Purpose: The aim of this study was to examine whether diabetes changes the in vivo effects of adrenomedullin (ADM) on diameter of retinal arteriole and blood pressure in rats.
Methods: Male Wistar rats were treated with streptozotocin (65 mg/kg, intravenously [i.v.]) and experiments were performed 6-8 weeks later. Under artificial ventilation, rats were injected with tetrodotoxin (50 microg/kg, i.v.) to eliminate any nerve activity and prevent movement of the eye. A mixture solution of norepinephrine and epinephrine (1:9) was used to maintain adequate systemic circulation. Diameters of retinal vessels were measured from the fundus images and were captured by a digital camera that was equipped with a special objective lens.
Results: ADM dose-dependently increased diameters of retinal arterioles and decreased blood pressure in streptozotocin-induced diabetic rats and the age-matched controls. The depressor responses, but not vasodilator responses of retinal arterioles, to ADM were reduced in diabetic rats.
Conclusions: These results suggest that mechanism(s) of ADM-induced vasodilation of retinal arterioles is preserved in diabetes, even when depressor effects of ADM are impaired. ADM may play a role as a regulatory mechanism of retinal circulation in nondiabetic and diabetic conditions.