Deaver D R, Glass J D, Grieger D M, Reeves J J
Department of Dairy and Animal Sciences, Penn State University.
Domest Anim Endocrinol. 1988 Oct;5(4):307-16. doi: 10.1016/0739-7240(88)90005-7.
Two experiments were conducted in order to determine the effects of estradiol (E2) on the development of the hypothalamic-pituitary-testicular axis in bull calves. In experiment 1, calves were assigned randomly to one of the following groups: 1) intact, 2) intact E2-treated, 3) castrated, or 4) castrated E2-treated. Treatments began when the calves were 7.5 wk of age and continued for 16.5 wk. Samples of blood were collected once a week from 3 to 14 wk of age and every 10 min for 6 hr at 8, 12 and 16 wk of age. Concentrations of E2 in plasma decreased between 3 and 4 wk of age and were further reduced by castration. Maximum concentrations of E2 (24.3 pg/ml) were observed 72 hr after insertion of E2 implants, however, plasma E2 stabilized at 5.9 pg/ml by 2 wk after insertion of E2 implants. Treatment with E2 eliminated the pulsatile secretion of LH in intact and castrated calves and retarded testicular growth. In experiment 2, calves were assigned to a control (n = 4) or E2-treated (n = 6) group. Implants of E2 were inserted at 7.5 wk of age. At 24 wk of age, calves were bled and then sacrificed to collect hypothalamic and pituitary tissues. Age-related changes in testicular weight and secretion of LH were blocked by E2. Neither the morphology nor the intensity of immunostaining of GnRH nerve cell bodies in the preoptic area (POA) were affected by E2. However, the density of GnRH fibers and beads in the stalk median eminence (SME), and concentrations of pituitary GnRH receptors were greater (P less than .01) in E2-treated compared to control calves. In addition, concentrations of norepinephrine (NE) in the SME were lower in E2-treated calves when compared to controls. Based on these observations, it is concluded that administration of E2 at 7.5 wk of age causes profound alterations in hypothalamic function including, changes in metabolism of NE and suppression of GnRH release.
为了确定雌二醇（E2）对公牛犊下丘脑 - 垂体 - 睾丸轴发育的影响，进行了两项实验。在实验1中，犊牛被随机分配到以下组之一：1）完整组，2）完整E2处理组，3）阉割组，或4）阉割E2处理组。处理在犊牛7.5周龄时开始，持续16.5周。在3至14周龄时每周采集一次血样，在8、12和16周龄时每10分钟采集一次血样，共采集6小时。血浆中E2的浓度在3至4周龄之间下降，阉割后进一步降低。在植入E2植入物72小时后观察到E2的最大浓度（24.3 pg/ml），然而，在植入E2植入物2周后，血浆E2稳定在5.9 pg/ml。E2处理消除了完整和阉割犊牛中LH的脉冲式分泌，并抑制了睾丸生长。在实验2中，犊牛被分配到对照组（n = 4）或E2处理组（n = 6）。在7.5周龄时植入E2植入物。在24周龄时，对犊牛进行采血，然后处死以收集下丘脑和垂体组织。E2阻断了睾丸重量和LH分泌的年龄相关变化。视前区（POA）中GnRH神经细胞体的形态和免疫染色强度均未受E2影响。然而，与对照犊牛相比，E2处理的犊牛在垂体柄正中隆起（SME）中GnRH纤维和珠的密度以及垂体GnRH受体的浓度更高（P小于0.01）。此外，与对照组相比，E2处理的犊牛SME中去甲肾上腺素（NE）的浓度较低。基于这些观察结果，得出结论：在7.5周龄时给予E2会导致下丘脑功能发生深刻改变，包括NE代谢变化和GnRH释放受抑制。
