USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301, USA.
J Anim Sci. 2011 Jul;89(7):2086-95. doi: 10.2527/jas.2010-3565. Epub 2011 Mar 7.
The objectives of this study were 1) to evaluate the ability of trenbolone acetate (TBA) administered in tandem with LHRH immunization to suppress reproductive function in bulls and 2) to examine the effects of LHRH and androgen (TBA) signaling on pituitary gland function. Forty-four Angus × Hereford crossbred calves (BW=225 ± 2 kg; age=187 ± 6 d) received castration, LHRH immunization, or TBA administration in a 2 × 2 × 2 factorial design. Treatment groups receiving LHRH immunization contained 6 animals, whereas other treatment groups contained 5 animals. Animals immunized against LHRH received a primary injection and 2 booster injections of ovalbumin-LHRH-7 fusion protein on d 0, 42, and 196, respectively. Animals treated with TBA were implanted on d 224. Serum LHRH antibodies increased (P<0.05) after each booster for immunized animals, but were negligible in nonimmunized animals throughout the experiment. Serum testosterone concentration (P<0.001) and scrotal circumference (P<0.05) were depressed in LHRH-immunized bulls compared with nonimmunized bulls by d 84 and 168 of the experiment, respectively. Treatment with TBA tended (P=0.08) to decrease serum testosterone concentrations of nonimmunized bulls. Weights of testes at slaughter were decreased (P<0.001) for LHRH-immunized (232 ± 41 g) compared with nonimmunized (752 ± 45 g) bulls, but did not differ (P=0.80) between TBA-implanted (500 ± 49 g) and nonimplanted bulls (484 ± 36 g). Both LHRH immunization and castration decreased pituitary gland stores of LH and FSH (P<0. 001). There was no effect (P>0.10) of TBA on pituitary gland FSH content and only a tendency (P=0.09) to increase pituitary gland LH content. Immunization against LHRH decreased expression of LH β-subunit and common α-subunit genes (P<0.001). Castration increased expression of LH β-subunit and common α-subunit genes (P=0.02). Treatment with TBA further suppressed (P=0.04) α-subunit mRNA expression in LHRH-immunized steers. In summary, LHRH immunization decreased synthesis and storage of LH and decreased storage, but not synthesis of FSH in bulls. The increased synthesis of LH and FSH in nonimmunized, but not LHRH-immunized steers suggests that castration removes the negative feedback on gonadotropin synthesis but that LHRH is still needed for release of these hormones. Androgen replacement with TBA did not restore the negative feedback control of gonadotropin synthesis.
本研究的目的是 1）评估醋酸群勃龙（TBA）与 LH 免疫接种联合给药抑制公牛生殖功能的能力，2）研究 LH 和雄激素（TBA）信号对垂体功能的影响。44 头安格斯×赫里福德杂交小牛（BW=225±2kg；年龄=187±6d）接受阉割、LH 免疫接种或 TBA 给药，采用 2×2×2 析因设计。接受 LH 免疫接种的治疗组有 6 只动物，而其他治疗组有 5 只动物。接受 LH 免疫的动物在第 0、42 和 196 天分别接受一次原发性注射和两次卵白蛋白-LHRH-7 融合蛋白增强注射。TBA 处理组于第 224 天进行植入。免疫接种动物的血清 LH 抗体在每次增强后增加（P<0.05），但在整个实验过程中，非免疫接种动物的 LH 抗体可以忽略不计。与未免疫的公牛相比，LH 免疫接种的公牛在实验的第 84 天和第 168 天血清睾酮浓度（P<0.001）和阴囊周长（P<0.05）降低。TBA 处理有降低未免疫公牛血清睾酮浓度的趋势（P=0.08）。免疫接种的公牛（232±41g）与未免疫的公牛（752±45g）相比，睾丸重量降低（P<0.001），但 TBA 植入（500±49g）与未植入公牛（484±36g）之间无差异（P=0.80）。LH 免疫接种和阉割均降低了垂体 LH 和 FSH 的储存量（P<0.001）。TBA 对垂体 FSH 含量没有影响（P>0.10），仅对垂体 LH 含量有增加的趋势（P=0.09）。LHβ亚基和共同α亚基基因的表达（P<0.001）。阉割增加了 LHβ亚基和共同α亚基基因的表达（P=0.02）。TBA 处理进一步抑制了 LH 免疫接种牛的α亚基 mRNA 表达（P=0.04）。综上所述，LH 免疫接种降低了公牛 LH 的合成和储存，并降低了 FSH 的储存，但不影响其合成。未免疫的公牛 LH 和 FSH 的合成增加，而 LH 免疫的公牛则没有增加，这表明阉割去除了对促性腺激素合成的负反馈，但 LH 仍然需要释放这些激素。雄激素替代治疗用 TBA 并不能恢复促性腺激素合成的负反馈控制。
