CARDIOVASCULAR JOURNAL OF AFRICA • Vol 24, No 3, April 2013
78
AFRICA
Here we found that decreased vascular contractility induced
by hemin incubation was associated with a reduction in the
relaxation effect ofY-27632. SinceY-27632 is a specific inhibitor
of rho-kinase activity,
7
this effect suggests that following
incubation in hemin, the activity of rho-kinase in aortic smooth
muscle was partially inhibited. As rho-kinase is involved with
calcium sensitivity in vascular smooth muscle, this reduced
activity of rho-kinase could explain in part the reduced contractile
force developed by aortic rings in response to phenylephrine.
Previously, we have shown that the relaxation effect of
Y-27632 was greater in aortic rings from hypertensive rats than
in those from normotensive Wistar rats. Moreover, 21 days’
administration of hemin resulted in a reduction in the relaxation
effect of Y-27632 on aortic rings from hypertensive rats but
was without significant effect on the relaxation of aortic rings
induced by Y-27632.
17
Therefore, although six-hour incubation
of aortic rings in hemin resulted in a reduction of the relaxation
effect of Y-27632, suggesting a decrease of rho-kinase activity,
21 days’ administration of hemin did not alter the rho-kinase
activity in the aortas of Wistar normotensive rat.
However, this long-term administration of hemin decreased the
rho-kinase activity in vessels from spontaneously hypertensive
rats where this activity was higher than in normotensive rats. To
explain the absence of effect on Wistar rat blood pressure during
long-term administration of hemin, some mechanisms could
have occurred to prevent the reduction of rho-kinase activity and
maintain vascular contractility.
Conclusion
Six-hour incubation of aortic rings in hemin solution resulted
in increased heme oxygenase 1 expression and decreased aortic
contractility associated with a partial inhibition of rho-kinase
activity. The mechanism of this hemin-induced inhibition of
rho-kinase activity remains to be elucidated.
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Fig. 3. Expression of heme oxygenase (HO-1) in aortic rings. Images represent 7-μm-thick transverse sections of
aortic rings in which expression of heme oxygenase 1 (HO-1) was detected by immunofluorescence using an Alexa
fluo-labelled secondary antibody after incubation with an anti-HO-1 antibody. On the left, a section of control aortic
ring and on the right, a section of aortic ring incubated for six hours in physiological saline solution containing hemin
at 10
-4
M. Increased expression of HO-1 (light fluorescence) is observed in the hemin aortic ring compared to that in
the control ring.
Control
Hemin
