CIRCULATORY AND METABOLIC EFFECTS OF ALPHA-ADRENERGIC BLOCKADE IN THEHYPERINSULINEMIC OVINE FETUS

OBJECTIVES: Fetuses a diabetic women exhibit hypoxemia, elevated catec holamine concentrations at birth, and increased incidence of death. Ou r previous findings suggested that experimental fetal hyperinsulinemia results in a surge in catecholamines with cardiovascular hanger suppo rted by increased beta-adrenergic activity. The present experiments we re designed to assess the contribution of alpha-adrenergic stimulation to the hemodynamic changes in the hyperinsulinemic ovine fetus. METHO DS: Combined ventricular output, regional organ blood flow, vascular r esistance, metabolism, and catecholamine concentrations were measured before and during an infusion of insulin and during continued infusion with alpha-adrenergic blockade (phentolamine) in eight chronically ca theterized fetal sheep. RESULTS: Fetal insulin infusion produced hyper insulinemic-hypoglycemia, a surge in epinephrine and norepinephrine co ncentration, and increases in the combined ventricular output (bloodfl ow to the fetus plus placenta) and regional blood flow to the fetus, h eart, stomach, gastrointestinal tract, rat, and carcass. In the hyperi nsulinemic state, alpha-adrenergic blockade was associated with additi onal increases in fetal norepinephrine concentration and no major chan ges in combined ventricular output or bloodflow to the body of the fet us, except for decreased blood flow to the stomach and lungs, and a de crease in stroke volume. CONCLUSIONS: Because vasodilation characteriz es the hyperinsulinemic state, alpha-adrenergic stimulation contribute s less to compensatory cardiovascular changer in the hyperinsulinemic fetus than that which we previously have shown for beta-adrenergic sti mulation.