Badura L L
Behavioral Neuroscience Division, Psychology Department, State University of New York at Buffalo, NY 14260, USA.
Neuroendocrinology. 1996 Dec;64(6):462-6. doi: 10.1159/000127153.
Prolactin (PRL) secretion from the anterior pituitary is tonically controlled by the activity of the hypothalamic tuberoinfundibular dopaminergic (TIDA) system. Changes in TIDA activity have been associated with the decrease in basal PRL levels shown by hamsters exposed to a short-day photoperiod. Potential concurrent changes in the sensitivity of pituitary lactotropes to the inhibitory actions of dopamine on PRL release were investigated in tissue harvested from animals that had been preexposed to either a stimulatory, long-day 16-hour-light:8-hour-dark (16L:8D) photoperiod, or to a nonstimulatory, short-day (10L:14D) photoperiod for 8-10 weeks. Tissue was maintained in a perifusion tissue culture system and received a 1-hour pulse of varying concentrations of dopamine (DA) shortly after the equilibration period. Fractions of the media were collected every 1/2 h and PRL concentrations in each sample determined via radioimmunoassay. At the highest concentration of DA (10(-6) M), a highly significant inhibition of PRL levels was seen for both 16L and 10L pituitaries. At both mid range concentrations of DA (10(-7) and 10(-8) M), both tissue types showed a significant suppression of PRL, but the reduction was greater for tissue that had been obtained from 10L animals. At the lowest concentration of DA (10(-9) M), a significant suppression of PRL occurred for tissue harvested from 10L animals, but not for tissue taken from 16L animals. These results indicate that the responsiveness of anterior pituitary tissue to the inhibitory effects of DA are altered by photoperiod exposure, and this change is likely a consequence of changes in the characteristics of the D2 receptor population on pituitary lactotropes. Short-day-induced increases in sensitivity to the inhibitory effects of DA may be due to increases in receptor number, or to increased affinity of the D2 receptor for its ligand.
垂体前叶催乳素（PRL）的分泌受下丘脑结节漏斗多巴胺能（TIDA）系统活动的紧张性控制。TIDA活动的变化与暴露于短日照光周期的仓鼠所表现出的基础PRL水平降低有关。在从预先暴露于刺激性长日照16小时光照：8小时黑暗（16L:8D）光周期或非刺激性短日照（10L:14D）光周期8 - 10周的动物身上采集的组织中，研究了垂体催乳细胞对多巴胺对PRL释放抑制作用敏感性的潜在同时变化。组织被维持在灌注组织培养系统中，在平衡期后不久接受1小时不同浓度多巴胺（DA）的脉冲。每半小时收集一次培养基部分，并通过放射免疫测定法测定每个样品中的PRL浓度。在最高浓度的DA（10⁻⁶ M）下，16L和10L垂体的PRL水平均受到高度显著的抑制。在中等浓度的DA（10⁻⁷和10⁻⁸ M）下，两种组织类型均显示PRL有显著抑制，但从10L动物获得的组织抑制作用更大。在最低浓度的DA（10⁻⁹ M）下，从10L动物采集的组织中PRL有显著抑制，但从16L动物采集的组织则没有。这些结果表明，垂体前叶组织对DA抑制作用的反应性会因光周期暴露而改变，这种变化可能是垂体催乳细胞上D2受体群体特征变化的结果。短日照引起的对DA抑制作用敏感性增加可能是由于受体数量增加，或D2受体对其配体的亲和力增加。
