Effects of Prolactin on Pancreatic Function in Mice

在体内外，催乳素治疗可直接刺激大鼠胰岛B细胞分泌胰岛素，而胰岛素在体外可刺激子宫蜕膜细胞和垂体肿瘤细胞分泌催乳素。这些发现表明，催乳素和胰岛素的分泌之间存在密切关系。因此，有必要在动物模型中研究催乳素对胰腺的长期影响。近交系BALB/c和SHN小鼠被用于这些实验。这些品系的雄性和雌性小鼠在50日龄时分别在胰腺移植前脑垂体，并在移植后不同的时间间隔使用。这些品系的对照小鼠在相同的位置分别被给予一块颌下腺。异位垂体移植导致血浆催乳素水平升高，高催乳素血症，胰腺重量增加，这主要是由于胰腺腺泡的增生所致。此外，接受垂体移植的小鼠的血糖水平高于未移植的小鼠。另一方面，接受脑垂体移植的小鼠的血清胰岛素水平显著高于未移植的小鼠。垂体移植还导致肝脏重量显著增大。人们普遍认为，任何导致高血糖的情况都与胰腺肿瘤的发生高度相关。本研究结果提示，高催乳素血症合并高血糖是胰腺肿瘤发生的原因之一。结论：异位垂体移植引起的高催乳素循环水平在胰腺增生症的发生发展中起重要作用。

Prolactin treatment directly stimulates insulin release from B-cells of rat pancreatic islets in vitro and in vivo, whereas insulin is shown to stimulate prolactin secretion from uterine decidual cells and pituitary tumor cells in vitro. These findings indicate an intimate relationship between prolactin and insulin secretion. Thus, it is worthwhile examining the long-term effects of prolactin on pancreas in an animal model.Inbred strains of BALB/c and SHN mice were used in these experiments. Male and female mice of these strains were grafted with anterior pituitaries single each at the pancreata at 50 days of age and used at various intervals after the transplantation. Control mice of these strains were given a piece of submaxillary gland each at the same site. All grafts were obtained from the 50-day-old male mice of the respective strains.Ectopic pituitary transplantation resulted in an elevation of plasma prolactin level, hyperprolactinemia, and an increase in the pancreatic weight, mainly due to hyperplastic proliferation of the pancreatic acinar glands. In addition, blood glucose levels in the mice with pituitary grafts were higher than in mice without pituitary grafts. On the other hand, serum insulin levels in mice with pituitary grafting were significantly higher than in mice without pituitary grafts. Pituitary grafting also induced an significant enlargement of the liver weight.It is widely recognized that any conditions leading to hyperglycemia are highly related to pancreatic tumorigenesis. The present results imply that hyperprolactinemia associated with hyperglycemia is one of the causes of pancreatic tumorigenesis. In conclusion, the high circulating level of prolactin induced by the ectopic pituitary grafting plays an important role in the development of pancreatic hyperplasia.