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

Abstract

Purpose: Calcitonin gene-related peptide (CGRP) produces vasodilatation, hypotension, and tachycardia. Tachycardia induced by CGRP may be due to sympathetic activation. Volatile anaesthetics attenuate activation of arterial baroreflexes. We examined the haemodynamic and endocrine effects of CGRP infusion (4/~g-l~ t) during anaesthesia with either enflurane or isoflurane in dogs. Methods: Measurements of haemodynamic variables and hormone assays for plasma catecholamines were made before, during, and after CGRP infusion, Anaesthesia consisted of induction with 25 mg.l<g -i pentobarbital, followed by either enflurane (n = 7) or isoflurane (n = 7) to achieve a 1.0 end-tidal minimum alveolar concentration in oxygen 10096. Results: Mean arterial pressure and systemic vascular resistance decreased (P < 0.0 I) and the reductions in both variables were similar during CGRP infusion in both groups. Cardiac index (CI) was increased (P < 0,01) in the enflurane group throughout the study while CI increased (P < 0.01) only during infusion in the isoflurane group. Heart rate (HR) remained unchanged (from 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 concentrations increased (from 42.4_+ 12.7 pg.ml -~ to I 15.3_+41.8 pg'ml -I, P < 0.01) during infusion in the isoflurane group. However, these increases were suppressed (from 46,6_+23.2 pg.ml -r to 64.7-+32.4 pg'ml -j) 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 tachycardia induced by CGRP is greater with enflurane than with isoflurane. The differences in HR may be due to the roles of catecholamine responses resulting from the anaesthetic-induced sympathetic suppression. Objectif : Le peptide lie au gEne de la calcitonine (PLGC) produit une vasodilatation, de rhypotension et de la tachycardie. La tachycardie induite par le PLGC peut &re due ~ une activation sympathique. Les anesth&iques volatils attEnuent ractivation des barorEflexes artEdels. Nous avons Etudi6 les effets hEmodynamiques et endocriniens d'une perfusion de PLGC (4/~g-kg-') pendant I'anesth&ie avec de renflurane ou de I'isoflurane chez les chiens. M&hode : La mesure des variables hEmodynamiques et le dosage hormonal des cat&holamines plasmatiques ont &E fairs avant, pendant et awes la perfusion de PLGC. I'anesth&ie s'est dEroulEe comme suit : une induction avec 25 mg.kg-' de pentobarbital, suivie de radministration d'enflurane (n = 7) ou d'isoflurane (n = 7) pour produire une concentration alvEolalre minimale de fin d'expiration de 1,0 dans 100 % d'oxygEne. R~sultats : La tension art&ielle moyenne et la r&istance vasculaire gEnErale ont diminuE (P < 0,01) et les rEductions enregistrEes pour les deux variables ont &6 similaires pendant la perfusion de PLGC dans les deux groupes. 15ndex cardiaque (IC) a augm...