Intrathecal administration of calcitonin gene-related peptide (CGRP) increases heart rate and decreases arterial pressure in the urethane anesthetized rat

Intrathecal administration of CGRP (2.15-8.60 nmol) to the ninth thoracic vertebral segment of the spinal cord in the urethane anesthetized rat provoked an increase in heart rate (peak effect of 72 bpm) and a decrease in arterial pressure (maximum fall of 15 mmHg). Administration of CGRP to the T2 level (n = 10) or intravenously (n = 6) produced qualitatively and quantitatively similar effects to those observed following administration to the T9 level. The drop in pressure resulting from intrathecal administration was unaffected by prior intrathecal administration of lidocaine (250 micrograms), systemic administration of hexamethonium (5 mg/rat), bilateral vagotomy, or combined bilateral vagotomy/hexamethonium treatment. The failure of these manipulations to alter the hypotension induced by intrathecal CGRP injection suggests that this effect was caused by leakage into the periphery. The cardioacceleration elicited by intrathecal CGRP was attenuated by intrathecal lidocaine administration and by combined bilateral vagotomy/hexamethonium treatment, but not by either treatment alone. These results suggest that CGRP's tachycardic effect is mediated by a direct spinal action involving both sympathetic and parasympathetic mechanisms.