| Abstrakt: |
It has recently been shown that both α1‐ and α2‐adrenoceptors mediate vasoconstriction in the canine external carotid circulation. The present study set out to identify the specific subtypes (α1A, α1Band α1Das well as α2A, α2Band α2C) mediating the above response.Consecutive 1 min intracarotid infusions of phenylephrine (α1‐adrenoceptor agonist) and BHT933 (α2‐adrenoceptor agonist) produced dose‐dependent decreases in external carotid blood flow, without affecting mean arterial blood pressure or heart rate.The responses to phenylephrine were selectively antagonized by the antagonists, 5‐methylurapidil (α1A) or BMY7378 (α1D), but not by L‐765,314 (α1B), BRL44408 (α2A), imiloxan (α2B) or MK912 (α2C). In contrast, only BRL44408 or MK912 affected the responses to BHT933.The above results support our contention that mainly the α1A, α1D, α2Aand α2C‐adrenoceptor subtypes mediate vasoconstriction in the canine external carotid circulation. |
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