Extent of structurally reduced venous distensibility in rats.

1. Venous pressure--volume relations were studied in maximally vasodilated whole-body preparations after cardiac arrest, as well as in fully vasodilated, perfused hindquarter preparations of spontaneously hypertensive rats (SHR) and normotensive controls. Central venous pressures were measured also in the anaesthetized animals before cardiac arrest. 2. Central venous pressure in intact, anaesthetized SHR was 1.9 +/- 0.20 mmHg compared with 0.75 +/- 0.25 in controls (P less than 0.001). 3. In both preparations SHR showed a nearly 20% reduction in venous compliance, whereas calculated 'unstressed' volumes (volumes at zero transmural pressure) were largely equal in SHR and controls. 4. SHR capacitance vessels thus appear to have a structurally reduced wall distensibility of about 10% with no change in overall size. It probably reflects a structural adaptation to a modest increase of average transmural pressure that also affects the low-pressure side.