Influence of dixyrazine on intestinal and renal vasoconstrictor responses during fentanyl-nitrous oxide anaesthesia.

In cats (n = 24) anaesthetized with fentanyl-nitrous oxide and diazepam, stimulation of the hypothalamic defence-alarm area (DA) or afferent activation of somatic pain fibres (SA), elicited a pronounced increase in intestinal (DA 297%, SA 107%) and renal (DA 214%, SA 90%) vascular resistance as well as a decrease in diuresis. These stress-related responses were markedly counteracted by dixyrazine (0.15-0.5 mg X kg-1 b.w.i.v.), especially in the kidney where the subsequent increase in vascular resistance to DA and SA stimulations amounted to only 25% and 13%, respectively, while diuresis increased. Corresponding data for stimulation-induced increases in intestinal vascular resistance after dixyrazine were DA 156% and SA 28%. Dixyrazine is suggested to act both through interaction with peripheral alpha-adrenergic mechanisms in control of vascular tone and through central nervous cardiovascular reflex depression. In man (n = 7), during a similar form of anaesthesia, portal vein blood flow (1137 +/- 177 ml) was measured by the continuous thermodilution method. Preportal tissue vascular resistance during surgery decreased significantly (11.3 vs 8.7 kPa X min X ml-1 X 10(-3] after i.v. dixyrazine (0.15 mg X kg-1 b.w.). A concomitant increase in oxygen uptake in preportal tissues occurred (19.9 ml min-1 vs 24.5 ml X min-1).