Decreased plasma concentrations and clinical effects of alprenolol during combined treatment with pentobarbitone in hypertension.

The antihypertensive effect of alprenolol has been studied before, during and after additional pentobarbitone treatment. The combined alprenolol-pentobarbitone treatment significantly decreased alprenolol levels by 59% and 4-hydroxyalprenolol by 24%. The effect was significant after three doses and declined over 4-5 days after pentobarbitone withdrawal. The decreased alprenolol plasma levels were associated with increased pulse rate (6%), and systolic (8%) and diastolic (9%) blood pressure. The inhibition of exercise tachycardia by alprenolol was reduced by 18% at the end of pentobarbitone treatment compared to initial monotherapy with alprenolol. The interaction is probably clinically important in those patients with hypertension and angina pectoris that are treated with barbiturates and alprenolol.

Cytochrome P-450-dependent oxidation of felodipine--a 1,4-dihydropyridine--to the corresponding pyridine.

Felodipine, a 1,4-dihydropyridine diester, is metabolized to its corresponding pyridine analogue by rat-liver microsomes. Kinetic studies showed similar Km, Vmax and t1/2 for the formation of the pyridine metabolite and the disappearance of felodipine, indicating that oxidation of felodipine to the corresponding pyridine analogue is the major pathway of metabolism. Response to inhibitors such as CO, SKF 525-A and metyrapone indicates participation of cytochrome P-450 in the aromatization of felodipine. Phenobarbital pretreatment markedly increased the metabolism of felodipine and its pyridine analogue. Felodipine pretreatment had no effect on the cytochrome P-450 concn. in rat-liver microsomes, nor on the rate of its own metabolism, but a slight increase was observed in the rate of metabolism of four standard substrates.

Urinary metabolites of felodipine, a new vasodilator drug, in man, dog, rat and mouse.

The urinary excretion of total 14C after oral administration of 25 mg (approximately 1 mumol/kg) 14C-felodipine to man, and intragastric administration (5 mumol/kg) to dog, rat and mouse, was 70, 39, 44 and 53% dose, respectively, in 72 h. Metabolites of felodipine were separated and quantified by h.p.l.c. Unchanged felodipine and its oxidized analogue were not excreted by any of the species studies. Three metabolites, present in all species studied, were isolated from urine and identified as products of the oxidation of felodipine to its pyridine analogue followed by hydrolysis of one or both of the pyridine carboxylic acid esters.

The metabolic disposition of the selective beta 1-adrenoceptor agonist prenalterol in mice, rats, dogs, and humans.

The metabolic routes of the selective beta 1-adrenoceptor agonist prenalterol have been studied in mice, rats, dogs, and humans after oral administration. The drug was well absorbed from the gastrointestinal tract and most of the administered radioactivity was excreted in urine from all species within 24 hr. Prenalterol was metabolized to a varying extent in the species studied. About 20% of the 10-mg dose was recovered unchanged in man, the corresponding figures being 1.8% in the mouse, 7% in the rat, and 54% in the dog at 0.263 mg/kg (1 mumol/kg). Three metabolites were characterized and quantified by thin-layer chromatography, high-performance liquid chromatography, nuclear magnetic resonance (1H and 13C), and gas chromatography-mass spectrometry. Pronounced species variations in the metabolic pattern were observed. The phenolic sulfate ester of prenalterol was the main urinary metabolite in man, important in the dog, minor in the rat but not detectable in the mouse. Prenalterol glucuronide was formed in significant amounts in the animals and, in addition, beta-4(hydroxyphenoxy)lactic acid was present in dog urine. In the rat and the mouse the degree of biotransformation of prenalterol was significantly decreased at high oral doses of 2630 mg/kg (10 mmol/kg). The synthesis of prenalterol sulfate ester with use of ion pair extraction techniques is described.

Effect of noise on blood pressure and 'stress' hormones.

1. Noise stimulation (95 dBA) for 20 min caused a significant increase in diastolic (12%, P less than 0.001) and mean arterial pressure (7%, P less than 0.001) in 15 healthy normotensive male subjects. 2. There was no significant change in systolic blood pressure or heart rate during exposure to noise. 3. Adrenaline, noradrenaline, prolactin, cortisol and growth hormone concentration in venous plasma were not affected during noise stimulation.

Influence of pentobarbital on metoprolol plasma levels.

Induction of microsomal enzymes with barbiturates in rats has little effect on the metabolism of metoprolol, compared with propranolol and alprenolol, which undergo extensive hepatic extraction in animals and man. Our study was designed to examine whether the metabolism of metoprolol is inducable by barbiturate in man. In 8 healthy subjects the area under the plasma concentration/time curve after 0.1 gm metoprolol was reduced by a mean of 32% after treatment with 0.1 gm pentobarbital at bedtime for 10 days. There was considerable interindividual variability in the reduction after pentobarbital treatment (2% to 46%).

Influence of pentobarbital on effect and plasma levels of alprenolol and 4-hydroxy-alprenolol.

Six healthy subjects were given placebo and a single oral 0.2-gm dose of alprenolol (Aptin) before and after 0.1 gm pentobarbital at bedtime for 10 days. The plasma concentrations of alprenolol and its metabolite 4-hydroxy-alprenolol and the inhibition of exercise tachycardia were studied for 7 hr after the alprenolol. Alprenolol and 4-hydroxy-alprenolol plasma levels were decreased by about 40% by pentobarbital but plasma half-lives were unchanged. The inhibition of exercise tachycardia during a 7-hr period was reduced from 14.0% to 10.7% by pentobarbital. The reduction was proportional to the decreased drug plasma levels. There was a significant contribution of the metabolite to alprenolol effect. The estimation of relative potency of metabolite against parent compound was 0.9 before pentobarbital and 1.9 after pentobarbital.

Biotransformation of alprenolol in dog, guinea-pig and rat liver microsomes.

1. Metabolites of alprenolol were isolated and identified in dog, guinea-pig and rat liver microsomes by means of g.l.c.-mass spectrometry and comparison with synthetic reference compounds. 2. The compounds were chromatographed as n-butylboronate derivatives, giving a series of diagnostic ions in the mass spectral fragmentation, which was elucidated by using stable isotopes. 3. Alprenolol was metabolized by aromatic ring hydroxylation, oxidation of the allylic function, and degradation of the isopropylaminopropanol side-chain. Alprenolol and four metabolites were quantified by h.p.l.c. and batch extraction techniques based on radioactivity measurements. 4. Five metabolites were detected in rat and guinea-pig liver microsomes and four in the dog. A species variation in the biotransformation of the allyl function in alprenolol was observed. The metabolite formed by oxidation of the allyl double bond was detected in significant amounts in the guinea-pig, and was also formed in the rat but could not be detected in dog liver microsomes.

Identification of urinary and biliary metabolites of alprenolol in the rat.

1. After oral administration of alprenolol to rat, 12 metabolites were isolated and characterized as trifluoroacetyl, trimethylsilyl and n-butylboronate derivatives, using a g.l.c.-mass spectrometry-computer system. Fragmentation pathways of derivatives in the mass-spectrometric analysis are discussed. 2. Metabolic reactions involved are oxidative degradation of the propanolisopropylamine side-chain, aromatic hydroxylation, oxidation of the allyl group, and conjugation. A method for direct analysis of epoxide functions in the allyl group is described. 3. In comparison with metabolism of alprenolol in vitro, more polar metabolites are formed in vivo but the same principal metabolic pathways are valid. Structural features for biliary excretion are discussed.

Species differences in the metabolism of pamatolol, a cardioselective beta--adrenoceptor antagonist.

The metabolism of pamatolol was studied in man, dogs, rats and mice after oral administration of a single dose. The drug was well absorbed in the gastro-intestinal tract and excreted in the urine, mainly in unchanged form, within 24 hrs. Four urinary metabolites were identified by gas chromatographic-mass spectrometric techniques. The metabolic data, in man, dog and mouse was found to be similar, both qualitatively and quantitatively. One metabolism route, involving aliphatic hydroxylation and subsequent oxidation, was found, to a significant extent only in the rat. The species variation between the mouse and the rat with regard to long-term toxicity of pamatolol is discussed. Artefact formation during trace analysis was observed.

Hemodynamic and hormonal changes induced by noise.

Eighteen healthy male volunteers with normal hearing were exposed to industrial noise at different sound levels (75, 85 and 95 dB A) in a noise laboratory. Blood pressure, heart rate, stroke volume and cardiac output were recorded with noninvasive techniques. Adrenaline and noradrenaline concentration in venous plasma were analyzed before and during noise exposure. The mean resting blood pressure of the whole group was 120/70 mm Hg. During noise stimulation diastolic blood pressure increased (12.2%, p less than 0.001) as did mean arterial pressure (6.6%, p less than 0.001) and total peripheral resistance (12.7%, p less than 0.001). Stroke volume (7.3%, p less than 0.001) and cardiac output (5.0%, p less than 0.01) were both reduced at 95 dB A. Heart rate and systolic blood pressure did not change significantly. At 75 and 85 dB A there were similar but smaller changes in the hemodynamic parameters. There were no changes in adrenaline and noradrenaline in plasma during maximal noise exposure. The noise induced hemodynamic changes remained 5 minutes after the noise stimulation was stopped but had disappeared after 10 minutes of rest.

Kinetic studies of dose-dependent metabolism of alprenolol: in vitro and in vivo studies in different species.

Kinetic studies of the metabolism of alprenolol were performed with isolated microsomes from the rat, guinea-pig, dog and man at an initial substrate concentration of 0.17--150 micrometer. In all species the rate of aromatic hydroxylation reached a plateu above 50 micrometer of alprenolol in contrast to the rate of desisopropylation, where consistent saturation level was not obtained. The Km-values for the aromatic hydroxylation in the guinea-pig and man, 2,7 micrometer and 1.3 micrometer respectively, showed no concentration dependency in contrast to the rat (Km1 = 0.20 micrometer, Km2 = 26 micrometer) and the dog (Km1 = 0.78 micrometer, Km2 = 66 micrometer). The apparent Km-value of 0.20 micrometer for aromatic hydroxylation in the rat seemed to be of the same order of magnitude as reported spectral dissociation constant (Ks = 0.34 micrometer). In vivo experiments in the rat by oral administration of 7--700 mu mol/kg demonstrated a dose-dependent presystemic elimination of alprenolol. The urinary excretion of hydroxy-alprenolol was significantly lower after the highest dose. It is proposed, that the saturation of the aromatic hydroxylation, catalyzed by a high affinity site or subspecies of cytochrome P-450 with a low capacity, contributes to the dose-dependent kinetics in vivo.

Study of the metabolic pathways of alprenolol in man and the dog using stable isotopes.

The metabolic pathways of alprenolol have been investigated in man and the dog, using an ion doublet technique of deuterium labelling combined with gas chromatography mass spectrometry. The drug is eliminated mainly by aromatic hydroxylation and glucuronidation. Specific analytical methods are applied to demonstrate that allylic oxidation and oxidative deamination are quantitatively of minor importance. The mechanism for oxidative deamination via an intermediary aldehyde could be elucidated by using the deuterium labelled compound. A method for characterization of 4-hydroxy-alprenolol glucuronides based on formation of stable derivatives and the following enzymatic hydrolysis is described. This approach has a general applicability to hydroxylated metabolites from compounds with an aminopropanol structure common for beta-adrenoceptor antagonists, for example. The metabolic routes for alprenolol in man and the dog are almost identical and in man more than 95% of a given dose can be accounted for.

Metabolism of metoprolol in the rat in vitro and in vivo.

1. Metoprolol was metabolized in rat liver microsomes in vitro by O-demethylation with subsequent oxidation and by aliphatic hydroxylation of the methoxy-ethyl substituent and by oxidative deamination of the propanolisopropylamine side-chain. The same routes of metabolism in the rat in vivo were revealed from urinary metabolites. Eight metabolites were identified by g.l.c.-mass spectrometry by comparison with synthetized reference compounds. 2. Metoprolol binds to cytochrome-P-450 eliciting a type I difference spectrum with KS = 23 +/- 2-0 muM. The apparent Michaelis-Menten constant Km = 39 +/- 4-0 muM and Vmax = 1-28 +/- 0-22 nmol/mg protein X min were not significantly affected by pre-treatment of the rats with metoprolol or phenobarbital. Metoprolol pre-treatment had no effect on the cytochrome-P-450 level in the microsomes nor on the rate of metabolism of four standard substrates. Phenobarbital increased the cytochrome P-450 as expected. 3. Four metabolites representing the three main routes of metabolism were quantitatively determined after metabolism with rat liver microsomes and compared with the urinary levels of the same compounds. The same major metabolites were found in vitro and in vivo. The total amount of metabolites was not influenced by pre-treatment with metoprolol or phenobarbital. The relative amounts of the three main metabolites were slightly affected by pre-treatment.