In vitro reactivity of ventral aorta to acetylcholine and noradrenaline inyellow freshwater eel (Anguilla anguilla L.) acclimatized to 10.1 MPa hydrostatic pressure

We examined in vitro vascular reactivity of eels previously acclimatized to 10.1 MPa hydrostatic pressure (HP) for 21 days. The isometric tension deve loped by ventral aortic rings was measured at atmospheric pressure. Dose-re sponse curves for either acetylcholine (ACh) or noradrenaline (NA), as well as contractions evoked by 80 mM K+, were compared with time-matched experi ments conducted on rings obtained from control eels. Results showed that ne ither the optimal tension nor the maximal force of the K+-evoked contractio n were significantly modified, suggesting that acclimatization to high HP d id not change the vascular smooth muscle contractile machinery. The dose-re sponse curve to ACh was not significantly changed. Conversely, although NA always relaxed aortic rings, the response of acclimatized eels was signific antly reduced over the entire range of the agonist concentration tested (10 (-8) to 10(-3) M), except for the lowest one (10(-9) M). The maximal amplit ude of the NA-induced relaxation was significantly reduced in aortic rings from acclimatized eels as compared with non-acclimatized samples (339.3 +/- 86.5 vs. 744.3 +/- 72.1 mg.mg(-1) dry weight, P < 0.005). Our results sugg est that acclimatization to high HP could selectively alter the control of vascular tone by catecholamines.