Vasodilator effects of adrenomedullin on retinal arterioles in streptozotocin-induced diabetic rats.
OBJECTIVE
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.
Kaneko
Yoshiko
Y
Department of Molecular Pharmacology, Kitasato University School of Pharmaceutical Sciences, Tokyo, Japan.
Saito
Maki
M
Mori
Asami
A
Sakamoto
Kenji
K
Nakahara
Tsutomu
T
Ishii
Kunio
K
D053607:Adrenomedullin / Q000494:pharmacology*; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D001794:Blood Pressure / Q000187:drug effects; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced* / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012161:Retinal Artery / Q000033:anatomy & histology / Q000187:drug effects* / Q000503:physiopathology; D013311:Streptozocin; D014665:Vasodilator Agents / Q000494:pharmacology*
D001786:Blood Glucose; D014665:Vasodilator Agents; D053607:Adrenomedullin; D013311:Streptozocin