Effect of metoclopramide on orthostatic hypotension in diabetes mellitus: failure to demonstrate the role of vasoconstrictive hormones.

Effect of metoclopramide (MCP), a dopaminergic antagonist, on orthostatic hypotension associated with diabetes mellitus, was investigated to prove its plausible role of renin-angiotensin-aldosterone and catecholamine activation by comparative study in 6 diabetics with orthostatic hypotension (OH) and 9 diabetics without OH. With MCP treatment, drop of systolic blood pressure (SBP) on standing was significantly improved. However, the postural responses of plasma renin activity (PRA), plasma aldosterone and norepinephrine were not enhanced by MCP treatment. Moreover, MCP treatment did not modify the vascular reactivity to the exogenously infused angiotensin II and norepinephrine. Thus, it would be interesting to speculate that MCP can improve SBP through its suppressive effect on some depressor substance(s) such as bradykinin which liberates exaggeratively in diabetic OH.