Idiopathic orthostatic hypotension: circulating noradrenaline and ultrastructure of saphenous vein.
The present study indicates that patients who can be clinically classified as idiopathic orthostatic hypotensives of the peripheral type are heterogeneous. There is the typical hypoadrenergic type characterized by low levels of circulating noradrenaline, much reduced or absent noradrenaline stores, and correspondingly little or no adrenergic innervation in the saphenous vein, a major capacitance vessel, as confirmed by ultrastructural examination. In one patient of this type, an abnormally high occurrence of mast cells in the blood vessel wall was noted. There also exists a category of individuals of the hyperadrenergic type, analogous to certain diabetics with noradrenergic abnormalities. These patients also are characterized by low levels of circulating noradrenaline, but noradrenaline stores are high; an exaggerated release of neurotransmitter occurs in response to stimuli; the saphenous vein with noradrenergic innervation remains ultrastructurally normal; however, the effector cell response are greatly blunted. In one patient of this type, the smooth muscle cells of the saphenous vein contained excessively high glycogen deposits. Further, it should be anticipated that a variety of intermediate types can be found as exemplified by one patient with variable, low to normal levels of circulating noradrenaline, a sluggish response to release neurotransmitter upon postural challenge, and considerable innervation of saphenous vein but with the majority of axons and terminals undergoing active degeneration.