Minoxidil sulphation in human liver and platelets

Summary Minoxidil requires to be sulphated to exert its hypotensive effect. We report on interindividual variability in the rate of minoxidil sulphation in 118 specimens of human liver and in platelets obtained from 100 healthy subjects and 100 newborns.The frequency distribution histogram of the hepatic activity of minoxidil sulphotransferase was positively skewed; the mean was 631 pmol · min^–1 · mg^–1. After logarithmic transformation of the enzyme activity, the frequency distribution histogram became symmetrical and did not significantly deviate from normality. The rate of minoxidil sulphation was not different in platelets from adults (0.74 pmol · min^–1 · mg^–1) and newborns (1.16 pmol · min^–1 · mg^–1). The frequency distribution histograms were positively skewed and the results of normal equivalent deviation analysis was compatible with the presence of at least two subgroups of sulphotransferase in liver and platelets.Thus, two phenotypes of sulphotransferase exist in human liver and platelets, and the extensive sulphator phenotype contributes to skewing the frequency distribution. In platelets, the percentage of subjects that fall in the two subgroups is different at birth and in adulthood. This can explain the different shape of the frequency distribution in newborn and adult platelets and suggests that platelet minoxidil sulphotransferase undergoes modification after birth.     

Comparison of Skin Esterase Activities from Different Species

Purpose Many topically applied drugs contain esters that are hydrolyzed in the skin. Minipigs have emerged as potential models of human dermatology and, in some aspects, may be superior to commonly used rat skin. The aims of this study were to evaluate the suitability of minipig and rat skin as in vitro models of human epidermal esterase activity. Methods Naphthyl acetate and para-nitrophenyl acetate were tested as prototypical substrates of carboxylesterases from skin, plasma, and liver. Reaction products were monitored by high-performance liquid chromatography/ultraviolet analysis. Results Hydrolysis efficiency in skin was higher than plasma, but lower than liver. The esterase efficiency of rat skin microsomes (580–1100 min⁻¹ mg⁻¹) was two to three orders of magnitude higher than human (1.3–4.2 min⁻¹ mg⁻¹) and minipig microsomes (1.2–4.2 min⁻¹ mg⁻¹). Rat skin cytosol (80–100 min⁻¹ mg⁻¹) was 2- to 10-fold more efficient than human (2.4–67 min⁻¹ mg⁻¹) or minipig cytosol (18–61 min⁻¹ mg⁻¹). Most importantly, human skin fractions displayed kinetics of hydrolysis very similar to minipig skin. Conclusions These studies show minipig skin as an appropriate, potentially valuable model for human epidermal ester metabolism and support the use of minipig skin in preclinical development of topically applied compounds.     

Sensitivity of residual nephrons to high dose furosemide described by diuretic efficiency

Ten haemodialysis (HD) patients with a median residual creatinine clearance (CL_CR) of 1.9 ml·min^–1·1.73 m^–2 (range 0.6–5.3) were treated with oral furosemide (F) 2.0 g. Overall-efficiency (O-E, daily sodium excretion/total urinary F) and total-efficiency (-E, increase in daily sodium excretion/total urinary F) were measured on the last 24 hours of each interdialysis interval. In addition, O-E was measured during the complete interdialysis interval in 10 HD patients with a median CL_CR of 5.6 ml·min^–1·1.73 m^–2 (range 0.7–6.8) treated for 1 year with a fixed oral dose of F between 250–1000 mg (median 625 mg).In the short study the median O-E was 10.6 mmol·mg^–1 (range 1.9–22.0) and -E 6.2 mmol·mg^–1 (range 1.3–11.2). The fractional excretion of sodium FE_Na was significantly increased from 9.6% (range 4.1–22.9) to 27% (range 14.6–56.2) during F treatment. A positive correlation was found between the basal FE_Na and -E. In the long-term study median O-E was 6.4 mmol·mg^–1. O-E and FE_Na showed no change over time although median RCC decreased from 5.6 to 1.9 ml·min^–1·1.73 m^–2 and median F excretion from 11.8 to 7.5 mg per day.It can be concluded that diuretic efficiency in haemodialysis patients is dependent on FE_Na and the state of hydration during the interdialysis interval.     

The pharmacokinetics of theβ 2-adrenoceptor agonist fenoterol in healthy women

Summary We have studied the pharmacokinetics of fenoterol in healthy women during and after a 3 h intravenous infusion of different doses within the therapeutic range for tocolysis (0.5 g·min^–1, 1.0 g·min^–1, and 2.0 g·min^–1). A specific and sensitive radioimmuno-assay was used for the determination of fenoterol. For compartmental analysis the plasma concentration time data were fitted with the TOPFIT program, assuming two exponentials.The total clearance of fenoterol increased with dose (1299 ml·min^–1 at 0.5 g·min^–1, 1483 ml·min^–1 at 1.0 g·min^–1, and 1924 ml·min^–1 at 2.0 g·min^–1), as did the apparent volume of distribution (from 491 at the lowest to 851 at the highest dose).In contrast, the apparent half-lives were not dose-dependent, with t_{1/2· 1} 4.8 min and t_{1/2· 2} 52 min.This paper is dedicated to Prof. Dr. Ellen Weber, Heidelberg, FRG     

A Comparison of Peptidase Activities and Peptide Metabolism in Cultured Mouse Keratinocytes and Neonatal Mouse Epidermis

One of the barriers to transdermal delivery of peptides is the metabolic activity of the epidermis. To define this metabolic activity, aminopeptidase activity and Leu-enkephalin metabolism were measured in the epidermis obtained from neonatal mouse skin and in cultured mouse keratinocytes. Aminopeptidase activity was measured fluorometrically using leucine, tyrosine, lysine, and aspartic acid derivatives of -naphthylamine as substrates. Similarities in substrate kinetic values (K _m and V _max) and substrate specificity of the enzyme(s) in homogenates prepared from neonatal mouse skin epidermis and cultured mouse keratinocytes strongly suggest that the keratinocytes in culture express the same aminopeptidase(s) with the same relative activity as in neonatal skin. The K _m and V _max values for aminopeptidase(s) with different substrates in epidermis homogenates are as follows: leucine -naphthylamide (11 µM and 38 nmol · min^–1 · mg^–1), tyrosine (-naphthylamide (21 µM and 18 nmol · min^–1 · mg^–1), and lysine -naphthylamide (11 µM and 35 nmol · min^–1 · mg^–1). Aspartic acid -naphthylamide and glutamic acid -naphthylamide were not hydrolyzed by these homogenates at pH 7.4 (37°C). Leu-enkephalin hydrolysis by the homogenates from cultured mouse keratinocytes and neonatal mouse epidermic gave similar K _m (32 and 24 µM), V _max (9.77 and 7.55 nmol · min^–1 · mg^–1) and K _i (223 and 194 µM) values. In addition, the cellular homogenates gave similar metabolite profiles for Leu-enkephalin.     

Bioavailability and pharmacokinetics of oxazepam

Summary Six healthy volunteers received oxazepam 15 mg i.v. and orally at an interval of at least one week. The kinetic variables of i.v. oxazepam were: elimination half-life (t_1/2) 6.7 h, total clearance (CL) 1.07 ml·min^–1·kg^–1, volume of distribution (V_c) 0.27 l·kg^–1 (0.21–0.49) and volume of distribution at steady-state (V_ss) 0.59 l·kg^–1. The intravenous disposition of unbound oxazepam was characterized by a clearance of 22.5ml·min^–1·kg^–1 and a distribution volume of 12.3 l·kg^–1. After oral oxazepam the peak plasma level was reached in 1.7 to 2.8 h. The plasma t_1/2 at 5.8 h was not significantly different from the i.v. value. Absorption was almost complete, with a bioavailability of 92.8%. Urinary recovery was 80.0 and 71.4% of the dose after intravenous and oral administration, respectively. Renal clearance (CL_R) of the glucuronide metabolite was 1.10 ml·min^–1·kg^–1 (0.98–1.52). Oxazepam was extensively bound to plasma protein with a free fraction of 4.5%.     

Depression of drug metabolizing activity in the human liver by interferon-α

Summary The depressant effect of interferon- on drug metabolizing activity in the liver has been investigated in 12 patients with chronic active hepatitis B. 7-methoxy-coumarin (7-MC) O-demethylase and 7-ethoxycoumarin (7-EC) O-deethylase, in specimens obtained by liver biopsy, were measured before and after interferon treatment. 7-MC and 7-EC O-dealkylase activity were significantly reduced after interferon treatment, from 13.4 to 9.24 nmol·g^–1 liver·min^–1, and from 3.22 to 2.16 nmol·g^–1 liver·min^–1, respectively. The magnitude of the fall varied widely between individual patients. The study provides the first direct evidence that interferon- can impair the activity of drug metabolizing enzymes in the human liver.     

The disposition and protein binding of batanopride and its metabolites in subjects with renal impairment

Summary We have studied the disposition of batanopride and its three major metabolites (the erythro-alcohol, threo-alcohol, and N-desethyl metabolites) in 27 subjects with various degrees of renal function after intravenous infusion of a single dose of 3.6·mg·kg^–1 of batanopride over 15 min.The subjects were assigned to one of three treatment groups: group 1, normal renal function (creatinine clearance 75 ml·min^–1·1.73 m^–2; n=13); group 2, moderate renal impairment (creatinine clearance 30–60 ml·min^–1·1.73 m^–2; n=8); group 3, severe renal impairment (creatinine clearance 30 ml·min^–1·1.73 m^–2; n=6).The terminal half-life of batanopride was significantly prolonged from 2.7 h in group 1 to 9.9 h in group 3. The renal clearance of batanopride was significantly lower in group 3 (25 ml·min^–1) compared with group 1 (132 ml·min^–1).There were no differences in plasma protein binding or steady-state volume of distribution of batanopride among the groups.There were significantly lower renal clearances for all three metabolites in groups 2 and 3 compared with group 1. The half-lives of all three metabolites were significantly prolonged in group 3 compared with group 1.The dose of batanopride may need to be reduced in patients with creatinine clearances less than 30 ml·min^–1·1.73 m^–2 to prevent drug accumulation and avoid possible dose-related adverse effects.     

Human liver budesonide sulphotransferase is inhibited by testosterone and correlates with by testosterone sulphotransferase

Budesonide, a corticosteroid used in the treatment of asthma and allergic reactions, is almost entirely cleared by metabolism in man. We describe the sulphation of budesonide in human liver and lung and provide evidences that the sulphation of budesonide is catalysed by testosterone sulphotransferase. A rapid and reproducible radiometric assay for budesonide sulphotransferase is described. Liver specimens were obtained from 35 men and 65 women and lung specimens from 2 women and 17 men.The average hepatic budesonide sulphation rate was significantly higher in men (41.1 pmol·min^–1·ml^–1) than women (28.2 pmol·min^–1·mg^–1). In the lung, the mean budesonide sulphation rate was 5.0 pmol·min^–1·mg^–1.Testosterone strongly inhibited the hepatic sulphation of budesonide, whereas p-nitrophenol and dopamine were poor inhibitors; the IC₅₀ was 7.0 uM (testosterone), 320 uM (p-nitrophenol) and 510 uM (dopamine). The hepatic rates of testosterone, p-nitrophenol and dopamine sulphation were measured in the same samples assayed for budesonide sulphotransferase. There was a correlation between the hepatic rates of budesonide and testosterone sulphation (P<0.001; r=0.810). The activity of testosterone sulphotransferase was significantly greater in men than women (22.0 vs. 17.2 pmol·min^–1·mg^–1), wheres those of dopamine and p-nitrophenol sulphotransferase were not sex dependent.The hepatic activity of budesonide sulphotransferase parallels that of testosterone suggesting that sulphation is an important reaction in the metabolism of budesonide.     

Simvastatin reduces plasma lipid levels and improves insulin action in elderly,non-insulin dependent diabetics

Summary Twelve elderly non-insulin dependent diabetic patients took part in a double-blind, cross-over, randomized study comparing simvastatin 30 mg/day and placebo. Each treatment period lasted 3 weeks and was separated by a 3 week wash-out period. At the end of each treatment period all subjects underwent in randomized order an oral glucose tolerance test (OGTT; 75 g) and an euglycaemic hyperinsulinaemic (50 mU/kg·h) glucose clamp.Simvastatin compared to placebo significantly reduced plasma total cholesterol (7.9 vs 5.3 mmol·l^–1), LDL-cholesterol (7.2 vs 4.3 mmol·l^–1), triglycerides (2.9 vs 2.1 mmol·l^–1), free fatty acids (1106 vs 818 mmol^–1) and glucose (7.4 vs 6.6 mmol·l^–1) levels.After simvastatin, and in the last 60 min of the glucose clamp, there was an improvement in the action of insulin as demonstrated by stronger inhibition of hepatic glucose output (2.7 vs 5.2 mol·kg^–1·min^–1) and stimulation both of the glucose disappearance rate (26.3 vs 19.5 mol·kg^–1·min^–1) and glucose metabolic clearance rate (4.3 vs 3.6 ml·kg^–1·min^–1).The changes in glucose turnover parameters were significantly correlated with basal plasma free fatty acids and were independent of plasma glucoregulatory hormones. In conclusion, simvastatin seems to exert beneficial effects both on lipid and glucose metabolism.     

Plasma insulin during physiological and pathophysiological changes in atrial natriuretic factor

Summary Changes in plasma insulin in response to a physiological or pathophysiological elevation in circulating atrial natriuretic factor (ANF) have been investigated.Plasma insulin, glucose, immunoreactive (ir) ANF, effective renal plasma flow (ERPF), glomerular filtration rate (GFR), absolute and fractional excretion of sodium (FENa), have been measured in 14 volunteers before and during infusion of low doses of ANF or vehicle (V). Each subject received single-blind in a randomized sequence at 2 week-intervals: V alone, or ANF 4, 8 and 16 ng·kg^–1·min^–1, indused over 90 min.Plasma irANF was increased 2.5- to 11-fold during the ANF infusion as compared to the test with the vehicle. Plasma insulin did not change during V administration (baseline vs V: 22 vs 21 U·ml^–1) and was unchanged during ANF at 4, 8 and 16 ng·kg^–1·min^–1 (19, 19, 21 U·ml^–1, respectively). Blood pressure, ERPF and GFR were not affected, and diuresis, FENa and urinary Na excretion were increased significantly and dose-dependently during ANF, but not V infusion. Compared to baseline, ANF 4, 8 and 16 ng·kg^–1·min^–1 increased urinary Na excretion by 147, 241 and 446 mol·min^–1, respectively.The findings indicate that, in normal humans, an acute increase in irANF within or slightly above the physiological range, which modified natriuresis and diuresis, did not alter circulating plasma insulin.The work was supported in part by the Swiss National Science Foundation     

Renal effects of atrial natriuretic peptide during dopa-decarboxylase inhibition in patients with essential hypertension

Summary To assess whether intrarenal dopamine synthesis could contribute to the renal response to ANP in essential hypertension, the effects of -human ANP influsion (50 ng·min^–1·kg^–1 b.w. for 30 min) on the urinary excretion of dopamine and sodium, urine flow rate and arterial pressure were evaluated in 7 patients with mild-moderate essential hypertension before (control period) and during DOPA-decarboxylase inhibition with carbidopa (carbidopa period).In the control period, urinary dopamine excretion was 400 pg·min^–1 in baseline conditions and 340 pg·min^–1 during ANP infusion. Carbidopa significantly decreased urinary dopamine excretion both before (210 pg·min^–1) and during ANP (99 pg·min^–1). In contrast, carbidopa did not affect sodium excretion (control from 184 to 460 Eq·min^–1; carbidopa period from 140 to 390 Eq·min^–1) or urine flow rate (control from 5.35 to 11.21 ml·min^–1; carbidopa period from 4.29 to 11.54 ml·min^–1).Arterial pressure fell significantly during ANP infusion in both periods, and no significant difference was observed between the two study days, i.e. in the absence of and during carbidopa administration.We conclude that DOPA-decarboxylase inhibition does not influence the diuretic and natriuretic response to -human ANP infusion in patients with essential hypertension.     

Pharmacokinetics of exogenous adenosine in man after infusion

Summary The plasma kinetics of adenosine was investigated in healthy volunteers after a 1 minute infusion of 2.5, 5 and 10 mg (38, 79 and 148 g·kg^–1 respectively) and after infusion of 200 g·kg^–1 in 10 min followed by 400 g·kg^–1 in 10 min.As the dose in the 1 min infusion study was increased the mean CL of adenosine decreased (10.7, 4.70 and 4.14 l·min^–1, respectively), its mean half-life increased (0.91, 1.24 and 1.86 min, respectively), and the mean volume of distribution did not show any clear trend (8–13 l).After the 20 minute infusion the plasma level of adenosine reached a peak value comparable to that observed after infusion of 5 mg in 1 min (about 0.5 g·ml^–1), but the mean clearance and half-life were significantly different (12.1 l·min^–1 and 0.63 min respectively).In all the subjects the plasma concentration of adenosine had returned to the baseline value in 5–15 min after the end of the infusion.     

Disposition of oral quinine in acute falciparum malaria

Summary Plasma quinine concentrations following oral quinine sulphate 10 mg salt/kg have been measured by HPLC in 15 adult Thai patients with uncomplicated falciparum malaria. In 10 of the same patients the study was repeated in convalescence. In acute malaria plasma concentrations were approximately 50% higher than in convalescence; the mean acute peak plasma quinine concentration was 8.4 mg·l^–1 compared to 5.7 mg·l^–1 in convalescence.There was considerable variation in the rate of drug absorption, particularly in acute malaria. The mean time to peak plasma concentration was 5.9 h in acute malaria and 3.2 h in convalescence. The apparent clearance of oral quinine (CL/f) during the illness was 1.51 ml·kg^–1·min^–1, which was significantly lower than in convalescence — 2.67 ml·kg^–·min^–1. Estimated free quinine clearance was also lower in the acute phase: 30.6 compared to 49.0 ml·kg^–1·min^–1 in convalescence. Mean (SD) plasma protein binding of quinine was 94.7% in acute malaria and 92.8% in convalescence. Binding was significantly correlated with the plasma concentration of ₁ acid glycoprotein (r=0.5), which was significantly higher in the acute phase; 1.48 g·l^–1 compared to 1.05 g·l^–1 during convalescence.Oral quinine sulphate was well absorbed in uncomplicated falciparum malaria. High blood concentrations following the administration of oral quinine in acute malaria are probably related to increased plasma protein binding, lower apparent volume of distribution, and a reduction in its systemic clearance.     

The pharmacokinetics ofα-human atrial natriuretic polypeptide in healthy subjects

Summary We have analysed the pharmacokinetics of-human atrial natriuretic polypeptide (-hANP) in healthy subjects, using a two-compartment open model following bolus intravenous injection. The plasma half-times for the fast and slow components were 1.7±0.07 min and 13.3±1.69 min respectively. V₁ (the volume of the central compartment), V_z (volume of distribution) and V_ss (volume of distribution at steady-state) were 5370±855 ml (89.5±14.3 ml·kg^–1), 32000±4620 ml (533±77.0 ml·kg^–1), and 11900±1530 ml (198±25.5 ml·kg^–1) respectively. The mean plasma clearance was 1520±121 ml·min^–1 (25.4±2.0 ml·min^–1·kg^–1.     

Coumarin-7-hydroxylase activity in microsomes from needle biopsies of normal and diseased human liver

Summary The specific activity of coumarin-7-hydroxylase was measured in liver microsomes from normal subjects and patients with liver disease. Liver specimens were obtained by needle biopsy and the microsomal fraction was separated by differential centrifugation. Its freedom from mitochondria was demonstrated by the absence of succinic dehydrogenase, a marker enzyme for mitochondria. Liver from healthy subjects showed variation in the specific activity of coumarin-7-hydroxylase from 0.16 to 0.65 nmol·mg^–1·min^–1, which is probably due to genetic factors. Patients with cirrhosis of the liver, chronic fatty hepatitis (chronic alcoholic hepatitis) and chronic active hepatitis showed a significantly lower mean hydroxylase activity. There was no significant difference in the mean level of hydroxylase between patients with subacute viral hepatitis or chronic persistent hepatitis and the normal controls.In memory of Professor Dr. med. Hans Voegt     

Venous plasma levels of endothelin-1 are not altered immediately after nitroglycerin infusion in healthy subjects

Endothelin-1 and nitric oxide play an important regulatory role in the control of vascular smooth muscle tone. Nitroglycerin (NTG), a nitric oxide donating drug, may inhibit endothelin production. In this double-blind placebo-controlled crossover study, plasma levels of endothelin-1 were measured before and immediately (5–30 s) after 80 min infusion of NTG (glyceryl trinitrate) or saline in 12 healthy subjects. On two different days separated by at least 1 week, NTG in four different doses, 0.015, 0.25, 1.0, and 2.0 g·kg^–1·min^–1, or placebo (isotonic saline) was infused successively for 20 min each dose. During the infusion blood pressure and heart rate were measured. NTG infusion significantly decreased systolic blood pressure from 112.4 to 103.4 mmHg and pulse pressure from 39.3 to 29.5 mmHg. Heart rate increased from 62.7 to 73.1 beats·min^–1. No changes in endothelin-1 plasma levels were induced by NTG infusion (2.4 pg·ml^–1 before NTG vs. 2.7 pg·ml^–1 after NTG) and placebo infusion also did not affect plasma endothelin-1. It is concluded that venous plasma levels of endothelin-1 are not altered immediately after NTG infusion.     

Changes in muscle blood flow after smoking a cigarette determined by a new noninvasive method

Summary The pharmacokinetics of the H₂-receptor antagonist famotidine, after oral administration of a 20 mg tablet, has been studied in 10 elderly patients with normal renal function (CL_CR59 ml·min^–1, Mean=80 ml·min^–1), 5 elderly patients with renal insufficiency (CL_CR38 ml·min^–1, Mean=15 ml·min^–1), and 6 healthy young volunteers.Elimination half-life in the elderly patients with renal insufficiency was significantly prolonged compared to the elderly patients with normal renal function and the young volunteers. The correlation coefficient between creatinine clearance and the elimination rate constant of famotidine was 0.672. Mean urinary recovery of unchanged drug up to 24 h in the young volunteers was 44%. The mean renal clearance of famotidine in the young volunteers (270 ml·min^–1) was substantially greater than the creatinine clearance, 128 ml·min^–1, which suggests the possibility of tubular secretion of famotidine.     

Dopamine pharmacokinetics in critically ill newborn infants

Summary Dopamine is frequently used in critically ill newborn infants for treatment of shock and cardiac failure, but its pharmacokinetics has not been evaluated using a specific analytical method. Steady-state arterial plasma concentrations of dopamine were measured in 11 seriously ill infants receiving dopamine infusion, 5–20 g · kg^–1 · min^–1, for presumed or proven sepsis and hypotensive shock.Steady-state concentrations of dopamine ranged from 0.013–0.3 g/ml. Total body clearance averaged 115 ml · kg^–1 · min^–1. The apparent volume of distribution and elimination half life averaged 1.8 1 · kg^–1 and 6.9 min, respectively.No relationship was observed between dopamine pharmacokinetics and gestational age, postnatal age or birthweight. Substantial interindividual variation was seen in dopamine pharmacokinetics in seriously ill infants, and plasma concentrations could not be predicted accurately from its infusion rate.Marked variation in clearance explains in part, the wide dose requirements of dopamine needed to elicit clinical response in critically ill newborn infants.VBM was a Fellow at Ohio State University and Children's Hospital at the time of study and is now at the Department of Pharmacy Services and College of Pharmacy, University of Michigan, Ann Arbor, MI, USA     

Sulphation and glucuronidation of ritodrine in human foetal and adult tissues

Summary Ritodrine is a ₂-adrenoceptor agonist used for the management of preterm labour. It is inactivated by conjugation with sulphate and glucuronic acid. There is more ritodrine sulphate than ritodrine glucuronide in urine from the newborn whereas equal amounts of ritodrine glucoronide and sulphate are excreted in maternal urine [Clin. Pharmacol. Ther 44, 634–641, 1988]. We show that, in the mid-gestational human fetal liver, ritodrine sulphotransferase is well expressed, whereas the glucuronidation of ritodrine is little developed compared to the adult liver. The average sulphotransferase activity was 308 pmol·min^–1 per mg protein in fetal (N=48) and 145 pmol·min^–1 per mg protein in adult (N=32) liver. The rates of ritodrine sulphation in fetal gut, lung and kidney were higher than in the corresponding adult tissues. The development and tissue distribution patterns of ritodrine sulphotransferase are consistent with those of dopamine sulphotransferase. Ritodrine and dopamine are sulphated by thermolabile enzymes. The activity of glucuronyl transferase was measurable in only 5 of the 48 foetal livers assayed, and in those in which could be assayed, the average activity was 44.6 pmol·min^–1 per mg protein, one-tenth of that in adult livers (524 pmol·min^–1 per mg protein).