[Effects of sulfur dioxide on cardiac function of isolated perfusion heart of rat]

To observe the effects of sulfur dioxide (SO2) on cardiac function of isolated perfused heart of rat and to explore the physiological regulation of endogenous SO2 on myocardial action.

The hearts of 64 Wistar rats were isolated, perfused with Krebs-Henseleit (KH) solution through Langendorff apparatus, and randomly divided into 8 equal groups: Four groups underwent perfusion of SO2 of the concentrations 1, 10, 100, 1000 micromol/L respectively for 5 min and then perfused with KH solution for 15 min. Eight hearts underwent perfusion of SO2 of the physiological concentration (10 micromol/L) for 20 min. The control group underwent perfusion of KH solution for 20 min. Eight hearts of the nicardipine group underwent perfusion of nicardipine, a L-type calcium channel blocker, 2.5 micromol/L for 5 min, SO2 10 micromol/L for 5 min, and then KH solution for 10 min. The heart in the hydroxamate (HDX) group underwent perfusion of HDX, an inhibitor of SO2 endogenous generating enzymes, for 5 min, and then perfused by KH solution for 15 min. The heart rate (HR), difference of left ventricular pressure (LVP), left ventricular peak rate of contraction (+ dp/dtmax), peak rate of relaxation (- dp/dtmax), and coronary flow (CF) were measured. Then transmission electron microscopy was conducted.

SO2 concentration-dependently inhibited the left ventricular +/- dp/dtmax, LVP, HR, and CF (all P < 0.01). The left ventricular +/- dp/dtmax, LVP, and HR were inhibited (P < 0.05) by the physiological concentration (10 micromol/L) SO2 donor continuous perfusion for 20 min. During perfusion 20 min, the LVP, + dp/dtmax, - dp/dtmax, and HR after perfusion for 20 min of the physiological concentration (10 micromol/L) SO2 donor continuous perfusion group were (15 +/- 3) mm Hg, (485 +/- 74) mm Hg/s, (339 +/- 64) mm Hg/s, and (114 +/- 26)/min respectively, all significantly lower than those 5 min after perfusion [(23 +/- 7) mm Hg, (595 +/- 93)mm Hg/s, (436 +/- 83) mm Hg/s, and (159 +/- 31)/min, all P < 0.05]. The LVP, + dp/ dtmax, -dp/dtmax, and HR of the nicardipine group were(37 +/- l0)mm Hg, (1025 +/- 287)mm Hg/s, (570 +/- 181)mm Hg/s, and (139 +/- 48)/min respectively, all not significantly different from those of the control group. The LVP, + dp/dtmax, - dp/dtmax, and CF after perfusion of the HDX group were (50 +/- 11)mm Hg, (1167 +/- 270) mm Hg/s, (889 +/- 72) mm Hg/s, and (6.3 +/- 1.9) ml/min respectively, all significantly lower than those before perfusion [(69 +/- 16) mm Hg, (1579 +/- 315) mm Hg/s, (1186 +/- 263) mm Hg/s, and (9.5 +/- 1.3) ml/min, all P < 0.05].

Exogenous SO2 has negative inotropic effect on myocardium. by the mechanism related to voltage-gated calcium channel. Nicardipine blocks the inhibitory effect of SO2 at physiological concentration.