The Responses of Norepinephrine, Renin and Aldosterone to Standing in Diabetic Patients with Orthostatic Hypotension

Autonomic neuropathy is one of the complications of diabetes, and several lines of evidence, supporting that sympathetic neural dysfunction may play the major role in the orthostatic hypotension (OH) of diabetic patients have been presented. In this paper the responses of plasma norepinephrine (PNE), plasma renin activity (PRA) and plasma aldosterone (PAC) to upright standing were studied in 17 diabetic patients without OH, 25 diabetics with OH and 17 age-matched, non-diabetic normotensives (controls). All were kept on a 200mEq sodium diet. Assay procedure for PNE was high-performance liquid chromatography with trihydroxyindol method and fluorimetric detection using dihydroxybenzylamine as internal standard. Intra- and inter-assay coefficient variations by this method were 3.4 and 5.8% respectively. PRA and PAC were determined by radioimmunoassay. Total blood volume was examined by the plasma tracer method using 131I-HSA and expressed in percent normal. Mean PNE level in the non-diabetic controls was 217 pg/ml in recumbency and increased to a level of 551 at 15 minutes on standing. The PNE responses to standing in the diabetic subjects without OH (defined as group I) were not significantly different from those in the controls. In the diabetics with OH, 14 cases, with the PNE increments less than 1SD below the mean in the controls, were defined as group III, and discriminated from other 11 subjects with OH (group II). PNE levels in group III were significantly lower than in the controls at both recumbency and upright posture. PRA was significantly elevated by standing in the controls and the diabetics except for group II. PRA in all the diabetic groups was significantly lower than in the controls, at both recumbent and upright. The mean values of PAC in the diabetics but group II at supine were significantly lower than those of the control group. PAC levels increased after standing contemporaneously with PRA, though significant rise in group II was shown without PRA response. Total blood volume was significantly (p less than 0.025) decreased in only group II. The results suggest: 1) PNE was normal in the diabetic patients without OH, 2) there are at least two types of OH in diabetes mellitus: one is hypoadrenergic and the other hypovolemic, 3) adrenergic neuropathy may be a cause of low PRA in diabetics with OH but another factor may also be involved in both with and without OH, 4) low PRA is a main factor of low PAC in diabetics (group I and III), but the dissociation between PRA and PAC responses to orthostasis is present in some cases (group II), which reflects disturbances in other regulatory mechanisms of aldosterone secretion.