Abstract
Previous investigators have reported the development of spontaneous tone, a spontaneous decrease in diameter in response to application of intraluminal pressure, in isolated microvessels bathed in physiological salt solution (PSS) containing albumin. In contrast, myogenic activity and spontaneous tone are rare in microvessels bathed in albumin-free PSS. The purpose of this study was to determine whether albumin and/or the development of spontaneous tone altered coronary microvessel responsiveness to vasoactive agents. Microvessels (70-150 μm) were isolated from the hearts of domestic pigs and studied in vitro using video dimension analysis. Control microvessels were bathed in albumin-free PSS while albumin-treated vessels were bathed in PSS containing 10 mg/ml albumin. Vasoconstrictor responses were determined for acetylcholine (3 × 10 -10 to 1 × 10 -5 M) and KCl (20-120 m M). Concentration-response curves were generated for an endothelium-dependent vasodilator, bradykinin (1 × 10 -12 to 1 × 10 -7 M), and a direct smooth muscle dilator, sodium nitroprusside (1 × 10 -10 to 1 × 10 -4 M ). Seventy-seven percent of the albumin-treated microvessels developed spontaneous tone, whereas only 20% of the control microvessels developed tone. KCl and acetylcholine induced contraction in both control and albumin-treated microvessels. Maximal response to acetylcholine (percentage constriction) was significantly greater in albumin-treated microvessels (79.93 ± 2.53 and 68.86 ± 3.20 in control and albumin-treated groups, respectively). Responses to bradykinin and sodium nitroprusside were not different between albumin-treated and control groups. The results indicate that microvessels develop spontaneous tone more frequently when bathed in PSS containing albumin. Also, the presence of spontaneous tone in albumin-treated vessels does not affect relaxation responses, whereas responses to vasoconstrictors are enhanced in albumin-treated vessels which develop spontaneous tone.
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