Sympathoadrenal reactions during asphyxia in hypoglycemia and hyperglycemia of cats

In 26 cats anesthetized with alpha-chloralose and urethane, cardiovascular changes during asphyxia in hypoglycemia and hyperglycemia were studied. Systemic hypoglycemia (serum glucose decrease from 148 to 31 mg/100 ml) was produced by i.v. injection of insulin 20 U/kg, followed by continuous I.V. infusion of 10 U/kg/hr. Systemic hyperglycemia (serum glucose increase from 187 to 657 mg/100 ml) was produced by I.V. infusion of 25% glucose at a rate of 1.5 gm/kg/hr. During hypo- or hyperglycemia, resting mean systemic arterial pressure (MSAP) and heart rate did not change significantly. Brain transection at various levels, i.e., midcollicular decerebration, ponto-medullary or medulla-spinal transection progressively decreased the resting MSAP, but not the heart rate. The most apparent reduction was at the medulla-spinal junction. After induction of systemic hypo- or hyperglycemia, plasma catecholamine concentrations increased significantly. Further increase occurred during asphyxia. Increases of MSAP and plasma catecholamine concentrations during asphyxia were attenuated after midcollicular decerebration and decreased further after subsequent ponto-medullary and medulla-spinal transections. Increases in plasma catecholamines during asphyxia were greater in hypoglycemic than those in hyperglycemic state. The increase in plasma catecholamine persisted in hypoglycemic animals during asphyxia after midcollicular decerebration and ponto-medullary transections. As the terminal stage of asphyxia approached spasmodic contractions of urinary bladder occurred. Bladder contractions were abolished after intracerebroventricular (lateral) injection of insulin (0.25 unit/kg). In conclusion, asphyxia produced very marked cardiovascular and plasma catecholamine responses during hypo- or hyperglycemia and more so during the former condition. These reactions depend mainly on the neural mechanisms of medullary structures. Neural structures rostral to the midcollicular level are not essential.