Increased red cell sodium lithium countertransport activity, total exchangeable sodium, and hormonal control of sodium balance in normoalbuminuric type 1 diabetes

Low plasma aldosterone despite normal plasma renin activity in uncomplicated type 1 diabetes mellitus: effects of RAAS stimulation

BACKGROUND

Data on levels and responsiveness of PRA and aldosterone in type 1 diabetes mellitus are conflicting. Earlier studies were not standardized with respect to the type of diabetes mellitus, the presence of diabetic complications or sodium intake. Therefore, we studied plasma renin activity and plasma aldosterone in uncomplicated type 1 diabetes mellitus by evaluating the effects of endogenous (sodium restriction) and exogenous (angiotensin I infusion) stimulation.

DESIGN

Twenty-four type 1 diabetic patients and 24 matched healthy subjects were studied after 1 week of liberal sodium diet (200 mmol 24 h-1) and 1 week of low sodium diet (50 mmol 24 h-1). Angiotensin (Ang)I was infused at 4 and 8 ng kg-1 min-1 during both study days.

RESULTS

During liberal and low sodium intake, plasma aldosterone was lower in type 1 diabetic patients compared with healthy subjects both at 08:00 h (P < 0.05) and after a 2-h euglycaemic clamp (P < 0.05), despite similar PRA levels. The correlations between changes in PRA and changes in plasma aldosterone when shifting sodium intake were similar in both groups. During liberal sodium intake, the aldosterone levels after AngI infusion were lower in type 1 diabetic patients, whereas during low sodium they were not different.

CONCLUSIONS

Plasma aldosterone was deceased relative to PRA in uncomplicated type 1 diabetic patients, irrespective sodium intake. The responsiveness to sodium restriction was adequate and sodium restriction was able to overcome the decreased plasma aldosterone response to exogenous AngI, which was observed during liberal sodium in diabetic patients. The lower aldosterone is not secondary to diabetic complications and does not depend on the level of sodium intake.

Sodium-lithium countertransport: physiology and function

Current opinions on the relationships between erythrocyte sodium-lithium countertransport kinetics and primary hypertension, hyperlipidaemia and diabetic nephropathy are reviewed. Problems associated with the assay are analysed. Some possible mechanisms that could modify the kinetics of ion exchange are examined. The question of what catalyses sodium-lithium countertransport is discussed, but not answered. Some models are put forward showing how a study of sodium-lithium countertransport kinetics could further our understanding of important disease processes.