Uptake of atrial natriuretic peptide and production of cGMP in cultured human glomerular endothelial cells.

Interactions between human glomerular endothelial cells and atrial natriuretic peptide (ANP) were studied with 125I-alpha-human-ANP binding and intracellular accumulation of cGMP. Uptake for alpha-hANP (1-28 or 5-28) by homogeneous cultures of human glomerular endothelial cells was dose and time dependent with optimal uptake occurring after 30 min of incubation at 37 degrees C. Scatchard analysis of the specific binding data with a two-compartmental model identified both high (Kd = 0.3 nM)- and low (Kd = 10 nM)-affinity receptors, with a binding site density of 12,000 and 18,060 receptors per cell, respectively. alpha-hANP markedly stimulated glomerular endothelial cell-associated cGMP. After a 2-min incubation, cGMP increased 1.3-fold (from 17.88 +/- 1.29 to 23.33 +/- 3 pmol/mg of protein), in the presence of 1 nM ANP, to more than threefold (from 21 +/- .1 to 80.5 +/- 14.5 pmol/mg of protein) with 1 microM ANP (P < 0.05). In contrast, a 10 microM concentration of the clearance receptor C-ANP4-23 increased cGMP by 1.6 +/- 0.6 fold. ANP stimulation of intracellular cGMP was 100 times more sensitive in human glomerular endothelial than in mesangial cells. In comparison, higher doses of bradykinin were necessary to evoke similar responses in glomerular endothelial cells. In the presence of 10 microM bradykinin, cellular cGMP increased by 1.75 +/- 0.6-fold versus control cells. However, unlike ANP, bradykinin-stimulated cGMP synthesis was significantly inhibited by prior treatment with oxyhemoglobin (10(-5) M), an inhibitor of soluble guanylate cyclase, and NG-nitro-L-arginine (NO2Arg), a specific inhibitor of endothelial-derived relaxing factor (EDRF).(ABSTRACT TRUNCATED AT 250 WORDS)

Thiopurine methyltransferase activity in a sample population of black subjects in Florida.

Thiopurine methyltransferase (TPMT), is an enzyme detected in the human red blood cell that catalyzes the S-methylation of thiopurine drugs and is known to exist as a genetic polymorphism in white subjects. Investigations in this laboratory of red blood cell TPMT showed interethnic differences also existed in North American black subjects. A sample group of black subjects in Florida had a mean activity of 8.64 +/- 3.47 U/ml red blood cells and an antimode of 6.5 units, which represented values significantly lower than those obtained for both the mean activity and the antimode in other populations. The findings of this study suggest the possibility that TPMT activity may be under genetic control in North American black subjects and that this ethnic group may be at greater risk of experiencing thiopurine-induced toxicity caused by the lower overall mean activity of the enzyme.

A pilot clinical and pharmacological study of intra-arterial infusion of thiotepa.

Fourteen patients with progressive localized tumors were treated on a clinical and pharmacological study with intra-arterial Thiotepa. A transfemoral percutaneous catheter was inserted into the major artery supplying the tumor. A venous catheter was inserted into the vein draining the tumor area for blood sampling. Doses of Thiotepa ranged from 0.3 mg/kg to 1.0 mg/kg. Courses were repeated monthly and doses of drug escalated as tolerated. Toxicity was mild and doses of drug at least up to 0.9-1.0 mg/kg were tolerable. Pharmacokinetic parameters suggest increasing binding of Thiotepa to tissue when the drug is administered by the intra-arterial route. Clinical responses were observed in a patient with melanoma and in another patient with unknown primary cancer.

Clinical and pharmacological study of intrahepatic artery infusion of thiotepa.

Twenty patients with primary or metastatic liver cancer were treated on a clinical and pharmacological study with intrahepatic artery infusion of Thiotepa. Toxicity was tolerable and included nausea and fatigue. Uncommon side effects were myelosuppression, abdominal pain and anemia. One patient with gallbladder cancer had a partial response for 11 (+) months. Recommended dose of Thiotepa for future Phase II clinical trials is 1.0 mg/kg. Pharmacokinetics of intrahepatic Thiotepa revealed an extraction ratio similar to that reported for cisplatin. The data suggest increased hepatic clearance for Thiotepa either by binding or metabolism.

Effect of cyclosporin A on the content of glutathione in the brain of the rat.

The effect of cyclosporin A on the content of glutathione was investigated in various regions of the brain of male Sprague-Dawley rats, weighing 275-300 g each. Treatment of rats with cyclosporin A (120 micrograms/kg/day, i.p.) resulted in approximately 50% decrease in the content of glutathione of the cerebellum within 1 hr, relative to time-matched controls, treated with olive oil vehicle. During the same period, cyclosporin A also caused an apparent, but statistically insignificant, decrease in the content of glutathione of the hypothalamus (37%), pontine nucleus (37%) and medulla oblongata (10%) and had no apparent effect on that of the cerebral cortex and the caudate nucleus. Within 24 hr of a single treatment, the content of glutathione of the rats treated with cyclosporin A returned to the control concentrations in all the regions of the brain. After 7 days of daily treatment with cyclosporin A, the content of glutathione of the hypothalamus remained within control levels, whereas that of the pontine nucleus showed an apparent decrease (30%) and those of the medulla oblongata and cerebellum decreased significantly, again by 58% and 64%, respectively, relative to their controls. This selective depletion of the content of glutathione in brain may contribute to some of the neurological side effects of cyclosporin A.

Effect of cyclosporin A on rat kidney catecholamines.

The immunosuppressive agent, Cyclosporin A, (CsA) has been associated with nephrotoxicity and hypertension. The mechanism for these effects are not known. We therefore determined the levels of the catecholamines; epinephrine (EPI), norepinephrine (NE) and dopamine (DA) and some of their metabolites; epinine, dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), metanephrine (ME) and 3-methoxy-4-hydroxy-phenylglycol (MHPG) in the kidneys of rats treated intraperitoneally with either CsA (120 micrograms/kg/body wt/day) or control vehicle (1 ml olive oil/kg body wt/day). Six control or CsA treated rats were sacrificed at 1 hour or 24 hours after a single treatment or after 7 days of daily treatment. Renal catecholamine levels were determined using HPLC-amperometric detector. Treatment with CsA increased renal NE and EPI levels by 59% and 70% respectively within 1 hour. In the rats sacrificed 24 hours after treatment, renal NE, EPI and DA levels were similar to or less than the control levels. Treatment with CsA for 7 days resulted in marginal increases in renal NE (22%) and EPI (30%). These changes were associated with a significant decrease in the levels of catecholamine metabolites in the CsA treated kidneys as compared to the controls. The above findings suggest that increases in renal catecholamines may be involved in the CsA-induced hypertension and nephrotoxicity, perhaps by increasing renovascular resistance.

Validity of a two-point acetaminophen pharmacokinetic study.

The pharmacokinetics of a single 650-mg intravenous dose of acetaminophen were determined in 82 volunteers using multiple (13 or more) plasma acetaminophen concentrations measured by high pressure liquid chromatography during 24 h after dosage. Kinetic values from the complete study were compared with kinetic estimates based on only two data points: (a) the 2- and 6-h points only; and (b) the 3 and 6-h points only. For elimination half-life, values from the complete study (mean 2.42 h) were highly correlated (r = 0.87 and 0.84) with methods a and b (means 2.41 and 2.43 h), with regression slopes of 1.00 and 0.99, respectively. For clearance, the complete study values (mean 312 ml/min) were highly correlated (r = 0.97 and 0.97) with method a and b values, but both two-point methods significantly overestimated clearance (means 350 and 355 ml/min) by an average of 13 and 14%, respectively. Results for volume of distribution were similar to those for clearance. Although acetaminophen elimination half-life can be estimated with reasonable precision using a two-point blood-sampling procedure, clearance and volume of distribution values using the two-point method overestimate the actual values.

Differential effect of cigarette smoking on antipyrine oxidation versus acetaminophen conjugation.

The effect of cigarette smoking on drug oxidation and conjugation was studied using antipyrine and acetaminophen as marker compounds. For the antipyrine study, healthy cigarette smokers (n = 30) and nonsmoking controls (n = 53) received a single 1.0-gram intravenous dose of antipyrine. For the acetaminophen study, 14 smokers and 15 nonsmokers received a 650-mg intravenous dose of acetaminophen. The clearance of antipyrine was significantly increased (0.93 vs. 0.60 ml/min/kg, p less than 0.0001) and elimination half-life was correspondingly reduced (8.9 vs. 13.0 h, p less than 0.0001) in smokers compared to nonsmoking controls. Total recovery of antipyrine and metabolites excreted in urine did not differ between groups, but there was a significantly increased fractional clearance of antipyrine via formation of 4-hydroxyantipyrine and 3-hydroxymethyl metabolites in smokers. Fractional clearance via formation of norantipyrine did not differ significantly between groups. Comparison of acetaminophen kinetics between smokers and nonsmokers indicated no significant differences in elimination half-life, clearance or volume of distribution. Thus, cigarette smoking is more likely to induce drug oxidation rather than drug conjugation. However, not all oxidative pathways are equally influenced; induction effects of smoking are highly substrate selective and pathway specific.

Lack of effect of influenza vaccine on the pharmacokinetics of antipyrine, alprazolam, paracetamol (acetaminophen) and lorazepam.

31 healthy male (n = 17) and female (n = 14) volunteers, aged 20 to 45 years, were divided into 4 groups and received on 3 separate occasions either: paracetamol (acetaminophen) 650mg intravenously (n = 9); alprazolam 1mg orally (n = 7); antipyrine (phenazone) 1g intravenously (n = 8); or lorazepam 2mg intravenously (n = 7). Doses were administered prior to influenza vaccine (0.5ml, intramuscularly) and at 7 and 21 days post-vaccination. The overall differences among the 3 trials in clearance of antipyrine were of borderline significance (p less than 0.0611), with a trend towards reduced clearance in both of the post-vaccination trials. There were no overall differences observed in the elimination half-life of antipyrine, nor were there significant differences between trials in cumulative urinary excretion or fractional recovery of intact antipyrine, 4-hydroxyantipyrine, norantipyrine, or 3-hydroxymethyl antipyrine. For paracetamol and alprazolam, there were no significant differences among the 3 trials in any of the kinetic variables. The elimination half-life of lorazepam varied significantly among trials, but differences were small and not systematic. Lorazepam clearance did not vary significantly among trials. Thus, clearance of drugs which undergo hepatic conjugative reactions such as glucuronidation and sulphation are unlikely to be affected by the coadministration of influenza vaccine. Furthermore, not all drugs which are biotransformed by hepatic microsomal oxidation necessarily have impaired clearance due to coadministration of influenza vaccine.

Effect of ciclosporin on rat liver and kidney glutathione content.

The effect of ciclosporin (CS) on hepatic and renal glutathione was investigated in 36 male Sprague-Dawley rats weighing 200-250 g each. CS (120 micrograms/kg/day, i.p.) treatment caused a significant decrease in both hepatic and renal glutathione content. The rat hepatic glutathione levels decreased by 16% within 1 h of a single CS treatment and continued decreasing to 50% following chronic treatment with CS for 7 days. Renal glutathione content decreased only marginally (3%) within 1 h of CS treatment. However, it decreased by 17% within 24 h and continued to decrease during the 7 days of chronic treatment. This decrease in the content of both hepatic and renal glutathione may contribute to the toxicity observed during treatment with CS.

Lidocaine pharmacokinetics during water immersion in normal humans.

Water immersion produces a marked diuresis, natriuresis, and kaliuresis in association with suppression of the renin-aldosterone system. These effects are mediated primarily by an increase in central blood volume. Consequently, this redistribution and the resultant marked increase in cardiac output is associated with alterations in the circulating levels of several volume regulatory hormones, including plasma renin activity and plasma aldosterone. Although the changes in these blood hormonal levels probably reflect perturbation of hormonal release, it is conceivable that the above-mentioned central hemodynamic modifications result in an altered splanchnic blood flow, thereby modulating hormonal clearances. We assessed the effects of immersion on hepatic blood flow by determining the pharmacokinetics of single doses of lidocaine administered intravenously. Seven normal male subjects were studied during a time-control period and during water immersion to the neck. The clearance of lidocaine was unaltered by immersion, suggesting that the presumed marked central hypervolemia and increased cardiac output was not associated with changes in splanchnic blood flow.

Simplified approaches to the determination of antipyrine pharmacokinetic parameters.

1. The pharmacokinetics of single intravenous doses of antipyrine were determined in 96 volunteers using multiple (12 or more) plasma antipyrine concentrations measured by high-pressure liquid chromatography during 24-48 h after dosage. These kinetic estimates were compared with those based on: A, the 4 h and 12 h points only; B, the 4 h through 12 h points; C, the 8 h and 24 h points only. 2. Mean clearance values for the complete study (48.0 ml min-1) were nearly identical to abbreviated approaches A, B, and C (49.1, 49.3, and 46.4 ml min-1), and were highly correlated (r = 0.99). 3. Coefficients of variation (CV) between individual clearance values for complete vs abbreviated studies averaged 5.5%, 5.8% and 2.9%, and CVs were less than 15% in 95.8%, 93.7% and 98.9% of subjects, respectively, for methods A, B, and C. 4. Overall mean values of elimination half-life (11.9, 12.1, 12.0 and 12.5 h) and volume of distribution (43.7, 45.1, 45.2, and 44.71) were likewise very similar for complete A, B and C analyses respectively. 5. The best correlation with the complete study was observed for the 8 and 24 h sampling scheme, for which clearance values were within 5% of the reference method in 84% of subjects, and within 10% in 97% of subjects. 6. Antipyrine pharmacokinetic parameters can be estimated with reasonable precision using a simplified two-point blood sampling procedure following a single intravenous dose. Estimates of elimination half-life, volume of distribution and clearance based on 8 h and 24 h data points correlated best with complete pharmacokinetic studies.

Antipyrine pharmacokinetics in women receiving conjugated estrogens.

The pharmacokinetics of a single 1.0 to 1.2-g intravenous dose of antipyrine was studied in 22 healthy female volunteers aged 28 to 70 years (mean, 45 years). Eleven subjects had been taking a conjugated estrogen preparation for at least 3 months; the other 11 subjects who were not taking conjugated estrogens and who were matched for age, weight, and smoking patterns, served as a control group. Plasma antipyrine concentrations were determined by high-pressure liquid chromatography (HPLC) in multiple plasma samples drawn 24 to 48 hours after dosage. Mean +/- SE pharmacokinetic variables in control and conjugated-estrogen groups were volume of distribution, 0.57 +/- 0.02 versus 0.56 +/- 0.02 L/kg; elimination half-life, 11.0 +/- 0.82 versus 12.6 +/- 0.89 hours; and clearance, 0.63 +/- 0.06 versus 0.54 +/- 0.03 mL/min/kg. None of the differences was significant. Although antipyrine clearance is significantly impaired by oral contraceptives, there is no evidence of altered antipyrine pharmacokinetics from treatment with conjugated estrogens.

Metronidazole impairs clearance of phenytoin but not of alprazolam or lorazepam.

Healthy volunteers received single doses of either phenytoin (300 mg IV), alprazolam (1 mg orally) or lorazepam (2 mg IV) on two occasions in random sequence. One of the two trials was a control; for the other trial, subjects ingested metronidazole, 250 mg three times daily beginning 4 days prior to and continuing for the duration of each kinetic study. Compared with control, metronidazole significantly prolonged phenytoin half-life (23 versus 16 hours, P less than .02) and reduced its clearance (.28 versus .33 mL/min/kg, P less than .005), known to depend on aromatic hydroxylation. However, metronidazole did not significantly alter kinetic variables for either alprazolam (metabolized by aliphatic hydroxylation) or lorazepam (metabolized by glucuronide conjugation). Thus, metronidazole has the capacity to impair the clearance of certain oxidatively metabolized drugs, but there is no apparent way to predict which drugs will be so influenced.

Effect of antipyrine coadministration on the kinetics of acetaminophen and lidocaine.

Pharmacokinetic interactions between antipyrine and acetaminophen were evaluated in 7 healthy volunteers. On 3 occasions subjects received: 1, antipyrine 1.0 g intravenously (i.v.); 2, acetaminophen 650 mg i.v.; 3, antipyrine 1.0 g and acetaminophen 650 mg i.v. simultaneously. Between Trials 1 and 3, antipyrine elimination t1/2 (17.2 vs 17.4 h), clearance (0.44 vs 0.43 ml.min-1.kg-1) and 24-h recovery of antipyrine and metabolites (313 vs 293 mg) did not differ significantly. Between Trials 2 and 3, acetaminophen VZ was reduced (1.14 vs 1.00 l.kg-1), t1/2 prolonged (2.7 vs 3.3 h), clearance reduced (4.8 vs 3.6 ml.min-1.kg-1), and fractional urinary recovery of acetaminophen glucuronide reduced. Eight additional subjects received 50 mg of lidocaine hydrochloride i.v. in the control state, and on a second occasion immediately after antipyrine 1.0 g given i.v. The two trials did not differ significantly in lidocaine VZ (2.6 vs 2.7 l.kg-1), t1/2 (2.0 vs 2.4 h) or clearance (15.0 vs 13.5 ml.min-1.kg-1). Although acetaminophen does not alter antipyrine kinetics, acute administration of antipyrine appears to impair acetaminophen clearance, possibly via inhibition of glucuronide formation. However, antipyrine has no significant effect on the kinetics of a single i.v. dose of lidocaine.

Prenatal effects of acute harmaline exposure on fetal brain biogenic amine metabolism.

Harmaline, a known type A monoamine oxidase (MAO) inhibitor in adult brain of various species was found to elevate whole brain levels of dopamine and serotonin (5-HT) in rat fetuses of mothers injected 2-4 h before Caesarean delivery. Similar stimulatory effects were observed for the norepinephrine metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG), however, no significant effect was obtained for norepinephrine. The dopamine metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindole acetic acid (5-HIAA) were decreased with the same treatment. These results imply that harmaline or one of its metabolites may cross the placental barrier to affect the fetal brain system not merely as a type A MAO inhibitor (i.e., relatively 5-HT-specific), but possibly also as a stimulatory agent for aldehyde reductase or catechol-O-methyltransferase (COMT) or alternately as an agent inhibiting the conjugation, efflux, or turnover of biogenic amine metabolites such as MHPG.

Trazodone kinetics: effect of age, gender, and obesity.

Single 25 mg intravenous and 50 mg oral doses of trazodone were given to 43 healthy subjects, divided into young men and women (aged 18 to 40 years) and elderly men and women (aged 60 to 76 years). Among men, trazodone volume of distribution (Varea) was increased in elderly vs. young subjects (1.15 vs. 0.89 L/kg; P less than 0.05), and clearance decreased (1.65 vs. 2.31 ml/min/kg; P less than 0.05), thereby increasing elimination half-life (t1/2) in elderly men (8.2 vs. 4.7 hours; P less than 0.001). Varea in women was also increased in the elderly (1.5 vs. 1.27 L/kg; P less than 0.02), causing increased t1/2 (7.6 vs. 5.9 hours; P less than 0.05), but clearance was unrelated to age. Absolute bioavailability of oral trazodone averaged 70% to 90% and was unrelated to age or sex. In 23 obese subjects (mean weight 112 kg) vs. 23 matched control subjects of normal weight (mean 65 kg), Varea was greatly increased (162 vs. 67 L; 1.43 vs. 1.04 L/kg; P less than 0.001) and was highly correlated with body weight (r = 0.91). Clearance was unchanged between groups (146 vs. 136 ml/min), but the increased Varea caused prolonged t1/2 in obese subjects (13.3 vs. 5.9 hours; P less than 0.001). Reduced clearance of trazodone among elderly men may indicate a need for dosage reduction during chronic therapy. In obese individuals, choice of dosage during chronic treatment should be based on ideal rather than total body weight.

Pharmacokinetics of antipyrine, acetaminophen and lidocaine in fed and fasted horses.

Previous studies demonstrated that plasma clearance of organic anions such as bilirubin, bile acid, sulfobromophthalein (BSP) and indocyanine green (ICG), was reduced from 36% (bile acid) to 55% (ICG) in fasted (3 days) horses. It is believed that a general decline in carrier-mediated hepatic uptake may have accounted for those changes. However, fasting may also affect hepatic blood flow, thereby contributing to reduced clearance of these compounds. In order to test this hypothesis, plasma clearance of antipyrine, acetaminophen and lidocaine, drugs known to be cleared by the liver yet not suspected of undergoing carrier-mediated hepatic uptake, were investigated in nine healthy adult mares (three horses/drug group) before and following a 3-day fast. Results demonstrate that fasting decreased clearance of organic anions from previous studies more than clearance of drugs used in these studies. In addition, clearance of lidocaine, the drug with the highest plasma clearance and therefore the drug most likely to be affected by reduced hepatic blood flow, was affected least by fasting. Therefore, reductions in clearance of these compounds due to fasting must not be due entirely to reductions in hepatic blood flow, but must also involve reductions in intrinsic hepatic clearance.

Antipyrine and lidocaine are cleared faster in horses than in humans: acetaminophen may be handled similarly.

The following studies were designed to evaluate plasma elimination kinetics of intravenously administered antipyrine, acetaminophen and lidocaine among 9 healthy adult horses and 9 healthy drug-free humans (3 each per drug group), in order to compare potential species differences in drug-metabolizing ability. Acetaminophen is largely biotransformed in humans by hepatic glucuronide and sulfate conjugation, whereas both antipyrine and lidocaine are oxidized by hepatic microsomal mixed-function oxidases. Thus, plasma clearances of these drugs are thought to reflect differences in hepatic oxidative and conjugative activity, and possibly hepatic blood flow in the case of lidocaine. Results showed that mean (+/- SD, n = 3) acetaminophen clearance was similar in both horses (4.84 +/- 0.637 ml/min/kg) and humans (4.68 +/- 0.691 ml/min/kg). However, antipyrine clearance was 10 times greater in horses (5.83 +/- 2.21 ml/min/kg) than in humans (0.536 +/- 0.110 ml/min/kg), which may reflect enhanced hepatic microsomal activity in horses. Although lidocaine clearance in humans was similar to estimated hepatic blood flow (20.6 +/- 5.81 ml/min/kg), clearance in horses was more than 2 times greater (52.0 +/- 11.7 ml/min/kg). The cause of the higher clearance of lidocaine in horses (like dogs) remains unexplained, and may involve significant metabolism of lidocaine at extrahepatic, extravascular sites, for intravascular degradation and renal excretion of intact lidocaine in horses was negligible. Although precise biochemical mechanisms underlying pharmacokinetic parameters for these drugs in horses were not determined, it is nonetheless concluded from antipyrine results that horses may have an enhanced ability (compared with humans) to clear drugs from the circulation that are primarily metabolized in the liver by phase I oxidative reactions.(ABSTRACT TRUNCATED AT 250 WORDS)