During late pregnancy, women with insulin-dependent diabetes (IDDM) are vulnerable to more frequent and more severe hypoglycemic episodes. The cause of this is not known, but has been suggested to be due in part to the intensive insulin treatment necessary to minimize perinatal morbidity and mortality. However, a few studies in pregnant women and the pregnant rat have indicated that the glucagon response, and probably the epinephrine response, to insulin-induced hypoglycemia is blunted by pregnancy itself. I have demonstrated in the pregnant dog that the increment in circulating norepinephrine is blunted as well, suggesting that a reduction in activation of the sympathetic nervous system in response to hypoglycemia may also accompany pregnancy. In the nonpregnant state, the magnitude of the counterregulatory hormone response appears to be modulated by a variety of factors that include sensitivity of the brain to insulin or the degree of hypoglycemia.
The aim of this proposal is to examine which counterregulatory mechanisms are altered by pregnancy. The ensuing metabolic consequences of potential impairments will also be assessed. The techniques required to answer the questions posed are invasive and the experimental conditions are potentially harmful to the fetus. Thus, a novel canine model of pregnancy will be employed to address these issues. Arteriovenous difference techniques across the pancreas will be used to assess whether there is a defect in the alpha cell's ability to respond to a fall in glucose in pregnancy, and whether the defective glucagon response to insulin-induced hypoglycemia correlates with a decrease in neural drive to the pancreas. A technique for cannulation of the third cerebroventricle will be used to establish brain neuroglycopenia to assess whether pregnancy causes changes in the brain's sensitivity to hypoglycemia per se. Finally, the altered endocrine environment of pregnancy is the likely cause of the altered counterregulatory response, and three of the major hormones of pregnancy (estrogen, progesterone and prolactin) will be chronically elevated in nonpregnant female dogs to determine whether re-creating part of the hormonal environment of pregnancy attenuates the rise in counterregulatory hormones in response to insulin-induced hypoglycemia, similar to that seen in pregnancy. The studies in this proposal should help to identify which counterregulatory mechanisms are affected by pregnancy, thereby potentially contributing to the more frequent and severe episodes of hypoglycemia experienced by pregnant women with diabetes. Preliminary studies in the pregnant dog model in fact suggest that multiple counterregulatory mechanisms are altered by pregnancy.
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| Connolly, Cynthia C; Papa, Tracy; Smith, Marta S et al. (2007) Hepatic and muscle insulin action during late pregnancy in the dog. Am J Physiol Regul Integr Comp Physiol 292:R447-52 |
| Canniff, Kathryn M; Smith, Marta S; Lacy, D Brooks et al. (2006) Glucagon secretion and autonomic signaling during hypoglycemia in late pregnancy. Am J Physiol Regul Integr Comp Physiol 291:R788-95 |
| Batista, Marcia R; Smith, Marta S; Snead, Wanda L et al. (2005) Chronic estradiol and progesterone treatment in conscious dogs: effects on insulin sensitivity and response to hypoglycemia. Am J Physiol Regul Integr Comp Physiol 289:R1064-73 |
| Connolly, Cynthia C; Aglione, Lisa N; Smith, Marta S et al. (2004) Pregnancy impairs the counterregulatory response to insulin-induced hypoglycemia in the dog. Am J Physiol Endocrinol Metab 287:E480-8 |
