Buntin J D, Advis J P, Ottinger M A, Lea R W, Sharp P J
Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA.
Gen Comp Endocrinol. 1999 Apr;114(1):97-107. doi: 10.1006/gcen.1998.7239.
Intracerebroventricular (ICV) injections of prolactin (PRL) exert potent antigonadal and antigonadotropic effects in ring doves (Streptopelia risoria) at doses that are insufficient to stimulate prolactin-dependent crop growth. To explore the physiological basis of these effects, we tested the ability of ICV-injected PRL to influence pituitary responsiveness to chicken gonadotropin-releasing hormone-I (cGnRH-I) and to alter GnRH content and concentration in the preoptic area (POA) and median eminence (ME). cGnRH-I-induced changes in plasma LH were monitored by radioimmunoassay (RIA) in photostimulated male doves after they received five daily ICV injections of ovine PRL (1 microg/2 microl) or saline vehicle. Although PRL treatment reduced basal plasma LH levels and testes weight, it did not reduce the amount or alter the pattern of LH released in response to a bolus injection of cGnRH-I. This suggests that ICV PRL does not suppress LH by reducing pituitary responsiveness to GnRH. In two subsequent studies, GnRH content (ng/region) and concentration (pg/microg protein) in the POA and ME were measured in male doves by RIA and by competitive enzyme immunoassay after 5 days of ICV PRL or vehicle treatment. Although ICV PRL reduced plasma LH levels in both studies, no significant PRL-induced alterations in GnRH content or concentration were apparent. In a final study, PRL-treated female doves had lower plasma LH levels than vehicle-treated control females at 12 and 24 h after a single ICV injection. GnRH content of the POA was also lower in PRL-treated females than in controls at 24 h. However, the two treatment groups did not differ in POA or ME GnRH content at earlier postinjection sampling intervals. Analysis of GnRH concentration data revealed no treatment group differences in either region at any sampling interval (1, 6, 12, or 24 h post-PRL injection). Collectively, these results are consistent with the idea that ICV-injected PRL acts at the level of the CNS to inhibit the reproductive system. However, the nature of the alterations involved remains to be clarified. Plausible hypotheses are (1) that ICV PRL suppresses the gonadal axis by influencing the activity of GnRH neurons at brain sites other than the POA or ME or (2) that PRL alters the synthesis, storage, degradation, and/or release of GnRH in the POA or ME, but the dynamic changes involved are not reflected in integrated, steady-state measures such as peptide content or concentration in tissue.
向环鸽（Streptopelia risoria）脑室内（ICV）注射催乳素（PRL），在剂量不足以刺激催乳素依赖性嗉囊生长时，会产生强大的抗性腺和促性腺激素作用。为了探究这些作用的生理基础，我们测试了脑室内注射PRL影响垂体对鸡促性腺激素释放激素-I（cGnRH-I）反应性以及改变视前区（POA）和正中隆起（ME）中GnRH含量和浓度的能力。在光刺激的雄性鸽子每日接受5次脑室内注射绵羊PRL（1微克/2微升）或生理盐水载体后，通过放射免疫分析（RIA）监测cGnRH-I诱导的血浆促黄体生成素（LH）变化。尽管PRL处理降低了基础血浆LH水平和睾丸重量，但它并未减少对一次推注cGnRH-I反应释放的LH量或改变其释放模式。这表明脑室内注射PRL并非通过降低垂体对GnRH的反应性来抑制LH。在随后的两项研究中，通过RIA和竞争性酶免疫分析测量了脑室内注射PRL或载体5天后雄性鸽子POA和ME中的GnRH含量（纳克/区域）和浓度（皮克/微克蛋白质）。尽管在两项研究中脑室内注射PRL均降低了血浆LH水平，但PRL并未引起GnRH含量或浓度的明显改变。在最后一项研究中，单次脑室内注射后12小时和24小时，接受PRL处理的雌性鸽子血浆LH水平低于接受载体处理的对照雌性鸽子。在24小时时，接受PRL处理的雌性鸽子POA中的GnRH含量也低于对照组。然而，在注射后早期采样间隔时，两个处理组在POA或ME的GnRH含量上没有差异。对GnRH浓度数据的分析显示，在任何采样间隔（PRL注射后1、6、12或24小时），两个区域的处理组之间均无差异。总体而言，这些结果与脑室内注射PRL在中枢神经系统水平作用以抑制生殖系统的观点一致。然而，所涉及改变的性质仍有待阐明。合理的假设是：（1）脑室内注射PRL通过影响POA或ME以外脑区的GnRH神经元活性来抑制性腺轴；（2）PRL改变POA或ME中GnRH的合成、储存、降解和/或释放，但所涉及的动态变化未反映在诸如组织中肽含量或浓度等综合稳态测量中。
