Hypertension in insulin-dependent diabetes.

Hypertension is seen in approximately 85% of IDDM patients with diabetic nephropathy and blood pressure elevation is an early event in the development of this complication. In IDDM patients with clinical nephropathy, a positive correlation has been demonstrated between the blood pressure and the urinary albumin excretion and reduction of blood pressure reduces albuminuria as well as the rate of decline in glomerular filtration rate. Also extrarenal abnormalities such as retinopathy, cardiovascular diseases and signs of endothelial dysfunction, sometimes seen in non-diabetics with severe and/or prolonged hypertension, are frequently demonstrated in IDDM patients with clinical nephropathy. The aim of the present study was to provide circumstantial evidence for the thesis that hypertension in IDDM patients with nephropathy is secondary to the kidney involvement and not the cause of the kidney disease. Furthermore, by familial and physiological studies the review also aimed to contribute to the understanding of the pathogenesis of hypertension in patients with clinical nephropathy. Finally the question of optimal pharmacological antihypertensive treatment was discussed. It was demonstrated that in IDDM patients with elevated urinary albumin excretion above normal level the prevalence of hypertension is 60%, whereas in patients without signs of renal impairment hypertension is not more prevalent as in the age and sex-matched background population (about 4% in both groups). Based upon the observation, that some of these IDDM patients with hypertension but normal UAE were hypertensive for many years, we designated this group as IDDM patients with essential hypertension for further studies. In this group, we had the opportunity to study the association between blood pressure and the development of extrarenal complications in patients with IDDM. The group with essential hypertension and IDDM showed to have less retinopathy compared with diabetics with similar blood pressure but elevated UAE. In contrast to the hypertensive patients with nephropathy, a normal transcapillary escape rate of albumin and normal plasma levels of von Willebrand factor, of angiotensin-converting-enzyme and of inactive renin were demonstrated in the former group of patients. Thus, the extrarenal abnormalities found in IDDM patients with hypertension are more closely associated to the presence of albuminuria than to the elevation of blood pressure, indirectly supporting the hypothesis that hypertension per se is not the cause of these abnormalities in the IDDM patients with nephropathy. Furthermore, the present study does not disclose a genetic disposition to hypertension in IDDM patients with elevated UAE.