In vitro vasoactive effects of dexmedetomidine on isolated human umbilical arteries

Abstract

We aimed to investigate the vasoactive effects of dexmedetomidine on isolated human umbilical arteries and possible mechanisms involved. Human umbilical artery strips were suspended in Krebs-Henseleit solution and dose-response curves were obtained for cumulative dexmedetomidine before and after incubation with different agents; propranolol, atropine, yohimbine, prazosin, indomethacin, verapamil. Effects of calcium on cumulative dexmedetomidine-induced contractions were also studied. Cumulative dexmedetomidine resulted in dose dependent contraction responses. Incubation with propranolol (Emax: 93.3 ± 3.26 %), atropine (Emax: 92.0 ± 6.54 %), or indomethacin (Emax: 94.25 ± 2.62 %), did not attenuate dexmedetomidine-elicited contractions (p > 0.05). There were significant decreases in the contraction responses of cumulative dexmedetomidine with yohimbine (Emax: 12.1 ± 11.9 %), prazosin (Emax: 28.8 ± 4.6 %) and verapamil (Emax: 11.2 ± 13.6 %) (p < 0.05). In Ca+2 free medium contraction responses to cumulative dexmedetomidine was insignificant (Emax: 5.20 ± 3.42 %). Addition of cumulative calcium to the Ca+2 free medium resulted in concentration dependent increase in contractions (Emax: 64.83 ± 37.7 %) (p < 0.05). Dexmedetomidine induces vasoconstriction in endothelial-free umbilical arteries via both, α1- and α2-adrenergic receptors and also extracellular Ca+2 concentrations play a major role. β-adrenergic receptors, muscarinic cholinergic receptors, and inhibition of cyclooxygenase enzyme are not involved in this vasoconstriction (Fig. 3, Ref. 36).