Cardiovascular responses to autonomic blockade in brain-injured fetal lambs.

The cardiovascular responses to autonomic blockade were investigated in 15 late-gestation fetal lambs in utero. 4 animals had normal brains and 11 had hydranencephalic-like cerebral injury secondary to bilateral carotid artery obstruction (BCO). Following atropine administration, heart rate increased only 0.7 +/- 0.7% in the BCO lambs compared to 25.7 +/- 5.2% in the controls. alpha-Blockade with phentolamine resulted in a small decrease in systolic (2.2 +/- 0.8%) and diastolic (1.8 +/- 1.4%) blood pressure, and beta-blockade with propranolol produced a small decrease in heart rate (2.5 +/- 0.8%) as compared to control fetuses. Post mortem examination revealed extensive destruction of the cerebrum but normal hypothalamus and brain stem. These data suggest that supramedullary modification of autonomic cardiovascular control involves the cerebrum.