H. Suzuki et al., VASODILATOR RESPONSE OF MESENTERIC ARTERIOLES TO HISTAMINE IN SPONTANEOUSLY HYPERTENSIVE RATS, Hypertension, 26(3), 1995, pp. 397-400
Recent evidence suggests that spontaneously hypertensive rats (SHR) ex
hibit an impaired response to inflammatory mediators. We designed this
study to analyze the response of arterioles of SHR after stimulation
with a proinflammatory agent, histamine, compared with the response of
arterioles of normotensive Wistar-Kyoto (WKY) controls. We observed m
esenteric arterioles by intravital microscopy in rats under general an
esthesia and measured their lumen diameters after histamine superfusio
n. To compare the concentration-response curve with histamine, we also
studied the effect of an endothelium-dependent vasodilator: acetylcho
line, and an independent vasodilator, sodium nitroprusside. At the end
of each experiment we applied papaverine topically to determine the m
aximal diameter for each vessel, from which we computed arteriolar ton
e. Arteriolar tone in SHR is set at a higher steady state level than i
n WKY. The concentration required for a 50% dilator response (EC(50))
of histamine in SHR was significantly higher than that in WKY. In SHR
the arteriolar response showed the same refractory pattern to histamin
e as to acetylcholine. In contrast, the EC(50) of sodium nitroprusside
in SHR was similar to that in WKY. Our results indicate that SHR exhi
bit an impaired dilator response to histamine that is due to a blunted
endothelium-dependent vasodilation.