Charoenphandhu N, Limlomwongse L, Krishnamra N
Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.
Can J Physiol Pharmacol. 2001 May;79(5):430-8.
Prolactin has been postulated to be a novel calcium-regulating hormone during pregnancy and lactation. It stimulates both passive and active duodenal calcium transport in several experimental models. Our study was performed on sexually mature female Wistar rats (200-250 g) to study the direct action of prolactin on calcium transport in the duodenum using the Ussing chamber technique. To evaluate the effect of prolactin on total calcium transport in the duodenum, we intraperitoneally injected rats with 0.4, 0.6, and 0.8 mg/kg prolactin. The total calcium transport was divided into voltage-dependent, solvent drag-induced, and transcellular active fluxes by applying short-circuit current and by mucosal glucose replacement with mannitol. The effect of prolactin on each flux was studied separately. Finally, to evaluate the direct action of prolactin on duodenal transcellular active flux, we directly exposed duodenal segments to prolactin that had been added to the serosal solution with or without calcium transport inhibitors. We found that 0.6 and 0.8 mg/kg prolactin ip significantly increased the total mucosa-to-serosa calcium flux from the control value (nmol x hr(-1) x cm(-2)) of 34.53+/-6.81 to 68.07+/-13.53 (P < 0.05) and 84.43+/-19.72 (P < 0.01), respectively. Prolactin also enhanced the solvent drag-induced calcium flux and transcellular active calcium flux, but not the voltage-dependent calcium flux. The duodenal segments directly exposed to 200, 400, and 800 ng/mL prolactin showed a significant increase in the transcellular active calcium absorption in a dose-dependent manner, i.e., from the control value (nmol x hr(-1) x cm(-2)) of 2.94+/-0.47 to 5.45+/-0.97 (P < 0.01), 8.09+/-0.52 (P < 0.001), and 18.42+/-2.92 (P < 0.001), respectively. Its direct action was inhibited by mucosal exposure to 50 microM lanthanum chloride, a calcium transporter protein competitor, and serosal exposure to 0.1 mM trifluoperazine, a Ca2+-ATPase inhibitor. These studies demonstrate that the duodenum is a target organ of prolactin, which enhances transcellular active calcium transport.
催乳素被假定为妊娠和哺乳期一种新型的钙调节激素。在多个实验模型中，它能刺激十二指肠钙的被动和主动转运。我们对性成熟的雌性Wistar大鼠（200 - 250克）进行了研究，采用Ussing chamber技术来研究催乳素对十二指肠钙转运的直接作用。为评估催乳素对十二指肠总钙转运的影响，我们给大鼠腹腔注射0.4、0.6和0.8毫克/千克的催乳素。通过施加短路电流以及用甘露醇替代黏膜葡萄糖，将总钙转运分为电压依赖性、溶剂拖曳诱导性和跨细胞主动通量。分别研究了催乳素对每种通量的影响。最后，为评估催乳素对十二指肠跨细胞主动通量的直接作用，我们将十二指肠段直接暴露于添加到浆膜溶液中的催乳素中，同时添加或不添加钙转运抑制剂。我们发现，腹腔注射0.6和0.8毫克/千克的催乳素能使黏膜到浆膜的总钙通量从对照值（纳摩尔×小时⁻¹×厘米⁻²）34.53±6.81分别显著增加到68.07±13.53（P < 0.05）和84.43±19.72（P < 0.01）。催乳素还增强了溶剂拖曳诱导的钙通量和跨细胞主动钙通量，但未增强电压依赖性钙通量。直接暴露于200、400和800纳克/毫升催乳素的十二指肠段，跨细胞主动钙吸收呈剂量依赖性显著增加，即从对照值（纳摩尔×小时⁻¹×厘米⁻²）2.94±0.47分别增加到5.45±0.97（P < 0.01）、8.09±0.52（P < 0.001）和18.42±2.92（P < 0.001）。其直接作用受到黏膜暴露于50微摩尔/升的氯化镧（一种钙转运蛋白竞争者）和浆膜暴露于0.1毫摩尔/升的三氟拉嗪（一种Ca²⁺ - ATP酶抑制剂）的抑制。这些研究表明，十二指肠是催乳素的靶器官，催乳素可增强跨细胞主动钙转运。
