Motomaru Masutani, Mitsumasa Ohyanagi, Jun Shibuya, Yasuhiro Ishigami
and Tadaaki Iwasaki
First Department of Internal Medicine, Hyogo College of Medicine, 1-1,
Mukogawa-cho, Nishinomiya 663-8501, Japan
Abstract: The inhibitory GTP-binding protein (Gi protein) plays
an important role in regulation of vascular tone. Many studies have implicated
the role of Gi protein in conduit vessels. However, the physiological role
of Gi protein in the control of peripheral microvascular tone in hypertension
has not been established yet. Therefore, we investigated the concentration
of Gi protein in the peripheral resistance arteries and aorta in the spontaneously
hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY) and renovascular
hypertensive rats (RHR), using immunohistochemical methods semiquantitatively.
Changes in the function of Gi protein in relation to alpha2-adrenoceptor
were also investigated by microcannulation techniques. We have shown that
the amount of alpha2 subunits of Gi protein in the cremaster
small artery was significantly lower in SHR aged 4 weeks and older than
in age-matched WKY and that there were no significant differences between
RHR and WKY. We also demonstrated that the function of Gi protein in relation
to alpha2-adrenoceptor was already lower in SHR before the onset
of hypertension. The quantitative and functional decline in Gi protein in
the smooth muscle cells of peripheral small arteries were observed in SHR
even before the onset of hypertension, whereas rats with secondary hypertension
did not exhibit this finding.
Keywords: Gi protein, Spontaneously hypertensive rats, Resistance artery,
Immunohistochemistry, alpha2-Adrenoceptor