1. The distensibility of the resistance vessels of the skin at the dorsum of the foot was determined in 11 long-term type 1 (insulin-dependent) diabetic patients with nephropathy and retinopathy, nine short-term type 1 diabetic patients without clinical microangiopathy and in nine healthy non-diabetic subjects.

2. Blood flow was measured by the local 133Xexenon washout technique in a vascular bed locally paralysed by the injection of histamine. Blood flow was measured before, during and after a 40 mmHg increase of the vascular transmural pressure, induced by head-up tilt.

3. The mean increase in blood flow during headup tilt was only 24% in diabetic subjects with and 48% in diabetic patients without clinical microangiopathy, compared with 79% in normal non-diabetic subjects (P < 0.0005 and P < 0.05, respectively).

4. An inverse correlation between microvascular distensibility and degree of hyalinosis of the terminal arterioles in biopsies from the skin was demonstrated (r = − 0.57, P < 0.001).

5. Our results suggest that terminal arteriolar hyalinosis reduces the microvascular distensibility and probably increases the minimal vascular resistance, thereby impeding hyperaemic responses.

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