The fetal and maternal catecholamine response to insulin-induced hypoglycemia in the rat

This study was undertaken to evaluate the catecholamine response of the fetal rat to insulin-induced hypoglycemia in the mother. Twenty-four Sprague-Dawley rats at day 21 of gestation were used. Hypoglycemia was induced with regular insulin; then at timed intervals, the rats were anesthetized with pentobarbital. When the rats were completely unresponsive, the abdomen was opened, the fetuses were exteriorized, and fetal blood was obtained by sectioning the axillary vessels. Maternal blood was obtained from the vena cava. Plasma glucose was measured by the glucose oxidase technique. Norepinephrine, epinephrine, and dopamine were measured by radioenzymatic assay. Maternal animals demonstrated a fall in glucose to a nadir of 23 +/- 0.7 mg/dl (mean +/- SEM) and a significant rise in plasma epinephrine to a maximum of 2,548.0 +/- 1,071.2 pg/ml. Fetal glucose fell to a nadir of 23.8 +/- 3.3 mg/dl (mean +/- SEM) and fetal catecholamines demonstrated a rapid significant rise: norepinephrine rose to a maximum of 5,077.3 +/- 932.6 pg/ml; epinephrine rose to a maximum of 4,295.8 +/- 538.9 pg/ml; dopamine rose to a maximum of 869 +/- 203.3 pg/ml. The fetal correlation coefficients were r = -0.56 (p less than 0.01) for plasma glucose compared to norepinephrine and r = -0.58 (p less than 0.01) for plasma glucose compared to epinephrine. The maternal correlation coefficient for plasma glucose compared to epinephrine was r = -0.54 (p less than 0.01). These data demonstrate that the near-term fetal rat is able to respond significantly to hypoglycemia with a rapid output of catecholamines.