Direct effects of propofol on myocardial and vascular tissue from mature and immature rats

Indicators of haemodynamic instability and left ventricular function in a porcine model of esmolol induced negative inotropy

To investigate if the Hypotension Prediction Index was an early indicator of haemodynamic instability in a negative inotropy porcine model, and to assess the correlation of commonly measured indicators of left ventricular systolic function. Eight anaesthetised pigs were volume resuscitated and then underwent an incremental infusion of esmolol hydrochloride (0-3000 mg/hr), following which it was then reduced in a stepwise manner. Full haemodynamic measurements were taken at each stage and measurements of left ventricular systolic function including left ventricular stroke work index, ejection fraction and peripheral dP/dT were obtained. At an infusion rate of 500 mg/hr of esmolol there were no significant changes in any measured variables. At 1000 mg/hr MAP was on average 11 mmHg lower (95% CI 1 to 11 mmHg, p = 0.027) with a mean of 78 mmHg, HPI increased by 33 units (95% CI 4 to 62, p = 0.026) with a mean value of 63. No other parameters showed significant change from baseline values. Subsequent increases in esmolol showed changes in all parameters except SVV, SVR and PA mean. Correlation between dP/dt and LVSWI was 0.85 (95% CI 0.77 to 0.90, p < 0.001), between LVEF and dP/dt 0.39 (95% CI 0.18 to 0.57, p < 0.001), and between LSWI and LVEF 0.41 (95% CI 0.20 to 0.59, p < 0.001). In this model haemodynamic instability induced by negative inotropy was detected by the HPI algorithm prior to any clinically significant change in commonly measured variables. In addition, the peripheral measure of left ventricular contractility dP/dt correlates well with more established measurements of LV systolic function.

Rapid cardiotonic effects of lipid emulsion infusion*

OBJECTIVES

Bolus infusion of lipid emulsion can reverse cardiac pharmacotoxicity caused by local anesthetics and other lipophilic drugs. The mechanisms of this effect are not completely elucidated. The authors test the hypothesis that lipid emulsion infusion exerts direct, positive inotropic effects.

DESIGN

Prospective, randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Rats anesthetized with isoflurane were given intravenous infusions (9 mL/kg over 1 min) of either 20% soybean oil-based emulsion or saline.

MEASUREMENTS AND MAIN RESULTS

Arterial pressure and aortic flow were measured continuously in intact animals. Lipid infusion increased aortic flow and arterial pressure faster and to a greater degree than did the same volume of saline infusion. Isolated rat hearts were studied using an isovolumetric, constant flow, nonrecirculating system. Left ventricular pressure was monitored. The infusion of lipid emulsion in the isolated heart dose-dependently increased rate pressure product, dP/dt, -dP/dt, and myocardial oxygen demand.

CONCLUSIONS

Lipid emulsion exerts rapid, positive inotropic and positive lusitropic effects in both intact animal and isolated heart models. We hypothesize that this inotropy and the resulting increase in tissue blood flow contribute to the phenomenon of lipid reversal of cardiac toxicity caused by drug overdose.

Propofol increases the Ca2+ sensitivity of BKCa in the cerebral arterial smooth muscle cells of mice

AIM

Propofol has the side effect of hypotension especially in the elderly and patients with hypertension. Previous studies suggest propofol-caused hypotension results from activation of large conductance Ca(2+)-sensitive K channels (BKCa). In this study, the effects of propofol on the Ca(2+) sensitivity of BKCa were investigated in mice cerebral arterial smooth muscle cells.

METHODS

Single smooth muscle cells were prepared from the cerebral arteries of mice. Perforated whole-cell recoding was conducted to investigate the whole-cell BKCa current and spontaneous transient outward K(+) current (STOC). Inside-out patch configuration was used to record the single channel current and to study the Ca(2+)- and voltage-dependence of BKCa.

RESULTS

Propofol (56 and 112 μmol/L) increased the macroscopic BKCa and STOC currents in a concentration-dependent manner. It markedly increased the total open probability (NPo) of single BKCa channel with an EC(50) value of 76 μmol/L. Furthermore, propofol significantly decreased the equilibrium dissociation constant (K(d)) of Ca(2+) for BKCa channel. The K(d) value of Ca(2+) was 0.881 μmol/L in control, and decreased to 0.694, 0.599 and 0.177 μmol/L, respectively, in the presence of propofol 28, 56 and 112 μmol/L. An analysis of the channel kinetics revealed that propofol (112 μmol/L) significantly increased the open dwell time and decreased the closed dwell time, which stabilized BKCa channel in the open state.

CONCLUSION

Propofol increases the Ca(2+) sensitivity of BKCa channels, thus lowering the Ca(2+) threshold of the channel activation in arterial smooth muscle cells, which causes greater vasodilating effects.

Aging alters mechanical and contractile properties of the Fisher 344/Nnia X Norway/Binia rat aorta

Vascular mechanical and contractile properties were compared in adult (6 months old) and very-aged (36 months old) Fischer 344/NNiaHSd X Brown Norway/BiNia (F344/NXBN) rats. Our previous work has indicated that aging is associated with aortic medial thickening. This morphological alteration was accompanied by a leftward shift in the aortic stress/strain curve indicating increased vessel stiffness in very-aged animals. Disruption of the endothelium as well as pretreatment of tissues with the nitric oxide (NO) donor sodium nitroprusside eliminated differences, suggesting a link between deficient endothelial NO release and reduced compliance in very-aged aortae. In addition, the Rho kinase inhibitor Y-27632 increased vessel compliance in both adult and very-aged tissues suggesting that the Rho cascade contributed to the stress/strain relationship. Maximal force developed in response to high potassium (K(+)) was reduced by approximately 70% in intact and endothelium-denuded aortae from very-aged rats. In contrast to contractile force development, calcium-dependent stress relaxation was increased in very-aged aorta. Finally, gel electrophoresis indicated a significantly higher tissue content of myosin heavy chain and a higher ratio of SM1/SM2 isoforms with aging. The results suggest multiple molecular changes with aging, which may be expected to alter vascular tissue function.

Comparative Pharmacokinetics and Pharmacodynamics of the New Propofol Prodrug GPI 15715 and Propofol Emulsion: Retracted

BACKGROUND

GPI 15715 is a new water-soluble prodrug that is hydrolyzed to release propofol. The objectives of this crossover study in volunteers were to investigate the pharmacokinetics and pharmacodynamics of GPI 15715 in comparison with propofol emulsion.

METHODS

In two separate sessions, nine healthy male volunteers (19-35 yr, 70-86 kg) received GPI 15715 and propofol emulsion as a target controlled infusion over 60 min. In the first 20 min, the propofol target concentration increased linearly to 5 microg/ml. Subsequently, the targets were reduced to 3 microg/ml and 1.5 microg/ml for 20 min each. The plasma concentrations of GPI 15715 and propofol were measured from arterial and venous blood samples up to 24 h and pharmacokinetics were analyzed. The pharmacodynamic effect was measured by the median frequency of the power spectrum of the electroencephalogram, and a sigmoid model with effect compartment was fitted to the data.

RESULTS

Compared with propofol emulsion, propofol from GPI 15715 showed a different disposition function and especially larger volumes of distribution. The propofol effect site concentration for half maximum effect was 2.0 +/- 0.5 microg/ml for GPI 15715 and 3.0 +/- 0.7 microg/ml for propofol emulsion (P < 0.05). Propofol from GPI 15715 did not show a hysteresis between plasma concentration and effect.

CONCLUSIONS

Compared with propofol emulsion, propofol from GPI 15715 showed different pharmacokinetics and pharmacodynamics, particularly a higher potency with respect to concentration. These differences may indicate an influence of the formulation.

Pharmacokinetics and clinical pharmacodynamics of the new propofol prodrug GPI 15715 in volunteers

BACKGROUND

GPI 15715 (AQUAVAN injection) is a new water-soluble prodrug which is hydrolyzed to release propofol. The objectives of this first study in humans were to investigate the safety, tolerability, pharmacokinetics, and clinical pharmacodynamics of GPI 15715.

METHODS

Three groups of three healthy male volunteers (aged 19-35 y, 67-102 kg) received 290, 580, and 1,160 mg GPI 15715 as a constant rate infusion over 10 min. The plasma concentrations of GPI 15715 and propofol were measured from arterial and venous blood samples up to 24 h. Pharmacokinetics were analyzed with compartment models. Pharmacodynamics were assessed by clinical signs.

RESULTS

GPI 15715 was well tolerated without pain on injection. Two subjects reported a transient unpleasant sensation of burning or tingling at start of infusion. Loss of consciousness was achieved in none with 290 mg and in one subject with 580 mg. After 1,160 mg, all subjects experienced loss of consciousness at propofol concentrations of 2.1 +/- 0.6 microg/ml. A two-compartment model for GPI 15715 (central volume of distribution, 0.07 l/kg; clearance, 7 ml. kg-1 min-1; terminal half-life, 46 min) and a three-compartment model for propofol (half-lives: 2.2, 20, 477 min) best described the data. The maximum decrease of blood pressure was 25%; the heart rate increased by approximately 35%. There were no significant laboratory abnormalities.

CONCLUSIONS

Compared with propofol lipid emulsion, the potency seemed to be higher with respect to plasma concentration but was apparently less with respect to dose. Pharmacokinetic simulations showed a longer time to peak propofol concentration after a bolus dose and a longer context-sensitive half-time.

Cardiotrophin-1 is a prophylactic against the development of chronic hypoxic pulmonary hypertension in rats

BACKGROUND

Cardiotrophin-1 (CT-1) reduces arterial blood pressure by activating nitric oxide synthesis. This study attempted to elucidate the effect of CT-1 on pulmonary arteries of pulmonary hypertensive rats.

METHODS

Pulmonary hypertension was induced in rats in a hypoxic chamber containing 10% to 11% oxygen. Rats kept in the hypoxic environment received either recombinant mouse CT-1 at a concentration of 50 micro g/kg (CT-1+hypoxia group, n = 21) or phosphate-buffered saline (hypoxia group, n = 30) once per day. Control rats housed in room air also received either the equivalent concentration of CT-1 (CT-1+normoxia group, n = 18) or phosphate-buffered saline (normoxia group, n = 39). Pulmonary arterial pressure, pulmonary vasorelaxation, and ventricular hypertrophy were measured.

RESULTS

The mean pulmonary arterial pressures were as follows (from lowest to highest; p values are relative to the hypoxia group): normoxia group (20.3 +/- 4.0 mm Hg, p < 0.0001), CT-1+normoxia group (21.1 +/- 2.4 mm Hg, p < 0.0001), CT-1+hypoxia group (27.9 +/- 4.1 mm Hg, p = 0.0019), and hypoxia group (33.9 +/- 6.6 mm Hg). The endothelium-dependent vasorelaxation value was largest in the normoxia group (59.5% +/- 17.4%, p < 0.0001), with it decreasing in the other groups in the following order (p values are relative to the hypoxia group): CT-1+normoxia group (52.8% +/- 15.5%, p = 0.0005), CT-1+hypoxia group (42.3% +/- 14.8%, p = 0.0061), and hypoxia group (17.4% +/- 4.8%). Right ventricular hypertrophy was significant only in the hypoxia group.

CONCLUSIONS

Our results demonstrate that treatment with CT-1 in a chronic hypoxic pulmonary hypertension model protects the endothelial function of the pulmonary artery; decreases pulmonary arterial pressure; and attenuates right ventricular hypertrophy.