Possible role of prostacyclin synthase in altered prostacyclin generation in DOCA-salt hypertensive rats

Influences of prostanoids and nitric oxide on post-suspension hypotension in female Sprague-Dawley rats

Impairment in cardiovascular functions sometimes manifested in astronauts during standing postflight, may be related to the diminished autonomic function and/or excessive production of endothelium-dependent relaxing factors. In the present study, using the 30 degrees head-down tilt (HDT) model, we compared the cardiovascular and biochemical effects of 7 days of suspension and a subsequent 6-h post-suspension period between suspended and non-suspended conscious female Sprague-Dawley rats. Mean arterial pressure (MAP) and heart rate were measured prior to suspension (basal), daily thereafter, and every 2h post-suspension. Following 7 days of suspension, MAP was not different from their basal values, however, upon release from suspension, MAP was significantly reduced compared to the non-suspended rats. Nitric oxide levels were elevated while thromboxane A(2) levels declined significantly in both plasma and tissue samples following post-suspension. The levels of prostacyclin following post-suspension remained unaltered in plasma and aortic rings but was significantly elevated in carotid arterial rings. Therefore, the post-suspension reduction in mean arterial pressure is due mostly to overproduction of nitric oxide and to a lesser extent prostacyclin.

Acute inhibition of glutathione biosynthesis alters endothelial function and blood pressure in rats

The cardiovascular and biochemical responses during acute oxidative stress induced by D,L-buthionine-(S,R)-sulfoximine (BSO) were investigated in Sprague-Dawley rats. Mean arterial pressure, heart rate and vascular reactivity were measured after subcutaneous injection of BSO (4 mmol/kg). Control rats received saline. Levels of GSH and GSSG in blood and tissues as well as renal superoxide were determined. Nitric oxide, prostacyclin and thromboxane A(2) in plasma and aorta, and isoprostane in plasma were also measured. Blood pressure was elevated at 24 h (121+/-2 vs. 104+/-2 mm Hg), with increased reactivity to phenylephrine (by a 59+/-4 vs. 45+/-2 mm Hg change), and impaired response to sodium nitroprusside (by a -35+/-2 vs. -63+/-2 mm Hg change), P<0.05. The GSH:GSSG ratio was reduced at 8 and 24 h in blood (4.1+/-0.6 and 5.1+/-0.3, respectively, vs. 8.5+/-0.2), and at 8 h in the aorta (1.0+/-0.2 vs. 2.9+/-0.5), heart (1.6+/-0.3 vs. 2.3+/-0.1) and kidney (2.1+/-0.2 vs. 3.7+/-0.4), P<0.05. Superoxide fluorescence was increased at 24 h via NADH (4131+/-194 vs. 2853+/-199), NADPH (2874+/-272 vs.1479+/-257) and succinate (2475+/-133 vs. 1594+/-2150), P<0.05. Plasma prostacyclin was reduced at 8 and 24 h (36+/-4 and 52+/-13, respectively, vs. 310+/-44 pg/ml), P<0.001, whereas nitric oxide was reduced at 24 h (6.4+/-1 vs. 22+/-2 microM), P<0.01. Also at 24 h, thromboxane A(2) was increased both in plasma (374+/-154 vs. 61+/-10 pg/ml) and the aorta (174.4+/-38 vs. 27+/-3.4 pg/mg), P<0.05. Thus, acute BSO-induced oxidative stress alters blood pressure and endothelial function by mechanisms involving increased plasma levels and aortic release of thromboxane A(2) and reduced nitric oxide and prostacyclin.

1A-779 attenuates angiotensin-(1-7) depressor response in salt-induced hypertensive rats

Chronic infusion of angiotensin-(1-7) [Ang-(1-7)] lowers blood pressure in salt-induced and spontaneously hypertensive (SHR) rats. In the present study, we have examined the acute effect of Ang-(1-7) in salt-induced hypertension using Dahl salt-sensitive rats placed on low (0.3%) or high (8.0% NaCl) salt diets for 2 weeks. Rats fed a high salt diet showed a greater rise in BP than those fed a low salt diet. Ang-(1-7) (24 microg/kg) reduced mean arterial pressure (MAP), enhanced the release of prostacyclin and nitric oxide, and suppressed thromboxane A(2) levels. A-779 (48 microg/kg, i.v), a selective Ang-(1-7) antagonist, partially blocked these effects of Ang-(1-7). The Ang-(1-7)-induced depressor response observed in these animals was related to an increase in vasodilatory prostanoids, a decrease in the constrictor prostanoid thromboxane A(2), and an increase in nitric oxide levels in both plasma and isolated aortic rings.

Alterations in prostaglandin production in spontaneously hypertensive rat smooth muscle cells

We have characterized angiotensin binding sites in cultured smooth muscle cells obtained from the aorta of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. In both strains of rats the binding of 125I-angiotensin II (125I-Ang II) in smooth muscle cells was time dependent and reached a maximum at 60 minutes. Scatchard analysis revealed a single binding site in both strains with equilibrium constants (KD) of 5.35 nmol/L in SHR and 3.47 nmol/L in WKY rats. Binding capacities (Bmax) in smooth muscle cells averaged 270 and 150 fmol/mg protein in SHR and WKY rats, respectively. Angiotensin peptides competed for 125I-Ang II binding with an order of potency of Ang II > angiotensin-(1-7) = angiotensin I. In smooth muscle cells of the SHR, basal prostaglandin E2 (PGE2) and prostacyclin (prostaglandin I2 [PGI2]) release were threefold and 15-fold lower than that found in WKY rat smooth muscle cells. Ang II as well as angiotensin-(1-7) stimulated PGE2 and PGI2 release in WKY rat smooth muscle cells. In smooth muscle cells from SHR, Ang II increased the production of both PGE2 and PGI2, whereas angiotensin-(1-7) enhanced only PGE2 but not PGI2 release. There was no significant difference between Ang II-stimulated PGE2 and PGI2 release or angiotensin-(1-7)-stimulated PGE2 production in SHR and WKY rat smooth muscle cells. However, angiotensin-(1-7)-stimulated PGI2 release was significantly lower (p < 0.0005) in SHR compared with WKY smooth muscle cells. Collectively, the data suggest that smooth muscle cells of SHR contain a higher number of angiotensin binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)