Positive Inotropic/Vasodilator Agents

Inotropic therapy: an important role in the treatment of advanced symptomatic heart failure

Inotropic therapy remains an option in the management of patients with advanced heart failure symptoms from systolic dysfunction who do not respond to conventional therapies. The decision to use this class is largely predicated on an accurate evaluation of the patient's fluid and perfusion status. Selection of the appropriate agent and dosing regimens requires an understanding of the underlying pathophysiology of heart failure and concomitant therapy. Most important, the goals of care should be stated clearly, given inherent risks associated with this class of drug.

Effect of phosphodiesterase III inhibitor on contractility, afterload, and vascular capacitance during right heart bypass preparation

OBJECTIVES

Phosphodiesterase III inhibitors, which have both positive inotropic and vasodilatory effects, occasionally cause hypotension due to afterload reduction and possibly due to preload reduction caused by the increase in vascular capacitance.

METHODS

Six open-chest adult mongrel dogs were used to compare the effects on left ventricular contractility, afterload, and vascular capacitance of the phosphodiesterase III inhibitor, olprinone, with those of dobutamine using a right-heart-bypass model. Contractility and afterload were evaluated by the left ventricular pressure-volume relations with the use of a conductance catheter to derive the end-systolic elastance (Ees) and the effective arterial elastance (Ea). Vascular capacitance change was evaluated by reservoir volume change under a constant bypass flow (80 ml/kg per minute).

RESULTS

Ees increased significantly both with dobutamine (7.6 +/- 2.8 to 14.3 +/- 4.8 mmHg/ml, p < 0.05) and with olprinone (7.6 +/- 2.9 to 11.5 +/- 4.2 mmHg/ml, p < 0.05). Ea did not change with dobutamine (14.4 +/- 3.5 to 14.5 +/- 3.6 mmHg/ml, p = 0.9), whereas it decreased with olprinone (14.0 +/- 4.1 to 11.4 +/- 3.8 mmHg/ml, p = 0.093). Reservoir volume increased after the infusion of dobutamine (-94.0 +/- 39.8 ml), and decreased after the infusion of olprinone (-114.0 +/- 62.3 ml). The difference was statistically significant (p = 0.007). The reservoir volume change indicated that vascular capacitance decreased with dobutamine, and increased with olprinone.

CONCLUSIONS

Pre- and afterload reduction of olprinone combined with the positive inotropic effect are useful in treating congestive heart failure and managing low cardiac output syndrome after cardiac surgery.

Cardioprotective effect afforded by transient exposure to phosphodiesterase III inhibitors: the role of protein kinase A and p38 mitogen-activated protein kinase

BACKGROUND

Phosphodiesterase III inhibitors (PDEIII-Is) improve the hemodynamic status of heart failure via inotropic/vasodilatory effects attributable to the increase in intracellular cAMP level. Direct cardioprotection by PDEIII-Is and its underlying mechanisms, however, have not been identified. We tested the infarct size-limiting effect of PDEIII-Is and the roles of cAMP, protein kinase (PK) A, PKC, and mitogen-activated protein kinase (MAPK) families in open-chest dogs. Methods and Results-- Milrinone, olprinone (PDEIII-Is), or dibutyryl-cAMP (db-cAMP) was injected intravenously 30 minutes before 90-minute ischemia, followed by 6 hours of reperfusion. Olprinone was also examined with an intracoronary cotreatment with a PKA inhibitor (H89), a PKC inhibitor (GF109203X), an extracellular signal-regulated kinase kinase (MEK) inhibitor (PD98059), or a p38 MAPK inhibitor (SB203580) throughout the preischemic period. Either PDEIII-Is or db-cAMP caused substantial hemodynamic changes, which returned to control levels in 30 minutes. Collateral flow and percent risk area were identical for all groups. Both PDEIII-Is and db-cAMP increased myocardial p38 MAPK activity during the preischemic period, which was blocked by H89, but not by GF109203X. Both PDEIII-Is and db-cAMP reduced infarct size (19.1+/-4.1%, 17.5+/-3.3%, and 20.3+/-4.8%, respectively, versus 36.1+/-6.2% control, P<0.05 each). Furthermore, the effect of olprinone was blunted by either H89 (35.5+/-6.4%) or SB203580 (32.6+/-5.9%), but not by GF109203X or PD98059. H89, GF109203X, PD98059, or SB203580 alone did not influence infarct size.

CONCLUSIONS

Pretreatment with PDEIII-Is has cardioprotective effects via cAMP-, PKA-, and p38 MAPK-dependent but PKC-independent mechanisms in canine hearts.

Cardiotoxicity of vasodilators and positive inotropic/vasodilating drugs in dogs: an overview

Standard toxicological studies in dogs using high doses of vasodilators and positive inotropic/vasodilating agents give rise to a species-specific cardiotoxicity. The reason may be the extreme sensitivity of the dog to the pharmacological effects of these drugs; exaggerated pharmacodynamic effects and prolonged disturbance of homeostasis mechanisms often are responsible for the observed organ lesions. An assessment of the toxicological relevance and the risk for patients taking the drugs at therapeutic doses cannot be made without taking into account their pathomechanisms and the pathophysiological basis of the exceptional reaction patterns occurring in dogs. A large series of vasodilating and positive inotropic agents are presented, their pharmacological properties are described, and toxicological effects in dogs are compared. In view of the poor correlation between the distinct cardiac lesions induced in dogs and a lack of comparable toxicity in humans, it appears desirable to reassess the adequacy of the standard toxicological approaches for these substances.

The effects of milrinone in the neonatal pig heart

Milrinone, a selective inhibitor of phosphodiesterase (PDE), was examined in neonatal hearts and in ventricular myocytes. Isolated, paced (180 beats/min), isovolumically beating hearts from pigs, less than 3 days of age, were perfused with an erythrocyte-enriched solution. In one group (control, n = 6), milrinone was studied at perfusate concentrations of 1, 10, and 100 micrograms/ml. In a second group (postischemia, n = 10), hearts were subjected to 30 minutes of no-flow ischemic arrest, prior to the addition of milrinone. Left ventricular peak systolic pressure (PSP) and end-diastolic pressure, coronary flow (CF), heart rate (HR), and myocardial oxygen consumption (MVO2) were measured. The PSP averaged approximately 100 mmHg during the baseline periods for both groups and decreased to approximately 85 mmHg in those hearts subjected to ischemic arrest. In both groups, PSP increased approximately 14% at the 1 micrograms/ml concentration of milrinone. No additional increases in PSP were observed in the control group at the higher concentrations. However, PSP increased 28% and 41% (p less than 0.05), in the postischemia group at the 10 and 100 micrograms/ml concentrations, respectively. The CF averaged approximately 3 ml/min/g during the baseline periods of both groups and increased significantly at each milrinone concentration. The HR in both groups increased to approximately 200 and approximately 250 beats/min at the 10 and 100 micrograms/ml concentrations, respectively. Additionally, milrinone's effects in intact hearts were found to be comparable to those of isobutylmethyl xanthine (IBMX), a nonspecific PDE inhibitor. In isolated myocytes, however, milrinone produced only modest increases in cAMP levels, compared to IBMX.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of flosequinan (BTS 49465) on myocardial oxygen consumption

BTS 49465 (flosequinan), a putative selective, balanced arterial and venous vasodilator, displays positive inotropic effects in doses lower than those producing vasodilation. Thus rather than unloading the myocardium, flosequinan may increase myocardial work and oxygen consumption (MVO2), and may adversely affect the patient with myocardial ischemia or compromised coronary blood flow. This study compared the effects of flosequinan with milrinone, a mixed positive inotropic agent and vasodilator, and with nitroprusside (SNP), a standard direct-acting vasodilator, on myocardial dP/dT, MVO2, and myocardial energetics in the normal pentobartital-anesthetized dog. The effect of flosequinan on myocardial work was also evaluated in the dog with propranolol-induced heart failure (PIHF). Fifteen minutes after intraduodenal (id) administration of flosequinan (0.3, 1.0, and 3.0 mg/kg) to seven dogs, mean myocardial dP/dT was increased by 11%, 27%, and 54%, respectively, whereas stroke MVO2 was increased by 10%, 24%, and 47%, respectively. Doses of flosequinan greater than 0.3 mg/kg decreased left ventricular (LV) work but LV efficiency decreased in a dose-related manner. Milrinone (0.1, 0.3, and 1.0 mg/kg, id) increased LV dp/dt by 34%, 68%, and 104% above basal values, while increasing stroke MVO2 by 24%, 106%, and 249%, respectively (n = 7). LV work and LV efficiency decreased after each dose of milrinone. SNP (0.001, 0.003, and 0.01 mg/kg/min, intravenously) did not increase dP/dT but decreased LV work by 28%, 42%, and 46% (n = 5). In animals with PIHF, flosequinan (1 and 3 mg/kg, id) increased LV dP/dT 58% and 87% and increased LV work by 58% and 76% above control values. It was concluded that (1) flosequinan is a positive inotropic agent as well as a vasodilator; (2) in the normal animal the energy cost of positive inotropic activity is less with flosequinan than with milrinone, despite the lesser vasodilating action of the former; and (3) in the animal with a depressed myocardium, flosequinan may adversely affect myocardial work and wall tension.