The endocrine pancreas of pregnant rats shows evident plasticity, which allows the morphological structures to return to the nonpregnant state right after delivery. Furthermore, it is well-known the role of melatonin in the maintenance of the endocrine pancreas and its tropism. Studies indicate increasing nocturnal serum concentrations of maternal melatonin during pregnancy in both humans and rodents. The present study investigated the role of melatonin on energy metabolism and in pancreatic function and remodeling during pregnancy and early lactation in rats. The results confirm that the absence of melatonin during pregnancy impairs glucose metabolism. In addition, there is a dysregulation in insulin secretion at various stages of the development of pregnancy and an apparent failure in the glucose-stimulated insulin secretion during the lactation period, evidencing the role of melatonin on the regulation of insulin secretion. This mechanism seems not to be dependent on the antioxidant effect of melatonin and probably dependent on MT2 receptors. We also observed changes in the mechanisms of death and cell proliferation at the end of pregnancy and beginning of lactation, crucial periods for pancreatic remodeling. The present observations strongly suggest that both functionality and remodeling of the endocrine pancreas are impaired in the absence of melatonin and its adequate replacement, mimicking the physiological increase seen during pregnancy, is able to reverse some of the damage observed. Thus, we conclude that pineal melatonin is important to metabolic adaptation to pregnancy and both the functionality of the beta cells and the remodeling of the pancreas during pregnancy and early lactation, ensuring the return to nonpregnancy conditions.

中文翻译：

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褪黑激素在怀孕和哺乳期间调节母体胰腺重塑和 B 细胞功能

妊娠大鼠的内分泌胰腺显示出明显的可塑性，使形态结构在分娩后立即恢复到非妊娠状态。此外，众所周知，褪黑激素在维持内分泌胰腺中的作用及其趋向性。研究表明，妊娠期间人类和啮齿动物的母体褪黑激素的夜间血清浓度都会增加。本研究调查了褪黑激素对大鼠妊娠和泌乳早期能量代谢和胰腺功能和重塑的作用。结果证实，怀孕期间缺乏褪黑激素会损害葡萄糖代谢。此外，妊娠发育的各个阶段存在胰岛素分泌失调，泌乳期葡萄糖刺激的胰岛素分泌明显失效，证明了褪黑激素对胰岛素分泌调节的作用。这种机制似乎不依赖于褪黑激素的抗氧化作用，而可能依赖于 MT2 受体。我们还观察到妊娠末期和哺乳期开始时死亡和细胞增殖机制的变化，这是胰腺重塑的关键时期。目前的观察结果强烈表明，在缺乏褪黑激素的情况下，内分泌胰腺的功能和重塑都会受损，而褪黑激素的充分替代（模仿怀孕期间观察到的生理增加）能够逆转观察到的一些损伤。因此，