Close F T, Freeman M E
Department of Biological Science, Florida State University, Tallahassee 32306-4075, USA.
Neuroendocrinology. 1997 Jun;65(6):430-5. doi: 10.1159/000127206.
Dopamine (DA), a well-established inhibitor of prolactin (PRL) secretion, has also been shown to stimulate PRL secretion from the anterior lobe of the pituitary gland of the rat. It has been reported that low doses of DA stimulate PRL whereas high doses inhibit PRL secretion. Our laboratory has previously reported that these PRL secretory responses are dependent upon the stages of the estrous cycle of the rat. The objective of the present study was to determine the steroid requirements for the differing PRL secretory responses to low and high doses of DA in perifusion. Animals were ovariectomized (OVX) and immediately given Silastic implants containing estradiol (E2) which has previously been shown in our laboratory to produce blood levels of 70-100 pg/ml, progesterone which has previously been shown in our laboratory to produce blood levels of 30-40 ng/ml, or the combination. OVX rats served as controls. Ten days later, the anterior lobes of the pituitary glands were harvested and enzymatically dissociated. Cells were mixed with Sephadex G-10 and placed in six 0.5-ml perifusion chambers (1 x 10(6) cells/chamber). Cells were perifused for 24 h with Dulbecco's modified Eagle's medium containing 0.2% bovine serum albumin and 0.1 mM ascorbic acid. The PRL secretory pattern was characterized in response to the following treatment sequence: (1) 30 min media alone (maximally uninhibited); (2) 24 min 100 pM DA; (3) 30 min media alone (DA withdrawal); (4) 24 min 1 microM DA, and (5) 30 min media alone (DA withdrawal). PRL secretion in the presence of 100 pM DA was unchanged in cells obtained from OVX animals, but exposure to 1 microM DA inhibited PRL release in these cells. Subsequent withdrawal stimulated PRL secretion relative to that of the initial exposure to media alone. The responses of cells from OVX rats implanted with progesterone alone was indistinguishable from those of the OVX controls. In cells obtained from animals implanted with E2 alone, 100 pM DA and its subsequent withdrawal neither stimulated nor inhibited PRL secretion. In contrast, 1 microM DA exposure initially stimulated and then inhibited PRL secretion in cells from E2-treated animals. Here, subsequent withdrawal of DA enhanced PRL secretion. In cells obtained from E2+progesterone-treated animals, 100 pM DA exposure robustly enhanced PRL secretory responses. Withdrawal of this dose of DA had no further effect on PRL secretion. However, exposure of E2+progesterone-treated cells to 1 microM DA robustly stimulated and subsequently only slightly inhibited PRL secretion. The results of these studies suggest that inhibition of PRL secretion by DA is independent of ovarian steroids while E2 and progesterone in combination favors stimulation of PRL secretion in response to DA. Taken together, these data suggest that PRL secretory responses in this system are determined by the ovarian steroid milieu.
多巴胺（DA）是一种公认的催乳素（PRL）分泌抑制剂，但也已被证明可刺激大鼠垂体前叶分泌PRL。据报道，低剂量的DA刺激PRL分泌，而高剂量则抑制PRL分泌。我们实验室先前曾报道，这些PRL分泌反应取决于大鼠发情周期的阶段。本研究的目的是确定在灌流实验中，不同剂量的DA对PRL分泌产生不同反应时所需的类固醇。将动物进行卵巢切除（OVX），并立即植入含雌二醇（E2）的硅橡胶植入物（我们实验室先前已证明其可使血液中E2水平达到70 - 100 pg/ml）、孕酮（我们实验室先前已证明其可使血液中孕酮水平达到30 - 40 ng/ml）或两者的组合。OVX大鼠作为对照。10天后，摘取垂体前叶并进行酶解。将细胞与葡聚糖凝胶G - 10混合，放入六个0.5 ml的灌流室（每个室1×10⁶个细胞）。用含有0.2%牛血清白蛋白和0.1 mM抗坏血酸 的杜尔贝科改良伊格尔培养基对细胞进行24小时灌流。根据以下处理顺序来表征PRL分泌模式：（1）单独用培养基30分钟（最大程度无抑制）；（2）100 pM DA处理24分钟；（3）单独用培养基30分钟（撤去DA）；（4）1 μM DA处理24分钟，以及（5）单独用培养基30分钟（撤去DA）。在从OVX动物获得的细胞中，100 pM DA存在时PRL分泌未发生变化，但暴露于1 μM DA会抑制这些细胞中的PRL释放。随后撤去DA相对于最初单独暴露于培养基时刺激了PRL分泌。单独植入孕酮的OVX大鼠的细胞反应与OVX对照的细胞反应无差异。在仅植入E2的动物获得的细胞中，100 pM DA及其随后撤去既不刺激也不抑制PRL分泌。相反，在E2处理的动物的细胞中，暴露于1 μM DA最初刺激然后抑制PRL分泌。在此，随后撤去DA增强了PRL分泌。在E2 +孕酮处理的动物获得的细胞中，暴露于100 pM DA强烈增强了PRL分泌反应。撤去此剂量的DA对PRL分泌没有进一步影响。然而，E2 +孕酮处理的细胞暴露于1 μM DA会强烈刺激并随后仅轻微抑制PRL分泌。这些研究结果表明，DA对PRL分泌的抑制作用独立于卵巢类固醇，而E2和孕酮共同作用有利于在DA作用下刺激PRL分泌。综上所述，这些数据表明该系统中的PRL分泌反应由卵巢类固醇环境决定。
