Effect of vasoactive agents and applied stress on the albumin space of excised rabbit carotid arteries.

Experiments were undertaken on excised rabbit common carotid arteries to assess whether the distribution volume for radioactively labelled albumin is influenced by smooth muscle tone or externally applied stress. In arteries at relaxed length and zero transmural pressure, the distribution volume in the media was reduced by noradrenaline at concentrations exceeding 10(-9) M and increased by both sodium nitrite and isosorbide dinitrate at concentrations exceeding 10(-4) M. The distribution volume was lower in both the media and adventitia of segments at in vivo length pressurized with air to prevent convection through the wall, than in segments at relaxed length and zero transmural pressure. Noradrenaline decreased and sodium nitrite increased the medial distribution volume of the tracer in these air-pressurized segments. The vasoactive agents did not change the [51Cr]EDTA space in vessels at relaxed length and zero transmural pressure, although there were small alterations of medial water content. Transient conditions raise interpretative difficulties because of uncertainty about endothelial permeability and time-dependent changes of wall properties. The changes of the distribution volume for labelled albumin are thought to reflect changes in the properties of the interstitium.