Haemodynamic and catecholamine responses to calcitonin gene-related peptide during volatile anaesthesia

Purpose: Calcitonin gene-related peptide (CGRP) produces vasodilatation, hy potension, and tachycardia. Tachycardia induced by CGRP may be due to sympa thetic activation. Volatile anaesthetics attenuate activation of arterial b aroreflexes. We examined the haemodynamic and endocrine effects of CGRP inf usion (4 mu g.kg(-1)) during anaesthesia with either enflurane or isofluran e in dogs. Methods: Measurements of haemodynamic variables and hormone assays for plas ma catecholamines were made before, during, and after CGRP infusion. Anaest hesia consisted of induction with 25 mg.kg(-1) pentobarbital, followed by e ither enflurane (n = 7) or isoflurane (n = 7) to achieve a 1.0 end-tidal mi nimum alveolar concentration in oxygen 100%. Results: Mean arterial pressure and systemic vascular resistance decreased (P < 0.01)and the reductions in both variables were similar during CGRP inf usion in both groups. Cardiac index (CI) was increased (P < 0.01) in the en flurane group throughout the study while CI increased (P < 0.01) only durin g infusion in the isoflurane group. Heart rate (HR) remained unchanged (fro m 135+/-6 bpm to 134+/-7 bpm) in the enflurane group but tended to increase (from 162+/-9 bpm to 171+/-9 bpm) in the isoflurane group during infusion. Intergroup differences in HR were found (P < 0.05), Plasma epinephrine con centrations increased (from 42.4+/-12.7 pg.ml(-1) to 115.3+/-41.8 pg.ml(-1) , P < 0.01) during infusion in the isoflurane group. However, these increas es were suppressed (from 46.6+/-23.2 pg.ml(-1) to 64.7+/-32.4 pg.ml(-1)) to a greater extent in the enflurane group. Conclusion: The haemodynamic responses. except for HR, of CGRP infusion are similar during enflurane and isoflurane anaesthesia. Suppression of tachyc ardia induced by CGRP is greater with enflurane than with isoflurane. The d ifferences in HR may be due to the roles of catecholamine responses resulti ng from the anaesthetic-induced sympathetic suppression.