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 µg/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.
