Transient beta adrenergic stimulation can precondition the rat heart against postischaemic contractile dysfunction.

OBJECTIVE

The aim was to assess the abilities of exogenous noradrenaline, isoprenaline, and phenylephrine to precondition the isolated rat heart against ischaemic and reperfusion injury.

METHODS

The isovolumetric Langendorff rat heart model was used to determine postischaemic recovery of left ventricular function. The hearts were subjected to 30 min of normothermic global ischaemia followed by 30 min reperfusion. Treated hearts were perfused with noradrenaline (10(-7) M), isoprenaline (10(-8) M), or phenylephrine (10(-6) M, 10(-5) M, and 10(-4) M) for 5 min followed by 5 min washout before the 30 min ischaemic period.

RESULTS

Control hearts recovered 47.6(SEM 4.3)% of baseline heart rate x developed pressure after 30 min reperfusion, whereas noradrenaline and isoprenaline treated hearts recovered 75.1(4.6) and 76.4(4.6)%, respectively (p < 0.001 v control). Left ventricular end diastolic pressures at the end of reperfusion were 48.8(4.0), 20.0(2.4), and 21.6(2.7)mm Hg for control, noradrenaline treated (p < 0.001 v control), and isoprenaline treated (p < 0.001 v control) hearts respectively. beta Blockade with propranolol during noradrenaline treatment blocked the protective effects. No concentration of phenylephrine used was able to enhance postischaemic heart rate x developed pressure significantly, or result in improved (lower) postischaemic left ventricular end diastolic pressure. During treatment with noradrenaline and phenylephrine (10(-5) M), lactate release was 13.0(1.0) and 11.0(0.9) mumol.5 min-1, respectively (p = NS); these values were significantly (p < 0.001) greater than baseline value of 3.7(0.5) mumol.5 min-1. Immediately before the 30 min ischaemic period, control and phenylephrine treated groups had glycogen levels of 132(14) and 128(5) nmol.mg-1 protein, respectively (p = NS), whereas the glycogen content of the noradrenaline treated group was only 96(5) nmol.mg-1 protein (p < 0.05 v control and phenylephrine treated).

CONCLUSIONS

Transient beta adrenergic but not alpha 1 adrenergic stimulation can precondition the isolated perfused rat heart. The mechanism of protection may, at least in part, be due to transient demand ischaemia. Partial depletion of glycogen following treatment may play a role in the observed protective effects.