Regulatory Mechanism Of Leptin Secretion During Pregnancy And Lactation In The Golden Hamster And Japanese Monkey

In these studies, the golden hamster were used as a animal model and a serial of methods were used to determine the regulatory mechanism of leptin secretion during pregnancy and lactation.1. Development of a RIA for leptin.Recombinant human leptin (rh-Leptin) was used as standard, iodinated rh-Leptin was used as a tracer and anti-rh-Leptin rabbit serum was used as the first antibody to establish a radioimmunoassay for the measurement of leptin. Evaluation of this assay system showed no cross reaction between leptin and FSH, LH, GH, TSH, insulin and prolactin. This assay system is stale and had a large measuring range. It can beused in the measurement of the leptin in the serum of human, monkey, mouse and the golden hamster, but can not be used in the measurement of leptin in serum of rat, horse and porcine. Using this leptin assay system, we measured changes of leptin level in one estrous cycle in cycling golden hamsters at a interval of 4 hours. Our results showed that a clear diurnal rhythm of leptin secretion existed during the estrous cycle in the golden hamster which is consistent with the results reported before.2. Determination of leptin secretion pattern during pregnancy in the golden hamster.Using this leptin assay system, we measured leptin secreting pattern during pregnancy in the golden hamster. 100 golden hamsters were sampled daily and leptin levels in these samples were measured using the specific RIA established in our laboratory before. Body weight and food intake of these animals were recorded daily, and Group of animals were hysterectomized to determine the maternal body weight ( Except for that of conceptus ) . Our results showed that plasma leptin level significantly elevated on day 9 of pregnancy and and peaked at day 12 of pregnancy. Leptin level decrease from day 13 of pregnancy and it kept decreasing from then on and on day 15 of pregnancy, Leptin level decreased to the level of the. pre-pregnancy. No significant correlation were observed between leptin and total body weight. These suggested that a obvious leptin resistance exist during mid to late pregnancy in the golden hamster.3. Relationships between leptin and pregnancy-related hormones, and lipid content during pregnancy in the golden hamster.To determine the relationships between leptin and other pregnancy-related hormones, body weight, food intake and lipid content during pregnancy, the same serum were used to deterimine plasma concentration of estradiol, progesterone, inhibin, LH, FSH, GH. Groups of animals were used to determine the lipid content during different days of the pregnancy. The results showed that sex gonad hormones, other than pituitary hormones, significantly correlated with plasma leptin. No changes on the lipid content was observed before day 12 of pregnancy. After day 12 of pregnancy, the lipid content significantly decreased compared with that of the pre-pregnancy (P<0. 001) . All these results 博士论文 金黄仓鼠和猴妊娠及泌乳期瘦素分泌及其调节机制研究suggested that: 1) Before day 12 of pregnancy, there might be some factors stimulate leptin secretion; or 2) There might be non-adipose derived leptin secretion during pregnancy; or 3) Both. Meanwhile, the decrease of the lipid content during may contribute to the decrease of the leptin secretion after day 12 of pregnancy.4. Contribution of placenta to the gestational leptin profile.Based on experiment 3. we hypothesis that placenta maybe another non-adipose leptin source. To hypothesis this result, immunohistochemistry were used to determine if placenta secret leptin; placenta from different pregnant stages were weighted and homogenated to determine leptin content; Animals were hysterectomized or fetectomized to see the changes of plasma leptin level. Results showed that leptin expresses on the placenta. Homogenate RIA shows a very low or undetectable leptin in the placental homogenate. No correlation is observed between plasma leptin and the placenta weight and finally hysterectomy and fetectomy have no effect on...