Diabetic state, high plasma insulin and angiotensin II combine to augment endothelin-1-induced vasoconstriction via ETA receptors and ERK.
OBJECTIVE
Mechanisms associated with the enhanced contractile response to endothelin-1 in hyperinsulinaemic diabetes have been examined using the rat aorta. Functions for angiotensin II, endothelin-1 receptor expression and extracellular signal-regulated kinase (ERK) have been investigated.


METHODS
Streptozotocin-induced diabetic rats were infused with angiotensin II or, following insulin treatment, were treated with losartan, an angiotensin II receptor antagonist. Contractions of aortic strips with or without endothelium, in response to endothelin-1 and angiotensin II, were examined in vitro. Aortic ET(A) receptors and ERK/MEK expression were measured by western blotting.


RESULTS
Insulin-treated diabetic rats exhibited increases in plasma insulin, angiotensin II and endothelin-1. The systolic blood pressure and endothelin-1-induced contractile responses in aortae in vitro were enhanced in insulin-treated diabetic rats and blunted by chronic losartan administration. LY294002 (phosphatidylinositol 3-kinase inhibitor) and/or PD98059 (MEK inhibitor) diminished the enhanced contractile response to endothelin-1 in aortae from insulin-treated diabetic rats. ET(A) and ET(B) receptors, ERK-1/2 and MEK-1/2 protein expression and endothelin-1-stimulated ERK phosphorylation were all increased in aortae from insulin-treated diabetic rats. Such increases were blunted by chronic losartan administration. Endothelin-1-induced contraction was significantly higher in aortae from angiotensin II-infused diabetic rats. angiotensin II-infusion increased ERK phosphorylation, but the expression of endothelin receptors and ERK/MEK proteins remained unchanged.


CONCLUSIONS
These results suggest that the combination of high plasma angiotensin II and insulin with a diabetic state induced enhancement of endothelin-1-induced vasoconstriction, ET(A) receptor expression and ERK expression/activity in the aorta. Losartan improved both the diabetes-related abnormalities and the diabetic hypertension.
Kobayashi
T
T
Department of Physiology and Morphology, Institute of Medicinal Chemistry, Hoshi University, Shinagawa-ku, Tokyo, Japan.
Nogami
T
T
Taguchi
K
K
Matsumoto
T
T
Kamata
K
K
D000804:Angiotensin II / Q000378:metabolism* / Q000494:pharmacology; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000378:metabolism / Q000503:physiopathology; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000503:physiopathology; D003922:Diabetes Mellitus, Type 1 / Q000150:complications / Q000503:physiopathology*; D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1 / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006973:Hypertension / Q000209:etiology; D007328:Insulin / Q000097:blood / Q000378:metabolism / Q000494:pharmacology; D019808:Losartan / Q000494:pharmacology; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D044022:Receptor, Endothelin A / Q000378:metabolism*; D013311:Streptozocin; D014661:Vasoconstriction / Q000187:drug effects
D047228:Angiotensin II Type 1 Receptor Blockers; D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1; D007328:Insulin; D044022:Receptor, Endothelin A; D000804:Angiotensin II; D013311:Streptozocin; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D019808:Losartan