Chronic administration of nimodipine and propranolol in elderly normotensive subjects--an interaction study

Nimodipine (30 mg t.i.d.) and propranolol (40 mg t.i.d.) were given orally to 24 healthy elderly subjects in a randomized, un-blinded, threefold crossover study. Each of the study periods lasted 8 days with a 5-day treatment phase separated by 2-week washout phases. Mean peak nimodipine plasma concentration was decreased after combined administration of the two drugs (16.1 +/- 8.1 micrograms/l vs. 12.4 +/- 9.5 micrograms/l). Nimodipine AUCss slightly decreased under propranolol co-medication from 44.9 +/- 15.1 micrograms x l/l to 38.8 +/- 22.5 micrograms x h/l, resulting in an AUC ratio of 88.8 +/- 44.5%. The relative bioavailability of propranolol was 104.1 +/- 38.3% after the combined propranolol and nimodipine medication, all other pharmacokinetic parameters remained unchanged. The pharmacological effects on the cardiovascular system were negligible after nimodipine alone. The reductions in blood pressure and pulse rate and the prolongations of typical ECG times observed after propranolol monotherapy and after the combination therapy were of similar size and were almost solely attributed to the action of the beta-blocker. The findings of this study indicate that chronic treatment with nimodipine together with propranolol should not be associated with a clinically relevant interaction.

Contribution of the small intestine to the first-pass uptake and systemic clearance of propranolol in rabbits

Epithelial cells of the intestine enclose isozymes able to metabolize propranolol, raising the possibility that the gut contributes with the liver to the first-pass uptake and systemic clearance of propranolol. To assess the role of the liver in the first-pass uptake, propranolol was injected into the jugular vein and a mesenteric vein of anesthetized New Zealand rabbits, and blood samples were drawn from the abdominal aorta, or it was injected into the intestine and samples were drawn simultaneously from the portal vein and the abdominal aorta. Extraction of propranolol by the liver was estimated to be 96-97%. To assess the intestinal extraction of oral propranolol, a porto-cava transposition was conducted in two groups of animals, and propranolol was injected into the first 30 cm of the small intestine or into the jugular vein and samples were withdrawn from the abdominal aorta; propranolol extraction by the intestine was 43%. To document the contribution of the intestine in the systemic clearance of propranolol, propranolol was injected into the jugular vein and blood samples were drawn simultaneously from the abdominal aorta (before the gut) and from the portal vein (after the gut); propranolol extraction from the systemic circulation by the intestine was 24%. Only the liver generated detectable amounts of conjugated metabolites of propranolol. In the in vitro studies, it was shown that propranolol was rapidly metabolized by the liver, yielding 4-hydroxypropranolol and conjugates of propranolol; propranolol metabolism in the proximal small intestine was slower and yielded only 4-hydroxypropranolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal hepatic propranolol metabolism. Studies in the isolated perfused fetal sheep liver

We have used an isolated perfused fetal sheep liver preparation to study the fetal hepatic metabolism of propranolol in vitro in the intact organ. Eight livers were perfused in situ via the umbilical vein in an oxygenated recirculating system at 300 ml/min. Radiolabeled 15-microns microspheres were used to quantify the hepatic ductus venosus shunt. Propranolol (4 mg) was dosed into the reservoir as a single bolus and perfusate and bile sampled over 150 min. Propranolol, 4-hydroxy propranolol (4OHP), 5-hydroxy propranolol (5OHP), desisopropylpropranolol (DIP), naphthoxylactic acid (NLA), and alpha-naphthoxyacetic acid (NAA) were assayed by HPLC, before and after deconjugation by enzyme hydrolysis. Mean age was 125 +/- 10 days, and mean liver weight was 66.1 +/- 18.8 g. Oxygen consumption (1.10 +/- 1.03 mumol/g/min), bile flow (0.51 +/- 0.18 microliters/g/min), and perfusion pressure (8.7 +/- 3.3 mm Hg) were stable. Ductus venosus shunt was 41.6 +/- 17.4% of umbilical vein flow. Propranolol clearance was 26.2 +/- 13.4 ml/min, and shunt-corrected extraction of propranolol was 0.26 +/- 0.13. The relative amounts of metabolites in perfusate after 150 min were: 4OHP (25.1%), 5OHP (5.08%) (ring-oxidation products), DIP (6.57%), and NLA (4.33%) (side-chain oxidation products). No alpha NAA (a product of N-dealkylation of NLA) was detected. Except for NLA, metabolites were present predominantly as conjugates. Biliary excretion of unchanged drug and metabolites accounted for a further 1.33% of the propranolol dose. These data indicate that, although the hepatic clearance and extraction of propranolol are low, the fetal sheep liver can metabolize propranolol by both ring- and side-chain oxidation reactions and can conjugate these metabolites.

Influence of severity of inflammation on the disposition kinetics of propranolol enantiomers in ketoprofen-treated and untreated adjuvant arthritis

Clearance of the beta-blocker, propranolol (PR), is decreased in inflammatory conditions such as arthritis, in both humans and rats. However, inflammation in arthritic patients is often controlled by drugs such as the nonsteroidal antiinflammatory drugs (NSAIDs). Therefore, it is possible that arthritic-induced changes in drug disposition are minimized or suppressed in subjects receiving NSAIDs. To examine this hypothesis, we induced mild and severe adjuvant arthritis (AA) in rats and daily doses of the NSAID, ketoprofen (KT), were given to half of these rats. The pharmacokinetics of PR were thus examined in nontreated (MILDcontrol and SEVEREcontrol) and KT-treated (MILDKT and SEVEREKT) arthritic rats. Treatment with KT significantly reduced the arthritic index (AI) in the severe model of AA. In AA, the AUC0-8 of R- and S-PR were not significantly different in MILDKT rats (R, 15.8 +/- 9.5; S, 1.72 +/- 9.1 mg.hr/liter) as compared with MILDcontrol rats (R, 16.2 +/- 12; S, 1.76 +/- 1.2 mg.hr/liter). On the other hand, the AUC0-8 of both enantiomers were significantly lower in SEVEREKT (R, 39.2 +/- 13.2; S, 2.92 +/- 1.2 mg.hr/liter) as compared with SEVEREcontrol (R, 79.9 +/- 17; S, 6.88 +/- 2.1 mg.hr/liter). A high correlation between disease severity (AI) and the AUC0-8 of R- (r = 0.82) and S-PR (r = 0.81) was observed in all groups. Furthermore, the relationship between the AI and protein binding of R- and S-PR was significant in severe AA. Therefore, increased plasma concentrations of PR in arthritis are related to the degree of inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)

On the suitability of urethane bonds between the carrier and the drug moiety in poly(ethyleneglycol)-based oligomeric prodrugs

Some poly(ethyleneglycol) derivatives of propranolol were prepared, in which the drug molecule was linked to the oligomeric carrier via urethane bonds in order to study the suitability of this bond as a linkage between the carrier and the drug moiety in oligomeric prodrugs. For comparison purposes also ethanol- and butanol-based prodrugs of propranolol were prepared, with the same linkage between drug and promoiety. The urethane compounds were obtained by condensation via N,N'-carbonyldiimidazole. None of these compounds gave rise to appreciable blood concentrations of propranolol after oral administration, thus suggesting in this particular case, a relative in vivo resistance of urethane bonds towards cleavage.

Enantioselective assay of beta-receptor antagonists present in microdialysis and plasma samples of rats

The enantiomers of alprenolol, metoprolol, and propranolol have been separated on an enantioselective cellulase column and analysed using a fully automated HPLC system involving coupled column chromatography and fluorescence detection. The assays had sufficient selectivity and sensitivity to investigate the disposition of these beta 2-receptor antagonists in blood and brain extracellular fluid of rats. A cellulase column was used as the first column to separate the enantiomers giving separation factors between 2.9 and 4.3. After the separation, the enantiomers were trapped on two small precolumns by the use of a switching valve and were then introduced on an achiral C18 analytical column by eluting the small columns backward. The enantiomers in blood and brain tissue dialysates were analysed by direct injection of 8 microliters samples. The limit of quantitation was 0.025-0.4 micrograms/ml of the different enantiomers. Plasma samples were analysed after a simple extraction procedure. The intraassay precision of the lowest quality control plasma samples (0.2-0.8 micrograms rac-drug/ml) was 4-8% for the different enantiomers.

Stereoselective pharmacokinetics of oxprenolol, propranolol, and verapamil: species differences and influence of endotoxin

The influence of endotoxin-induced inflammation was studied on the pharmacokinetics of the enantiomers of the racemic drugs oxprenolol, propranolol, and verapamil in rabbits and dogs. Enantioselective pharmacokinetics were seen for oxprenolol and propranolol in the rabbit and for propranolol and verapamil in the dog. In the dog, the enantioselective differences in plasma concentrations are due to differences in both protein binding and metabolism, whereas in the rabbit the differences are due solely to differences in metabolism. In both species endotoxin treatment increases the plasma concentrations of the enantiomers of the three drugs; both protein binding and metabolism are influenced. In rabbits and in dogs, the influence of endotoxin on the disposition of the three drugs is less enantioselective than was previously observed in the rat.

Toxicokinetics of a single intravenous dose of rac-propranolol versus optically pure propranolol in the rat

Conscious male Wistar SPF Riv:TOX rats were dosed intravenously with 2.5, 5, or 10 mg/kg rac-propranolol.HCl, or with 5 mg/kg of either (-)-(S)- or (+)-(R)-propranolol.HCl. Disposition of (-)-(S)- and (+)-(R)-propranolol after dosing of rac-propranolol was linear in the dose range examined. Total plasma clearance was not changed in animals dosed with the individual enantiomers compared to the animals that were dosed with rac-propranolol. However, for (-)-(S)-propranolol both volume of distribution and elimination half-life decreased, whereas for (+)-(R)-propranolol increases were observed for these characteristics, in animals dosed with the individual enantiomers. Our observations suggest that the (+)-(R)-enantiomer competes with (-)-(S)-propranolol for plasma protein binding sites, resulting in lower plasma protein binding of the (-)-(S)-enantiomer when the racemate is administered. From recent toxicological experiments, it was concluded that rac-propranolol is more toxic than the individual enantiomers in the rat, when dosed iv at the same total mass. It is concluded that the observed potentiation of toxic effects of propranolol enantiomers when administered as a racemate can at least partly be explained by a pharmacokinetic interaction.

Direct enantioselective determination of (R)- and (S)-propranolol in human plasma. Application to pharmacokinetic studies

In order to examine possible drug interactions of (R)- and (S)-propranolol a randomized, double blind, crossover study has been performed, administering orally single doses of 40 mg (R,S)- and of 20 mg (S)-propranolol. HCl three times daily over a week to reach steady state conditions. After the first single dose of 40 mg (R,S)-propranolol. HCl, the AUC0-infinity and Cmax values of the (S)-isomer were greater than those of the (R)-isomer: the ratio of AUC(S) over AUC(R) was 1.77 (P < 0.05) and that of Cmax 1.57 (P < 0.01). When (S)-propranolol.HCl was given as a single 20 mg dose, the AUC(S) value was a factor of 0.55 lower than that administration of 40 mg (R,S)-propranolol.HCl. At steady state, the AUC of (S)-propranolol was 1.52 times higher (P < 0.01) than that of the (R)-isomer after administration of 40 mg racemate, and comparing the (S)-isomer, the ratio was 1.21. Following administration of the first single dose of 40 mg of the racemate, the mean (SD) clearance of the (R)- and (S)-isomers was 110 (84) and 61 (37) ml min-1 kg-1, respectively; at steady state these values were 89 (55) and 57 (37) ml min-1 kg-1, respectively. Respective values for (S)-propranolol after single isomer administration (20 mg) were 86 (36) and 57 (25) ml min-1 kg-1 in single dose and steady state situations. The data are based on the quantitative analysis of (R)- and (S)-propranolol in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselective hydrolysis of O-isovaleryl propranolol and its influence on the clearance of propranolol after oral administration

The stereoselective hydrolysis of O-isovaleryl propranolol (isovaleryl-PL) was studied using phosphate and Tris-HCl buffers (pH 7.4), dog plasma, and liver preparations. The 10000g supernatant, microsomes, and cytosol were prepared from the liver homogenate. The hydrolysis rate of isovaleryl-PL was accelerated in the order Tris buffer < plasma = phosphate buffer << 10000g supernatant of liver = liver cytosol < liver microsomes. The high plasma protein binding of the prodrug brought about the extremely slow hydrolysis rate of isovaleryl-PL in plasma. No difference was observed in the hydrolysis rate between the isomers of isovaleryl-PL in buffers. The hydrolysis rate was 2-3 times faster with the (R)-isomer than with the (S)-isomer using racemate in dog plasma and liver preparations. The hydrolysis of each enantiomer was inhibited by the other enantiomer. For hydrolysis in microsomes the Km values of (R)- and (S)-isomers were same, and the Vmax of the (R)-isomer was 3 times greater than that of the (S)-isomer. These data suggested the mutual interaction of (R)- and (S)-isomers during the hydrolysis process and the rapid hydrolysis of isovaleryl-PL in liver after absorption. The AUC of PL enantiomers after oral administration of racemic isovaleryl-PL was about 2 times higher compared to 2 mg/kg equivalent molar dose of racemic PL in beagle dogs, and the corresponding plasma levels were not stereoselective from both PL and prodrug. The amount of (R)-PL absorbed after administration of a 5 mg/kg dose of racemic PL was 2-fold greater than (S)-PL, because of the stereoselective oxidation and glucronidation of (S)-PL.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of the drug permeation process across the intestinal epithelium

The rat intestinal lumen and the blood vessel were simultaneously perfused to study drug permeation across the intestinal epithelium. On the basis of drug disappearance from the intestinal lumen and its appearance into the vascular outflow, the mean time required for permeation across the intestinal membrane (MPT) and the permeation clearance (CLp) were calculated. MPT values of water, antipyrine, propranolol, imipramine and mannitol, varied from 0.45 min to 9.91 min depending on their physicochemical property. From both MPT and CLp, five drugs were classified as being (i) highly and rapidly absorbed (water, antipyrine), (ii) highly but slowly absorbed (propranolol, imipramine) and (iii) low and slowly absorbed (mannitol). Permeation profiles of these drugs were analyzed based on the diffusion model which defined the parameter for each permeation process, i.e. partitioning to and diffusion through the epithelium and clearance into the blood flow. Propranolol and imipramine partitioned into the membrane at a higher level than the other drugs. However, the clearance of both drugs from the epithelium was extremely slow, suggesting that this process is the rate-limiting step in their permeation. On the other hand, the rate-limiting step in the permeation of water and antipyrine was found to be the diffusion process in the epithelial layer.

Propranolol disposition in the single-pass isolated, perfused rat liver in the presence and absence of insulin and glucagon

The large increase in propranolol (PL) bioavailability when administered with food cannot be entirely explained by a transient increase in hepatic blood flow. A change in metabolic capacity or tissue uptake induced by changes in insulin and/or glucagon associated with food ingestion may contribute to the food effect. This hypothesis was tested in three groups of four isolated, perfused rat livers in the single-pass mode. PL (20 micrograms/ml) was infused to steady state at 30 ml/min for 120 min, then washed out for 30 min. Insulin or glucagon at 2 x 10(-9) M, or saline (control), was introduced at 70 min. Although neither insulin nor saline perturbed effluent PL or metabolite steady-state concentrations, glucagon caused a transient (15-min) reduction in PL, N-deisopropylpropranolol, propranolol glycol, and naphthoxylactic acid, indicating increased PL uptake, but not a change in metabolic activity. PL uptake was 668 +/- 108 micrograms/g liver tissue overall, and additional uptake after initiation of glucagon infusion was significant at 29 +/- 11.6 micrograms/g liver tissue (4% of initial uptake). Although the increase in PL uptake was small under the described conditions, this interaction with glucagon may contribute to the food effect. In this model system, hormonal effects on PL metabolism were not observed.

Carrier-mediated transport of H1-antagonist at the blood-brain barrier: a common transport system of H1-antagonists and lipophilic basic drugs

The blood-brain barrier (BBB) transport system for H1-antagonists was studied using primary cultured bovine brain capillary endothelial cells (BCEC). The uptake of [3H]mepyramine was inhibited by various H1-antagonists. Ketotifen competitively inhibited [3H]mepyramine uptake with an inhibition constant (Ki) of 46.8 microM. Lipophilic basic drugs such as propranolol, lidocaine and imipramine significantly inhibited [3H]mepyramine uptake. In particular, propranolol inhibited [3H]mepyramine uptake competitively at an inhibition constant (Ki) of 51.1 microM. Moreover, in ATP-depleted BCEC, [3H]mepyramine uptake was stimulated by preloading with H1-antagonists and lipophilic basic drugs. These results indicated that H1-antagonists are transported across the BBB via a carrier-mediated transport system common to lipophilic basic drugs.

[The functional characteristics of the beta 2-adrenoreceptors on the isolated membranes and intact erythrocytes of rats]

The main parameters of [3H]-propranolol binding were determined for beta-adrenoreceptors of membrane preparations and intact erythrocytes of white rats. It was shown that two molecules of [3H]-propranolol bind to one beta-adrenoreceptor. Two pools of adrenoreceptors differing in their affinity to the ligand and their number on the erythrocyte membrane were identified. In experiments on ligand binding to intact erythrocytes, dissociation constants (Kd) of high-affinity and low-affinity pools differed by a factor of 17 (0.92 +/- 0.22 and 15.39 +/- 2.69 nM, respectively); the number of receptors per cell differed by a factor of 9 (28 +/- 6 and 258 +/- 58). The maximal number of adrenoreceptors per erythrocyte was 286 +/- 57. In experiments with erythrocyte membrane preparations, dissociation constants of high-affinity and low-affinity pools differed by a factor of 25 (0.74 +/- 0.04 and 18.47 +/- 0.71 nM, respectively). The number of binding sites for the ligand differed by a factor of 3 (15.88 +/- 7.53 and 71.55 +/- 43.68 fmoles/mg protein, respectively). The main parameters of the ligand-receptor interaction obtained using two methods gave similar quantitative characteristics of the functional activity of erythrocyte beta-adrenoreceptors.

Microassay of propranolol enantiomers and conjugates in human plasma and urine by high-performance liquid chromatography after chiral derivatization for pharmacokinetic study

A microdetermination of propranolol enantiomers and of their glucuronide and sulphate conjugates in human plasma and urine by reversed-phase HPLC after chiral derivatization is described. After extraction from 100 microliters of plasma or urine with racemic 4-methylpropranolol as internal standard (I.S.), the enantiomers are derivatized with R(+)-phenylethylisocyanate as chiral derivatization reagent. Chromatography is performed on Novapak C18 column with fluorescence detection. Glucuronide and sulphate conjugates are cleaved prior to extraction by incubating, respectively, the samples with glucuronidase-arylsulphatase and saccharic acid 1-4 lactone as specific glucuronidase inhibitor. The retention times of propranolol and I.S. enantiomer derivatives are short (tR = 5.5-6.2 min and 8.8-10.1 min, respectively). The diastereomeric derivatives are very stable and show good peak symmetry and resolutions (RS = 2 and 2.2). The use of 4-methylpropranolol as I.S. improves significantly relative standard deviations (RSD: 1.7-5.1). Sensitivity is about 1 ng ml-1 per enantiomer. The method is applied to pharmacokinetic studies of racemic propranolol in human plasma and urine. S-propranolol and its conjugates show higher concentrations than R-propranolol and its conjugates in plasma and urine.

Effects of diltiazem on the disposition and metabolism of the enantiomers of propranolol in the dog during multiple oral dosing

The intravenous and oral dose kinetics and metabolism of the enantiomers of propranolol were investigated in five dogs during steady-state oral racemic propranolol dosing (5 mg/kg, every 8 hr for 3 days). These results were compared with those obtained during concomitant administration of oral diltiazem (2.5 mg/kg, every 8 hr for 3 days) in the same animals. The oral and intravenous propranolol test doses consisted of a pseudoracemic mixture of equal amounts of hexadeuterated-(R-(+))- and dideuterated-(S-(-))-propranolol. Propranolol metabolism in the urine was evaluated by coadministering 150 muCi of [4'-3H]racemic propranolol HCl, along with the deuterium-labeled compounds. Plasma concentrations of the deuterated enantiomers were measured by HPLC-thermospray MS, using undecadeuterated racemic propranolol as the internal standard. Diltiazem coadministration had no significant effects on either the systemic clearance, renal clearance, the apparent volume of distribution, or the elimination half-lives of either enantiomer. On the other hand, concomitant diltiazem treatment significantly reduced the oral clearance of S-(-)- and R-(+)-propranolol by 58 and 61%, respectively. These reductions resulted in an increase in their respective apparent steady-state oral availabilities of 129 and 106%. The S/R enantiomeric ratio of the oral availability of propranolol was not significantly changed from control. The urinary propranolol metabolites were isolated and purified by solvent extraction and HPLC and quantitated by radioactivity. Twelve metabolites, including propranolol, were isolated and quantitated in the urine. A significant reduction in the percentage of ring oxidation products and a significant increase in the percentage of naphthoxylactic acid and propranolol glucuronide excreted in the urine occurred in the diltiazem-treated animals. The S/R enantiomeric ratios of urinary excreted propranolol, propranolol glucuronide, 4'-hydroxypropranolol glucuronide, and its sulfate were not altered by diltiazem. These results suggest that the decreased oral clearances of the enantiomers of propranolol by diltiazem is caused by a selective decrease in the formation of ring-oxidized products.

Comparison of the effects of dilevalol and propranolol on systemic and regional haemodynamics in healthy volunteers at rest and during exercise

The effects of single oral doses of dilevalol 400 mg and propranolol 80 mg on systemic and regional haemodynamics at rest and after sub-maximal exercise, were compared, in a placebo-controlled, randomised, double-blind, crossover study in 6 healthy male volunteers. At rest, as compared to placebo, neither dilevalol nor propranolol significantly affected arterial pressure and heart rate but, whereas propranolol decreased cardiac output (-27% at 2 h) and tended to increase total peripheral resistance, dilevalol tended to increase cardiac output and decreased total peripheral resistance (-7% at 2 h). Neither dilevalol nor propranolol affected brachial artery diameter. Propranolol tended to decrease brachial artery flow (-20% at 2 h) and to increase brachial vascular resistance (+25% at 2 h), but dilevalol did not and the brachial irrigation ratios did not change. Neither of the drugs affected carotid haemodynamics or plasma atrial natriuretic factor. Both drugs tended to decrease plasma renin activity, and dilevalol (+82% at 2 h) increased norepinephrine more than propranolol (+19% at 2 h). After exercise, dilevalol and propranolol produced similar falls in the induced increases in arterial pressure, heart rate and cardiac output, and had the same effects on regional haemodynamics, plasma renin activity and atrial natriuretic factor. Finally, dilevalol greatly increased plasma norepinephrine. We conclude that the beta 2-adrenoceptor agonist activity of dilevalol was clearly expressed at rest, thus inducing vasodilation and counteracting the beta-adrenoceptor blockade-induced negative chronotropic and inotropic effects. However, during sub-maximal exercise, only the beta-adrenoceptor antagonist activity of dilevalol was apparent.

Liver function improvement following increased portal blood flow in cirrhotic rats

BACKGROUND/AIMS

Liver microcirculation in cirrhosis is characterized by development of intrahepatic shunts and capillarization of sinusoids secondary to cell necrosis and deposition of new collagen, resulting in both decreased drug elimination and increased vascular resistance with portal hypertension. The aim of this study was to examine the effects of increased portal blood flow on hepatic microcirculation and drug elimination in 13 perfused livers from cirrhotic rats.

METHODS

Intrahepatic resistance was assessed under basal conditions (21.2 +/- 0.3 mL/min) and 1 hour after doubling the flow (41.6 +/- 1.0 mL/min). A multiple indicator dilution technique was used at both flow rates to measure sinusoidal volume, albumin and sucrose extravascular volumes, and cellular water volume. Hepatic elimination of labeled taurocholate and propranolol was also measured, and the recovery of 15-microns microspheres was used to evaluate large intrahepatic shunts.

RESULTS

After doubling the flow, intrahepatic resistance decreased by 31%. Sinusoidal and extravascular volume increased significantly without a change in microsphere recovery. However, there was a marked increase in taurocholate and propranolol elimination by cirrhotic livers. Moreover, during high flow, significant correlations were found between changes in albumin extravascular volume and taurocholate and propranolol elimination.

CONCLUSIONS

Increased portal blood flow in cirrhotic rats induces a decrease in intrahepatic resistance without changes in intrahepatic shunting and improves drug elimination by the liver without deleterious effects on hepatocyte viability.

Propranolol metabolism in normal subjects: association with sex steroid hormones

The objective of this study was to determine the potential role of circulating testosterone and estradiol in regulation of the activity of the sex-dependent pathways of propranolol metabolism (i.e., alpha-naphthoxylactic acid and propranolol glucuronide). The pharmacokinetics of a single 80 mg oral dose of propranolol and the plasma levels of the sex steroid hormones were therefore determined in normal volunteers. In 33 young men there was a positive correlation between the testosterone levels and the propranolol clearances through both alpha-naphthoxylactic acid (p < 0.001) and propranolol glucuronide (p < 0.002), as well as the total clearance (p < 0.05), but not through aromatic ring hydroxylation. Testosterone cypionate administration led to an increased clearance of propranolol through alpha-naphthoxylactic acid in nine of the 11 men studied, further supporting a stimulatory effect of testosterone on propranolol metabolism. In 23 young women there was no significant association between the circulating levels of either estradiol or testosterone and any of the clearances of propranolol. These observations may be clinically relevant for propranolol therapy and may provide improved insight into the influence of gender and circulating gonadal hormones on drug metabolism in humans.

The effect of different calcium antagonists and a calcium agonist on the metabolism of propranolol by isolated rat hepatocytes

The influence of the dihydropyridine calcium entry blockers nicardipine, amlodipine, nifedipine, isradipine and of the dihydropyridine calcium entry promotor BAY K 8644 on the disappearance rate of propranolol by isolated rat hepatocytes was compared to the effect of diltiazem and verapamil, two non-dihydropyridine calcium channel blockers and known inhibitors of hepatic cytochrome P450 mixed function oxidases. All compounds dose-dependently inhibited the disappearance rate of propranolol. Nicardipine and isradipine were more potent in inhibiting the disappearance rate of propranolol than the other dihydropyridines and than diltiazem and verapamil. The inhibitory effect of nicardipine on the disappearance rate of propranolol was not stereoselective and was not influenced by age.

Product inhibition and dose-dependent bioavailability of propranolol in the isolated perfused rat liver preparation

We investigated in the isolated perfused rat liver (IPRL) whether product inhibition of metabolism contributes to the dose-dependent bioavailability of propranolol, a drug with a high, but saturable, hepatic first-pass effect. (+/-)-Propranolol was infused in the IPRL, using a recirculating design, for three 36-min periods (n = 9). Mean steady-state reservoir, i.e. hepatic inflow concentrations (Cin), were 4.97, 10.4, and 20.4 microM, respectively. Mean reservoir concentrations of the metabolites 4'-hydroxypropranolol, 5'-hydroxypropranolol, N-desisopropylpropranolol, and naphthoxylactic acid (NLA), a major side-chain-oxidation metabolite, increased disproportionately with propranolol dose, but their production rate did not reach steady state. In separate experiments (n = 4), perfusate containing 7.1, 12.8, and 21.6 microM (+/-)-propranolol, corresponding to administration rates of 114, 205, and 346 nmol/min, respectively, was passed through the liver for 30 min each using a single-pass design. The bioavailability (hepatic outflow concentration/Cin) of propranolol increased with Cin from 0.012 to 0.150 to 0.288 in the recirculating IPRL. In the single-pass IPRL the increase (0.0077 in 0.0669 to 0.136) was significantly less (P < 0.001). The greater bioavailability of propranolol in recirculating experiments was attributed to product inhibition since metabolites do not accumulate with the single-pass design. NLA did not appear to be the inhibiting metabolite because in further single-pass experiments with propranolol Cin of 21.6 microM the presence of NLA (21.6 microM) in perfusate had no effect on propranolol bioavailability (n = 7) compared with control experiments (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of everted intestinal rings for in vitro examination of oral absorption potential

The ability to predict in vivo oral absorption potential based on ex vivo screening in an everted intestinal ring model was examined. In vitro drug accumulation in cross sectional rings of everted rat jejunum was determined with 12 compounds whose in vivo absorptions (as distinct from bioavailabilities) are well characterized. The compounds examined ranged from well- to poorly-absorbed and included compounds absorbed by active and passive mechanisms. The effects of drug concentration, pH, cosolvents, and tissue origin site on drug accumulation were determined. Light microscopic observation indicated that the mucosal tissue remained intact up to 3 h after the intestine was excised. Accumulations of two nonabsorbable markers were also determined as measures of tissue integrity. A strong correlation (slope = 23 pmol/mg of tissue weight per percent oral absorption, r2 = 0.9430 by linear regression analysis) of in vitro uptake into everted rings from a 10 mM drug solution versus the known in vivo bioavailability for each compound was observed. These results indicated that under appropriate conditions, in vitro uptake of drug by the everted intestinal ring model closely paralleled known in vivo bioavailability and was relatively independent of pH, cosolvent, and tissue origin.

Effects of chronic stress on beta-adrenergic receptors in the homeless

This study examined the role of chronic life stress (homelessness), coping style, and hypertension on beta-adrenergic receptors in a sample of homeless men. Sixteen healthy normotensive subjects and nine untreated hypertensive subjects were studied. Life stress was measured with the Brown and Harris categorization; coping style was measured with the Ways of Coping Scale. Lymphocyte beta-adrenergic receptors were characterized in terms of receptor density (Bmax). Individuals with high life stress had lower Bmax (p < .005). In multiple regression analyses, 50% of the variance in Bmax was accounted for by life stress and coping style (p = .01). Receptor measures may be useful for characterizing the physiological response to continuing life adversity.

Organogel-based system for transdermal delivery of propranolol

The reverse micelle-based microemulsion was proposed as a vector for the transdermal delivery of propranolol. Soya-lecithin forms reverse micelle in iso-octane with increased solubilizing potential. The lecithin/iso-octane system was studied for the nature of solubilized water, the effect of added water on viscosity, and drug-micelle interaction. The amount and nature of solubilized water was investigated by spectroscopic methods using potassium nitrate as the polarity probe. With increasing water content the viscosity of the system was found to increase. And at a molar ratio (R) = 3, the system showed gel-like consistency (8.1 x 10(3) poise). The polarity probe study suggested the difference in environment of solubilized water as compared with the bulk water. The permeability rate of propranolol contained in the water/lecithin/iso-octane system was calculated to be 1212.0 micrograms h cm-2 while in the case of petrolatum jelly it was recorded to be 122.8 micrograms h-1 cm-2.

Effect of gugulipid on bioavailability of diltiazem and propranolol

The effect of single oral dose of 1 gm gugulipid was studied on bioavailability of single oral dose of propranolol (40 mg) and diltiazem (60 mg) in 10 and 7 normal healthy male volunteers respectively. It was a randomised within group crossover study. Blood samples were collected at hourly intervals upto 8 hrs. Gugulipid significantly reduced (P < .01) peak plasma concentration (Cmax) and area under curve (AUC 0-8 hrs) of both the drugs in normal volunteers. Such interaction in patients receiving propanolol or diltiazem with gugulipid may lead to diminished efficacy or nonresponsiveness due to significant reduction in bioavailability.