时静脉注射一次的方式在较长时间（2天）内逐渐给予少得多的bFF（6.3 ml；410 mg蛋白质）时，血浆FSH浓度得到了更有效的抑制。单次静脉推注bFF后，免疫反应性抑制素迅速从循环中清除（半衰期51±8（标准误）分钟，n = 5），这可能解释了以这种方式给药时其抑制FSH分泌的能力有限。在第二个实验中，以15微克/2小时的剂量率给卵巢切除的小母牛（每组三头）注射高纯度分子量32,000的牛抑制素，持续2天，显著（P<0.05）抑制了血浆FSH浓度，在治疗的第2天达到最低值（抑制40%）。在较低剂量率（5微克/2小时）下，抑制素对血浆FSH水平没有显著影响。给予bFF也与FSH分泌的剂量依赖性抑制有关。对于所测试的三个剂量率中的每一个（每组三头小母牛），血浆FSH浓度在治疗的第2天被最大程度地抑制（65 mg/2小时，抑制86%，P<0.001；21.7 mg/2小时，抑制66%，P<0.001；7.2 mg/2小时，抑制15%，P>0.05）。高纯度抑制素和bFF均未显著影响平均血浆LH浓度、LH脉冲频率或LH脉冲幅度。因此，我们首次表明，高纯度分子量32,000的牛抑制素在牛体内确实具有生物活性，能选择性抑制血浆FSH浓度，其性质与无类固醇bFF引起的相似。（摘要截短至250字）
