RESUMO
To investigate the observed variation in glucose tolerance and insulin secretion in intrauterine growth retarded newborn rats and to explore the mechanism of the variations, Sprague-Dawley pregnant rats were allocated into two groups: a control group and an intrauterine energy restricted group. The intrauterine growth retardation (IUGR) in the rats was induced by 50% calorie restriction in pregnant rats from gestational day 15 until term as compared to the control group. The pancreata of control and IUGR newborn rats were dissected respectively. RT-PCR was used to study the mRNA level related to insulin synthesis and exocytosis. Intraperitoneal glucose tolerance tests were done to study the function of the pancreatic islet. We found that birth weight and pancreas mass of IUGR newborn rats were significantly lower than those of controls. Although no significant differences were observed in mRNA level of insulin and PDX-1, the expression of genes related to insulin exocytosis such as munc13-1, vamp-2, syntaxin1a, rab3a were reduced significantly in IUGR newborn rats. IUGR animals were glucose-intolerant. The observed blood insulin level and insulin secretion response to glucose challenge were both found to be at reduced level in IUGR newborn rats as compared with the normal control group rats. With these findings, we hypothesize that IUGR can induce changes in glucose homeostasis due to, at least in part, a reduced function of insulin exocytosis in newborn rats.
Assuntos
Retardo do Crescimento Fetal/metabolismo , Insulina/metabolismo , Animais , Animais Recém-Nascidos , Feminino , Retardo do Crescimento Fetal/genética , Expressão Gênica , Teste de Tolerância a Glucose , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Insulina/sangue , Insulina/genética , Secreção de Insulina , Ilhotas Pancreáticas , Masculino , Pâncreas/metabolismo , Gravidez , Ratos , Ratos Sprague-Dawley , Transativadores/genética , Transativadores/metabolismoRESUMO
Munc13-1 may be a key factor in regulating insulin exocytosis, but its exact expression and role have not been clarified yet, especially during pancreatic development. We attempted to investigate the expression and function of Munc13-1 during embryonic pancreatic development in rats and determine the effects on insulin secretion. In the present study, pancreata of rats at embryonic day 12.5 (E12.5), E15.5, E18.5, new-born, 21 after birth (P21), and adult stage were dissected under microscope. The rat model of intrauterine growth retardation (IUGR) was made by 50% calorie restriction in pregnant rats from gestational day 15 until term. The expression of Munc13-1 and insulin secretion was studied by the techniques of RTPCR, real-time PCR, Western blot, and enzyme-linked immunosorbent assay. Immunohistochemistry and immunofluorescence were used to define the location of Munc13- 1. We found that Munc13-1 was located at islet along with insulin. Insulin- and Munc13-1-specific mRNA were not detected until E12.5 and E15.5, respectively, and increased with the development of the fetus. Western blot showed that Munc13-1 was low at E15.5 and E18.5 and increased later. The blood insulin level and Munc13-1 were reduced simultaneously in IUGR newborn rats compared with normal ones. These results suggest that Munc13-1 exists in pancreas islets during fetus development and its deficiency in the pancreas, as occurs in IUGR, was in accordance with decreased blood insulin level. Munc13-1 may play an essential role in insulin exocytosis.
