[Shy-Drager syndrome: its autonomic function, alpha 2 receptor density and mechanism of postprandial hypotension].

The autonomic function, platelet alpha 2 receptor (alpha 2R) density, and mechanism of postprandial hypotension were examined in a 58-year-old man with Shy-Drager syndrome (SDS). His chief complaints were orthostatic syncope and impotence. His blood pressure was kept within normal limits in a supine position, but severe hypotension and fainting occurred when he assumed an upright posture. There were diminished sweating response to warm stress, abnormal pupil reactions to drugs, lack of blood pressure elevation at phase IV during the Valsalva maneuver, and a lack of pressor response to hyperventilation and cold stress. The plasma norepinephrine levels (pNE) were very low in a supine position at rest and in a head-up tilt position. Severe blood pressure fall (hypotension) associated with a lack of pNE elevation occurred during an oral glucose tolerance test (oGTT). Platelet alpha 2R density increased and the pressor response to infused norepinephrine (NE-R) was pronounced. The heart rate response to injected atropine was clearly attenuated. The coefficient of the R-R interval variation in the ECG (CVRR), which may reflect parasympathetic activity, was markedly low at rest. In addition, a decrease in a head-up tilt position and increase during oGTT also resolved. These results indicate that a dysfunction of the parasympathetic and sympathetic nervous systems and the up-regulation in the alpha 2R system that leads to an increase in alpha 2R density in SDS are involved in this disease and that the mechanism of postprandial hypotension in SDS may be different from that in normal elderly subjects.