Schlinger B A, Arnold A P
Department of Psychology and Laboratory of Neuroendocrinology, University of California, Los Angeles 90024-1563.
Endocrinology. 1993 Dec;133(6):2610-6. doi: 10.1210/endo.133.6.8243284.
Aromatase activity is abundant in limbic and nonlimbic neural structures in zebra finches, especially in the telencephalon near neural circuits that control singing behavior. Also, male songbirds can have high estrogen levels in blood. Because it is difficult to detect aromatase activity in other male tissues, we have postulated that the brain itself is the source of the estrogen present in the blood of males. Previously, we developed methods to measure estrogen synthesis in vivo by injecting [3H]androgen into the systemic circulation or directly into tissues and then determining the quantity of [3H]estrogen entering or leaving the brain. Our results support our hypothesis that the brain is the primary site of estrogen synthesis in males of this species. Here, we confirm that [3H]estrogen emanates from the brain after systemic [3H]androgen injection by showing that the presumptive estrogen in jugular plasma is significantly reduced by treatment with an aromatase inhibitor. In females, but not males, estrogens can be found in large amounts in carotid plasma after systemic androgen injection, presumably due to ovarian estrogen synthesis. However, carotid estrogen levels are variable in females, so it is difficult to determine if the female brain contributes estrogen to blood as is seen in males. The data presented here suggest that the adrenal of males is not an important site of aromatization, because [3H]estrogens are undetected in the adrenals of castrated or sham-castrated males after adrenal injections of [3H] androgen. Nevertheless, at least 2.8- to 17.3-fold more [3H]estrogen was present in the jugular than in the carotid of castrated males after systemic injection of [3H]androgen. Because androgen levels were in the physiological range, we conclude that the brain routinely enriches the estrogen content of blood in normal adult males of this species.
芳香化酶活性在斑胸草雀的边缘和非边缘神经结构中丰富存在，尤其在控制鸣叫行为的神经回路附近的端脑中。此外，雄性鸣禽血液中的雌激素水平可能较高。由于很难在其他雄性组织中检测到芳香化酶活性，我们推测大脑本身是雄性血液中雌激素的来源。此前，我们开发了通过将[3H]雄激素注入体循环或直接注入组织，然后测定进入或离开大脑的[3H]雌激素量来测量体内雌激素合成的方法。我们的结果支持了我们的假设，即大脑是该物种雄性雌激素合成的主要部位。在这里，我们通过表明用芳香化酶抑制剂处理后颈静脉血浆中假定的雌激素显著减少，证实了全身注射[3H]雄激素后[3H]雌激素从大脑中释放出来。在雌性中，而非雄性中，全身注射雄激素后，颈动脉血浆中可发现大量雌激素，这可能是由于卵巢雌激素合成。然而，雌性的颈动脉雌激素水平是可变的，因此很难确定雌性大脑是否像在雄性中那样向血液中贡献雌激素。此处呈现的数据表明，雄性的肾上腺不是芳香化的重要部位，因为在对去势或假去势雄性的肾上腺注射[3H]雄激素后，肾上腺中未检测到[3H]雌激素。尽管如此，全身注射[3H]雄激素后，去势雄性的颈静脉中[3H]雌激素的含量至少比颈动脉中的高2.8至17.3倍。由于雄激素水平处于生理范围内，我们得出结论，在该物种正常成年雄性中，大脑通常会使血液中的雌激素含量增加。
