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

Fluid Intake Habits in Type 1 Diabetes Individuals during Typical Training Bouts

BACKGROUND/AIMS

Hyperglycemia may influence the hydration status in diabetic individuals. During exercise, type 1 diabetes mellitus (T1DM) individuals may be challenged by a higher risk of dehydration due to a combination of fluid losses from sweat and increased urine output via glycosuria. So far, no study has characterised spontaneous fluid intake in T1DM individuals during active trainings.

METHODS

A validated questionnaire was used to assess T1DM participants' diabetes therapy, sports characteristics and fluid intake during training; results were then compared to an age- and sport-matched sample of non-diabetic individuals.

RESULTS

Ninety individuals completed the survey (n = 45 T1DM individuals, n = 45 matched controls). A proportion of T1DM -individuals reported blood glucose levels greater than 10.0 mmol at both the start (28.9%) and end (24.4%) of the exercise. The mean self-reported fluid intake was greater in T1DM (0.60 ± 0.47 L·h-1) compared to that of the control (0.37 ± 0.28 L·h-1, p < 0.05). In spite of drinking fluid volumes in line with international guidelines, 84.4% of those with T1DM reported that they were still feeling thirsty at the end of their training session.

CONCLUSIONS

T1DM individuals self-report spontaneously consuming fluid adequate volumes suggested by sport nutrition guidelines for non-diabetic athletes. Discrepancies in the T1DM subjectively reported feelings of thirst suggest that more education on hydration during exercise is needed for this population to adequately compensate for elevated blood glucose levels. It remains to be established whether fluid volumes suggested for healthy athletes are adequate for maintaining euhydration in T1DM patients due to their altered diuresis.

A 4-h hyperglycaemic excursion induces rapid and slow changes in major electrolytes in blood in healthy human subjects

Hyperglycaemia is well known to cause reductions in plasma Na(+) levels or even hyponatraemia due to an osmotically induced dilution of the interstitium and blood. It is, however, unclear whether this dilution is significantly counteracted by ion regulatory homeostatic mechanism(s) or not. Furthermore, the effects of moderate hyperglycaemia on other major ions are less well known. To further clarify these questions, we measured the changes in blood osmolarity and concentrations of Na(+), K(+), Cl(-), Mg(2+) and Ca(2+) during a 4-h-long experimental hyperglycaemia in healthy subjects rendered temporarily insulin deficient using the hyperglycaemic clamp. Hyperglycaemia, 16.8 mM, was rapidly imposed from a baseline of 4.4 mM by intravenous somatostatin and glucose infusions in 19 healthy subjects (10 m, 9 f; age 36 ± 5 years (mean ± SD); BMI 22.7 ± 2.9 kg/m(2)). Subsequently, glycaemia was returned to basal and measurements continued until all dynamic changes had stopped (at ~8 h). Osmolarity increased from 281.8 ± 0.7 to 287.9 ± 0.7, while Na(+) decreased from 143.9 ± 0.3 to 138.7 ± 0.2, Cl(-) from 101.7 ± 0.2 to 99.5 ± 0.1, Ca(2+) from 1.98 ± 0.04 to 1.89 ± 0.02 and Mg(2+) from 0.84 ± 0.01 to 0.80 ± 0.00 mM. All these changes were rapidly reaching stable levels. K(+) increased from 4.02 ± 0.02 to 4.59 ± 0.02 mM (P < 0.0001) also reaching stable levels but with some delay. Na(+), Cl(-), Mg(2+) and Ca(2+) are essentially determined by blood dilution, and their values will remain diminished as long as the hyperglycaemia lasts. Partial suppression of insulin-stimulated Na(+)/K(+) pumping lead to increased K(+) levels. The combination of elevated K(+) and decreased Mg(2+) and Ca(2+) levels may lead to an altered excitability, which is particularly relevant for diabetic patients with heart disease.

Beneficial effects of potassium on human health

Until recently, humans consumed a diet high in potassium. However, with the increasing consumption of processed food, which has potassium removed, combined with a reduction in the consumption of fruits and vegetables, there has been a large decrease in potassium intake which now, in most developed countries, averages around 70 mmol day-1, i.e. only one third of our evolutionary intake. Much evidence shows that increasing potassium intake has beneficial effects on human health. Epidemiological and clinical studies show that a high-potassium diet lowers blood pressure in individuals with both raised blood pressure and average population blood pressure. Prospective cohort studies and outcome trials show that increasing potassium intake reduces cardiovascular disease mortality. This is mainly attributable to the blood pressure-lowering effect and may also be partially because of the direct effects of potassium on the cardiovascular system. A high-potassium diet may also prevent or at least slow the progression of renal disease. An increased potassium intake lowers urinary calcium excretion and plays an important role in the management of hypercalciuria and kidney stones and is likely to decrease the risk of osteoporosis. Low serum potassium is strongly related to glucose intolerance, and increasing potassium intake may prevent the development of diabetes that occurs with prolonged treatment with thiazide diuretics. Reduced serum potassium increases the risk of lethal ventricular arrhythmias in patients with ischaemic heart disease, heart failure and left ventricular hypertrophy, and increasing potassium intake may prevent this. The best way to increase potassium intake is to increase the consumption of fruits and vegetables.

Addison's disease and the regulation of potassium: the role of insulin and aldosterone

It is proposed that insulin has a cardinal role in the regulation of serum potassium levels in man, which may be of greater importance than the effect of insulin on glucose metabolism. Although the first described action of insulin was on glucose transport, it is a hormone with many functions some of which may operate in a metabolic hierarchy depending on the relative importance of the action required. Insulin also promotes the transport of potassium ions from the extracellular space to the intracellular space and it is suggested that there are occasions where this action may take place at the expense of glucose regulation. In metabolic terms, tight control of serum potassium is of greater importance than precise control of serum glucose, because quite small variations in serum potassium may cause death whereas wide variations in serum glucose may be tolerated. Serum potassium levels generally remain very stable despite large daily variations in potassium intake. It follows that potassium control mechanisms must be of outstanding efficiency as serious disturbances of potassium balance are relatively uncommon. 'Nature makes experiments on Man': shadowy but important physiological mechanisms that may almost be taken for granted in normal health are often brightly illuminated by unusual pathological conditions. This paper describes two remarkable patients who presented with extreme hyperkalaemia. This condition was the result of simultaneous insulin and aldosterone deficiency occurring because of concomitant diabetes and Addison's disease. Other medical conditions with disturbances in aldosterone, insulin and potassium control will be referred to in support of the hypothesis that insulin secretion is central to potassium regulation. This hypothesis explains the secondary disturbances in glucose metabolism that occurs in clinical situations where the primary problem is perturbation of potassium regulation.

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.

Hyperkalaemia in diabetes: prevalence and associations

Hyperkalaemia is associated with diabetes, but there are no recent reports of its prevalence and associations. Serum potassium concentrations were measured in all 1764 patients attending a diabetic clinic over a 12-month period and found to be > 5.0 mmol/l in 270 (15%), and > 5.4 mmol/l in 67 (4%). There was no other evident cause of hyperkalaemia in 41 of these 67 patients. These data serve to highlight the risk of dangerous hyperkalaemia in diabetic patients, particularly with concurrent administration of angiotensin-converting-enzyme inhibitors and potassium-sparing diuretics.

Angiotensin-converting enzyme (ACE) inhibition. Therapeutic option for diabetic hypertensive patients

When choosing antihypertensive agents for the treatment of diabetic patients with hypertension, it is necessary to consider the individual characteristics of these patients. In this respect, angiotensin-converting enzyme (ACE) inhibitors constitute an attractive option for diabetic patients. The effects of enalapril alone for 16 weeks in 23 non-insulin-dependent diabetic (NIDD) patients and in 10 non-diabetic patients with mild to moderate essential hypertension (EH) [diastolic blood pressure greater than 95 mm Hg and less than 115 mm Hg] were evaluated. Similar reductions in both systolic and diastolic blood pressure were observed in 17 NIDD patients (from 155 +/- 18/100 +/-11 mm Hg to 128 +/- 12/82 +/- 8 mm Hg, respectively) and in 6 EH patients (from 155 +/- 21/100 +/- 6 mm Hg to 125 +/- 20/84 +/- 8 mm Hg, respectively) who achieved and maintained blood pressure control (diastolic blood pressure less than 90 mm Hg) for 16 weeks. In 4 NIDD and 4 EH patients blood pressure was not controlled. Two NIDD patients discontinued the medication, one because of symptomatic postural hypotension and the other, who had a plasma creatinine level of 1.8 mg/dl, because of hyperkalaemia (K = 6.1 mEq/L). In the responders, enalapril did not alter glucose tolerance, plasma or urinary excretion of creatinine, potassium, sodium and aldosterone. Plasma renin activity increased in the NIDD group only. In 11 patients (6 NIDD and 5 EH), the elevated protein or albumin excretions decreased. It is concluded that enalapril is a good therapeutic option for NIDD patients with hypertension.

Hypertension and diabetes. Clinical problems

The choice of an appropriate antihypertensive agent and the hazards of postural hypotension are common problems faced in the treatment of diabetic hypertensive patients. The results of 3 studies addressing these problems are described in this report. In the first study, indoramin, an alpha-blocking agent, was administered to patients with non-insulin-dependent diabetes and mild to moderate hypertension. Blood pressure control was achieved in 57% of patients with mild, and in none with moderate hypertension. The blood glucose and insulin responses to an oral 50g glucose loading, as well as the blood concentrations of HbA1 did not change during therapy. Seven patients were excluded because of side effects. In 4 of them postural hypotension was observed. In the second study, the effects of angiotensin-converting enzyme (ACE) inhibitors, administered to patients with non-insulin-dependent diabetes and mild to moderate hypertension, were evaluated. Blood pressure control was achieved in 78% of the patients on captopril (n = 14) and in 74% of patients on enalapril therapy (n = 23). Symptomatic postural hypotension (n = 2) and hyperkalaemia (n = 2) were observed with both drugs. Significant reductions in 24-hour urinary protein or albumin excretion were detected in 12 patients on enalapril therapy. No changes in 2-hour postprandial blood glucose and HbA1 levels were observed during therapy with ACE inhibitors. In the third study, dopaminergic antagonist agents were evaluated in diabetic patients with orthostatic hypotension. In 7 patients metoclopramide (20mg intravenously) reduced the fall in mean arterial pressure induced by upright tilt.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperkalaemia in diabetes mellitus--potential hazards of coexisting hyporeninaemic hypoaldosteronism

Two patients with insulin-dependent diabetes mellitus (Type I), developed severe, life-threatening hyperkalaemia, the first following treatment with spironolactone, the second during treatment for staphylococcal septicaemia when glucose-induced hyperkalaemia occurred. Investigations demonstrated co-existing hyporeininaemic hypoaldosteronism. Prompt recognition of this combined hormone-deficiency syndrome led to appropriate treatment and recovery. The biochemical features and clinical importance of hyporeninaemic hypoaldosteronism are discussed.