Vijayan E, Carraway R, Leeman S E, McCann S M
School of Life Sciences, University of Hyderabad, India.
Proc Natl Acad Sci U S A. 1988 Dec;85(24):9866-9. doi: 10.1073/pnas.85.24.9866.
Previous studies have indicated that the brain peptide neurotensin can stimulate prolactin release by direct action on the pituitary gland, whereas its action within the hypothalamus is inhibitory. The inhibitory action is mediated by the release of dopamine into the hypophyseal portal veins, which deliver the neurotransmitter to the anterior pituitary gland to inhibit prolactin release. Our experiments were done to evaluate the physiologic significance of these neurotensin actions by injecting the globulin fraction of highly specific neurotensin antiserum either intravenously or intraventricularly. Injection into the third ventricle of either 1 or 3 microliter of neurotensin antiserum significantly increased plasma prolactin concentrations in (i) ovariectomized and (ii) ovariectomized estrogen- and progesterone-primed rats within 1 hr of injection. The response was more pronounced in the ovariectomized than in the ovariectomized estrogen- and progesterone-treated animals and was dose related. Intraventricular injection of these doses of neurotensin antiserum also evoked elevations in plasma prolactin in intact males, which were significant but smaller in magnitude than those seen in female rats. To evaluate the effect of the antiserum on the pituitary directly, the antiserum was injected intravenously at a dose of 40 microliter, which was sufficient to block the blood pressure-lowering effect of neurotensin. After the intravenous injection of antiserum, a highly significant suppression of plasma prolactin occurred, detectable when first measured at 1 hr after injection in both ovariectomized and ovariectomized estrogen- and progesterone-treated animals; however, the intravenous injection of antiserum had no significant effect on the prolactin release in males. These data indicate the physiological significance of the hypothalamic inhibitory actions of neurotensin on prolactin release, which are probably mediated by its stimulation of dopamine release that in turn, inhibits prolactin secretion by the lactotropes. The direct stimulatory effect of the peptide on prolactin release after its presumed release into portal vessels also appears to be physiologically significant in female but not in male rats.
以往的研究表明，脑肽神经降压素可通过直接作用于垂体来刺激催乳素释放，而其在下丘脑内的作用却是抑制性的。这种抑制作用是由多巴胺释放到垂体门脉中介导的，垂体门脉将神经递质输送到腺垂体以抑制催乳素释放。我们进行实验，通过静脉内或脑室内注射高特异性神经降压素抗血清的球蛋白部分，来评估这些神经降压素作用的生理意义。向第三脑室内注射1微升或3微升神经降压素抗血清，在注射后1小时内，可使（i）去卵巢大鼠和（ii）去卵巢并用雌激素和孕酮预处理的大鼠的血浆催乳素浓度显著升高。去卵巢大鼠的反应比去卵巢并用雌激素和孕酮处理的动物更明显，且与剂量相关。向完整雄性大鼠脑室内注射这些剂量的神经降压素抗血清，也会引起血浆催乳素升高，虽然有统计学意义，但幅度小于雌性大鼠。为了直接评估抗血清对垂体的作用，以40微升的剂量静脉注射抗血清，该剂量足以阻断神经降压素的降压作用。静脉注射抗血清后，在去卵巢大鼠和去卵巢并用雌激素和孕酮处理的动物中，注射后1小时首次测量时，血浆催乳素出现高度显著的抑制；然而，静脉注射抗血清对雄性大鼠的催乳素释放没有显著影响。这些数据表明神经降压素对催乳素释放的下丘脑抑制作用具有生理意义，这可能是由其刺激多巴胺释放介导的，而多巴胺释放反过来又抑制催乳素细胞分泌催乳素。该肽在假定释放到门脉血管后对催乳素释放的直接刺激作用，在雌性大鼠中似乎也具有生理意义，但在雄性大鼠中并非如此。
