Role of Endogenous Agonists of Opioid Receptors in the Regulation of Heart Resistance to Postischemic Reperfusion Injury.

Intravenous injection of nonselective antagonists of opioid receptors (OR) naltrexone (5 mg/kg) and naloxone methiodide (5 mg/kg), selective δ-OR antagonist BNTX (0.7 mg/kg), selective δ-OR blocker naltriben (0.3 mg/kg), selective κ-OR antagonist norbinaltorphimine (2 mg/kg), and selective blocker of ORL1 opioid receptors JTC-801 (0.1 mg/kg) produced no effect on reperfusion injury to the heart in rats narcotized with α-chloralose. In contrast, selective μ-OR antagonist CTAP (1 mg/kg) limited the infarct size, although this effect was not observed at a lower CTAP concentration of 0.1 mg/kg. Probably, the myocardial infarct size-limiting effect of CTAP was associated with activation of the non-opioid receptors. It was hypothesized that endogenous OR agonists did not affect heart resistance to reperfusion injury in unadapted rats.