Faculty Bibliography

We have examined insulin-induced hypoglycemia to determine whether prazosin inhibits the response to sympathetic stimulation, either centrally or at beta adrenergic receptors. Nine patients with essential hypertension were studied during administration of prazosin, hydralazine or placebo. Plasma renin activity increased significantly with hydralazine and was unchanged during prazosin administration. In response to insulin, blood glucose decreased equally with both drugs and placebo, and small increases in dopamine beta-hydroxylase occurred. Plasma renin activity and heart rate increased during hypoglycemia; the increases were greater in patients taking prazosin or hydralazine. The unimpaired responses of plasma dopamine beta-hydroxylase, renin activity and heart rate to insulin-induced hypoglycemia provide evidence that prazosin does not block either the sympathetic discharge elicited by central stimulation (hypoglycemia) or the responses mediated through beta adrenergic receptors.

To determine whether orthostatic hypotension in patients with cervical spinal cord lesions is the result of impaired sympathetic nerve response and/or impaired renin release, serum dopamine-beta-hydroxylase (DbetaH) activity and plasma renin activity (PRA) were examined during passive tilting in 6 quadriplegic patients and in 6 able-bodied control subjects. Serum DbetaH was measured by an isotopic enzymatic method and PRA by radioimmunoassay. Following head-up tilting, quadriplegic subjects demonstrated a prompt, significant decrease in mean arterial pressure (MAP) and increase in heart rate (HR). DbetaH and PRA both increased significantly 15 minutes after tilt. In normal subjects, although HR increased, MAP was unchanged; DbetaH and PRA did not increase significantly during head-up tilt. The finding of increased DbetaH during tilt hypotension in quadriplegic patients provides evidence that reflex sympathetic nerve stimulation persists despite cervical cord transection. Increased PRA may be attributed to decreased renal perfusion pressure and increased sympathetic stimulation during tilt hypotension. These data suggest that orthostatic hypotension in quadriplegia patients cannot be attributed solely to failure of the sympathetic nervous system or the renin-angiotensin system to respond to the stimulus of orthostasis