Identification of benzomorphan-κ opiate receptors in cerebral arteries which subserve relaxation

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Abstract
1 Several ‘so-called’ κ-opiate receptor agonists e.g., ketocyclazocine (Kc), ethylketocyclazocine (Eke), bremazocine, MR-2034 and U-50488H, were tested on basilar and middle cerebral arteries of the dog in vitro for relaxant or contractile activities. 2 Eke, Kc and bremazocine were found to produce concentration-dependent reductions in basal tone and to relax cerebral arteries contracted with prostaglandin F2α (PGF2α). All three agonists appear to act on benzomorphan-κ opiate receptors which subserve relaxation in cerebral blood vessels. 3 MR-2034 and U-50488H were found to induce contraction in the cerebral arteries. These opiate agonists appear to act on phencyclidine (PCP) or σ-opiate receptors which subserve contraction. 4 A variety of pharmacological antagonists (phentolamine, propranolol, methysergide, atropine, diphenhydramine, cimetidine, naloxone) did not modify any of the cerebral vascular effects produced by the opiates. 5 These results suggest: (1) specific benzomorphan-κ opiate receptors which subserve relaxation exist in cerebral blood vessels; (2) some κ agonists appear to produce, primarily, contraction in cerebral vessels via PCP or σ-opiate receptors: and (3) cerebral vascular muscle may provide a useful tool to analyse the molecular constitution of these two distinct and opposite-acting opiate receptors.