Dose-related effects of adenosine and bradykinin on microvascular permselectivity to macromolecules in the hamster cheek pouch

The hamster cheek pouch preparation was used to assess microvascular permselectivity responses to three vasodilating agents: bradykinin, adenosine, and papaverine. Fluorescein isothiocyanate-dextran 150 was injected intravenously as a macromolecular tracer. To quantify changes in permeability, we calculated fluorochrome clearance values from the ratio of suffusate to plasma fluorescein isothiocyanate-dextran 150 concentration. The microcirculation was recorded on videotape, using epifluorescence and bright-field light microscopy. Topical application of bradykinin elicited dose-dependent increases in macromolecular permeability. Adenosine also augmented permeability in a dose-dependent fashion. The increases in tracer clearance, relative to control, were 9.4 nl/min for 10(-5) M adenosine and 39.4 nl/min for 10(-4) M adenosine. The standard error for these doses was 1.5 nl/min. Adenosine, 10(-6) M, did not alter permeability. The increment in clearance induced by 10(-4) M was comparable to that of bradykinin, 8 X 10(-7) M. Pretreatment with phenidone had no effect on the permeability response mediated by 10(-5) M adenosine. Topical application of papaverine enhanced the transvascular exchange of macromolecules in one-half of the preparations examined. Comparable doses of adenosine were approximately three times as effective. This study indicated that adenosine, like bradykinin, is capable of modifying microvascular permeability responses in the hamster cheek pouch. This modulatory effect appears to be due to a direct action on the postcapillary microvascular membrane.