The causes of raised blood pressure in insulin-dependent and non-insulin-dependent diabetes

Abstract

Blood pressure is generally normal in insulin-dependent diabetic patients in the absence of nephropathy. Despite this, exchangeable sodium is increased. Blood pressure rises with the development of incipient nephropathy, and hypertension is common in patients with overt nephropathy. Exchangeable sodium is then markedly increased, but plasma renin is not suppressed. Raised BP in diabetic nephropathy is probably sustained, in part at least, by sodium retention and inappropriate activity of the renin-angiotensin system. There is an increased prevalence of hypertension among patients with non-insulin-dependent diabetes (NIDDM). In normotensive patients, exchangeable sodium is elevated and plasma renin is suppressed. In hypertensive patients, exchangeable sodium is less markedly increased, while plasma renin is again suppressed. These findings are in contrast with those in diabetic nephropathy, and are in keeping with the hypothesis that hypertension in NIDDM is usually due to coexisting essential hypertension. Also in keeping with this suggestion is an increased prevalence of raised BP among the siblings of NIDDM patients. Prolonged hyperinsulinaemia precedes the diagnosis of NIDDM, and hypertension is often present at the time of diagnosis. Insulin resistance and compensatory hyperinsulinaemia might lead to an increase in BP by a number of putative mechanisms, such as enhancing renal sodium retention, by an effect on cell membrane ion exchange mechanisms or by enhancing activity of the sympathetic nervous system. This seems a fertile area for further research, although a causal link between insulin resistance and hyperinsulinaemia on the one hand, and raised BP on the other, remains to be proved.