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Vol. 305, Issue 2, 581-586, May 2003
2-Adrenoceptors Potentiate Angiotensin II- and
Vasopressin-Induced Renal Vasoconstriction in Spontaneously
Hypertensive Rats
Center for Clinical Pharmacology (L.G., C.Z., E.K.J.), Department
of Medicine (L.G., C.Z., E.K.J.), and Department of Pharmacology
(E.K.J.), University of Pittsburgh School of Medicine, Pittsburgh,
Pennsylvania
Hypertension in spontaneously hypertensive rats (SHRs) is due in part
to enhanced effects of vasoactive peptides on the renal vasculature. We
hypothesize that the Gi signal transduction pathway enhances renovascular responses to vasoactive peptides in SHRs more so
than in normotensive Wistar-Kyoto (WKY) rats. To test this hypothesis,
we examined in isolated perfused kidneys from SHRs and WKY rats the
renovascular responses (assessed as changes in renal perfusion pressure
in mm Hg) to angiotensin II (10 nM) and vasopressin (3 nM) in the
presence and absence of UK-14,304 [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine;
an agonist that selectively activates the Gi pathway by
stimulating
2-adrenoceptors]. In SHR, but not WKY,
kidneys, UK-14,304 (10 nM) enhanced (P < 0.05)
renovascular responses to angiotensin II (control WKY, 43 ± 6;
UK-14,304-treated WKY, 52 ± 19; control SHR, 66 ± 17;
UK-14,304-treated SHR, 125 ± 16) and vasopressin (control WKY,
42 ± 17; UK-14,304-treated WKY, 36 ± 11; control SHR,
16 ± 8; UK-14,304-treated SHR, 83 ± 17). Pretreatment of SHRs with pertussis toxin (30 µg/kg, intravenously, 3-4 days before study) to inactivate Gi blocked the effects of UK-14,304.
Western blot analysis of receptor expression in whole kidney and
preglomerular microvessels revealed similar levels of expression of
AT1, V1a, and
2A receptors in
SHRs compared with WKY rats. We conclude that activation of
2-adrenoceptors selectively enhances renovascular responses to angiotensin II and vasopressin in SHRs via an enhanced cross talk between the Gi signal transduction pathway and
signal transduction pathways activated by angiotensin II and vasopressin.
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