I. Maragno

Impairment of endothelium‐dependent but not of endothelium‐independent dilatation in guinea‐pig aorta rings incubated in the presence of elevated glucose

Purine compounds such as ATP and adenosine, respectively endothelium‐dependent and‐independent vasodilators, are largely involved in the control of vascular tone and vascular reactivity to contracting stimuli. We investigated the relaxing activity of ATP and adenosine in guinea‐pig aorta rings exposed for 6 h to elevated glucose concentration (50 mM), in order to mimic hyperglycaemic conditions. Guinea‐pigs were reserpine‐treated (2 mg kg−1, i.p., 48 and 24 h before death). Rings of aortae incubated in 50 mM glucose, contracted submaximally by 1 μM noradrenaline, lost endothelium‐dependent relaxation in response to acetylcholine (10 nM to 10 μM). Aortae incubated with 50 mM mannose, as a hyperosmotic control, relaxed to acetylcholine normally. Rings of aortae incubated in 50 mM glucose, contracted submaximally by 3 mM 4‐aminopyridine, lost endothelium‐dependent relaxation in response to ATP (30 μM) whereas endothelium‐independent relaxation in response to adenosine (0.3 mM) was well preserved. The relaxation induced by A23187 or sodium nitroprusside (10 nM to 0.1 μM) did not differ between rings exposed to control (5.5 mM) or elevated glucose (50 mM) and contracted submaximally by 3 mM 4‐aminopyridine. When incubated with aortic tissue in the presence of elevated glucose, the cyclo‐oxygenase inhibitors, indomethacin (10 μM) and mefenamic acid (30 μM), or the scavenger of superoxide anions, superoxide dismutase (150 u ml−1), prevented the impairment of ATP‐mediated relaxation. The present results indicate that endothelium‐dependent, receptor‐induced relaxation in response to acetylcholine and ATP is impaired in guinea‐pig aorta rings exposed to elevated glucose. The endothelial dysfunction caused by glucose might be located at a step between receptor activation and intracellular calcium increase, and might be related to an increased metabolism of arachidonic acid coupled to an increased production, or to a reduced inactivation of superoxide anions.

Low- and medium-dose diltiazem in chronic atrial fibrillation: Comparison with digoxin and correlation with drug plasma levels

The safety and efficacy of diltiazem were compared with digoxin maintenance therapy for control of ventricular response in 19 patients with chronic atrial fibrillation. The relationship between drug plasma levels and cardiovascular effects was also investigated. After 7 days of combined therapy with diltiazem (60 mg three times a day in 10 patients and four times a day in nine patients) and digoxin (0.125 mg/day in two patients and 0.250 mg/day in 17 patients), the 24-hour mean heart rate derived from ambulatory ECG recording was reduced by 16.3% in comparison with digoxin therapy alone; the serum digoxin level was not significantly changed (1.06 +/- 0.43 vs 1.05 +/- 0.61 ng/ml). After a standardized bicycle exercise test (50 watts for 3 minutes), maximal heart rate was reduced by 19.9%, diastolic blood pressure was decreased by 8.9%, and systolic pressure-rate product was decreased by 12.5%. Diltiazem plasma levels (mean 120.9 +/- 63.3 ng/ml) were linearly correlated with percentage variations in maximal heart rate, diastolic blood pressure, systolic blood pressure, and pressure-rate product during exercise. Eighteen patients in succession discontinued digoxin therapy; after 14 days of diltiazem alone, the 24-hour mean heart rate returned to control values of digoxin therapy, whereas maximal heart rate and pressure-rate product during exercise were significantly reduced (-17.2% and -14.1%, respectively), with no changes in blood pressure. Diltiazem plasma levels (135.0 +/- 83.2 ng/ml) showed a linear correlation with the percentage of reduction in maximal heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of amrinone with endogenous adenosine in guinea‐pig atria

1 In spontaneously beating atria from reserpine‐treated guinea‐pigs, amrinone (10 μm to 2 mm) induced a positive inotropic and chronotropic effect that was preceded by a transient reduction in contractile force and in frequency. Both the positive and negative effects were concentration‐dependent. 2 The inotropic action of amrinone was antagonized by low concentrations of 8‐phenyltheophylline that compete with adenosine at R‐receptors on plasma membrane without significantly influencing phosphodiesterase activity. 3 Cumulative concentrations of amrinone (1 mm) antagonized the reduction of rate of contraction and amplitude induced by dipyridamole 1 μm in spontaneously beating atria and restored the maximum contractile effect reached in the absence of dipyridamole. 4 In spontaneously beating preparations incubated in the presence of adenosine deaminase (1u ml−1), amrinone lost its positive effects on the atria and only reduction of rate and contractile force was evident. Both effects were antagonized by scopolamine 1 mm thus indicating their cholinergic nature. 5 Adenosine at 0.1 μm and 0.5 μm significantly inhibited the inotropic effect induced by amrinone (0.03 to 3 mm) and the concentration‐effect curves of amrinone obtained in the absence and presence of adenosine clearly indicate a competitive antagonism between the two drugs. Thus the contractile activity of amrinone in spontaneously beating atria from reserpine‐treated guinea‐pigs originates from a displacement of adenosine from its R‐receptor sites in the cardiac cell.

Plasma atrial natriuretic peptide (ANP) fragments proANP (1–30) and proANP (31–67) measurements in chronic heart failure: a useful index for heart trasplantation?

The family of the atrial natriuretic peptides, proANP fragments and the active αANP, is strongly related to heart disease. The aim was to study in CHF subjects the relation of mdANP and NtANP with brain natriuretic peptide (BNP) and with other traditional medical parameters. Sixteen CHF patients (aged 51.9±13.7 years) and 16 healthy subjects age matched (50.8±5.9 years) were selected. Both NtANP and mdANP were higher in CHF patients than in healthy subjects (1436±288 vs. 288±22 pmol/l p<0.001 and 2305±383 vs. 423±65 pmol/l p<0.0001, respectively). BNP in CHF patients was 28.0±9 pmol/l (reference values 1.7±1.8 pmol/l). Both NtANP and mdANP demonstrated positive correlation with BNP, p<0.0001 and with left atrial end-systolic volume, p<0.05. BNP correlated with left ventricular mass, p<0.03. In conclusion, plasma NtANP and mdANP analyses are useful laboratory markers in CHF patient investigation and follow up. In particular, they could be employed as non-invasive parameters to follow up worsening of systolic dysfunction until heart transplantation is required.

Effect of Captopril on Blood Pressure and on the Renin-Angiotensin-Aldosterone System in Coarctation of the Aorta

UNLABELLED To investigate the role of the renin-angiotensin-aldosterone system in hypertension due to coarctation of the aorta (COA), upright mean arterial pressure (MAP), plasma renin activity (PRA) and plasma aldosterone (Aldo) were determined before and 90 minutes after a single oral dose of captopril (25 mg) in eight patients with COA and in fourteen with essential hypertension (EH). There was no significant difference in MAP, PRA or Aldo values between the two groups in baseline conditions. After captopril administration, MAP and Aldo decreased significantly in both groups (p less than 0.01), whereas PRA showed a marked increase in patients with COA (p less than 0.001) and no significant changes in EH patients (from 1.5 +/- 2.2 to 49.7 +/- 9.8 and from 5.6 +/- 0.9 to 8 +/- 1.5 ng/ml/3h respectively). CONCLUSIONS 1) MAP reduction and marked renin increase after captopril in COA patients support the view that systemic hypertension in COA is, at least in part, renin mediated and 2) the evaluation of PRA after captopril could be helpful in the decision to proceed with more invasive procedures in patients with suspicious clinical features of COA or with residual post-coarctectomy hypertension.

Involvement of purine compounds in the inotropic action of milrinone

SummaryIn spontaneously beating atria from reserpinetreated guinea pigs, milrinone (1–100 μg/ml) induced a positive inotropic and chronotropic effect but was ineffective in preparations preincubated with adenosine deaminase (1 U/ml). Both in spontaneously beating and in electrically driven atria, ATP and adenosine evoked a dual effect: a first negative phase characterized by a reduction in contractile force, followed by a positive phase of increased inotropism. In these preparations milrinone inhibited the early negative influence exerted by purine compounds and amplified the following positive phase. These data suggest that the positive inotropic and chronotropic effect of milrinone may originate from its interference with endogenous purines.

Comparison between the cardiac effects induced by muzolimine and furosemide in guinea-pig atria

SummaryMuzolimine (10–500 μM) induced a concentration-dependent reduction of both the contractile force and frequency in spontaneously beating atria and in electrically driven left atrium from reserpine-treated guinea pigs. This negative inotropic response was unaffected by the addition of atropine to the perfusion fluid, and it was highly sensitive to changes in external Ca2+ concentration. Both in spontaneously beating and in electrically driven atrium, muzolimine (50–400 μM) antagonized, in an apparently competitive manner, the increase in contractile force induced by cumulative addition of CaCl2 (0.68–9.59 mM) to the bathing fluid. Muzolimine (50–100 μM) reduced the inotropic response to low (5–30 nM), but not high (50–100 nM) concentrations of Bay K 8644, a calcium-channel agonist. The inotropic effects of 8-phenyltheophylline and of ouabain were antagonized by muzolimine (10–100 μM) in a noncompetitive manner, while the response to noradrenaline was not altered. Similar to muzolimine, verapamil at a concentration suitable to block calcium channels inhibited, in a noncompetitive way, the inotropic effect induced by 8-phenyltheophylline and by ouabain without altering the contractile response to noradrenaline. Furosemide (10 and 100 μM) did not influence the contractile force or the frequency of spontaneously beating atria, nor the inotropic effect induced by CaCl2, 8-phenyltheophylline, ouabain, or noradrenaline. These results indicate that the influence of muzolimine on guinea-pig atria originates from an inhibition of Ca2+ influx into cardiac cells and that furosemide does not mimic the effect of muzolimine at this level.

An analysis of the mechanism of the inotropic action of some milrinone analogues in guinea-pig isolated atria.

1 It has been reported previously that the milrinone analogues, ethyl 5‐cyano‐1,6‐dihydro‐2‐methyl‐6‐oxo‐3 pyridine carboxylate (I) and ethyl 5‐cyano‐1,6‐dihydro‐2‐ethyl‐6‐oxo‐3 pyridine carboxilate (II) exert a positive inotropic effect (EC50 = 15.6 ± 0.2 μm and 40.3 ± 0.1 μm) both on spontaneously beating and on electrically driven atria from reserpine‐treated guinea‐pigs. In the present study the mechanism of the inotropic action of these two agents was investigated. 2 In electrically driven left atrium from resperpine‐treated guinea‐pigs the EC50 values for inotropic activity for compounds (I) and (II) corresponded to that of milrinone (EC50 = 25 ± 0.1 μm) but compound (I) induced a greater maximum effect. This corresponded to a percentage increase in developed tension over control of 63 ± 0.3 whereas the maximum inotropic effect of milrinone was 48 ± 0.3 and that of compound (II) was 47 ± 0.2. 3 The inotropic activity of compounds (I) and (II) (10–100 μm) was resistant to propranolol (0.1 μm), thus excluding the involvement of β‐adrenoceptors. 4 Since the inotropism induced by compounds (I) and (II) was not reduced by carbachol (1 nm‐0.5 μm), an action involving changes in adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) can be excluded. 5 The inotropic action of compounds (I) and (II) was blocked selectively by 8‐phenyltheophyline (10 μm) or adenosine deaminase (2 u ml−1). 6 Both (I) and (II) inhibited, in an apparently competitive manner, the negative inotropic effect induced by N6‐(l‐phenylisopropyl) adenosine (l‐PIA), a stable adenosine agonist. The pA2 values for (I) and (II) were 4.79 and 4.36, respectively. 7 In rat brain compounds (I) and (II) inhibited the specific binding of N6‐cyclohexyl[3H]‐adenosine‐([3H]‐CHA) with an IC50 of 0.18 ± 0.01 mm and 0.25 ± 0.02 mm, respectively, which were similar to their IC50 values for blocking the PIA‐induced negative inotropic effect and which are also in the range of concentrations that are effective in inducing positive inotropism in guinea‐pig atria. 8 The results from the present study suggest that antagonism of endogenous purines causes positive inotropism without affecting intracellular cyclic AMP levels.

Plasma renin activity in coarctation of the aorta before and after surgical correction.

In 37 patients with coarctation of the aorta, arterial blood pressure and ambulant plasma renin activity (PRA) were determined before and, in 15 patients, after surgical correction. The systolic blood pressure was raised in all the cases and the diastolic pressure was raised in 30 patients. Ambulant PRA was increased in 11 patients when compared with normal subjects of similar age. Twelve of the 15 operated patients had a significant decrease of systolic pressure after operation. Eight had raised PRA, and in 7 of these PRA fell to normal after operation and the blood pressure also fell; in 1 patient the decrease of PRA was unaccompanied by a fall in blood pressure. Though there was no significant correlation between the changes in blood pressure and PRA after operation it seems possible from our results that the renin-angiotensin system may be activated and contribute to the raised arterial pressure which occurs in patients with aortic coarctation.

Early reduction in plasma norepinephrine during beta-blocking therapy with metoprolol in chronic heart failure

BACKGROUND The possible role exerted by modulation of sympathetic outflow in the clinical effects of beta-blockade in chronic heart failure was tested during short- and long-term treatment. METHODS AND RESULTS Oral metoprolol (30-150 mg/day) was added to conventional therapy in 14 patients with idiopathic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of <0.45, and New York Heart Association class II or III. Norepinephrine plasma levels, which are an index of sympathetic activation, decreased by 27.57 +/- 18.03% after 1 month (P < .005), but returned to pretreatment levels after 6 months. LVEF increased by 7.7 +/- 6.0 ejection fraction units after 6 months (P < .005 vs baseline and P < .05 vs 1 month). Long-term beta-blockade resulted in nonsignificant improvements in functional class, symptom score, and oxygen consumption at peak exercise. After 1 month, the reduction in plasma norepinephrine levels and the changes in LVEF were inversely correlated (P < .01). No other correlation emerged during short- or long-term treatment. CONCLUSION In conclusion, the reduction in plasma norepinephrine levels during short-term beta-blockade was not proportional to the clinical benefits and may have been attributed to the direct inhibition of sympathetic outflow. The early reduction in circulating norepinephrine levels may decrease cardiac performance through withdrawal of sympathetic support when the favorable effects of beta-blockade have not had time to occur. The role that sympathetic modulation may exert in the long-term clinical benefits of metoprolol deserves further investigation.