Ka. Aitchison et al., Opposing effects on infarction of delta and kappa opioid receptor activation in the isolated rat heart: implications for ischemic preconditioning, BAS R CARD, 95(1), 2000, pp. 1-10
delta-Opioid receptors are known to participate in the protection found fol
lowing ischemic preconditioning (IPC), but the role of kappa-receptors in I
PC is currently controversial. Langendorff-perfused rat hearts received 35
min regional ischemia and 2 h reperfusion. PC (2 cycles 5 min global ischem
ia) substantially reduced infarct size. Pharmacological PC with the delta-a
gonist DADLE (10 nmol/L) had similar protective effects. However, higher do
se DADLE (1 mu mol/L) had a less beneficial effect, and in conjunction with
the delta-antagonist naltrindole unexpectedly increased infarct size (61.5
+/- 2.0 %, p<0.05 v 45.9 +/- 2.4 % in controls) suggesting a non-delta eff
ect. The universal kappa-opioid agonist bremazocine (30 nmol/L) increased i
nfarct size (61.3 +/- 1.6 %, p<0.05 v controls), an effect abrogated by the
selective kappa(1)-antagonist nor-binaltorphimine (BNI).
Since opiates are known to have anti-adrenergic effects, which hypothetical
ly may help to mediate LPC, cyclic AMP levels were measured in DADLE and in
bremazocine-treated hearts. Decreased levels of cyclic AMP at the start of
the regional ischemic period were found in low dose DADLE hearts (0.485 +/
- 0/020, n = 8, vs controls, 0.654 +/- 0.025 nmol/g wet weight, p<0.001), b
ut not in high dose DADLE nor in bremazocine treated hearts.
Thus, in the isolated rat heart kappa(1)-opioid receptor activation exacerb
ates infarct size through an as yet unknown mechanism, suggesting that ther
e could be an "anti-preconditioned state". In contrast, delta-activity medi
ates protection which may be associated with a reduction of tissue cyclic A
MP levels.