PROSE: Prospective Randomized Trial of the On-X Mechanical Prosthesis and the St Jude Medical Mechanical Prosthesis Evaluation: Part 2: Study results-prostheses, positions, and economic development

Objectives

The Prospective Randomized On-X Mechanical Prosthesis Versus St Jude Medical Mechanical Prosthesis Evaluation (PROSE) trial purpose was to investigate whether a current-generation mechanical prosthesis (On-X; On-X Life Technologies/Artivion Inc) reduced the incidence of thromboembolic-related complications compared with a previous-generation mechanical prosthesis (St Jude Medical Mechanical Prosthesis; Abbott/St Jude Medical). This second report documents the valve-related complications by individual prostheses and by Western and Developing populations.

Methods

The PROSE trial study was conducted in 28 worldwide centers and incorporated 855 subjects randomized between 2003 and 2016. The study enrollment was discontinued on August 31, 2016. The study protocol, and analyses of 10 demographic variables and 24 risk factors were published in detail in 2021.

Results

The total patient population (N = 855) included patients receiving an On-X valve (n = 462) and a St Jude Medical valve (n = 393). The overall freedom evaluation showed no differences at 5 years between the prostheses for thromboembolism or for valve thrombosis. There were also no differences in mortality. There were several differences between Developing and Western populations. The freedom relations at 5 years for mortality favored Western over Developing populations. Valve thrombosis was differentiated by position and site: aortic < mitral (P = .007) and Western < Developing (P = .005). In the mitral position there were no cases in Western populations, whereas there were 8 in Developing populations (P = .217).

Conclusions

The On-X valve and St Jude Medical valve performed equally well in the study with no differences found. The only differentiation occurred with valve thrombosis in the mitral position more than the aortic position and occurring in Developing more than Western populations. The occurrence of valve thrombosis was also related to a younger population possibly due to anticoagulation compliance based on record review.

PROSE: Prospective Randomized Trial of the On-X Mechanical Prosthesis and the St Jude Medical Mechanical Prosthesis Evaluation : Part 1(Patient Dynamics): Preoperative demographics and preoperative and operative risk factors

OBJECTIVES

The PROSE trial purpose is to investigate whether the incidence of thromboembolic-related complications is reduced with a current generation mechanical prosthesis (On-X Life Technologies/CryoLife Inc.-On-X) compared with a previous generation mechanical prosthesis (St Jude Medical-SJM). The primary purpose of the initial report is to document the preoperative demographics, and the preoperative and operative risk factors by individual prosthesis and by Western and Developing populations.

METHODS

The PROSE study was conducted in 28 worldwide centres and incorporated 855 subjects randomized between 2003 and 2016. The study enrollment was discontinued on August 31, 2016. The preoperative demographics incorporated age, gender, functional class, etiology, prosthetic degeneration, primary rhythm, primary valve lesion, weight, height, BSA and BMI. The preoperative and operative evaluation incorporated 24 risk factors.

RESULTS

The total patient population (855) incorporated On-X population (462) and the St Jude Medical population (393). There was no significant difference of any of the preoperative demographics between the On-X and SJM groups. The preoperative and operative risk factors evaluation showed there was no significant difference between the On-X and St Jude Medical populations. The preoperative and operative risk factors by valve position (aortic and mitral) also documented no differentiation. The dominant preoperative demographics of the Western world population were older age, male gender, sinus rhythm, aortic stenosis, congenital aortic lesion, and mitral regurgitation. The dominant demographics of the Developing world population were rheumatic etiology, atrial fibrillation, aortic regurgitation, mixed aortic lesions, mitral stenosis and mixed mitral lesions. The Developing world group had only one significant risk factor, congestive heart failure. The majority of the preoperative and operative risk factors were significant in the Western world population.

CONCLUSIONS

The preoperative demographics do not differentiate the prostheses but do differentiate the Western and Developing world populations. The preoperative and operative risk factors do not differentiate the prostheses BUT do differentiate the Western and Developing world populations.

Hypoxia inducible factor-1 improves the negative functional effects of natriuretic peptide and nitric oxide signaling in hypertrophic cardiac myocytes

AIMS

Both natriuretic peptides and nitric oxide may be protective in cardiac hypertrophy, although their functional effects are diminished in hypertrophy. Hypoxia inducible factor-1 (HIF-1) may also protect in cardiac hypertrophy. We hypothesized that upregulation of HIF-1 would protect the functional effects of cyclic GMP (cGMP) signaling in hypertrophied ventricular myocytes.

MAIN METHODS

A cardiac hypertrophy model was created in mice by transverse aorta constriction. HIF-1 was increased by deferoxamine (150 mg/kg for 2 days). HIF-1alpha protein levels were examined. Functional parameters were measured (edge detector) on freshly isolated myocytes at baseline and after BNP (brain natriuretic peptide, 10(-8)-10(-7)M) or CNP (C-type natriuretic peptide, 10(-8)-10(-7)M) or SNAP (S-nitroso-N-acetyl-penicillamine, a nitric oxide donor, 10(-6)-10(-5)M) followed by KT5823 (a cyclic GMP-dependent protein kinase (PKG) inhibitor, 10(-6)M). We also determined PKG expression levels and kinase activity.

KEY FINDINGS

We found that under control conditions, BNP (-24%), CNP (-22%) and SNAP (-23%) reduced myocyte shortening, while KT5823 partially restored function. Deferoxamine treated control myocytes responded similarly. Baseline function was reduced in the myocytes from hypertrophied heart. BNP, CNP, SNAP and KT5823 also had no significant effects on function in these myocytes. Deferoxamine restored the negative functional effects of BNP (-22%), CNP (-18%) and SNAP (-19%) in hypertrophic cardiac myocytes and KT5823 partially reversed this effect. Additionally, deferoxamine maintained PKG expression levels and activity in hypertrophied heart.

SIGNIFICANCE

Our results indicated that the HIF-1 protected the functional effects of cGMP signaling in cardiac hypertrophy through preservation of PKG.

SERCA inhibition limits the functional effects of cyclic GMP in both control and hypertrophic cardiac myocytes

The negative functional effects of cyclic GMP are controlled by the sarcoplasmic reticulum calcium-ATPase (SERCA). The effects of cyclic GMP are blunted in cardiac hypertrophy. We tested the hypothesis that the interaction between cyclic GMP and SERCA would be reduced in hypertrophic cardiac myocytes. Myocytes were isolated from 7 control and 7 renal-hypertensive hypertrophic rabbits. Control and hypertrophic myocytes received 8-bromo-cGMP (8-Br-cGMP; 10(-7), 10(-6), 10(-5) mol/l), the SERCA blocker thapsigargin (10(-8) mol/l) followed by 8-Br-cGMP, or the SERCA blocker, cyclopiazonic acid (CPA; 10(-7) mol/l) followed by 8-Br-cGMP. Percent shortening and maximal rate of shortening and relaxation were recorded using a video edge detector. Changes in cytosolic Ca2+ were assessed in fura 2-loaded myocytes. In controls, 8-Br-cGMP caused a significant 36% decrease in percent shortening from 5.8 +/- 0.4 to 3.7 +/- 0.3%. Thapsigargin and CPA did not affect basal control or hypertrophic myocyte function. When 8-Br-cGMP was given following thapsigargin or CPA, the negative effects of 8-Br-cGMP on control myocyte function were reduced. In hypertrophic myocytes, 8-Br-cGMP caused a smaller but significant 17% decrease in percent shortening from 4.7 +/- 0.2 to 3.9 +/- 0.1%. When 8-Br-cGMP was given following thapsigargin or CPA, no significant changes occurred in hypertrophic cell function. Intracellular Ca2+ transients responded in a similar manner to changes in cell function in control and hypertrophic myocytes. These results show that the effects of cyclic GMP were reduced in hypertrophic myocytes, but this was not related to SERCA. In presence of SERCA inhibitors, the responses to cyclic GMP were blunted in hypertrophic as well as control myocytes.

Hypoxia inducible factor-1 improves the actions of positive inotropic agents in stunned cardiac myocytes

1. In the present study, we tested hypothesis that upregulation of hypoxia-inducible factor-1 (HIF-1) would improve the actions of positive inotropic agents in cardiac myocytes after simulated ischaemia-reperfusion (I/R). 2. Hypoxia-inducible factor-1α was upregulated with deferoxamine (150 mg/kg per day for 2 days). Rabbit cardiac myocytes were subjected to simulated ischaemia (15 min, 95% N(2)-5% CO2) and reperfusion (re-oxygenation) and compared with control myocytes. Cell contraction and calcium transients were measured at baseline and after forskolin (10(-7) and 10(-6) mol/L) or ouabain (10(-5) and 10(-4) mol/L). 3. Under control conditions, high-dose forskolin and ouabain increased percentage shortening by 20 and 18%, respectively. Deferoxamine-treated control myocytes responded similarly. In stunned myocytes, forskolin and ouabain did not significantly increase shortening (increases of 8% and 9%, respectively). Deferoxamine restored the effects of forskolin (+26%) and ouabain (+28%) in stunning. The results for maximum shortening and relaxation rates were similar. The increased calcium transients caused by forskolin and ouabain were also depressed in stunned myocytes, but were maintained by HIF-1 upregulation. 4. These results suggest that simulated I/R impaired the functional and calcium transient effects of positive inotropic agents. Upregulation of HIF-1 protects cardiac myocyte function after I/R by maintaining calcium release.

Role of phospholamban in cyclic GMP mediated signaling in cardiac myocytes

We tested the hypothesis that the negative functional effects of cyclic GMP on cardiac myocytes were mediated through phospholamban (PLB) and activation of sarcoplasmic reticulum Ca(2+)-ATPase. Using ventricular myocytes from wild type (WT, n=10) and PLB knockout (PLB-KO, n=10) mouse hearts, functional changes were measured using a video edge detector at baseline and after 10(-6), 10(-5)M 8-bromo-cyclic GMP (cGMP), 10(-8), 10(-7)M C-type natriuretic peptide (CNP), or 10(-6), 10(-5)M S-nitroso-N-acetyl-penicillamine (SNAP, nitric oxide donor). Changes in cytosolic Ca(2+) concentration were assessed in fura 2-loaded WT and PLB-KO myocytes. Cyclic GMP dependent phosphorylation analysis was also performed in WT and PLB-KO myocytes. 8-bromo-cGMP 10(-5)M caused a significant decrease in %shortening (3.6+/-0.2% to 2.3+/-0.1%) in WT, but little change in PLB-KO myocytes (3.4+/-0.1% to 3.2+/-0.2%). Similarly, CNP and SNAP reduced %shortening of WT, but not PLB-KO myocyte. Changes in other contractile parameters such as maximum rate of shortening and relaxation were consistent with the changes in % shortening. Intracellular Ca(2+) transients changed similarly to cell contractility in WT and PLB-KO myocytes treated with cGMP and CNP; i.e. Ca(2+) transients decreased with cGMP or CNP in WT myocytes, but were unchanged in PLB-KO myocytes. cGMP dependent phosphorylation analysis showed that some proteins were phosphorylated by cGMP to a lesser extent in PLB-KO compared with WT myocytes, suggesting impaired cGMP-kinase function in PLB-KO cardiac myocytes. These results indicated that cGMP-induced reductions in cardiac myocyte function were at least partially mediated through the action of phospholamban.

Chronic nitrates blunt the effects of not only nitric oxide but also natriuretic peptides in cardiac myocytes

Exposure to nitrates causes tachyphylaxis to nitric oxide (NO), which reduces the effects of the second messenger cyclic guanosine-3',-5'-monophosphate (cyclic GMP). We tested the hypothesis that prolonged exposure to NO would also blunt the effects of natriuretic peptides. Cardiac myocytes were isolated from control (N=7) and chronic nitroglycerin (patched, N=7) rabbits. Patched animals received a transdermal nitroglycerin patch (0.3mg/h for 5 days). Myocyte function was determined at baseline, after C-type natriuretic peptide (CNP, 10(-8) and 10(-7)M) or brain natriuretic peptide (BNP, 10(-8) and 10(-7)M) or S-nitroso-N-acetyl-penicilliamine (SNAP, a NO donor, 10(-6) and 10(-5)M) followed by KT5823 (a cyclic GMP protein kinase inhibitor, 10(-6)M). Soluble and particulate guanylyl cyclase activities were measured in vitro and phosphoprotein analysis was performed. In control animals, CNP 10(-8)M (5.14+/-0.5%) and 10(-7)M (4.4+/-0.7%) significantly reduced percentage shortening from baseline (6.1+/-1.6%). KT5823 restored percentage shortening to 4.9+/-0.8%. Similar data were obtained with BNP and SNAP. In patched animals, CNP, BNP, SNAP had no significant effects on percentage shortening. The data on maximal rate of shortening and relaxation were consistent with these results. Guanylyl cyclase activities were not different in the control and patched animals. The myocytes from control and patched animals had similar protein phosphorylation patterns. Our data suggested that in addition to NO, the responses to both natriuretic peptides were downregulated after chronic exposure to nitroglycerin, but these effects were not due to changes in either guanylyl cyclase or cyclic GMP protein kinase, suggesting an altered downstream pathway.

Brain natriuretic peptide reverses the effects of myocardial stunning in rabbit myocardium

We tested the hypothesis that brain natriuretic peptide (BNP) would decrease the effects of myocardial stunning in rabbit hearts. We also examined the mechanisms responsible for these effects. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by 2 15-min occlusions of the left anterior descending artery separated by 15 min of reperfusion. The treatment group had BNP (10(-3) mol/l) topically applied to the stunned area. Hemodynamic and functional parameters were measured. Coronary flow and O2 extraction were used to determine myocardial O2 consumption. In separate animals, we measured the function of isolated control and simulated ischemia (95% N2/5% CO2, 15 min)-reperfusion ventricular myocytes with BNP or C-type natriuretic peptide (10(-8)-10(-7) mol/l) followed by KT5823 (10(-6) mol/l, cyclic GMP protein kinase inhibitor). In the in vivo control group, baseline delay to contraction was 47+/-4 ms and after stunning it increased to 71+/-10 ms. In the treatment group, baseline delay to contraction was 40+/-7 ms, and after stunning and BNP it did not significantly increase (43+/-6 ms). Neither stunning nor BNP administration affected regional O2 consumption. In control myocytes, BNP (10(-7) mol/l) decreased the percent shortening from 6.7+/-0.4 to 4.5+/-0.2%; after KT5823 administration, the percent shortening increased to 5.4+/-0.5%. In ischemia-reperfusion myocytes, BNP (10(-7) mol/l) decreased the percent shortening less from 5.0+/-0.5 to 3.8+/-0.2%; KT5823 administration did not increase the percent shortening (3.8+/-0.2%). BNP similarly and significantly increased cyclic GMP levels in control and stunned myocytes. The data illustrated that BNP administration reversed the effects of stunning and its mechanism may be independent of the cyclic GMP protein kinase.

Negative functional effects of natriuretic peptides are attenuated in hypertrophic cardiac myocytes by reduced particulate guanylyl cyclase activity

We tested the hypothesis that the negative functional effects of natriuretic peptides would be blunted in thyroxine (T4)-induced hypertrophic cardiac myocytes. We also studied the causes of these changes. Ventricular myocytes were obtained from control (n=8) and T4 (0.5 mg/kg/16 days) treated rabbit hearts (n=7). Cell shortening parameters were studied with a video edge detector. We also determined particulate (pGC) and soluble (sGC) guanylyl cyclase activity and cyclic GMP levels. Myocyte function was examined at baseline and after brain natriuretic peptide (BNP 10(-7,-6) M) or C-type natriuretic peptide (CNP 10(-7,-6) M) or zaprinast (cyclic GMP phosphodiesterase inhibitor 10(-6)M) followed by BNP or CNP. Baseline function was similar in control and T4 myocytes. BNP (5.7 +/- 0.2 to 4.3 +/- 0.1%) and CNP (5.7 +/- 0.4 to 4.2 +/- 0.2%) significantly reduced percent shortening in control myocytes. These reductions were not observed with T4 (BNP, 5.7 +/- 0.6 to 5.6 +/- 0.6; CNP, 5.6 +/- 0.4 to 5.5 +/- 0.5). BNP and CNP responded similarly after zaprinast. Baseline cyclic GMP was similar in control and T4, but BNP only increased cyclic GMP in controls. The activity of pGC was similar at baseline in control and T4, but the stimulated activity was significantly lower in T4 myocytes. Both basal and stimulated sGC activity were similar in control and hypertrophic myocytes. These results demonstrated that the ability of natriuretic peptides to reduce ventricular myocyte function was blunted in T4 hypertrophic myocytes. This blunted response was related to the reduced ability of natriuretic peptides to increase cyclic GMP levels due to a reduced stimulated particulate guanylyl cyclase activity.

Negative inotropic effects of C-type natriuretic peptide are attenuated in hypertrophied ventricular myocytes associated with reduced cyclic GMP production

BACKGROUND

We tested the hypothesis that the negative inotropic effects of C-type natriuretic peptide (CNP) would be diminished in renal hypertensive (one-kidney-one-clip, 1K1C) hypertrophic rabbit hearts and that this attenuated effect would be due either to decreased cyclic GMP production or to reduced signaling.

MATERIAL AND METHODS

Using isolated control and 1K1C ventricular myocytes, cell shortening data (video edge detection) were collected: (1) at baseline and after CNP 10(-8,-7) M, followed by KT5823 (KT), a cyclic GMP-dependent protein kinase inhibitor; or (2) at baseline, following KT pre-treatment and subsequent CNP 10(-8,-7) M. In addition, cyclic GMP levels were determined by radioimmunoassay at baseline and CNP 10(-7) M.

RESULTS

In control myocytes, CNP decreased percent shortening (5.7 +/- 0.4 versus 4.0 +/- 0.4% at 10(-7) M), maximal rate of shortening (58.7 +/- 5.1 versus 45.2 +/- 3.6 microm/sec) and maximal rate of relaxation (57.1 +/- 4.9 versus 44.1 +/- 3.4 microm/sec) in a concentration-dependent manner. These effects were attenuated by subsequent KT administration. CNP failed to produce these negative functional effects in 1K1C myocytes. When pre-treated with KT, CNP had no negative functional effect in either normal and 1K1C myocytes. Basal levels of cyclic GMP were similar in control versus 1K1C myocytes; however, CNP produced a significant rise in cyclic GMP level in control (63.6 +/- 7.8 versus 83.5 +/- 11.3 pmol/10(5) myocytes) but not in 1K1C (49.2 +/- 2.6 versus 52.7 +/- 5.6) myocytes.

CONCLUSIONS

Thus, CNP acted through the cyclic GMP protein kinase in control myocytes. We conclude that in hypertrophic cardiac myocytes, the decreased effect of CNP was because of decreased production of cyclic GMP.

T4-induced cardiac hypertrophy disrupts cyclic GMP mediated responses to brain natriuretic peptide in rabbit myocardium

Brain natriuretic peptide (BNP) affects the regulation of myocardial metabolism through the production of cGMP and these effects may be altered by cardiac hypertrophy. We tested the hypothesis that BNP would cause decreased metabolism and function in the heart and cardiac myocytes by increasing cGMP and that these effects would be disrupted after thyroxine-induced cardiac hypertrophy (T4). Open-chest control and T4 rabbits were instrumented to determine local effects of epicardial BNP (10(-3) M). Function of isolated cardiac myocytes was examined with BNP (10(-8)-10(-7) M) with or without KT5823 (10(-6) M, cGMP protein kinase inhibitor). Cyclic GMP levels were measured in myocytes. In open-chest controls, O2 consumption was reduced in the BNP area of the subepicardium (6.6+/-1.3 ml O2/min/100 g versus 8.9+/-1.4 ml O2/min/100 g) and subendocardium (9.4+/-1.3 versus 11.3+/-0.99). In T4 animals, functional and metabolic rates were higher than controls, but there was no difference between BNP-treated and untreated areas. In isolated control myocytes, BNP (10(-7) M) reduced percent shortening (PSH) from 6.5+/-0.6 to 4.3+/-0.4%. With KT5823 there was no effect of BNP on PSH. In T4 myocytes, BNP had no effect on PSH. In control myocytes, BNP caused cGMP levels to rise from 279+/-8 to 584+/-14 fmol/10(5) cells. In T4 myocytes, baseline cGMP levels were lower (117+/-2 l) and were not significantly increased by BNP. Thus, BNP caused decreased metabolism and function while increasing cGMP in control. These effects were lost after T4 due to lack of cGMP production. These data indicated that the effects of BNP on heart function operated through a cGMP-dependent mechanism, and that this mechanism was disrupted in T4-induced cardiac hypertrophy.

Chronic nitric oxide synthase blockade desensitizes the heart to the negative metabolic effects of nitric oxide

The consequences of chronic nitric oxide synthase (NOS) blockade on the myocardial metabolic and guanylyl cyclase stimulatory effects of exogenous nitric oxide (NO) were determined. Thirty-three anesthetized open-chest rabbits were randomized into four groups: control, NO donor S-nitroso-N-acetyl-penicillamine (SNAP, 10(-4 )M), NOS blocking agent N(G)-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg/day) for 10 days followed by a 24 hour washout and L-NAME for 10 days followed by a 24 hour washout plus SNAP. Myocardial O(2) consumption was determined from coronary flow (microspheres) and O(2) extraction (microspectrophotometry). Cyclic GMP and guanylyl cyclase activity were determined by radioimmunoassay. There were no baseline metabolic, functional or hemodynamic differences between control and L-NAME treated rabbits. SNAP in controls caused a reduction in O(2) consumption (SNAP 5.9+/-0.6 vs. control 8.4+/-0.8 ml O(2)/min/100 g) and a rise in cyclic GMP (SNAP 18.3+/-3.8 vs. control 10.4+/-0.9 pmol/g). After chronic L-NAME treatment, SNAP caused no significant changes in O(2) consumption (SNAP 7.1+/-0.8 vs. control 6.4+/-0.7) or cyclic GMP (SNAP 14.2+/-1.8 vs. control 12.1+/-1.3). In controls, guanylyl cyclase activity was significantly stimulated by SNAP (216.7+/-20.0 SNAP vs. 34.4+/-2.5 pmol/mg/min base), while this increase was blunted after L-NAME (115.9+/-24.5 SNAP vs. 24.9+/-4.7 base). These results demonstrated that chronic NOS blockade followed by washout blunts the response to exogenous NO, with little effect on cyclic GMP or myocardial O(2) consumption. This was related to reduced guanylyl cyclase activity after chronic L-NAME. These results suggest that, unlike many receptor systems, the NO-cyclic GMP signal transduction system becomes downregulated upon chronic inhibition.

Heart failure reduces both the effects and interaction between cyclic GMP and cyclic AMP

BACKGROUND

We tested the hypothesis that the negative functional effects of cyclic GMP would be attenuated by cyclic AMP and this interaction would be reduced in pacing-induced failure of hypertrophic hearts.

MATERIALS AND METHODS

8-Bromo-cGMP (2 microg/kg/min) was infused into a coronary artery in eight control, eight ventricular hypertrophy (HYP), and eight hypertrophic failure (HYP-FAIL) dogs. Then isoproterenol (0.1 microg/kg/min) was infused, followed by 8 Br-cGMP. Regional myocardial work (force*shortening/min), and O(2) consumption (VO(2)) (coronary blood flow*O(2) extraction) were measured. Cyclic GMP levels were determined by radioimmunoassay.

RESULTS

8-Br-cGMP significantly decreased regional work from 3812 +/- 839 g*mm/min by 17% and VO(2) by 29% in control, but not in HYP (1073 +/- 182 by -10%, VO(2) by -16%) or HYP-FAIL (495 +/- 145 by -9%, VO(2) by 0%). Isoproterenol increased work by 43% and VO(2) by 48% in controls and in HYP (work by 54%, VO(2) by 39%), but not in HYP-FAIL (work by -28%, VO(2) by -5%). Subsequently, 8-Br-cGMP had no effect on work or VO(2) in control (-2%, -13%), HYP (-12%, -30%), or HYP-FAIL (+13%, +14%). Cyclic AMP levels were elevated by isoproterenol in control (381 +/- 115 versus 553 +/- 119 pmol/g) and HYP (313 +/- 55 versus 486 +/- 227), but not in HYP-FAIL (300 +/- 60 versus 284 +/- 126). After isoproterenol, 8-Br-cGMP further elevated cyclic AMP in control (687 +/- 122), but not in HYP or HYP-FAIL.

CONCLUSIONS

In controls, cyclic AMP attenuated cyclic GMPs negative functional and metabolic effects. The effects and the interaction were blunted in the HYP and HYP-FAIL groups.

Importance of ryanodine receptors in effects of cyclic GMP is reduced in thyroxine-induced cardiac hypertrophy

We tested the hypothesis that the negative functional effects of cyclic GMP were mediated by ryanodine receptors, and that these effects would be reduced in thyroxine (thyroxine, 0.5 mg/kg/day, 16 days)-induced hypertrophic myocytes. Using rabbit ventricular myocytes from control (n=9) and thyroxine (n=9) hearts, percent cell shortening (%) and maximum rate of contraction and relaxation were determined using a video edge detector at baseline and after 10(-6), 10(-5) M 8-bromo-cyclic GMP. Dantrolene 10(-6) M, ryanodine receptor inhibitor, was added alone or after 8-Br-cGMP treatment. Changes in cytosolic Ca(2+) concentration were assessed in fura-2-loaded control and thyroxine myocytes. 8-Br-cGMP caused a significant decrease in percent shortening, from 5.3+/-0.9% to 3.9+/-0.6% at 10(-5 )M in control, and 3.4+/-0.3% to 2.6+/-0.4% in thyroxine myocytes. Dantrolene significantly decreased percent shortening from 4.5+/-0.8% to 3.7+/-0.1% in control and from 3.7+/-0.1% to 2.8+/-0.3% in thyroxine myocytes. In 8-Br-cGMP treated control myocytes, dantrolene did not significantly change myocyte contractility, which suggested that cyclic GMP acted on ryanodine receptors. However, in 8-Br-cGMP treated thyroxine myocytes, dantrolene further reduced myocyte contractility implying that the interaction of cyclic GMP and ryanodine receptors appeared to be interrupted in thyroxine myocytes. Maximum rate of contraction data were consistent with the percent cell shortening data and Ca(2+) transients changed similarly to myocyte contractility. We conclude that effects of cyclic GMP on myocytes contractility were partially mediated though interaction with ryanodine receptors and the subsequent decrease in cytosolic calcium levels. This interaction was reduced in thyroxine hypertrophic myocytes.

Negative metabolic effects of cGMP are enhanced in obese rat hearts

Leptin resistance leads to obesity and may affect responses to the second messenger cGMP. We tested the hypothesis that the myocardial negative metabolic response to cGMP would be enhanced in leptin-resistant animals. This hypothesis was tested in anesthetized open-chest Zucker obese (n = 16) and age-matched control rats (n = 13). Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) measurements were used to determine myocardial O2 consumption (VO2). Protein phosphorylation by cGMP protein kinase and cAMP phosphodiesterase activity were also determined. Either vehicle (saline) or 8-Br-cGMP (10(-3) M) was topically applied to the left ventricular surface. Body weight was significantly greater in the obese rats (523 +/- 17 versus 322 +/- 12 g). There were no hemodynamic differences between groups. There was no difference in VO2 between lean (52 +/- 13 mL O2/min/100 g) and obese (54 +/- 9) vehicle-treated rats. 8-Br-cGMP significantly lowered VO2 in obese (35 +/- 6) but not lean (45 +/- 7) rats. This was not related to altered protein phosphorylation by the cGMP protein kinase. Cyclic GMP inhibited cAMP phosphodiesterase activity in lean but not obese hearts. Thus, the high myocardial oxygen consumption of lean rats was not significantly affected by cGMP but was reduced in obese hearts. This appeared to be related to a reduced inhibition of cAMP phosphodiesterase activity by cGMP in the Zucker obese rat.

Atrial natriuretic peptide reverses the negative functional effects of stunning in rabbit myocardium

We tested the hypothesis that atrial natriuretic peptide (ANP) would decrease both the effects of myocardial stunning and oxygen consumption in rabbit hearts. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by two 15 min occlusions of the left anterior descending (LAD) artery separated by 15 min of reperfusion. Either ANP (0.2 mg) or vehicle (lactated Ringers) was then injected into the affected area of the left ventricle. In a third group, ANP was injected into the LAD region of non-stunned rabbits. Hemodynamic (heart rate, aortic and left ventricular pressures) and functional (wall thickening (WT), delay of onset of WT, and rate of WT) parameters were measured. Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) were used to determine myocardial O2 consumption. Stunning was demonstrated by an increase in the time delay to contraction and depressed WT. In the control group, baseline delay to contraction was 25+/-7 ms, and this increased to 84+/-16 following stunning and vehicle administration. In the ANP group, baseline delay was 20+/-6 at baseline and after stunning and ANP administration it was 30+/-7. Wall thickening decreased by approximately 30% with stunning and vehicle but only 8% in the ANP treated hearts. Stunning did not affect regional O2 consumption (6.0+/-1.1 stunned vs. 7.4+/-1.2 mlO2/min/100g non-stunned). ANP administration did not affect O2 consumption (7.3+/-1.7 stunned vs. 6.4+/-1.0 non-stunned). We therefore concluded that ANP administration reversed the effects of stunning without alteration in local O2 consumption in stunned myocardium.

Functional interaction of a beta-adrenergic agonist and cyclic GMP phosphodiesterase inhibitor in control and hypertrophic cardiomyocytes

This study tested the hypothesis that the positive inotropic effect of beta-adrenoceptor stimulation would be inhibited by increases in cyclic GMP in control cardiomyocytes and that this response would be modified in hypertrophic cardiomyocytes. Cell functional data as well as GMP and cyclic AMP data were collected from 7 control and 7 1K1C (one-kidney-one-clip) renal hypertensive hypertrophic rabbits. Using isolated control and IKIC ventricular myocytes, data were obtained at baseline and after treatment with the beta-adrenoceptor agonist isoproterenol (10(-8, -6) mol/l) or the cyclic GMP-phosphodiesterase inhibitor zaprinast (10(-5) mol/l) followed by isoproterenol (10(-8, -6) mol/l). We found that in control rabbits, isoproterenol (10(-6) mol/l) increased percent shortening (4.8 +/- 0.2 to 6.4 +/- 0.3%) and cyclic AMP (2.3 +/- 0.3 to 5.0 +/- 0.7 pmol/10(5) cells). Zaprinast 10(-5) mol/l increased cyclic GMP (150 +/- 20 to 209 +/- 14 fmol/10(5) cells) and decreased percent shortening (6.2 +/- 0.4 to 5.2 +/- 0.3). Zaprinast 10(-5) mol/l prevented the functional response to isoproterenol in control (5.2 +/- 0.3 to 4.7 +/- 0.3), without changing cyclic AMP levels. In 1K1C rabbits, isoproterenol (10(-6) mol/l) increased cyclic AMP (4.9 +/- 0.8 to 7.6 +/- 1.4 pmol/10(5) cells) without changing function. Zaprinast 10(-5) mol/l increased cyclic GMP (182 +/- 23 to 233 +/- 24 fmol/10(5) cells) and decreased percent shortening (6.6 +/- 0.9 to 4.7 +/- 0.5), but did not alter the lack of effect of isoproterenol in 1K1C. In control cardiomyocytes, cyclic GMP blunted the isoproterenol contraction response without changing cyclic AMP levels, but isoproterenol's functional effect was not seen in 1K1C cardiomyocytes.

Alterations in ventricular myocyte contraction caused by C-type natriuretic peptide and nitric oxide in eNOS-/- mice

Lack of endothelial nitric oxide synthase (eNOS) may affect the sensitivity of cyclic GMP signaling through soluble guanylyl cyclase (sGC). We hypothesized that in eNOS knockout (eNOS-/-) mice, stimulation of guanylyl cyclase would have enhanced effects inhibiting cardiac contraction. We measured cell shortening and calcium transients in isolated ventricular myocytes from adult eNOS-/- and wild-type (WT) mice after stimulating particulate guanylyl cyclase (pGC) with C-type natriuretic peptide (CNP, 10(-8) and 10(-7) M) or sGC with S-nitroso-N-acetyl-penicillamine (SNAP, NO donor, 10(-6) and 10(-5) M). Although sGC activity was increased by +71% in eNOS-/-, SNAP had similar effects in the two groups (%shortening -39% control vs. -37% eNOS-/-), suggesting that the cyclic GMP pathway was desensitized in eNOS-/- myocytes. CNP had significantly smaller effects on cell contraction (%shortening -34% control vs. -14% eNOS-/-) and pGC activity was not changed in eNOS-/- myocytes. Similar effects were also produced by guanylin and carbon monoxide, stimulators of pGC and sGC. CNP's effects on Ca(2+) transients were also attenuated in eNOS-/- myocytes. SNAP did not alter Ca(2+) transients in eNOS-/- or control cells. In the eNOS-/- mice, cyclic GMP-dependent protein kinase and cyclic AMP phosphodiesterase activity were reduced. This study demonstrated that the downstream cyclic GMP pathway was attenuated in eNOS-/- mice and this was partially compensated for by increased sGC, but not pGC activity in ventricular myocytes.

Reduction in interaction between cGMP and cAMP in dog ventricular myocytes with hypertrophic failure

Baseline function and signal transduction are depressed in hearts with hypertrophic failure. We tested the hypothesis that the effects of cGMP and its interaction with cAMP would be reduced in cardiac myocytes from hypertrophic failing hearts. Ventricular myocytes were isolated from control dogs, dogs with aortic valve stenosis hypertrophy, and dogs with pacing hypertrophic failure. Myocyte function was measured using a video edge detector. Cell contraction data were obtained at baseline, with 8-bromo-cGMP (10(-7), 10(-6), and 10(-5) M), with erythro-9-(2-hydroxy-3-nonyl)adenine [EHNA; a cAMP phosphodiesterase (PDE(2)) inhibitor] plus 8-bromo-cGMP, or milrinone (a PDE(3) inhibitor) plus 8-bromo-cGMP. Baseline percent shortening and maximal rates of shortening (R(max)) and relaxation were slightly reduced in hypertrophic myocytes and were significantly lower in failing myocytes (R(max): control dogs, 95.3 +/- 17.3; hypertrophy dogs, 88.2 +/- 5.5; failure dogs, 53.2 +/- 6.4 mum/s). 8-Bromo-cGMP dose dependently reduced myocyte function in all groups. However, EHNA (10(-6) M) and milrinone (10(-6) M) significantly reduced the negative effects of cGMP on cell contractility in control and hypertrophy but not in failing myocytes (R(max) for control dogs: cGMP, -46%; +EHNA, -21%; +milrinone, -19%; for hypertrophy dogs: cGMP, -40%; +EHNA, -13%; +milrinone, -20%; for failure dogs: cGMP, -40%; +EHNA, -29%; +milrinone, -32%). Both combinations of EHNA-cGMP and milrinone-cGMP significantly increased intracellular cAMP in control, hypertrophic, and failing myocytes. These data indicated that the cGMP signaling pathway was preserved in hypertrophic failing cardiac myocytes. However, the interaction of cGMP with the cAMP signaling pathway was impaired in these failing myocytes.

Negative Inotropic Effect of Low-Dose Ethanol in Mouse Ventricular Myocytes is Mediated by Activation of Endothelial Nitric Oxide Synthase

Low doses of ethanol can produce negative functional effects in ventricular myocytes. This may be related to the nitric oxide-cyclic GMP signal transduction system. We tested the hypothesis that ethanol stimulated endothelial nitric oxide synthase and this caused the negative functional effects in cardiac myocytes. This hypothesis was tested in ventricular myocytes isolated from endothelial nitric oxide synthase-knockout (eNOS-/-) and wild-type (WT) control mice. Cell function was determined with a video edge detector at 37 degrees C. Myocytes were administered 5 or 10 mM ethanol alone or after 10(-6) M L-nitro-arginine-methyl ester (L-NAME, nitric oxide synthase inhibitor) or 10(-6) M 1H[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, soluble guanylyl cyclase inhibitor). There were no differences in basal perecentage shortening (2.6+/-0.2% WT versus 2.4+/-0.2% eNOS) or maximal rate of shortening (44+/-6 WT versus 47+/-6 microms eNOS) between groups. In the WT mice, 10 mM ethanol significantly decreased percentage shortening (1.8+/-0.1) and maximal rate of shortening (35+/-4). These effects were blocked by L-NAME and ODQ. In the eNOS-/- mice, these values were not affected by ethanol. Similar data were seen for both maximal rate of shortening and relaxation. These data provide both pharmacological and direct genetic proof that these low doses of ethanol act as a stimulator of endothelial nitric oxide synthase, and this leads to the negative functional effects in ventricular myocytes.

Peripheral Arterial Cannulation for Abiomed BVS 5000 Left Ventricular Assist Device Support

The Abiomed BVS 5000 is an external, pulsatile, ventricular assist device typically used for short-term mechanical support in post-cardiotomy patients experiencing cardiogenic shock when myocardial recovery is expected. We describe an as yet unreported approach where the left common femoral artery was utilized for Abiomed left ventricular assist device cannulation after reoperative mitral valve surgery.

Effects of natriuretic peptides on ventricular myocyte contraction and role of cyclic GMP signaling

Natriuretic peptides, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) act through different receptors and at different potencies to affect cardiac myocyte function. We tested the hypothesis that these three peptides would differentially reduce cardiomyocyte function through their effects on the cyclic GMP signaling pathway. Rabbit ventricular myocytes were isolated and stimulated by electrical field stimulation. Cell function was measured using a video edge detector. ANP BNP or CNP at 10(-9), 10(-8), 10(-7) M were added to the myocytes. Intracellular cyclic GMP was determined using a radioimmunoassay in the absence or presence of ANP, BNP or CNP. All natriuretic peptides decreased myocyte contractility in a similar concentration dependent manner. Myocyte percentage shortening was significantly decreased with all peptides at 10(-7) M compared with baseline (ANP from 5.4+/-0.4 to 3.9+/-0.2%; BNP from 5.0+/-0.2 to 3.5+/-0.1%; CNP from 5.6+/-0.3 to 4.0+/-0.3%). Maximum rate of shortening and relaxation were also decreased similarly and significantly. Intracellular cyclic GMP was significantly increased in myocytes treated with ANP, BNP or CNP (Baseline 1.0+/-0.2, ANP 2.1+/-0.2, BNP 2.3+/-0.3, CNP 2.0+/-0.2 pmol/10(5) myocytes). Furthermore, inhibition of the cyclic GMP protein kinase with KT5823 caused a reversal in the functional effects of CNP. We concluded that all natriuretic peptides had similar negative effects on ventricular myocyte function and their effects were accompanied by increased cyclic GMP. Blockade the effect of CNP by a cyclic GMP protein kinase inhibitor demonstrated that effects were mediated through the cyclic GMP signaling pathway.

Cyclic GMP signaling and regulation of SERCA activity during cardiac myocyte contraction

We tested the hypothesis that cGMP-induced reductions in cardiac myocyte function were related to activation of the sarcoplasmic reticulum Ca2+-ATPase (SERCA) and cGMP-dependent phosphorylation of phospholamban. Ventricular myocyte function was measured using a video edge detector (n = 11 rabbits). Thapsigargin (TG) or cyclopiazonic acid (CPA) were used to inhibit SERCA. 8-Bromo-cGMP was added at 10(-6), 10(-5) M followed by TG 10(-8) M or KT5823 (cGMP-protein kinase inhibitor, 10(-6) M) prior to TG or CPA. Cyclic GMP-dependent protein phosphorylation and immunoblotting with anti-phospholamban antibody were examined. TG 10(-8) M significantly increased percent shortening (from 6.6+/-0.7 to 9.1+/-1.3%). Cyclic GMP 10(-5) M significantly decreased cell shortening from 9.3+/-0.9 to 5.1+/-0.6%. This was partially reversed by KT5823 (5.1+/-0.6 to 8.2+/-1.4%) suggesting that negative functional effects of cGMP were partially through the cGMP-dependent protein kinase. Addition of TG after cGMP also reduced the negative effects of cGMP on myocyte shortening suggesting involvement of SERCA in cGMP signaling. TG after cGMP and KT5823 treatment did not alter myocyte contractility (8.2+/-1.4 to 7.2+/-1.3%). CPA had similar effects as those of TG. Protein phosphorylation and immunoblotting showed that phospholamban was a target of the cGMP protein kinase. These results indicated that the cyclic GMP-induced reductions in myocyte function were partially mediated through the action of SERCA. It further suggested that cGMP signaling affects myocyte function through phosphorylation of phospholamban which regulates SERCA activity.

Effects of cyclic GMP and its protein kinase on the contraction of ventricular myocytes from hearts after cardiopulmonary arrest

Hearts undergoing cardiopulmonary arrest and resuscitation have depressed function and may have changes in signal transduction. We hypothesized that the cyclic GMP (cGMP) signaling pathway would be altered in the post-resuscitation heart. This was studied in ventricular myocytes from 7 anesthetized open-chest rabbits. Cardiopulmonary arrest was achieved for 10 min through ventricular fibrillation and respirator shutdown. After cardiopulmonary arrest, respiration was resumed, the heart was defibrillated, and the heart recovered for 15 min. Seven additional rabbits served as controls. Myocyte function was measured via a video edge detector. Myocytes were treated with 8-bromo-cGMP (10(-5)-10(-6) mol/L) followed by KT5823 (10(-6) mol/L, cGMP protein kinase inhibitor). The baseline percent shortening was significantly depressed in the cardiac arrest myocytes compared with control (3.3 +/- 0.1 vs. 5.5 +/- 0.3%). Treatment with 8-Br-cGMP similarly and dose-dependently reduced cell contraction in both cardiac arrest (-24%) and control (-25%) myocytes. The negative effect of 8-Br-cGMP was partially reversed by KT5823 in control myocytes, but not in the arrest group, indicating reduced involvement of cGMP protein kinase. Multiple proteins were specifically phosphorylated when cGMP was present, but the degree of phosphorylation was significantly less in myocytes after cardiac arrest. The data suggested that the basal contraction was reduced, but the functional response to 8-Br-cGMP was preserved in myocytes from cardiopulmonary arrested hearts. The results also indicated that the action of cGMP appeared to be mainly through non-cGMP protein kinase pathways in the post-resuscitation heart.

Differential effects of cGMP produced by soluble and particulate guanylyl cyclase on mouse ventricular myocytes

Particulate guanylyl cyclase (pGC) and soluble guanylyl cyclase (sGC) are cGMP-generation systems distributed in different intracellular locations. Our aim was to test the hypothesis that the functional effects of cGMP produced by pGC and sGC on contraction and Ca2+ transients would differ in ventricular myocytes. We measured myocyte shortening from adult mice using a video edge-detector and investigated the functional changes after stimulating pGC with C-type natriuretic peptide (CNP; 10(-8) M and 10(-7) M) or sGC with S-nitroso-N-acetyl-penicillamine (SNAP; nitric oxide donor; 10(-6) M and 10(-5) M). Significant concentration-dependent decreases in percentage shortening (PCS), maximal rate of shortening (RSmax), and relaxation (RRmax) were produced by CNP. To a similar degree, SNAP concentration-dependently reduced PCS, RSmax, and RRmax. The addition of Rp-8-[(4-chlorophenyl)thio]-cGMPS triethylamine (cGMP-dependent protein kinase inhibitor; 5 x 10(-6) M) or erythro-9-(2-hydroxy-3-nonyl) adenine (cGMP-stimulated cAMP phosphodiesterase inhibitor; 10(-5) M) reduced the responses induced by CNP or SNAP, suggesting that their actions were through cGMP-mediated pathways. While SNAP significantly increased intracellular cGMP concentration by 57%, CNP had little effect on cGMP production. We also found that CNP markedly decreased the amplitude of Ca2+ transients while SNAP had little effect, suggesting the cGMP generated by sGC may decrease myofilament Ca2+ sensitivity. The small amount of cGMP generated by pGC had a major effect in reducing Ca2+ level. This study suggested the existence of compartmentalization for cGMP in ventricular myocytes.

Cyclic GMP reduces myocardial stunning through non-cyclic GMP protein kinase mechanisms

We tested the hypothesis that myocardial stunning would be reduced by increased cyclic GMP and cGMP protein kinase activity. Hearts were instrumented in eight open-chest anesthetized dogs. The left anterior descending coronary artery (LAD) was occluded for 15 minutes followed by a 30-minute recovery and infusion of 8-Bromo-cGMP (0.1 and 1 microg/kg/min) during functional and metabolic data collection. Myocytes from circumflex and LAD regions were then used to obtain data at baseline, with 8-Br-cGMP (10(-7, -6, -5) M) and KT5823 10(-6) M, cGMP protein kinase inhibitor. The in vivo time delay of regional shortening increased significantly from 55 +/- 12 to 99 +/- 3 msec following stunning, but was reduced to 81 +/- 2 by 1 microg/kg/min 8-Br-cGMP. The % regional work during systole decreased during stunning (93 +/- 2 to 76 +/- 8%), but was restored by 8-Br-cGMP (91 +/- 7). Stunning lengthened the time of myocyte contraction and relaxation and reduced baseline shortening. 8-Br-cGMP reduced myocyte shortening in both regions. However, KT5823 only restored myocyte shortening in controls. These data indicated that regional myocardial stunning could be reduced by cyclic GMP but this appeared to be through non-cGMP protein kinase mechanisms.

Cyclic GMP protein kinase activity is reduced in thyroxine-induced hypertrophic cardiac myocytes

1. We tested the hypothesis that the cGMP-dependent protein kinase has major negative functional effects in cardiac myocytes and that the importance of this pathway is reduced in thyroxine (T4; 0.5 mg/kg per day for 16 days) hypertrophic myocytes. 2. Using isolated ventricular myocytes from control (n = 7) and T4-treated (n = 9) rabbit hypertrophic hearts, myocyte shortening was studied with a video edge detector. Oxygen consumption was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically. 3. Data were collected following treatment with: (i) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT; 10-7 or 10-5 mol/L); (ii) 8-bromo-cAMP (10-5 mol/L) followed by PCPT; (iii) beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP; 10-7 or 10-5 mol/L); or (iv) 8-bromo-cAMP (10-5 mol/L) followed by SP. 4. There were no significant differences between groups in baseline percentage shortening (Pcs; 4.9 +/- 0.2 vs 5.6 +/- 0.4% for control and T4 groups, respectively) and maximal rate of shortening (Rs; 64.8 +/- 5.9 vs 79.9 +/- 7.1 micro m/ s for control and T4 groups, respectively). Both SP and PCPT decreased Pcs (-43 vs-21% for control and T4 groups, respectively) and Rs (-36 vs-22% for control and T4 groups, respectively), but the effect was significantly reduced in T4 myocytes. 8-Bromo-cAMP similarly increased Pcs (28 vs 23% for control and T4 groups, respectively) and Rs (20 vs 19% for control and T4 groups, respectively). After 8-bromo-cAMP, SP and PCPT decreased Pcs (-34%) and Rs (-29%) less in the control group. However, the effects of these drugs were not altered in T4 myocytes (Pcs -24%; Rs -22%). Both PCPT and cAMP phosphorylated the same five protein bands. In T4 myocytes, these five bands were enhanced less. 5. We conclude that, in control ventricular myocytes, the cGMP-dependent protein kinase exerted major negative functional effects but, in T4-induced hypertrophic myocytes, the importance of this pathway was reduced and the interaction between cAMP and the cGMP protein kinase was diminished.

Functional effects of C-type natriuretic peptide and nitric oxide are attenuated in hypertrophic myocytes from pressure-overloaded mouse hearts

Increases in the myocardial level of cGMP usually exert negative inotropic effects in the mammalian hearts. We tested the hypothesis that the negative functional effects caused by nitric oxide (NO) or C-type natriuretic peptide (CNP) through cGMP would be blunted in hypertrophied cardiac myocytes. Contractile function, guanylyl cyclase activity, cGMP-dependent protein phosphorylation, and calcium transients were assessed in ventricular myocytes from aortic stenosis-induced hypertrophic and age-matched control mice. Basal percentage shortening was similar in control and hypertrophic myocytes. S-nitroso-N-acetyl-penicillamine (SNAP, an NO donor, 10(-6) and 10(-5) M) or CNP (10(-8) and 10(-7) M) reduced percentage shortening in both groups, but their effects were blunted in hypertrophic myocytes. Maximal rates of shortening and relaxation were depressed at the basal level, and both reagents had attenuated effects in hypertrophy. Similar results were also found after treatment with guanylin and carbon monoxide, other stimulators of particulate, and soluble guanylyl cyclase, respectively. Guanylyl cyclase activity was not significantly changed in hypertrophy. Addition of Rp-8-[(4-chlorophenyl)thio]-cGMPS triethylamine (an inhibitor of cGMP-dependent protein kinase, 5 x 10(-6) M) blocked SNAP or the effect of CNP in control mice but not in hypertrophy, indicating the cGMP-dependent kinase (PKG) may not mediate the actions of cGMP induced by NO or CNP in the hypertrophic state. Calcium transients after SNAP or CNP were not significantly changed in hypertrophy. These results suggest that in hypertrophied mice, diminished effects of NO or CNP on ventricular myocyte contraction are not due to changes in guanylyl cyclase activity. The data also indicated that PKG-mediated pathways were diminished in hypertrophied myocardium, contributing to blunted effects.

Negative functional effects of cyclic GMP are altered by cyclic AMP phosphodiesterases in rabbit cardiac myocytes

In this study, we tested the hypothesis that the negative functional effects of cyclic GMP on cardiac myocytes would be affected by the actions of cyclic GMP on cyclic AMP phosphodiesterases. Ventricular myocytes from eight rabbits were used to determine the functional and cyclic AMP changes caused by 10(-7), 10(-6), 10(-5) M 8-Bromo-cGMP alone and after the administration of 10(-6) M milrinone (cyclic GMP-inhibited cyclic AMP phosphodiesterase inhibitor) or 10(-6) M erythro-9-(2-Hydroxy-3-3-nonyl)adenine (EHNA, cyclic GMP-stimulated cyclic AMP phosphodiesterase inhibitor). 8-Br-cGMP dose-dependently reduced %shortening by 35+/-4% of baseline at 10(-5) M. This effect was significantly blunted by EHNA at all doses. The maximum rate of shortening was reduced by 31+/-3% by 10(-5) M 8-Br-cGMP. This effect of 8-Br-cGMP was significantly enhanced (42+/-4%) in the milrinone group. A similar pattern was observed in the maximum rate of relaxation data. Cyclic AMP levels were significantly increased from a baseline level of 4.0+/-0.8 pmol/10(5) myocytes by milrinone (+60%), EHNA (+61%) and 8-Br-cGMP (+47%). The combination of EHNA plus 8-Br-cGMP increased cyclic AMP levels significantly more that the combination of milrinone plus 8-Br-cGMP. Exogenous cyclic GMP reduces myocyte function, while raising cyclic AMP possibly through cyclic GMP-inhibited cyclic AMP phosphodiesterase effects. Blocking cyclic GMP-inhibited cyclic AMP phosphodiesterase enhances the functional effects cyclic GMP, while blocking cyclic GMP-stimulated cyclic AMP phosphodiesterase reduced these effects. The study demonstrated a functional interaction between cyclic GMP and cyclic AMP related to the cyclic GMP affected cyclic AMP phosphodiesterases.

Negative metabolic and coronary flow effects of decreases in cAMP and increases in cGMP in control and renal hypertensive rabbit hearts

The interaction during stimulation of cGMP and inhibition of cAMP was investigated in control and renal hypertensive hearts. Control and hypertensive [1 kidney, 1 clip (1K1C)] rabbits were used. The anesthetized open-chest groups were vehicle, 8-bromo-cGMP (8-Br-cGMP; 10(-3)M), propranolol (Prop; 2 mg/kg), and Prop + 8-Br-cGMP. O(2) consumption levels (Vo(2)) in the subepicardium (Epi) and subendocardium (Endo) were determined from coronary flow (microspheres) and O(2) extraction (microspectrophotometry). Wall thickening and cAMP levels were also determined. In control, no significant change in Vo(2) was seen for the 8-Br-cGMP group, but Vo(2) was decreased from Epi (9.7 +/- 1.5 ml O(2) x min(-1) x 100 g(-1)) and Endo (10.5 +/- 0.4 ml O(2) x min(-1) x 100 g(-1)) to 6.8 +/- 0.6/7.8 +/- 0.5 ml O(2) x min(-1) x 100 g(-1) in the control Prop group. Control Prop + 8-Br-cGMP did not cause a further fall in Vo(2) but lowered Endo flow. In 1K1C, Vo(2) decreased from Epi/Endo (10.8 +/- 1.3/11 +/- 1.0 ml O(2).min(-1).100 g(-1)) to 7.8 +/- 1.1/8.7 +/- 0.5 ml O(2) x min(-1) x 100 g(-1) in the 1K1C 8-Br-cGMP group and to 7 +/- 0.5/8.1 +/- 0.5 ml O(2) x min(-1) x 100 g(-1) in the 1K1C Prop group. 1K1C Prop + 8-Br-cGMP did not cause a further fall in Vo(2) but lowered blood flow. No significant changes in cAMP levels were present with 8-Br-cGMP in control or 1K1C rabbits, but significant decreases were seen with Prop in both control and 1K1C rabbits. No further change was seen in Prop + 8-Br-cGMP for either control or 1K1C. Thus the negative metabolic effect of stimulating cGMP was seen only in the hypertensive rabbit heart. The negative metabolic effect of inhibiting cAMP was seen in both the control and the hypertensive rabbit heart. However, the negative metabolic effects of cGMP and cAMP were nonadditive.

Alterations in nitric oxide-cGMP pathway in ventricular myocytes from obese leptin-deficient mice

Leptin is a regulator of body weight and affects nitric oxide (NO) production. This study was designed to determine whether the myocardial NO-cGMP signal transduction system was altered in leptin-deficient obese mice. Contractile function, guanylyl cyclase activity, and cGMP-dependent protein phosphorylation were assessed in ventricular myocytes isolated from genetically obese (B6.V-Lepob) and age-matched lean (C57BL/6J) mice. There were no differences in baseline contraction between the lean and obese groups. After stimulation with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP, 10-6 and 10-5 M) or a membrane-permeable cGMP analog 8-bromo-cGMP (8-Br-cGMP, 10(-6) and 10(-5) M), cell contractility was depressed. However, 8-Br-cGMP had significantly greater effects in obese mice than in lean controls with percent shortening reduced by 47 vs. 39% and maximal rate of shortening decreased by 46 vs. 36%. The negative effects of SNAP were similar between the two groups. Soluble guanylyl cyclase activity was not attenuated. This suggests that the activity of the cGMP-independent NO pathway may be enhanced in obesity. The phosphorylated protein profile of cGMP-dependent protein kinase showed that four proteins were more intensively phosphorylated in obese mice, which suggests an explanation for the enhanced effect of cGMP. These results indicate that the NO-cGMP signaling pathway was significantly altered in ventricular myocytes from the leptin-deficient obese mouse model.

Negative effect of nitric oxide on shortening-frequency relationship in cardiac myocytes is diminished after simulated ischemia-reperfusion

Increasing stimulation rate increases function in cardiac myocytes and nitric oxide and cyclic GMP inhibit this effect. We tested the hypothesis that myocyte stunning would blunt both the effects of increases in rate and of nitric oxide and cyclic GMP. Ventricular myocytes from 11 rabbits were used to determine maximum rate of shortening (R(max), microm/s) and % shortening during control and after simulated ischemia [15 min 95% N(2)- 5% CO(2)] and reperfusion [reoxygenation]. Measurements were obtained at 1-4 Hz with vehicle, 1H[1,2,4]oxadiazolo[4,3,alpha] quinoxaline-1-one (ODQ) 10(-6) M, soluble guanylyl cyclase inhibitor, or N(G)-nitro-L-arginine methyl ester, nitric oxide synthase inhibitor (L-NAME) 10(-5) M. In control, increases in rate increased R(max) from 69 +/- 3 to 254+/-12 and % shortening from 5.3 +/- 0.3 to 8.7 +/- 0.5. Both ODQ and L-NAME shifted values higher. With stunning, the effects of pacing on Rmax and % shortening were blunted and ODQ and L-NAME failed to alter these values. Cyclic GMP was 322+/-37 pmol/10(5) myocytes at baseline and these values were lowered by ODQ (244 +/- 31) and LNAME (207 +/- 23), and similar changes were observed in stunned myocytes. Increasing frequency increased function, and reducing nitric oxide/cyclic GMP enhanced this relationship. The effect of nitric oxide was diminished by stunning, but this was not related to altered cyclic GMP levels. This suggested changes in effects of cyclic GMP downstream to its production during myocardial stunning.

Multiple isolated aneurysms in a case of "burned out" Takayasu aortitis

Takayasu aortitis (TA) is a chronic inflammatory disease predominantly seen in young Asian women. The disease is idiopathic and largely affects the aorta and its major branches. The basic pathologic changes in TA are fibrosis and subsequent occlusion of the large arteries. TA is classically termed "pulseless" disease, with manifestations during the occlusive stage including limb ischemia, renovascular hypertension, and heart failure. Arterial dilation and aneurysm are largely unappreciated manifestations of TA, but they occur in as many as 32% of affected patients. We report chronic "burned out" TA in a 23-year-old Hispanic woman with isolated aneurysms of the descending thoracic aorta, abdominal aorta, and common iliac arteries, without occlusive disease.

Increases in myocardial cyclic GMP attenuate contractile delay in myocardial stunning

We tested the hypothesis that the effects of myocardial stunning would be reduced by cyclic GMP in rabbit hearts. In three groups of anesthetized open-chest New Zealand white rabbits, myocardial stunning was produced by 15 min of occlusion of the left anterior descending coronary artery followed by 15 min of reperfusion repeated twice. Either control vehicle (saline plus 1% dimethyl sulfoxide) or 8-bromo-cyclic GMP (8-Br-cGMP (10(-4) and 10(-3) M)) was topically applied to the left ventricular surface. Hemodynamic (left ventricular and aortic pressures) and functional parameters (wall thickening, delay in onset of wall thickening, and rate of wall thickening) were determined. Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) were used to determine myocardial O2 consumption (VO2). Myocardial stunning was observed in the control group through an increased delay in onset of myocardial wall thickening (29 +/- 7 versus 55 +/- 16 ms) and decreased maximal rate of wall thickening (20 +/- 8 versus 11 +/- 3 mm x s(-1)). After treatment with 8-Br-cGMP 10(-4) and 10(-3) M, stunning did not increase the delay (37 +/- 5 versus 39 +/- 7 and 39 +/- 7 versus 28 +/- 8 ms). Myocardial stunning did not significantly alter VO2. 8-Br-cGMP 10(-3) M significantly decreased subepicardial VO2 (6.2 +/- 0.8 versus 3.7 +/- 0.6 mL O2 x min(-1) 100 g(-1)) and insignificantly decreased subendocardial VO2 (8.6 +/- 0.9 versus 6.3 +/- 1.2 mL O2 x min(-1) x 100 g(-1)) when compared with the vehicle-treated rabbits. We conclude that increasing cyclic GMP reduced the effects of myocardial stunning in the rabbit heart by ameliorating the delay in onset of wall thickening and decreasing the local O2 costs in the stunned region.

Ageing blunts the effects of nitric oxide on myocardial O2 consumption

1. In the present study, we tested the hypothesis that the negative myocardial metabolic effects of nitric oxide (NO) were reduced in old hearts. 2. Studies were conducted in 17 young (approximately 6 months) and 18 old (> 36 months) New Zealand anaesthetized open-chest rabbits. Either vehicle or s-nitroso-N-acetylpenicillamine (SNAP; 10-4 mol/L; a NO donor) was applied to the epicardial surface of the left ventricle. Coronary blood flow (microspheres) and artero-venous (a-v) O2 difference (microspectrophotometry) were used to determine subepicardial (EPI) and subendocardial (ENDO) O2 consumption. Wall thickening was determined ultrasonically. Cyclic GMP and guanylyl cyclase activity were also determined. Myocardial a-v O2 difference, flow, O2 consumption and wall thickening were comparable in young and old hearts. 3. The EPI and ENDO O2 consumption of SNAP-treated young hearts decreased significantly (> 25%) compared with vehicle (saline). However, SNAP had no significant effects on the O2 consumption of old hearts. In addition, SNAP decreased the percentage wall thickening in young (from 18.0 +/- 1.7 to 13.4 +/- 1.6%), but not old (from 14.5 +/- 0.9 to 11.4 +/- 1.6%), hearts. Basal cGMP levels in old hearts were greater (approximately 70%) than those in young hearts (15.7 +/- 2.0 vs 9.0 +/- 0.8 pmol/g, EPI). s-Nitroso-N-acetylpenicillamine increased cGMP in EPI (13.7 +/- 1.8 pmol/g) and ENDO of young, but not old (18.7 +/- 2.3 pmol/g, EPI), hearts. Similar results were also obtained using another NO donor, namely sodium nitroprusside (SNP; 10-4 mol/L). Guanylyl cyclase activity was elevated in old rabbit hearts with 0.5 mmol/L SNP (131 +/- 12 vs 80 +/- 12 pmol/min per mg protein for old and young rabbits, respectively). 4. Thus, while older hearts had similar O2 consumption and wall thickening compared with young hearts, they responded less well to NO and had significantly elevated basal levels of myocardial cGMP.

Diabetes mellitus increases short-term mortality and morbidity in patients undergoing coronary artery bypass graft surgery

OBJECTIVES

The aim of this study was to determine the impact of diabetes mellitus (DM) on short-term mortality and morbidity in patients undergoing coronary artery bypass surgery (CABG).

BACKGROUND

Diabetes mellitus is present in approximately 20% to 30% of patients undergoing CABG, and the impact of diabetes on short-term outcome is unclear.

METHODS

We performed a retrospective cohort study in 434 hospitals from North America. The study population included 146,786 patients undergoing CABG during 1997: 41,663 patients with DM and 105,123 without DM. The primary outcome was 30-day mortality. Secondary outcomes were in-hospital morbidity, infections and composite outcomes of mortality or morbidity and mortality or infection.

RESULTS

The 30-day mortality was 3.7% in patients with DM and 2.7% in those without DM; the unadjusted odds ratio was 1.40 (95% confidence interval [CI], 1.31 to 1.49). After adjusting for other baseline risk factors, the overall adjusted odds ratio for diabetics was 1.23 (95% CI, 1.15 to 1.32). Patients treated with oral hypoglycemic medications had adjusted odds ratio 1.13; 95% CI, 1.04 to 1.23, whereas those on insulin had an adjusted odds ratio 1.39; 95% CI, 1.27 to 1.52. Morbidity, infections and the composite outcomes occurred more commonly in diabetic patients and were associated with an adjusted risk about 35% higher in diabetics than nondiabetics, particularly among insulin-treated diabetics (adjusted risk between 1.5 to 1.61).

CONCLUSIONS

Diabetes mellitus is an important risk factor for mortality and morbidity among those undergoing CABG. Research is needed to determine if good control of glucose levels during the perioperative time period improves outcome.

Myocardial stunning reduces the effects of nitric oxide on coronary capillary perfusion in the rabbit

This investigation tested the hypothesis that the effects of nitric oxide synthase on myocardial capillary perfusion were reduced during myocardial stunning. Anaesthetized open-chest rabbits were assigned to either a control group or a group treated with a nitric oxide synthase inhibitor. To induce myocardial stunning, a coronary artery was occluded (for 15 min) and then reperfused (for 15 min) twice. During reperfusion, rabbits were given either saline or N(G)-nitro-L-arginine methyl ester (L-NAME, 30 mg kg(-1)) followed by i.v. injection of 150 mg kg(-1) fluorescein isothiocyanate (FITC)-labelled dextran (molecular weight, 150,000) for 14 s. Fluorescence microscopy was used to identify the perfused vessels and an alkaline phosphatase stain was used to locate the total microvasculature. The 'closest-individual' method was used to estimate the geometric distribution of capillaries. No significant differences were observed in the total volume fraction (mm(3) of capillaries per mm(3) of tissue) between the control and stunned regions in either the saline- (0.045 +/- 0.008 and 0.042 +/- 0.009, respectively) or the L-NAME-treated hearts (0.060 +/- 0.010 and 0.049 +/- 0.005, respectively). There were no significant differences in the percentage volume fraction of perfused capillaries between the control and the stunned regions (49 +/- 4 % and 54 +/- 4 %, respectively) in saline-treated hearts. In hearts treated with L-NAME, the percentage of perfused capillaries was significantly reduced. The reduction was significantly greater in the control region (approximately 27 %) than the stunned region (approximately 17 %). Closest-individual analysis of the perfused capillary distribution in both groups demonstrated a similar unchanged distribution. Thus, nitric oxide synthase is an important regulator of basal coronary capillary perfusion, and its effects are significantly reduced by myocardial stunning.

Cyclic GMP-induced reduction in cardiac myocyte function is partially mediated by activation of the sarcoplasmic reticulum Ca(2+)-ATPase

We tested the hypothesis that the mechanism through which cyclic GMP reduces cardiac function is mediated by activation of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA). Cardiac myocytes were isolated from New Zealand white rabbits (n = 11). Individual ventricular cells were stimulated by electrical field stimulation. The maximal rate of cell shortening and percentage shortening were measured with a video edge detector. Thapsigargin (10(-8) mol/l) was used as a specific inhibitor of SERCA. When 8-bromo-cyclic GMP (8-Br-cGMP, 10(-7, -6, -5) mol/l) was added to cells, the maximal rate of myocyte shortening (R(max), microm/s) and percentage shortening were both decreased in a concentration-dependent manner. R(max) decreased 27% from 117 +/- 12 at baseline to 85.2 +/- 13 when 10(-5) mol/l of 8-Br-cGMP was present, and percent shortening was reduced 28% from 6.0 +/- 0.5 to 4.3 +/- 0.5%. Thapsigargin (10(-8) mol/l) increased the maximal rate of myocyte shortening and percent shortening. Addition of thapsigargin prior to 8-Br-cGMP reduced the negative effects of cGMP on myocyte function. The percent shortening decreased only 11% and R(max) decreased 14% with 10(-5) mol/l 8-Br-cGMP, which was not significant. Cyclopiazonic acid, another SERCA inhibitor, was also used to test whether 8-Br-cGMP reduced myocyte function through SERCA. The results were similar to those when thapsigargin was used. These results indicated that the cyclic GMP-induced reduction in cardiac myocyte function was partially mediated through the action of the sarcoplasmic reticulum Ca(2+)-ATPase.

Nitric oxide and cGMP protein kinase activity in aged ventricular myocytes

We tested the hypothesis that nitric oxide-induced negative functional effects through cGMP would be reduced in aged cardiac myocytes. Maximum rate of shortening (R(max)) and percent shortening of ventricular myocytes from young (6 mo) and old (3 y) rabbits were studied using a video edge detector. cGMP-dependent phosphorylation was examined by electrophoresis and autoradiography. Myocytes received a nitric oxide donor S-nitroso-N-acetyl-penicillamine (SNAP, 10(-7), 10(-6), and 10(-5) M) followed by KT-5823 (10(-6) M), a cGMP protein kinase inhibitor. Baseline function was similar in young and old myocytes (89.1 +/- 4.5 young vs. 86.4 +/- 8.3 microm/s old R(max), 5.6 +/- 0.3 vs. 5.2 +/- 0.7%shortening). SNAP (10(-5) M) decreased R(max) in both young (25%, n = 6) and old myocytes (24%, n = 7). SNAP also reduced percent shortening by 28% in young and 23% in old myocytes. The negative effects of SNAP were partially reversed by KT-5823 only in young myocytes. Multiple proteins were phosphorylated by cGMP, and KT-5823 could reduce this effect. The degree of phosphorylation was significantly less in old myocytes. These results suggest that the functional response of ventricular myocytes to nitric oxide was preserved during aging. However, the importance of cGMP-dependent protein phosphorylation was decreased, indicating a shift to other pathways.

Ethanol-induced reduction in myocardial oxygen consumption can be attenuated by inhibiting guanylyl cyclase

We tested the hypothesis that low-dose ethanol-induced reductions in myocardial metabolism were related to increased cyclic guanosine monophosphate (GMP). Anesthetized open chest rabbits were divided into four groups: control (Ringers lactate and vehicle), ETOH (250 mg/kg i.v. ethanol and vehicle), ODQ (Ringers lactate and 1 H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ 10(-4) M ), and ETOH-ODQ (ethanol and ODQ). ODQ, a soluble guanylyl cyclase inhibitor, or vehicle was applied topically to the epicardium for 15 min, while either Ringers lactate or ethanol was administered intravenously. Oxygen consumption (VO2 ) in both the subepicardium (EPI) and subendocardium (ENDO) was determined from coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry). Cyclic GMP was determined by radioimmunoassay. ETOH significantly decreased VO2 in the subepicardium (9.2 +/- 1.0-5.6 +/- 0.7 ml O2 /min/100 g) and subendocardium (9.7 +/- 0.8-7.1 +/- 0.8) and increased cyclic GMP in the subepicardium (10.2 +/- 1.7-13.8 +/- 0.8 pmol/g) and subendocardium (11.0 +/- 0.5-13.7 +/- 0.9). With ODQ, there was no significant change in the subepicardial (9.5 +/- 1.3) or subendocardial (9.0 +/- 0.9) VO2. However, ODQ caused a significant increase in both wall thickening (12.9 +/- 0.9-17.2 +/- 1.2%) and maximal rate of change in wall thickness (10.8 +/- 0.9-16.3 +/- 1.9 mm/s) and decreased subepicardium (8.3 +/- 1.3) and subendocardium (7.8 +/- 1.2) cyclic GMP. The ETOH-ODQ group had cyclic GMP (subepicardium 9.0 +/- 1.8, subendocardium 8.6 +/- 2.4) and VO2 (subepicardium 7.9 +/- 0.5, subendocardium 8.4 +/- 0.4) values similar to control. Thus, the ethanol-induced rise in cyclic GMP was associated with a decrease in myocardial O2 consumption. When this rise was blocked with a soluble guanylyl cyclase inhibitor, the reduction in metabolic demand was also eliminated. This demonstrated that the alcohol-induced reduction in myocardial metabolism was related to increased cyclic GMP and suggests a novel mechanism for the effect of ethanol.

Interaction between cyclic GMP protein kinase and cyclic AMP may be diminished in stunned cardiac myocytes

We tested the hypothesis that the importance of the negative functional effects of the cyclic GMP protein kinase would be reduced in stunned (simulated ischemia/reperfusion) cardiac myocytes. Ventricular cardiac myocytes were isolated from New Zealand white rabbits (N=7). Myocytes were studied at baseline and after simulated ischemia (15 min of 95% N(2)-5% CO(2) at 37 degrees C) followed by simulated reperfusion (reoxygenation). Cell shortening was studied with a video edge detector; O(2) consumption was measured using O(2) electrodes. Protein phosphorylation was measured autoradiographically after gel electrophoresis. Functional and metabolic data were acquired after: (1) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by PCPT 10(-7) or 10(-5) M; (3) beta-phenyl-1, N(2)-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by SP 10(-7) or 10(-5) M. At baseline, percent of shortening (Pcs) and maximal rate of shortening (Rs) were significantly lower in the stunned myocytes (Pcs: 5.0+/-0.2% control vs. 3.8+/-0.3 stunned; Rs: 64.8+/-5.9 microm/s control vs. 46.9+/-4.8 stunned). In both groups, PCPT and SP dose-dependently decreased Pcs and Rs. The effects were slightly, but not significantly, less in stunned myocytes. 8-Br-cyclic AMP significantly increased function in control, but not stunned myocytes (Pcs, 4.5+/-0.5 to 6.2+/-0.8 control vs. 3.1+/-0.2 to 3.6+/-0.2 stunned). The negative functional effects of PCPT and SP were diminished after 8-Br-cyclic AMP in control (from -39% to-29%) and diminished significantly more in the stunned myocytes (-19%). PCPT and cyclic AMP phosphorylated similar protein bands. In stunned myocytes, three (22, 31 and 53 kDa) bands were enhanced less by PCPT.

Dose response to nitric oxide in adult cardiac surgery patients

STUDY OBJECTIVE

To determine the dose responsiveness to nitric oxide in adult cardiac surgery patients, especially in those patients with pulmonary hypertension.

DESIGN

Prospective, randomized, nonblinded study.

SETTING

University teaching hospital.

PATIENTS

62 consecutive cardiac surgery patients demonstrating pulmonary hypertension immediately before induction of anesthesia.

INTERVENTIONS

Subjects were assigned by random number allocation to receive one of five doses of inhaled nitric oxide on termination of cardiopulmonary bypass (CBP; i.e., restitution of pulmonary artery flow). Subjects in Group 1 (n = 11) received 10 ppm of inhaled nitric oxide, Group 2 subjects (n = 12) received 20 ppm, Group 3 subjects (n = 12) received 30 ppm, and Group 4 subjects (n = 12) received 40 ppm. The fifth group (n = 15) received no nitric oxide. This fifth group served as a control and was treated with milrinone only. Those patients who were randomized to the milrinone group, had milrinone initiated by bolus administration (50 microg/kg) 15 min before separation from CPB. Milrinone was maintained at 0.5 microg/kg/min in the operating room thereafter. The conduct of anesthesia, surgery, and CBP were controlled. A therapeutic algorithm dictated the use of vasoactive substances for all patients.

MEASUREMENTS

Heart rate, mean arterial pressure, pulmonary vascular resistance (PVR), peripheral vascular resistance, cardiac index, and right ventricular ejection fraction were monitored throughout the operative experience.

MAIN RESULTS

There were no significant differences found in demographic data, baseline hemodynamic data, surgical treatment, conduct of CBP, or the use of inotropic or vasoactive drugs among the five treatment groups. The percentage decrease in PVR on treatment with nitric oxide as compared to baseline values was not significantly different among the groups (10 ppm = 38%, 20 ppm = 50%, 30 ppm = 44%, 40 ppm = 36%, milrinone = 58%, p = 0.86).

CONCLUSIONS

Treatment with nitric oxide was associated with significant reductions in PVR in all groups. Dosages higher than 10 ppm were not associated with greater reductions in pulmonary vascular tone. In view of the fact that nitric oxide-related toxicity is dose-related, doses greater than 10 ppm do not appear to be justified in this patient population.

Interaction between the opposing functional effects of cyclic AMP and cyclic GMP in hypertrophic cardiac myocytes

We tested the hypothesis that in isolated cardiac myocytes, the negative functional effects of cyclic GMP would be blunted when the level of cyclic AMP was increased and that this interaction would be altered in renal hypertensive (One-Kidney-One-Clip, 1K1C) cardiac hypertrophic rabbits. Using isolated control and 1K1C ventricular myocytes, cyclic AMP and cell shortening (%) data were collected: 1) at baseline, 2) after the addition of 8-Br-cGMP 10(-7), -6, -5 M, and 3) after forskolin (10(-6) M), an adenylate cyclase activator, followed by 8-Br-cGMP 10(-7), -6, -5 M. Basal levels of cyclic AMP were similar in control vs. 1K1C myocytes (10.2 +/- 1.6 vs. 11.3 +/- 2.6 pmol/10(5) myocytes). We found that 8-Br-cGMP decreased the percent shortening in a dose related manner in both control myocytes (5.1 +/- 0.6 to 3.2 +/- 0.4%) and hypertrophic myocytes (5.2 +/- 0.4 to 3.6 +/- 0.5). The level of cyclic AMP significantly increased after the addition of 8-Br-cGMP in control myocytes (14.1 +/- 2.1), but not in 1K1C myocytes. Forskolin increased the percent shortening in the control myocytes (3.8 +/- 0.1 to 4.8 +/- 0.4), but no significant increase was noted in the hypertrophic myocytes (3.6 +/- 0.3 to 3.7 +/- 0.3). The level of cyclic AMP significantly increased after the addition of forskolin in both control (13.9 +/- 2.0), and 1K1C cells (14.6 +/- 3.8). Forskolin attenuated the negative functional effects of 8-Br-cGMP in the control (4.8 +/- 0.4 to 3.2 +/- 0.1) and 1K1C myocytes (3.7 +/- 0.3 to 2.7 +/- 0.3). The addition of 8-Br-cGMP did not affect the level of cyclic AMP after forskolin in either control (13.9 +/- 2.0 to 14.8 +/- 2.5) or 1K1C myocytes (14.6 +/- 3.8 to 13.8 +/- 1.9). These data indicated that in hypertrophic cardiac myocytes the negative functional effects of 8-Br-cGMP were similar to control, but the positive functional effects of cyclic AMP were blunted. There was an increase in cyclic AMP levels after addition of 8-Br-cGMP in control but not 1K1C cells. We conclude that in control and hypertrophic myocytes, the effects of cyclic GMP were blunted after forskolin, but this did not seem to be related to cyclic AMP phosphodiesterase activity.