Nitric oxide synthase inhibition by N$omega;-nitro--arginine methyl ester modulates G-protein expression and adenylyl cyclase activity in rat heart*1

Cephalic elevations in arterial pressure associated with microgravity and prolonged bed rest alter cerebrovascular autoregulation in humans. Using the head-down tail-suspended (HDT) rat to chronically induce headward fluid shifts and elevate cerebral artery pressure, previous work has likewise shown cerebral perfusion to be diminished. The purpose of this study was to test the hypothesis that 2 wk of HDT reduces cerebral artery vasodilation. To test this hypothesis, dose-response relations for endothelium-dependent (2-methylthioadenosine triphosphate and bradykinin) and endothelium-independent (nitroprusside) vasodilation were determined in vitro in middle cerebral arteries (MCAs) from HDT and control rats. All in vitro measurements were done in the presence and absence of the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (10−5 M) and cyclooxygenase inhibitor indomethacin (10−5 M). MCA caveolin-1 protein content was measured by immunoblot analysis. Endothelium-dependent vasodilation to 2-methylthioadenosine triphosphate and bradykinin were both lower in MCAs from HDT rats. These lower vasodilator responses were abolished with NG-nitro-l-arginine methyl ester but were unaffected by indomethacin. In addition, HDT was associated with lower levels of MCA caveolin-1 protein. Endothelium-independent vasodilation was not altered by HDT. These results indicate that chronic cephalic fluid shifts diminish endothelium-dependent vasodilation through alterations in the endothelial nitric oxide synthase signaling mechanism. Such decrements in endothelium-dependent vasodilation of cerebral arteries could contribute to the elevations in cerebral vascular resistance and reductions in cerebral perfusion that occur after conditions of simulated microgravity in HDT rats.

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Contribution of endothelin to the coronary vasoconstriction in the isolated rat heart induced by nitric oxide synthase inhibition

Acta Physiologica Scandinavica ◽

10.1046/j.1365-201x.1998.t01-1-00364.x ◽

1998 ◽

Vol 163 (4) ◽

pp. 325-330 ◽

Cited By ~ 20

Author(s):

Q.-D. Wang ◽

A. Gonon ◽

M. Shimizu ◽

P.-O. Sjöquist ◽

J. Pernow

Keyword(s):

Nitric Oxide ◽

Nitric Oxide Synthase ◽

Rat Heart ◽

Isolated Rat Heart ◽

Coronary Vasoconstriction ◽

Oxide Synthase ◽

Isolated Rat

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Prostaglandin E2 receptors in the heart are coupled to inhibition of adenylyl cyclase via a pertussis toxin sensitive G protein

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y92-011 ◽

1992 ◽

Vol 70 (1) ◽

pp. 77-84 ◽

Cited By ~ 5

Author(s):

Richard W. Lerner ◽

Gary D. Lopaschuk ◽

Peter M. Olley

Keyword(s):

Adenylyl Cyclase ◽

G Protein ◽

Pertussis Toxin ◽

Binding Sites ◽

Cyclase Activity ◽

Prostaglandin E ◽

Adenylyl Cyclase Activity ◽

Adp Ribosylation ◽

Number Of Binding Sites ◽

Guanine Nucleotide Binding

In previous studies we have identified and isolated a prostaglandin E2 (PGE2) receptor from cardiac sarcolemmal (SL) membranes. Binding of PGE2 to this receptor in permeabilized SL vesicles inhibits adenylyl cyclase activity. The purpose of this study was to determine if the cardiac PGE2 receptor is coupled to adenylyl cyclase via a pertussis toxin sensitive guanine nucleotide binding inhibitory (Gi) protein. Incubation of permeabilized SL vesicles in the presence of 100 μM 5′-guanylamidiophosphate, Gpp(NH)p, a nonhydrolyzable analogue of GTP, resulted in a shift in [3H]PGE2 binding from two sites, one of high affinity (KD = 0.018 ± 0.003 nM) comprising 7.7% of the total available binding sites and one of lower affinity (KD = 1.9 ± 0.7 nM) to one site of intermediate affinity (KD = 0.52 ± 0.01 nM) without a significant change in the total number of PGE2 binding sites. A shift from two binding sites to one binding site in the presence of Gpp(NH)p was also observed for [3H]dihydroalprenolol binding to permeabilized cardiac SL. When permeabilized SL vesicles were pretreated with activated pertussis toxin, ADP-ribosylation of a 40- to 41-kDa protein corresponding to Gi was observed. ADP-ribosylation of SL resulted in a shift in [3H]PGE2 binding to one site of intermediate affinity without significantly changing the number of binding sites. In alamethicin permeabilized SL vesicles, 1 nM PGE2 significantly decreased (30%) adenylyl cyclase activity. Pretreatment with activated pertussis toxin overcame the inhibitory effects of PGE2. These results demonstrate that the cardiac PGE2 receptor is coupled to adenylyl cyclase via a pertussis toxin sensitive Gi protein. They also demonstrate that the interaction of this Gi protein with the PGE2 receptor is important in the regulation of PGE2 binding to its receptor.Key words: prostaglandin E2, sarcolemma, heart, adenylyl cyclase, G protein.

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