Effect of adrenalectomy or sympathectomy on spinal cord blood flow in hypothermic rats

We used [14C]butanol distribution to measure regional spinal cord blood flow (RSCBF) in three groups of pentobarbital-anesthetized rats: 1) normals (n = 16); 2) after bilateral adrenalectomy (n = 18); and 3) after excision of the abdominal sympathetic chains (n = 12). Half of the rats in each group were maintained near normothermia; the remainder were colled to a rectal temperature of 25-27 degrees C. In intact rats, there was a 24-37% increase in RSCBF during hypothermia in the cord region C3-L6 inclusive. Neither operative procedure altered RSCBF during normothermia. In hypothermic adrenalectomized rats, RSCBF was elevated only in the C3-C5 cord segment. After sympathectomy, RSCBF was unchanged during hypothermia. In the cauda equina, flow fell in all hypothermic rats. The hypothermia-associated increases in RSCBF were not related to changes in mean arterial blood pressure. We conclude that adrenalectomy near-totally ablates the hypothermia-associated increase in RSCBF measured in intact rats and that abdominal sympathectomy totally ablates it. This evidence complements morphological evidence for adrenergic innervation of the spinal cord vasculature.