Detecting activation of the sympatho-adrenal axis from haemodynamic recordings, in conscious rabbits exposed to acute stress S. Roatta, M. Mohammed and M. Passatore Physiology Division, Department of Neuroscience, University of Torino, Medical School, Torino, Italy Received 10 February 2010, revision requested 20 March 2010, revision received 30 July 2010, accepted 13 August 2010 Correspondence: S. Roatta, PhD, Dipartimento di Neuroscienze, Sezione di Fisiologia, Universita ` di Torino, c.so Raffaello 30, 10125 Torino, Italy. E-mail: silvestro.roatta@unito.it Abstract Aims: When assessing sympathetic activation in acute stress, the attention is often limited to the sympatho-neural axis, whereas sympatho-adrenal acti- vation, that can only be detected with poor time resolution from the con- centration of plasma catecholamines, is often neglected. This study is aimed at reinvestigating the role and the relevance of the sympatho-adrenal system in acute stress based on the analysis of haemodynamic responses in conscious rabbits. Methods: Experiments were carried out on 19 rabbits implanted with chronic probes for arterial blood pressure and for blood flow in the facial artery. Cardiovascular responses to a randomized sequence of acute stressors (pinprick, air jet, oscillation of the cage, inhalation of formaldehyde vapours and im injection of hypertonic saline) were recorded before and after a-adrenergic blockade (phentolamine) and unilateral section of the cervical sympathetic trunk (decentralization). Plasma catecholamine concentrations were analysed in four animals. Results: All stressors induced an increase in arterial blood pressure and a reduction of vascular conductance in the facial artery ranging on aver- age from 24% (pinprick) to 55% (box oscillation). Such vasoconstrictor response was abolished by phentolamine. In decentralized arteries, the vasoconstriction was delayed by 10–15 s and decreased in magnitude in a stressor-dependent way, indicating an adrenaline-mediated effect in the late phase of the stress response that was confirmed by changes in plasma adrenaline concentration. Conclusions: In conscious rabbits, rapid release of adrenaline makes a prominent contribution to vasoconstriction in response to different stressors including box oscillation, muscle pain and air jet but not the nasopharyngeal stimulation. Keywords acute stress, adrenaline, blood flow, oro-facial area, sympa- thetic nervous system, vascular conductance. The sympathetic nervous system controls vegetative functions in the body by means of two different pathways: the sympatho-neural (SN) pathway, releasing mainly noradrenaline (NA) on directly reached target organs, and the sympatho-adrenal (SA) pathway releas- ing mainly adrenaline (ADR) from the adrenal glands into the blood stream. In the early 1950s, Von Euler (1954) already pointed out that ADR and NA are not equivalent in their effects and, accordingly, are also differentially released by the organism in different conditions or in response to different stressors (Von Euler 1954, de Diego et al. 2008). Acta Physiol 2011, 201, 323–337 Ó 2010 The Authors Acta Physiologica Ó 2010 Scandinavian Physiological Society, doi: 10.1111/j.1748-1716.2010.02179.x 323