Orthostatic hypotension induced by postural change in the rat (tilt test).

Postural-change-induced (orthostatic) hypotension is defined as an excessive drop in arterial blood pressure occurring when moving toward an upright position. This side effect, which may limit the therapeutic use of some agents, can occur with drugs, such as adrenoceptor blockers and vasodilators, that dampen sympathetic reflex activity. Described in this unit is a procedure for evaluating the effects of test substances on the changes in blood pressure and heart rate that occur in an anesthetized, normotensive rat during a tilting challenge (head-up position). In addition to being a relatively simple technique, this assay yields reproducible orthostatic hypotensive responses and allows for the investigation, in the same preparation, of several ascending doses of a test substance. Examples of results obtained with prazosin, an α1-adrenoceptor antagonist that is notorious for causing orthostatic hypotension, are provided for illustrative purposes.