Evaluation of the renin-aldosterone system during hypo- and hyperglycemia in children and adolescents

Dynamics of blood electrolytes in repeated hyper- and/or hypoglycaemic events in patients with type 1 diabetes

AIMS/HYPOTHESIS

Electrolyte disturbances are well-known consequences of the diabetic pathology. However, less is known about the cumulative effects of repeated changes in glycaemia, a characteristic of diabetes, on the electrolyte balance. We therefore investigated the ionic profiles of patients with type 1 diabetes during consecutive hyper- and/or hypoglycaemic events using the glucose clamp.

METHODS

In protocol 1, two successive hyperglycaemic excursions to 18 mmol/l were induced; in protocol 2, a hypoglycaemic excursion (2.5 mmol/l) was followed by a hyperglycaemic excursion (12 mmol/l) and another hypoglycaemic episode (3.0 mmol/l).

RESULTS

Blood osmolarity increased during hyperglycaemia and was unaffected by hypoglycaemia. Hyperglycaemia induced decreases in plasma Na(+) Cl(-) and Ca(2+) concentrations and increases in K(+) concentrations. These changes were faithfully reproduced during a second hyperglycaemia. Hypoglycaemia provoked rapid and rapidly reversible increases in Na(+), Cl(-) and Ca(2+). In sharp contrast, K(+) levels displayed a rapid and substantial fall from which they did not fully recover even 2 h after the re-establishment of euglycaemia. A second hypoglycaemia caused an additional fall.

CONCLUSIONS/INTERPRETATION

Repeated hyperglycaemia events do not lead to any cumulative effects on blood electrolytes. However, repeated hypoglycaemias are cumulative with respect to K(+) levels due to a very slow recovery following hypoglycaemia. These results suggest that recurring hypoglycaemic events may lead to progressively lower K(+) levels despite rapid re-establishment of euglycaemia. This warrants close monitoring of plasma K(+) levels combined with continuous glucose monitoring particularly in patients under intensive insulin therapy who are subject to repeated hypoglycaemic episodes.

TRIAL REGISTRATION

Clinicaltrial.gov NCT01060917.

Genetic variation in aldosterone synthase predicts plasma glucose levels

The mineralocorticoid hormone, aldosterone, is known to play a role in sodium homeostasis. We serendipitously found, however, highly significant association between single-nucleotide polymorphisms in the aldosterone synthase gene and plasma glucose levels in a large population of Chinese and Japanese origin. Two polymorphisms--one in the putative promoter (T-344C) and another resulting in a lysine/arginine substitution at amino acid 173, which are in complete linkage disequilibrium in this population--were associated with fasting plasma glucose levels (P = 0.000017) and those 60 (P = 0.017) and 120 (P = 0.0019) min after an oral glucose challenge. A C/T variant in intron 1, between these polymorphisms, was not associated with glucose levels. Arg-173 and -344C homozygotes were most likely to be diabetic [odds ratio 2.51; 95% confidence interval (C.I.) 1.39-3.92; P = 0.0015] and have impaired fasting glucose levels (odds ratio 3.53; 95% C.I. 2.02-5.5; P = 0.0000036). These results suggest a new role for aldosterone in glucose homeostasis.

Normal renin-aldosterone-insulin and potassium interrelationship in FMF patients and amyloid nephropathy

The renin-aldosterone system and plasma insulin were studied in 19 patients with familial Mediterranean fever (FMF). Their relationships to serum potassium level at rest and before and after oral glucose loading are described. An interesting finding is the occurrence of hyperkalemia in the absence of oliguria, in the advanced stages of renal failure. No differences were found in the activity of the renin-angiotensin-aldosterone system to explain these variations in serum potassium found in some of the patients. The response of the renin-aldosterone system to glucose loading showed no abnormality, and the regular relationship between serum potassium, plasma renin activity (PRA), aldosterone, insulin, and plasma pH is maintained. Levels of insulin, potassium, and bicarbonate in serum or plasma pH were found similar in FMF patients with normal renal function with and without proteinuria. Further decrease in renal function due to the progression of the underlying disease is manifested by an increase in FENa+ and FEK+ and a hyperchloremic metabolic acidosis, as is the case in other patients with chronic renal failure.

Effect of acute hyperglycaemia on plasma potassium and aldosterone levels in type 2 (non-insulin-dependent) diabetes

Potassium homeostasis during a 50-g oral glucose tolerance test was studied in 14 newly diagnosed, untreated Type 2 (non-insulin-dependent) diabetics. They showed a rise in plasma potassium from a mean +/- SEM basal of 3.9 +/- 0.1 to 4.4 +/- 0.1 mmol/l at 60 min and to 4.6 +/- 0.1 mmol/l at 90 min (p less than 0.01), whereas no change was seen in a group of 14 normal subjects. A possible role of mineralocorticoids was sought by measuring simultaneous serum aldosterone and deoxycorticosterone levels. Aldosterone was reduced after the glucose load in all subjects studied, falling to 73% of basal at 60 min in diabetics (p less than 0.01), and to 61% of basal at 90 min in normal subjects (p less than 0.001). Serum deoxycorticosterone showed a similar pattern. Thus it is unlikely that the rise in plasma potassium seen in the diabetic patients was due to abnormal levels of mineralocorticoids. Since the diabetic subjects were found to have an intact insulin response to the glucose load, it is suggested that resistance to insulin-stimulated potassium uptake into cells might be involved in the pathogenesis of the paradoxical hyperkalaemia induced by acute hyperglycaemia.