Haralambos Gavras

Independence and reproducibility across microarray platforms

Microarrays have been widely used for the analysis of gene expression, but the issue of reproducibility across platforms has yet to be fully resolved. To address this apparent problem, we compared gene expression between two microarray platforms: the short oligonucleotide Affymetrix Mouse Genome 430 2.0 GeneChip and a spotted cDNA array using a mouse model of angiontensin II–induced hypertension. RNA extracted from treated mice was analyzed using Affymetrix and cDNA platforms and then by quantitative RT-PCR (qRT-PCR) for validation of specific genes. For the 11,710 genes present on both arrays, we assessed the relative impact of experimental treatment and platform on measured expression and found that biological treatment had a far greater impact on measured expression than did platform for more than 90% of genes, a result validated by qRT-PCR. In the small number of cases in which platforms yielded discrepant results, qRT-PCR generally did not confirm either set of data, suggesting that sequence-specific effects may make expression predictions difficult to make using any technique.

Angiotensin converting enzyme inhibition in patients with congestive heart failure.

SUMMARY The etiology of afterload elevation in congestive cardiac failure is unclear, but experimental evidence suggests a role for the renin-angiotensin system in maintaining elevated peripheral vascular resistance. The angiotensin converting enzyme inhibitor SQ20,881 was administered to eight patients with congestive cardiac failure (four hypertensives, four normotensives) during or one day after diagnostic cardiac catheterization. Various hemodynamic measurements performed before and during blockade indicate that this agent caused improvement in cardiac function in all patients by decreasing afterload. This improvement correlated with the decrease in total vascular resistance but was independent of the baseline blood pressure and plasma renin activity. These results suggest that inhibition of angiotensin converting enzyme is a worthwhile approach to the treatment of congestive heart failure, although its exact mechanism of action remains unclear.

Acute regional circulatory and renal hemodynamic effects of converting-enzyme inhibition in patients with congestive heart failure.

The acute effects of the angiotensin converting-enzyme inhibitor captopril on regional blood flow, renal hemodynamics and sodium excretion were studied in 12 patients with severe congestive heart failure. Converting-enzyme inhibition decreased systemic vascular resistance by 27% and increased cardiac index by 16%. Estimated hepatic blood flow decreased 17%, but renal blood flow increased 60%. The ratio of renal-systemic blood flow increased from 0.10 ± 0.01 to 0.14 ± 0.02 (p = 0.031). Although renal plasma flow increased from 202.8 ± 28.8 to 323.7 ± 42.7 mI/min (p = 0.008), the glomerular filtration rate did not change significantly from the mean pretreatment value of 82.1 ± 12.3 mI/min. The filtration fraction decreased from 41.3 ± 3.8% to 33.4 ± 4.5% (p = 0.050), while urinary sodium excretion doubled, from 34.5 ± 9.6 to 68.2 ± 19.6 uEq/min. The plasma renin activity increased from 12.6 ± 5.0 to 29.9 ± 8.4 ng/ml/hr (p = 0.030) as plasma aldosterone concentration decreased from 30.5 ± 6.5 to 11.3 ± 1.2 ng/dl (p = 0.010) and norepinephrine concentrations decreased from 774 ± 105 to 618 ± 85 pg/nl (p = 0.020). We conclude that converting-enzyme inhibition reverses renal vasoconstriction in congestive heart failure and redistributes regional blood flow. The natriuresis may be mediated by one or more of the following: improved renal plasma flow, reduction in filtration fraction, suppression of hyperaldosteronism, and lowering of circulatory catecholamine concentrations.

Angiotensin inhibition in severe heart failure: Acute central and limb hemodynamic effects of captopril with observations on sustained oral therapy

The systemic, pulmonary, and limb circulatory responses to the angiotensin-converting enzyme inhibitor, captopril, were determined in 10 patients with severe, chronic heart failure. Immediate effects include sustained reductions in arterial pressure and pulmonary capillary wedge pressure and improvement in cardiac output, as reported with other vasodilator drugs. Calf vascular resistance did not change despite substantial lowering of total systemic vascular resistance, indicating that arteriolar dilatation occurred on a selective basis. Transient reduction in mean right atrial pressure paralleled slight calf venodilatation, but effects upon the resistance vasculature predominated. Plasma renin activity and norepinephrine concentrations increased after therapy in the acute phase as plasma aldosterone levels consistently fell. During maintenance oral treatment over 7 to 15 months (median, 11.5 months), patients displayed symptomatic benefit, improved functional capacity, and greater exercise tolerance. No major adverse reactions developed. These findings suggest that angiotensin converting enzyme inhibition with captopril in congestive heart failure patients improved cardiocirculatory function through selective arteriolar dilatation. The reordering of regional blood flow which appears to result from release of angiotensin-mediated vasoconstriction, as well as the suppression of aldosterone, may underlie the prolonged benefit observed in these patients. This oral vasodilator appears to represent an effective adjunct for the treatment of advanced, chronic heart failure refractory to conventional measures.

Interaction of the sympathetic nervous system with vasopressin and renin in the maintenance of blood pressure.

To evaluate the partial contributions and interaction of three vasopressor systems in blood pressure maintenance, nephrectomized rats and rats with intact kidneys were submitted sequentially to catecholamine depletion, elimination of vasopressins vasoconstrictor action, and (for those with kidneys in situ) angiotensin blockade. Catecholamine depletion decreased blood pressure and stimulated vasopressin levels in all rats, but significantly more so in the anephric ones. Subsequent injection of an antagonist to the vasopressor effect of vasopressin produced a lasting fall of blood pressure in anephric rats, but only transient fall in those with intact kidneys. Infusion of teprotide — an angiotensin converting enzyme inhibitor — in the latter animals also produced transient blood pressure fall, but if this were followed by injection of the vasopressin antagonist, the pressure remained low for several hours. Blood pressure levels were closely correlated with those of plasma catecholamines throughout these maneuvers. Catecholamine levels were inversely correlated with those of plasma vasopressin, which were far greater in anephric rats through both stimulation and accumulation. Plasma renin activity was increasingly stimulated by falling blood pressure after each maneuver in rats with intact kidneys. Thus, it appears that in the resting state the sympathetic nervous system is more involved in the maintenance of blood pressure, whereas vasopressin and renin are important backup mechanisms. (Hypertension 4: 400–405, 1982)

Central and peripheral hemodynamic effects of angiotensin inhibition in patients with refractory congestive heart failure.

The central and peripheral hemodynamic responses to the angiotensin-converting enzyme inhibitor teprotide (SQ20881) were simultaneously determined in 10 patients with severe, refractory congestive heart failure using Swan-Ganz catheterization and venous-occlusion calf plethysmography. Significant declines in mean arterial pressure (82.5 ± 4.9 to 67.1 4 5.0 mm Hg [SEM], p < 0.001), systemic vascular resistance (1787 ± 130 to 1272 i 115 dyn-sec-cm-5, p < 0.001) and mean pulmonary capillary wedge pressure (26.8 ± 2.5 to 17.1 ± 2.5 mm Hg, p < 0.001) accompanied improvement in cardiac index (2.04 4 0.17 to 2.47 i 0.20 I/min/m2, p < 0.001). Reduction in mean right atrial pressure (9.8 4 2.0 to 5.2 : 1.8 mm Hg, p < 0.005) was not a result of limb venodilation, as calf venous capacitance did not change. The decrease in limb vascular resistance (76.6 ± 11.0 to 62.9 + 10.7 units, p < 0.05) did not parallel the fall in systemic vascular resistance in either magnitude or duration (p < 0.05). Pulmonary arteriolar resistance was not appreciably changed.Teprotide therefore reduces ventricular afterload and significantly improves cardiac function in patients with congestive heart failure. The greater change in systemic than in limb vascular resistance implies preferential redistribution of flow to other regions. These findings shed light upon the role of the renin-angiotensin system in the regulation of regional vasoconstriction in congestive heart failure and suggest that teprotide may act as a unique “vasoreleaser” of pathophysiologic arteriolar constriction.

The effect of angiotensin converting enzyme inhibition on coronary blood flow and hemodynamics in patients without coronary artery disease

We examined the role of the renin-angiotensin system in the regulation of systemic and coronary vascular tone by studying the effect of converting enzyme inhibition by teprotide on systemic and coronary hemodynamic parameters in 14 normal patients undergoing routine cardiac catheterization. Serial hemodynamic measurements were made before and up to 30 minutes after 1 mg/kg of intravenous teprotide. A significant rise in cardiac index and stroke volume index occurred with a fall in systemic vascular resistance. The increase in cardiac index was related to the level of resting plasma renin activity. Blood pressure, pulmonary artery and left ventricular end-diastolic pressures remained unchanged. Coronary sinus thermodilution blood flow also showed no significant change; however, some patients demonstrated dramatic increase in flow. The change in blood flow was highly correlated with the resting plasma renin activity (r = 0.939 P less than 0.001). The change in coronary vascular resistance and myocardial oxygen consumption were likewise related to the resting plasma renin level. Converting enzyme inhibition produces significant systemic hemodynamic changes in normal patients which implies that the renin-angiotensin system is important in normal cardiovascular homeostasis. The direct relationship between plasma renin activity and coronary blood flow suggests that the renin-angiotensin system may play an important role in coronary vasomotor regulation.

Renin and Angiotensin II Receptor Gene Expression in Kidneys of Renal Hypertensive Rats

The aim of this investigation was to examine the interrelation between renal mRNA levels of renin and angiotensin II receptor type 1 (AT1) in a renin-dependent form of experimental hypertension. Rats were studied 4 weeks after unilateral renal artery clipping. Mean blood pressure and plasma renin activity were significantly higher in the hypertensive rats (n = 10 206 +/- mm Hg and 72.4 +/- 20.9 ng/mL-1/h-1, respectively) than in sham-operated controls (n = 10, 136 +/- 3 mm Hg and 3.3 +/- 0.5 ng/mL-1/h, respectively). Northern blot analysis of polyA+ RNA obtained from the kidneys of renal hypertensive rats showed increased levels of renin mRNA in the clipped kidney, whereas a decrease was observed in the unclipped kidney. Plasma renin activity was directly correlated with renin mRNA expression of the poststenotic kidney (r = .94, P < .01). AT1 mRNA expression was lower in both kidneys of the hypertensive rats. This downregulation was specific for the AT1A subtype since the renal expression of the AT1B subtype remained normal in hypertensive rats. The downregulation of the renal AT1A receptor may be due to high circulating angiotensin II levels. This is supported by the significant inverse correlation (r = .71, P < .01) between plasma renin activity and AT1A mRNA expression measured in the clipped kidney of the hypertensive rats.

Prediction of sustained antihypertensive efficacy of chronic captopril therapy: Relationships to immediate blood pressure response and control plasma renin activity

The blood pressure (BP) lowering effect of the orally active angiotensin converting enzyme inhibitor, captopril (SQ14225), was studied in 59 hypertensive patients maintained on a constant sodium intake. Within 2 hours of the first dose of captopril BP fell from 171/107 to a maximum low of 142/92 mm Hg (p less than 0.001), and after 4 to 8 days to treatment BP averaged 145/94 mm Hg (p less than 0.001). The magnitude of BP drop induced by captopril was significantly correlated to baseline plasma renin activity (PRA) both during the acute phase (r = -0.38, p less than 0.01) and after the 4 to 8-day interval (r = -0.33, p less than 0.01). Because of considerable scatter in individual data, renin profiling was not precisely predictive of the immediate or delayed BP response of separate patients. However, the BP levels achieved following the initial dose of captopril were closely correlated to BP measured after 4 to 8 days of therapy, and appeared to have greater predictive value than control PRA of the long-term efficacy of chronic captopril therapy despite marked BP changes occurring in some patients during the intermediate period. Because of these intermediate BP changes, addition of a diuretic to enhance antihypertensive effectiveness of angiotensin blockade should be restrained for several days after initiation of captopril therapy.

Safety and Efficacy of Chronic Therapy with Captopril in Hypertensive Patients: An Update

Abstract: Captopril, an orally active angiotensin‐converting enzyme inhibitor, has been administered to 81 patients with different types of clinical hypertension. Most of the patients had previously uncontrollable high blood pressure. In order to achieve a satisfactory blood pressure control during long‐term captopril therapy, a concomitant decrease in total body sodium was required in more than half of the patients. During our first two years of clinical experience with this new antihypertensive agent, side effects developed in 46.9 per cent of the patients and necessitated the withdrawal of the drug in 23.4 per cent of all patients. Only a few side effects such as hypotensive or syncopal episodes and cold extremities appeared to be due to the chronic blockade of the renin‐angiotensin system. The most frequent and the most serious adverse reactions such as skin rash, altered taste, pancytopenia, and pemphigus foliaceus seemed to be specifically drug related. The incidence of cutaneous and taste problems was markedly higher in patients with impaired renal function in whom retention of captopril has been previously demonstrated. This suggests that the occurrence of adverse reactions to captopril could be lowered in the future by using smaller daily doses and by titrating them according to the renal function.