Losartan counteracts the hyper-reactivity to angiotensin II and ROCK1 over-activation in aortas isolated from streptozotocin-injected diabetic rats.
BACKGROUND
In streptozotocin-injected rats (STZ-rats), we previously demonstrated a role for angiotensin II (AT-II) in cardiac remodelling and insulin resistance partially counteracted by in vivo treatment with losartan, an AT-II receptor antagonist.We now aimed to investigate the effect of treating diabetic STZ-rats with losartan on diabetes vascular response to vasoconstrictors.


METHODS
Male Wistar rats were randomly divided in four groups, two of them were assigned to receive losartan in the drinking water (20 mg/kg/day) until the experiment ending (3 weeks afterward). After 1 week, two groups, one of which receiving losartan, were injected in the tail vein with citrate buffer (normoglycemic, N and normoglycemic, losartan-treated, NL). The remaining received a single injection of streptozotocin (50 mg/kg in citrate i.v.) thus becoming diabetic (D) and diabetic losartan-treated (DL). Plasma glycaemia and blood pressure were measured in all animals before the sacrifice (15 days after diabetes induction).In aortic strips isolated from N, NL, D and DL rats we evaluated i) the isometric concentration-dependent contractile response to phenylephrine (Phe) and to AT-II; ii) the RhoA-kinase (ROCK1) activity and expression by enzyme-immunoassay and Western blot respectively.


RESULTS
The concentration-dependent contractile effect of Phe was similar in aortas from all groups, whereas at all concentrations tested, AT-II contraction efficacy was 2 and half and 1 and half times higher in D and DL respectively in comparison with N and NL. AT-II contracture was similarly reduced in all groups by AT-II receptor antagonists, irbesartan or irbesartan plus PD123319. HA-1077 (10 microM), an inhibitor of ROCK1 activity, reduced AT-II efficacy (Deltamg/mg tissue w.w.) by -3.5 +/- 1.0, -4.6 +/- 1.9, -22.1 +/- 2.2 and -11.4 +/- 1.3 in N, NL, D and DL respectively). ROCK1 activity and expression were higher in D than in N/NL and DL aortas.


CONCLUSIONS
Aortas isolated from STZ-rats present hyper-contracture to AT-II mainly dependent on the up-regulation of ROCK1 expression/activity. In vivo losartan treatment partially corrects AT-II hyper-contracture, limiting the increase in ROCK1 expression/activity. These data offer a new molecular mechanism supporting the rationale for using losartan in the prevention of diabetic vascular complications.
Failli
Paola
P
Dept. of Pharmacology, University of Florence, Viale G, Pieraccini 6, Florence, Italy. paola.failli@unifi.it
Alfarano
Chiara
C
Franchi-Micheli
Sergio
S
Mannucci
Edoardo
E
Cerbai
Elisabetta
E
Mugelli
Alessandro
A
Raimondi
Laura
L
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000804:Angiotensin II / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism*; D001713:Biphenyl Compounds / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy / Q000378:metabolism*; D066298:In Vitro Techniques; D000077405:Irbesartan; D019808:Losartan / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013777:Tetrazoles / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology
D001713:Biphenyl Compounds; D013777:Tetrazoles; D000804:Angiotensin II; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; C515851:ROCK1 protein, human; D054460:rho-Associated Kinases; D000077405:Irbesartan; D019808:Losartan; C049347:fasudil