Fitch C A, Freeman M E
Department of Biological Science, Florida State University, 32306-4075, Tallahassee, FL.
Endocrine. 1996 Feb;4(1):59-63. doi: 10.1007/BF02738875.
Dopamine (DA) will both stimulate and inhibit prolactin (PRL) secretion from the anterior pituitary gland in vitro and in vivo. The present study was designed to determine if there are selected times during the estrous cycle of the rat when one function is favored over the other. Anterior pituitary glands collected on diestrus-1 (D1), diestrus-2 (D2), the morning of proestrus (Pro-AM), the afternoon of proestrus (Pro-PM), and estrus (E) were enzymatically dissociated and placed in monolayer culture. On the fourth day in culture, cells were challenged for 10, 20, 30, 60, 120, 180, or 240 min with media alone or media containing either 100 pM or 1 μM DA. The concentration of PRL in the media was determined by radioimmunoassay. Regression analysis revealed that in the absence of DA, PRL secretion from cultured cells differed significantly depending on the stage of the estrous cycle during which they were obtained. Cells obtained during the morning of diestrus-2 secreted PRL at the greatest rate compared to other stages of the cycle. When all stages were compared, the rates of PRL secretion were: D2>E>D1>Pro-AM>Pro-PM (each significantly different from the others,P<0.01). By 20-30 min of exposure to 100 pM DA, the rate of PRL secretion from cells obtained during each stage of the cycle was significantly enhanced. This enhanced secretion persisted in cells obtained during D2 and Pro-PM but was short-lived in cells obtained during other stages. No inhibition of PRL secretion was induced by this dose of DA. PRL secretion was inhibited when treated with 1 μM DA in cells obtained at all stages of the estrous cycle. Inhibition was more prolonged in cells obtained on D1, D2, and Pro-AM. DA was least effective as an inhibitor of PRL secretion in cells obtained during Pro-PM and E. Prior to inhibiting PRL secretion in cells obtained during Pro-PM, 1 μM DA rapidly stimulated PRL secretion. This effect persisted for 60 min. These data suggest that in the absence of DA, the dynamics of PRL secretion from anterior pituitary cells in vitro differ depending on the stage of the estrous cycle during which the cells were obtained. Moreover, the in vivo environment of the cell determines the direction and magnitude of the PRL-secretory response to DA.
多巴胺（DA）在体外和体内均可刺激和抑制垂体前叶分泌催乳素（PRL）。本研究旨在确定在大鼠发情周期中是否存在某些特定时期，使得多巴胺的某一种作用比另一种作用更占优势。采集处于动情间期-1（D1）、动情间期-2（D2）、发情前期上午（Pro-AM）、发情前期下午（Pro-PM）和发情期（E）的大鼠垂体前叶，进行酶解并置于单层培养。培养的第4天，用不含多巴胺的培养基或含100 pM或1 μM多巴胺的培养基对细胞进行10、20、30、60、120、180或240分钟的刺激。采用放射免疫分析法测定培养基中PRL的浓度。回归分析显示，在无多巴胺的情况下，培养细胞的PRL分泌量因获取细胞时所处的发情周期阶段不同而有显著差异。与发情周期的其他阶段相比，动情间期-2上午获取的细胞分泌PRL的速率最高。比较所有阶段，PRL分泌速率为：D2>E>D1>Pro-AM>Pro-PM（各阶段之间差异均有统计学意义，P<0.01）。暴露于100 pM多巴胺20 - 30分钟时，发情周期各阶段获取的细胞PRL分泌速率均显著提高。这种分泌增强在D2和Pro-PM阶段获取的细胞中持续存在，但在其他阶段获取的细胞中持续时间较短。该剂量的多巴胺未诱导PRL分泌受抑制。在发情周期各阶段获取的细胞中，用1 μM多巴胺处理均能抑制PRL分泌。在D1、D2和Pro-AM阶段获取的细胞中，抑制作用持续时间更长。在Pro-PM和E阶段获取的细胞中，多巴胺作为PRL分泌抑制剂的效果最差。在抑制Pro-PM阶段获取的细胞分泌PRL之前，1 μM多巴胺能迅速刺激PRL分泌。这种作用持续60分钟。这些数据表明，在无多巴胺的情况下，体外垂体前叶细胞PRL分泌的动态变化因获取细胞时所处的发情周期阶段不同而有所差异。此外，细胞的体内环境决定了PRL对多巴胺分泌反应的方向和幅度。
