Role of cyclic AMP in the inhibition of mouse hepatocyte intercellular communication by liver tumor promoters

The liver tumor promoters phenobarbital (PB) (20-500 micrograms/ml) and 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) (1-10 micrograms/ml) inhibited intercellular communication between primary cultured B6C3F1 mouse hepatocytes after 8 hr of treatment. Intercellular communication was detected autoradiographically as the passage and incorporation of [5-3H]uridine nucleotides from prelabeled donor hepatocytes to recipient hepatocytes. The addition of either dibutyryl cyclic AMP (N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate) (0.001-0.1 mM) or caffeine (0.01-1 mM) decreased or completely abolished the inhibitory effects of PB and DDT on intercellular communication. Cyclic AMP (adenosine 3':5'-cyclic monophosphate; cAMP) in primary cultured mouse hepatocytes was measured by radioimmunoassay. Cyclic AMP in nontreated, freshly plated cultures declined from 4.2 +/- 0.7 pmol/mg protein after 1 hr in culture to 2.4 +/- 0.5 pmol/mg protein after 8 hr in culture. Phenobarbital at 250 and 500 micrograms/ml significantly decreased cyclic AMP below control values after 1 hr of treatment. However, no difference in the amount of cyclic AMP was detected between control and PB-treated cultures after 2, 4, and 8 hr in culture or with lower PB concentrations. DDT at 10 micrograms/ml decreased cAMP levels in the hepatocytes after 1, 2, 4, and 8 hr of treatment. No effects were seen after 8 hr of treatment or with lower DDT concentrations. DDT (10 micrograms/ml) also decreased cAMP levels in 24-hr-old cultures while PB (500 micrograms/ml) had no effect. Addition of dibutyryl cAMP (0.1 mM) or caffeine (1.0 mM) to freshly plated cultures elevated cAMP levels 50-fold and twofold, respectively. These data suggest that the inhibition of mouse hepatocyte intercellular communication by PB and DDT at the highest concentrations tested may be mediated by transient decreases in intercellular cAMP levels.     

The consequences of doxorubicin quinone reduction in vivo in tumour tissue.

A clear role for quinone reduction in the mechanism of action of doxorubicin has still to be established. There are three possible outcomes of this form of doxorubicin metabolism: (1) drug free radical formation, redox cycling and generation of reactive oxygen species (ROS) resulting in lipid peroxidation and DNA damage; (2) covalent binding of reactive drug intermediates to DNA; and (3) formation of an inactive 7-deoxyaglycone metabolite. In this work, the occurrence of each of these pathways has been studied in vivo in a subcutaneously growing rat mammary carcinoma (Sp 107). Doxorubicin was administered by direct intratumoural injection either as the free drug or incorporated in albumin microspheres (10-40 microns diameter). There was no evidence of an increase in lipid peroxidation over background after either treatment at any time point studied. In fact, doxorubicin administration resulted in a statistically significant reduction in lipid peroxidation at the later time points studied compared to control (no drug treatment), e.g. 24 hr: control, 21.7 +/- 2.8 SD nmol malondialdehyde/g tissue; free doxorubicin (70 micrograms drug), 14.5 +/- 4.0 SD nmol/g (P < 0.01 Student's t-test) and doxorubicin microspheres (70 micrograms drug), 17.4 +/- 1.1 nmol/g (P < 0.05). Covalent binding to DNA was measured by a 32P-post-labelling technique. Low levels of four putative drug-DNA adducts were detected; however, there were no qualitative or quantitative differences in profiles between free drug and microspheres. High 7-deoxyaglycone metabolite concentrations comparable to the parent drug itself were detected after administration of microspheres (3.0 micrograms/g +/- 1.7 SD at 24 hr and 3.1 micrograms/g +/- 1.1 SD at 48 hr). In contrast, these metabolites were present at levels close to the limit of detection of our HPLC assay after free drug (0.04 microgram/g +/- 0.03 SD at 24 hr and 0.02 microgram/g +/- 0.03 SD at 48 hr). Thus, 7-deoxyaglycone metabolite formation can occur in tumour tissue (indicating active drug quinone reduction) without concomitant increases in the level of lipid peroxidation or the levels of drug-DNA adducts. In conclusion, the main biological consequence of doxorubicin quinone reduction in vivo in tumour tissue would appear to be drug inactivation to a 7-deoxyaglycone metabolite rather than drug activation to DNA reactive species or ROS.     

Comparative cardiotoxicity and antitumour activity of doxorubicin (adriamycin) and 4'-deoxydoxorubicin and the relationship to in vivo disposition and metabolism in the target tissues

4'-Deoxydoxorubicin (4'-DOX) is an analogue of the anticancer drug Adriamycin (ADR) believed to lack its cardiotoxicity. Bioreduction to a semi-quinone free radical has been implicated in the etiology of ADR induced cardiotoxicity. We have studied (in a rat model) acute cardiotoxicity (after 16 mg/kg i.v. of both drugs), antitumour activity (after 5 mg/kg i.v.) and the relationship to disposition and metabolism in the target tissues (after 5 mg/kg i.v.). 7-Deoxyaglycones, which are considered inactive lipophilic metabolites derived from ADR semi-quinone, were utilised as markers of in vivo tissue free radical generation. Both drugs produced toxicity of equal severity to hearts after 24 hr, associated with high cardiac levels of 7-deoxyaglycones in the case of ADR (AUC0-48 hr, micrograms/g X hr: ADR, 47; ADR 7-deoxyaglycone (ADR-DONE), 24; and adriamycinol 7-deoxyaglycone (AOL-DONE), 35) compared to low cardiac levels of 7-deoxyaglycones but a times five higher peak cardiac concentration of parent drug in the case of 4'-DOX (AUC0-48 hr, micrograms/g X hr: 4'-DOX, 68; 4'-DOX-DONE, 3.8; and 4'-DOL-DONE, 0.8). 4'-DOX displayed superior antitumour activity to ADR against the MC 40A sarcoma growing sub-cutaneously, achieving higher concentrations of parent drug in tumour (AUC0-48 hr, micrograms/g X hr: 4'-DOX, 150; ADR, 60). There was an absence of 7-deoxyaglycones of both drugs in the tumour. These data suggest that drug bioreduction is involved principally only in ADR induced cardiotoxicity and that the level of unchanged parent drug achieved in the tumour is the most important pharmacokinetic determinant of antitumour activity for both ADR and 4'-DOX.     

Stimulation by oestradiol of the urinary excretion of perfluorooctanoic acid in the male rat

The urinary excretion of perfluorooctanoic acid (PFOA) was studied in male Wistar rats after castration and oestradiol administration as well as in intact females and males. During the first 24 hr females excreted 72 +/- 5% (N = 6) of a single intraperitoneal dose of PFOA (50 mg/kg) in urine whereas the intact males excreted only 9 +/- 4% (N = 6). After castration followed by oestradiol administration (500 micrograms/kg every 2nd day for 14 days), the males excreted PFOA in urine in similar amounts as the females (68 +/- 14% at 24 hr, N = 10). Oestradiol treatment of non-castrated males produced similar results (61 +/- 19% at 24 hr, N = 10). Also castration without oestradiol administration significantly enhanced the renal PFOA excretion, but not as effectively as oestradiol treatment. After 96 hr, the concentration of PFOA in serum of intact males was 17-40 times higher than in the serum of other groups. PFOA was similarly bound by the proteins in the serum of females and males. Phase II metabolism of PFOA was not shown either in males or females.     

Urinary pharmacokinetics of physostigmine in the rat

Urinary pharmacokinetics of 3H-Physostigmine (Phy) were studied in rat after an intramuscular administration of 650 micrograms/kg. Urine was collected at 0-1, 1-2, 2-4, 4-6, and 6-24 hr and every 24 hr for seven days. The rats were sacrificed by decapitation and the tissues were analyzed for radioactivity. Less than one percent (.87%) of the dose remained in tissues after the seventh day. Liver, followed by kidney, accounted for the highest activity compared to other tissues. The amounts of 3H-Phy and metabolites were determined by HPLC and the rapid decline of Phy in urine was observed. Most of the radioactivity found in the urine was due to metabolites (47% of dose in 24 hr) indicating extensive metabolism. The cumulative percent of radioactivity excreted in the urine was 30.3 +/- 12.6% in 6 hr, 44.4 +/- 13.1% in 24 hr which increased to 52.7 +/- 12.0% after seven days. Urinary elimination rate constant (Ku) of Phy was found to be .051 +/- .009 hr-1 indicating that the urinary elimination of Phy accounted for a minor part (2.5-4.%) of the systemic elimination.     

Caffeine metabolism in premature infants

Caffeine has been used frequently in the treatment and prevention of apnea of prematurity. The metabolism of caffeine depends on the activities of the hepatic enzymes that vary from one infant to another. The objective of this study was to determine the influence of postnatal age (PNA), birth weight (BW), study weight (SW), gestational age (GA), postconceptual age (PCA), and gender on the maturation of caffeine metabolism in premature infants. The caffeine base was administered orally as a loading dose of 10 mg/kg, followed by a maintenance dose of 2 mg/kg every 24 hours. The steady-state concentration of caffeine and metabolites was measured in plasma taken on the 5th-day postloading dose. The molar concentration ratios for the N3 (N3-), N7 (N7-), N1 (N1-), and all methyl (Nall-) demethylation processes; clearance (CL); and the percentage of molar concentration of caffeine found in plasma to that of the total caffeine and metabolites (%CAF) were calculated from samples collected from 80 neonatal infants. The 48 male and 32 female premature infants had median (range) BW (g), GA (weeks), SW (g), PCA (weeks), and PNA (days) of 1300 (650-2260), 30 (24-34), 1630 (980-2670), 34 (29-40), and 28 (5-60), respectively. The median (range) of the ratios for the %CAF, CL, and the N3-, N7-, N1-, and Nall- were 86.9 (52.9-99.0), 0.127 (0.046-0.503) ml.kg-1.min-1, 0.032 (0-0.438), 0.070 (0.007-0.471), 0.026 (0-0.283), and 0.0463 (0.003-0.303), respectively. When the patients were stratified into four PNA age groups, each older group showed a consistently higher level of caffeine metabolic activity for the N3-, N7-, and Nall- pathways with a corresponding decrease in the %CAF, whereas no significant differences were seen for the N1-pathway or for CL. No pattern of significant differences between the demethylation process ratios, %CAF, or CL was seen between groups of infants when they were stratified according to BW, SW, PCA, or GA. The female infants were found to have significantly higher rates of caffeine metabolism as shown by %CAF, N1-, N3-, and Nall- processes but not the N7-. Multivariate linear regression analysis by two methods demonstrated that PNA is significantly related to %CAF and Nall-, whereas the female patients had higher levels of metabolic activity for the %CAF and N1- process. The authors conclude that the N7-demethy-lation process is the predominate caffeine metabolic process in premature infants. Furthermore, the maturation of the caffeine metabolism in premature infants with a PNA of less than 60 days increases with postnatal age, regardless of birth weight, gestational age, postconceptual age, and study weight. The female neonatal patients demonstrated a higher rate of caffeine metabolism than the males.     

Inhibition and induction of theophylline metabolism by 8-methoxypsoralen. In vivo study in rats and humans

The effects of 8-methoxypsoralen (8-MOP) on the metabolism of theophylline were studied in rats and humans. Rats were randomized into three groups and prepared with iv jugular catheters. Group I (N = 4) received a single ip injection of 27 mg/kg of 8-MOP, group II (N = 5) vehicle (corn oil), and group III (N = 4) 50 mg/kg/day of 8-MOP for 3 days. Rats were subsequently administered 15 mg/kg of theophylline iv, and timed blood samples (0.2 ml) were assayed for theophylline by HPLC. Theophylline clearance (ml/min/kg; mean +/- SD) was 1.7 +/- 0.3, 2.4 +/- 0.5, and 9.5 +/- 1.6 in groups I, II, and III, respectively. The half-life (harmonic mean) from 0.5 to 12 hr was 7.2, 3.6, and 0.8 hr. Urinary excretion of unchanged theophylline (mean +/- SD) from 0 to 24 hr was 60 +/- 10, 41 +/- 6, and 13 +/- 3% of the administered dose. In a crossover study, three healthy, male, nonsmokers received 600 mg of oral theophylline. Urine and plasma were collected for 48 hr. One week later, subjects received 1.2 mg/kg of oral 8-MOP followed in 1 hr by 600 mg of oral theophylline. Mean residence time of theophylline increased from 10.7, 17.2, and 12.2 hr in the control period, to 20.3, 19.0, and 18.4 hr after 8-MOP. The AUC (microgram.hr/ml) of theophylline increased from 204, 213, and 204, to 555, 364, and 432, while clearance (ml/min/kg) decreased from 0.74, 0.57 and 0.63, to 0.27, 0.33, and 0.30, respectively. Urinary excretion of unchanged theophylline from 0 to 48 hr increased from 14, 14, and 15, to 24, 21, and 20%. We conclude that 8-MOP administered acutely is a potent inhibitor of theophylline metabolism and chronically in the rat is a powerful inducer.     

Methylprednisolone hemisuccinate and metabolites in urine from patients receiving high-dose corticosteroid therapy.

A reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the measurement of methylprednisolone hemisuccinate (MPHS) and its metabolites methylprednisolone (MP), 20-alpha- (20a-HMP), and 20-beta-hydroxymethylprednisolone (20b-HMP) in urine is described. The metabolites were extracted from urine samples using Extrelut columns and eluted with ethylacetate. The mobile phase for RP-HPLC comprised methanol:citrate buffer:tetrahydrofuran (30:65:5, vol/vol/vol) with UV detection at 251 nm. Fractions were collected, pooled and the metabolites present were identified by gas chromatography-mass spectrometry and normal-phase HPLC (NP-HPLC). By RP-HPLC 30 +/- 7.3% (mean +/- 1 SD) of the dose was detected in the 0-24 h urine sample following a 1 g MPHS infusion to patients with rheumatoid arthritis; MPHS contributed 9.9 +/- 5.0%, MP 12.1 +/- 2.9%, 20a-HMP 7.8 +/- 2.2%, and 20b-HMP 1.0 +/- 0.3%, respectively. A further 1.0 +/- 0.9% of the administered dose was detected in urine collected 24-48 h postinfusion.     

Effect of caffeine on ceftriaxone disposition and plasma protein binding in the rat

Previous studies have shown that caffeine can affect drug kinetics by altering drug binding to plasma protein, drug absorption, or drug distribution. In this study, the effect of caffeine on the in vivo protein binding and the disposition of ceftriaxone (a highly protein-bound cephalosporin) were investigated in the rat. Ceftriaxone 100 mg/kg and caffeine 20 mg/kg were i.v. injected via the tail vein and ceftriaxone in plasma, plasma filtrate, urine, feces, and tissues (brain, heart, kidney, liver, gut, lung, and muscle) was assayed by HPLC with UV detection. The fraction of free ceftriaxone in plasma ranged from 5.6 to 32.8% of total ceftriaxone (3-347 micrograms/ml) without caffeine and showed no alteration by caffeine. The total amount of ceftriaxone excreted in urine and feces was increased significantly (p less than 0.05) from 13.1 +/- 1.8 mg (mean +/- SD, 54.6% of total) to 15.3 +/- 1.1 mg (63.8% of total) by caffeine coadministration. The terminal half-life of ceftriaxone in plasma was shortened from 59 to 47 min, and the area under the plasma drug concentration-time curve (AUC) was reduced from 612 to 516 micrograms hr/ml. Although the peak drug concentrations and the times of peak concentration of ceftriaxone in tissues were not altered by caffeine administration, the elimination of ceftriaxone was increased, as indicated by generally shorter half-lives (decreases ranged from 17.5% in liver to 34.2% in brain) and lower AUC values (from 9.0% in heart to 54.5% in brain). These results suggest that caffeine does not alter the protein binding of ceftriaxone, but enhances the elimination of ceftriaxone in the rat.     

Long-term effects of irbesartan and atenolol on the renin-angiotensin-aldosterone system in human primary hypertension: the Swedish Irbesartan Left Ventricular Hypertrophy Investigation versus Atenolol (SILVHIA)

We examined long-term influence of the angiotensin II type 1-receptor blocker irbesartan and the beta1-adrenergic receptor blocker atenolol on some neurohormonal systems implicated in the pathophysiology of cardiac hypertrophy. Thus, 115 hypertensive patients with left ventricular hypertrophy were randomized to receive double-blind irbesartan or atenolol, with additional therapy if needed. Neurohormone measurements and echocardiography were performed at weeks 0, 12, 24, and 48. Left ventricular mass was reduced more by irbesartan than by atenolol (-26 g/m2 versus -14 g/m2, P = 0.024), despite similar reductions in blood pressure. Plasma renin activity and angiotensin II increased (P < 0.001) by irbesartan (0.9 +/- 0.7 to 3.4 +/- 4.2 ng/mL x h, and 3.0 +/- 1.6 to 13.0 +/- 17.7 pmol/L), but decreased (P < 0.01) by atenolol (1.0 +/- 0.6 to 0.7 +/- 0.6 ng/mL x h, and 3.4 +/- 1.6 to 3.2 +/- 2.2 pmol/L). Serum aldosterone decreased (P < 0.05) by both irbesartan (346 +/- 140 to 325 +/- 87 pmol/L) and atenolol (315 +/- 115 to 283 +/- 77 pmol/L). Changes in left ventricular mass by irbesartan related inversely to changes in plasma renin activity, angiotensin II, and aldosterone (all P < 0.05). Plasma levels and 24-hour urinary excretions of catecholamines, plasma leptin, proinsulin, insulin and insulin sensitivity remained largely unchanged in both groups. Thus, the renin-angiotensin aldosterone system appears to be an important non-hemodynamic factor in the regulation of left ventricular mass.     

Pharmacokinetics and therapeutic efficacy of metronidazole at different dosages.

Metronidazole, a drug effective against certain protozoal and anaerobic infections, was given female patients with Trichomoniasis urogenitalis. Group I received twice daily 250 mg of metronidazole (supplied as 250 mg tablets Vagimid). Group II received in a single dose 1.0 g (4 tablets); and group III, 2.0 g (8 tablets). Serum and urine metronidazole levels were measured polarographically. Kinetic parameters were determined from the measured values of the concentration time curve by a computing program. An exact control of the therapeutic result was carried out. In all patients peak serum levels occurred within 1-3 hr and averaged 5.1 +/- 1.7 microgram/ml after 250 mg doses, 19.6 +/- 3.8 microgram/ml after 1.0 g doses and 40.6 +/- 9.3 microgram/ml after 2.0 g doses. About 35% of the administered dose was recovered in the urine in 12 hr and about 50% in 24 hr. Metronidazole shows protein binding of 10-20% equally in vivo and in vitro. Minimum trichomonacidic concentrations of nearly 1 microgram/ml were still present 12 hr after oral application of 250 mg metronidazole, and 24 hr to 36 hr, respectively after 1.0 g and 2.0 g daily doses. The cure rate was 100%. No serious side effects ocurred in any of the patients.     

Studies on the metabolic fate of [14C]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the mouse

Studies on the Metabolic Fate of [14C]2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in the Mouse. KOSHAKJI, R. P., HARBISON, R. D., and BUSH, M. T. (1984). Toxicol. Appl. Pharmacol. 73, 69-77. After a single po dose (135 micrograms/kg; 62 microCi/kg) of 14C-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male ICR/Ha Swiss mice, 67 to 76% of the administered dose was eliminated via the feces and 1 to 2% in the urine during the first 24 hr following treatment. It seems likely that most of this material was simply not absorbed. Much of the remaining chemical was then excreted slowly in the urine (2%) and feces (7%) during the next 10 days, partly as the unchanged compound and partly as metabolites. One of the metabolites (Fraction II) appears to be a single polar, acidic metabolite characterized in urine (0.4 +/- 0.1%) and feces (2.2 +/- 0.2%), and is also likely excreted as a glucuronide conjugate. The rest of the radioactivity was in the form of unchanged TCDD in the animal body (17 +/- 2%). Steady rates of decline in the concentrations of the 14C as well as of the unchanged TCDD were reached in the feces and urine after the fifth day following the administration of the chemical. Based on this steady rate, the half-life of the radioactivity in the body was approximately 20 days. Urine, feces, and whole body were analyzed by solvent extraction, 14C counting, thin-layer chromatography, and countercurrent distribution.     

Theophylline: pharmacokinetics, metabolism and urinary excretion in dogs

The disposition of theophylline (aminophylline) administered either parenterally or orally to anesthetized dogs was studied. Pharmacokinetics of theophylline (8.2 mg/kg, n = 10) following intravenous administration could be analyzed by a two-compartment open model. The half-time (T1/2 beta) of theophylline was 5.63 +/- 0.83 hr, and the volume of distribution (Vd) was 0.73 +/- 0.04 l/kg. The elimination rate constant was 0.37 +/- 0.05 hr-1. Two metabolites of theophylline were isolated from urine and identified as 3-methyl xanthine (3-MX) and 1,3-dimethyl uric acid (1,3-DMU) by HPLC. The dogs excreted about 85% (n = 4) of the dose in urine in 24 hr. The majority (2/3) was excreted as changed theophylline, i.e., 3-MX 40.2 +/- 3.5% and 1,3-DMU 26.2 +/- 4.3%, while unchanged theophylline amounted to 18.2 +/- 2.4%. Absorption of theophylline (8.2 mg/kg, n = 5) administered intramuscularly was good as indicated by its high bioavailability (101.9 +/- 6.5%), but the value of bioavailability was low in oral administration (72.8 +/- 11.8%, n = 5). The percentage of protein binding (about 44%, n = 3-7) did not change by increasing the serum concentration (8.2-24.6 micrograms/ml).     

The role of metabolism in 2-methoxyethanol-induced testicular toxicity

The role of metabolism in 2-methoxyethanol (ME)-induced testicular toxicity has been investigated with Sprague-Dawley rats. Following administration of [14C]ME (250 mg/kg, ip) to a group of animals, there was evidence of testicular damage, identified as depletion of the spermatocyte population. Radioactivity detected in urine over 48 hr after treatment accounted for 55% of the dose. The major urinary metabolites were identified by HPLC and isotope dilution analysis, as methoxyacetic acid (MAA) and methoxyacetylglycine (accounting for 50 to 60% and 18 to 25%, respectively, of urinary radioactivity). Analysis of plasma revealed a rapid conversion of ME to MAA (t1/2 for disappearance of ME = 0.6 +/- 0.03 hr) and gradual clearance of radioactivity (t1/2 = 19.7 +/- 2.3 hr). Pretreatment of animals with pyrazole (400 mg/kg, ip) 1 hr prior to [14C]ME dosing gave complete protection against the testicular toxicity of ME. Radioactivity detected in the urine from the pyrazole-pretreated groups over 48 hr (18%) was significantly lower than in the ME-only group. The major radioactive peak co-chromatographed with ME (30 to 36% of the total urinary radioactivity). MAA and methoxyacetylglycine were not major metabolites. Analysis of plasma revealed almost complete inhibition of the conversion of ME to MAA (t1/2 for disappearance of ME = 42.6 +/- 5.6 hr, clearance of radioactivity t1/2 = 51.0 +/- 7.8 hr). The results demonstrate that metabolic activation is required for 2-methoxyethanol to exert toxicity to the male reproductive system.     

The metabolism and kinetics of tiflorex in the rat

14C-Tiflorex given either orally or intravenously to male rats (10 mg/kg; 250 microCi) was well absorbed orally; greater than 70% of the dose was excreted in the urine in the first 48 hr after dosing by either route of administration. Inasmuch as part of the dose (10%) was excreted in the feces after iv administration, it is probable that biliary excretion is a route of elimination. This was shown to be so by cannulation of the bile duct. The major route of metabolism was S-oxidation to give the sulfoxides and sulfones of tiflorex (7% each) and nortiflorex (10 and 20%, respectively) which were excreted together with the unchanged drug (1%) in the 0- to 48-hr urine. Examination of the plasma for the unchanged drug and its metabolites showed the drug to be rapidly absorbed orally, maximum levels being attained within 30 min. The plasma half-life for the elimination phase of the unchanged drug was relatively long (7.5 hr) compared with the metabolites (2.5 hr) with the exception of nortiflorex sulfone (9.8 hr) and two as yet unidentified metabolites which had half-lives in excess of 24 hr. The latter three compounds were responsible for the relatively long plasma half-life of total radioactivity (ca. 13 hr). The ratio of the areas under the plasma curve for unchanged drug indicated a low bioavailability (30%). It appears that the predominant route of metabolism of this group of compounds in the rat, p-hydroxyltation had been blocked by the trifluoromethylthio group, with consequent emphasis on S-oxidation.     

Aspects of chronic oral treatment with thyrotropin-releasing hormone: the hypothalamic-pituitary-thyroid axis in rats. A study with a pharmacological dose of thyrotropin-releasing hormone.

The effects of 16 days of oral treatment with thyrotropin-releasing hormone (TRH, 1 mg/24 h) on serum levels of thyrotropin (TSH), thyroxine (T4) and triiodothyronine (T3) and the kinetics of TRH in the blood were studied in normal rats. A second group of animals served as controls. TRH was dissolved by sonification (10 mg/l) and was stable in tap water. TRH was measured by a radioimmunoassay procedure (normal range: 20-80 pmol/l, antiserum K2B9 1:120,000 final dilution). An increase in basal TSH (7,200 +/- 440 ng/l, mean +/- SD) was found after 2 days of treatment (11,420 +/- 810 ng/l), but a significant increase was observed after 5 days of treatment (12,530 +/- 640 ng/l, p less than 0.001). T4 serum concentrations remained in the normal range during the entire period of study, whereas T3 serum concentrations (0.76 +/- 0.1 micrograms/l) were increased to 1.22 +/- 0.2 micrograms/l on day 5 (p less than 0.001). A subsequent decline of TSH, T4 and T3 up to the end of the study was observed. TRHmax concentrations were registered on day 5 (790 +/- 24 pmol/l). The mean value of TRHmax was 723 +/- 34 pmol/l. To improve the stability of TRH in tap water, 1-ml samples of drinking water with dissolved TRH were measured. The mean TRH concentration in drinking water was 73 +/- 1.5% (SD). No significant correlations were found between the area under the curve of TSH (184,340 ng.l-1.24 h) and that of TRH (14,954 pmol.l-1.24 h).(ABSTRACT TRUNCATED AT 250 WORDS)     

Concentrations of cefotaxime in serum and myocardial tissue

Serum and myocardial concentrations of cefotaxime (CTX) were measured in 20 adult patients undergoing cardiac surgery. To all of these patients 1.0 g of CTX was given intravenously (in the range of 13.7--29.0 mg/kg) at the beginning of operation. The serum concentrations of CTX were determined at 5, 10, 30, 60 minutes and 120 minutes after administration. Myocardial concentrations of CTX were also determined at about 30 minutes (group I), 60 minutes (group II) and 120 minutes (group III). The following results were obtained. Average serum CTX concentrations were 132.8 +/- 34.1 micrograms/ml at 5 minutes, 92.0 +/- 23.1 micrograms/ml at 10 minutes, 44.6 +/- 12.3 micrograms/ml at 30 minutes, 24.5 +/- 7.7 micrograms/ml at 60 minutes and 12.3 +/- 4.9 micrograms/ml at 120 minutes after administration. Average myocardial CTX concentrations were 10.0 +/- 3.7 micrograms/g in group I, 3.6 +/- 2.1 micrograms/g in group II and 2.3 +/- 1.8 micrograms/g in group III. The myocardial/serum concentration ratio was 0.22 +/- 0.14 in group I, 0.15 +/- 0.08 in group II and 0.18 +/- 0.12 in group III, respectively. These results suggested that the serum and myocardial concentrations of CTX were high enough to be prophylactic and therapeutic against not only aerobic but also anaerobic and opportunistic infections during and after cardiac surgery.     

Determination of the antiepileptics vigabatrin and gabapentin in dosage forms and biological fluids using Hantzsch reaction

A selective and sensitive method was developed for the determination of the anticonvulsants vigabatrin (I) (CAS 60643-86-9) and gabapentin (II) (CAS 60142-96-3). The method is based on the condensation of the drugs through their amino groups with acetylacetone and formaldehyde according to Hantzsch reaction yeilding the highly fluorescent dihydropyridine derivatives. The yellowish-orange color was also measured spectrophotometrically at 410 nm and 415 nm for I and II, respectively. The absorbance-concentration plots were rectilinear over the ranges 10-70 micrograms/ml and 20-140 micrograms/ml for I and II, respectively. As for the fluorescence-concentration plots, they were linear over the ranges 0.5-10 micrograms/ml and 2.5-20 micrograms/ml with minimum detection limits (S/N = 2) of 0.05 microgram/ml (approximately 2.1 x 10(-8) mol/l) and 0.1 microgram/ml (approximately 5.8 x 10(-7) mol/l) for I and II, respectively. The spectrophotometric method was applied to the determination of I and II in their tablets. The percentage recoveries +/- SD (n = 6) were 99.45 +/- 0.13 and 98.05 +/- 0.53, respectively. The spectrofluorimetric method was successfully applied to the determination of I and II in spiked human urine and plasma. The % recoveries +/- SD (n = 5) were 98.77 +/- 0.29 and 98.39 +/- 0.53 for urine and 99.32 +/- 0.74 and 98.90 +/- 0.96 for plasma, for I and II, respectively. No interference was encountered with the co-administered drugs: valproic acid (CAS 99-66-1), diphenylhydantoin (CAS 57-41-0), phenobarbital (CAS 50-06-6), carbamazepine (CAS 298-46-4), clonazepam (CAS 1622-61-3), clobazam (CAS 22316-47-8) or cimetidine (CAS 51481-61-9). A proposal of the reaction pathway is suggested. The advantages of the proposed methods over existing method are discussed.     

The disposition and metabolism of 14C-tiaramide . HCl in man

The disposition and metabolism of 14C-tiaramide HCl was examined in four healthy male volunteers, after administration of a 200-mg dose in solution. The mean cumulative recovery of administered radioactivity was 91.3 +/- 2.9% (mean +/- SD) in urine an 6.0 +/- 1.5% in feces. The elimination was rapid, with 83.9% of the radioactivity extracted in urine in the first 12 hr. The unchanged tiaramide serum concentration curve showed monoexponential elimination with a half-life of 1.3 hr. Peak serum levels, of 1.6-2.2 micrograms/ml were attained between 0.5 and 1.5 hr after dosing. Tiaramide was extensively metabolized, with less than 1% excreted unchanged. Urinary metabolites (80-95% of the dose) were identified by mass-spectral comparison to authentic standards. Biotransformation resulted in production of the N-acetic acid N-oxide, N-acetic acid, O-glucuronide, N-oxide, and desethanol metabolites of tiaramide.     

Excretion and tissue distribution of selenium following treatment of male F344 rats with benzylselenocyanate or sodium selenite.

Benzylselenocyanate (BSC), a synthetic organoselenium compound less toxic than sodium selenite (Na2SeO3), has been demonstrated to inhibit the development of neoplasia in several experimental animal models. We examined the excretion and tissue distribution of total Se after acute administration of BSC compared to Na2SeO3. Male F344 rats were treated po with approximately one-tenth of the LD50 values, our estimate of highest non-toxic dose. The doses administered were 9.85 mg/kg in the case of BSC and 4.35 mg/kg in the case of Na2SeO3. The rats were sacrificed at 1, 6, 24, 72, or 120 hr to obtain biological samples. The levels of total Se were determined by graphite furnace atomic absorption spectrophotometry following microwave digestion. In serum, the highest Se level was observed at 6 hr after administration of either BSC or Na2SeO3: 1.34 +/- 0.07 (mean +/- SE), or 2.09 +/- 0.11 micrograms/ml of serum, respectively. In urine and feces, the cumulative percentages of doses excreted within 3 days of BSC or Na2SeO3 treatment were, respectively, as follows: 11.36 +/- 0.82% and 18.33 +/- 0.77% in urine; and 6.67 +/- 0.66% and 31.14 +/- 4.66% in feces. Among the tissues of BSC-treated rats, the kidneys were found to have the highest Se levels throughout the experimental period (as much as 29 micrograms/g of tissue at 72 hr), followed by liver, small intestine, large intestine, lung, pancreas, heart, and spleen. The results indicate that Se from BSC-treated animals is excreted very slowly and is retained in the organs for a much longer period compared to rats treated with Na2SeO3. Whether the slow excretion and prolonged retention of BSC and/or its metabolites play a role in its chemopreventive action is currently under investigation.