Tjondronegoro S, Martin G B, Sutherland S R, Boukhliq R
Faculty of Agriculture (Animal Science), University of Western Australia, Nedlands, Australia.
Reprod Fertil Dev. 1996;8(5):855-62. doi: 10.1071/rd9960855.
The role of negative feedback by two testicular hormones, testosterone and inhibin, in the gonadotrophin responses of mature male sheep to changes in nutrition was tested. Six days after castration, 24 Merino rams were assigned to groups that were fed either a diet that maintained their initial liveweight (Intermediate diet), or about half of the Intermediate diet (Low diet), or the Intermediate diet with a supplement of lupin grain (High diet). One week after the change of diet, all animals were given subcutaneous testosterone implants, providing plasma testosterone concentrations of 3.06 +/- 0.14 ng mL-1 (mean +/- s.e.m.; n = 24). The implants were left in place for 7 days, during which time all the rams were also injected subcutaneously with 2 mL steroid-free bovine follicular fluid (bFF) every 8 h, to provide inhibin at mean plasma concentrations of 0.40 +/- 0.04 ng mL-1 (n = 24; compared with 1.50 +/- 0.12 ng mL-1 when the animals were intact). Five days after castration, there were significant increases in the frequency of luteinizing hormone (LH) pulses (from 1.83 +/- 0.23 to 17.3 +/- 0.96 pulses per 12 h; mean +/- s.e.m.; n = 24) and concentrations of FSH (from 0.45 +/- 0.07 to 14.19 +/- 2.7 ng mL-1; n = 24). Dietary treatment did not significantly affect these responses. Treatment with bFF and testosterone for 7 days reduced LH-pulse frequencies and follicle-stimulating hormone (FSH) concentrations in all groups. The degree of reduction was least in the group on the High diet, for which the FSH concentration (6.49 +/- 1.96 ng mL-1) and frequency of LH pulses (7.00 +/- 2.31 pulses per 24 h) were significantly higher than those observed in the other groups. The mean frequency of LH pulses did not differ significantly between the Intermediate group (0.88 +/- 0.61 pulses per 24 h) and the Low group (0.25 +/- 0.25 pulses per 24 h). Similarly, FSH concentrations did not differ significantly between these two groups (1.78 +/- 0.46 for the Intermediate group v. 1.33 +/- 0.26 ng mL-1 for the Low group). It is concluded that there is no response to diet in the absence of testicular hormones and the effects of nutrition on LH secretion in castrated rams given exogenous testosterone and inhibin are similar to those observed in intact rams.
研究了睾丸激素睾酮和抑制素的负反馈在成熟雄性绵羊促性腺激素对营养变化反应中的作用。阉割后6天，将24只美利奴公羊分为几组，分别给予维持其初始体重的日粮（中等日粮）、约为中等日粮一半的日粮（低日粮）或添加羽扇豆谷物的中等日粮（高日粮）。日粮改变一周后，给所有动物皮下植入睾酮，使血浆睾酮浓度达到3.06±0.14 ng/mL（平均值±标准误；n = 24）。植入物保留7天，在此期间，所有公羊每8小时还皮下注射2 mL无类固醇牛卵泡液（bFF），以使抑制素的平均血浆浓度达到0.40±0.04 ng/mL（n = 24；与动物完整时的1.50±0.12 ng/mL相比）。阉割后5天，促黄体生成素（LH）脉冲频率（从每12小时1.83±0.23次增加到17.3±0.96次；平均值±标准误；n = 24）和促卵泡激素（FSH）浓度（从0.45±0.07 ng/mL增加到14.19±2.7 ng/mL；n = 24）显著增加。日粮处理对这些反应没有显著影响。用bFF和睾酮处理7天可降低所有组的LH脉冲频率和促卵泡激素（FSH）浓度。高日粮组的降低程度最小，该组的FSH浓度（6.49±1.96 ng/mL）和LH脉冲频率（每24小时7.00±2.31次）显著高于其他组。中等日粮组（每24小时0.88±0.61次）和低日粮组（每24小时0.25±0.25次）的LH脉冲平均频率没有显著差异。同样，这两组的FSH浓度也没有显著差异（中等日粮组为1.78±0.46 ng/mL，低日粮组为1.33±0.26 ng/mL）。得出的结论是，在没有睾丸激素的情况下，对日粮没有反应，并且在给予外源性睾酮和抑制素的阉割公羊中，营养对LH分泌的影响与在完整公羊中观察到的相似。
