Antiplatelet effects of prostacyclin and nitric oxide in patients with type I diabetes and ischemic or edematous retinopathy.

The aim of this study was investigate prostacyclin and nitric oxide (NO) and their platelet second messengers cAMP and cGMP, in patients with type I diabetes with or without retinopathy. We compared 20 healthy volunteers and 97 patients with type I diabetes: 24 with no signs of diabetic retinopathy (DR), 43 with ischemicproliferative DR, and 30 with edematous DR. The following parameters were recorded: platelet aggregometry, nitrites/nitrates, 6-keto-prostaglandin-F(1alpha), and intraplatelet cAMP and cGMP. Platelet aggregation was greater in patients with edematous DR. The platelets in patients with diabetes were more resistant to inhibition by prostaglandin E(1) or sodium nitropruside. Nitrite concentration in patients with ischemic-proliferative DR was 80% lower than the value in healthy controls, but there was no significant difference between the control group and patients with edematous DR. In the latter group, stimulation of neutrophils with L-arginine increased nitrite + nitrate production by 44 +/- 3.6%, whereas in patients with ischemic-proliferative DR, the increase was 9.8 +/- 0.8%. We conclude that NO production is higher in patients with type I diabetes and edematous retinopathy than in those with ischemic-proliferative retinopathy. This finding, together with the possibly greater production of free radicals, may explain the greater impairment of platelet function in the former patients.