Pharmacological features of vascular responses of isolated dog and monkey lingual arteries to vasoactive substances

Abstract

Using a perfusion technique of isolated vessels, vasoconstrictor responses to alpha-adrenoceptor agonists (norepinephrine [NE], phenylephrine [PE], clonidine, xylazine and tyramine) and KCl were investigated in isolated, perfused dog and monkey lingual arteries. A stainless steel cannula was inserted into the lingual artery segment and perfused with Krebs-Henseleit solution at a constant flow rate. In dog lingual arteries, the agonists induced vasoconstrictions with the following order of potency: NE greater than PE greater than tyramine much greater than clonidine greater than xylazine greater than KCl. In monkey preparations, the order was NE greater than PE much greater than clonidine greater than or equal to tyramine greater than xylazine greater than KCl. In both preparations, NE- and PE-induced constrictions were blocked by bunazosin (an alpha-1 adrenoceptor antagonist), but not influenced by midaglizole (a potent alpha-2 antagonist). Diltiazem (a Ca entry blocker) significantly attenuated NE-induced vasoconstrictions in dog lingual arteries, but did not significantly influence these in monkey preparations. These results suggest that: [1] these arteries contain mostly alpha-1 but scarcely any alpha-2 adrenoceptors; [2] in dog preparations, tyramine induced a marked vasoconstriction which may contribute to investigation on the mechanisms of catecholamine releases from sympathetic nerve terminals; and [3] different blocking effects of diltiazem may indicate that extracellular Ca++ influx may have varying degrees of importance in alpha-1 adrenoreceptor-mediated constrictions in different species, although participation of an intracellular mechanism might not be ruled out.