Cardiovascular, biochemical and hormonal changes during food-induced hypotension in chronic autonomic failure.

The cardiovascular, biochemical and hormonal responses to a standard test meal have been investigated in patients with chronic autonomic failure and normal subjects. In autonomic failure there was a rapid (within 15 min), substantial and prolonged fall in blood pressure after the meal. A marked fall in blood pressure also occurred after a liquid meal of similar composition and caloric content, with no change in blood pressure in age-matched subjects with normal autonomic function. In autonomic failure after the test meal the blood pressure reached its nadir (45% fall) after 60 min, and had not returned to pre-meal levels after 3 h. There were no changes in cutaneous and forearm blood flow. In the normal subjects there were no changes in blood pressure after the meal; forearm blood flow fell and cardiac output increased. In autonomic failure there were no changes in plasma noradrenaline levels, unlike the normal subjects. Plasma adrenaline levels were unchanged in both groups. There was a similar rise in levels of plasma renin activity in both groups. The haematocrit and plasma osmolality did not change in either group. Changes in plasma glucose and plasma insulin levels were similar in both groups. The responses of 3 pancreatic gut peptides, neurotensin, pancreatic polypeptide and enteroglucagon, were greater in autonomic failure. Basal levels and responses of vasoactive intestinal polypeptide, cholecystokinin-8 and somatostatin were similar in both groups. The motilin response was greater in normal subjects. We conclude that in patients with autonomic failure there was a rapid, substantial and prolonged fall in blood pressure after a meal. This reduction in blood pressure was not counteracted by an increase in sympathetic nervous activity and other compensatory changes, as occur normally. It was unlikely that osmotic effects of the meal or gut secretions resulted in a significant loss of intravascular fluid into the gut. The fall in blood pressure probably results from vasodilatation within the splanchnic circulation, to which pancreatic and gastrointestinal hormones with vasodilatory actions may contribute.