1. A progressive but incomplete adaptation of the aortic baroreceptor was observed after 1 and 6 h of hypotension in rats subjected to controlled bleeding. Administration of phenoxybenzamine produced a greater downward displacement of baroreceptor activation range
2. Complete adaptation was observed after 48 h of maintained hypotension in rats treated with reserpine.
3. The range of the aortic baroreceptor activation shifted upward as pressure returned to normotension, indicating the reversibility of baroreceptor adaptation in hypotension.