Chronopharmacology of Methotrexate Pharmacokinetics in Childhood Leukemia

Survival has been shown to improve when maintenance therapy for acute lymphocytic leukemia in children is given at night rather during the day. We examined the possibility that diurnal variation in methotrexate pharmacokinetics may contribute to this improvement. In a crossover study, we determined the pharmacokinetics of intravenous methotrexate at 10:00 and 21:00 h in six children with standard or high-risk leukemia. During the study, children refrained from concomitant drugs (6-mercaptopurine and trimethoprim sulfamethoxazole). There was a significant fall in methotrexate plasma clearance at night (from 5.6 ± 3 ml/min/kg to 4.7 ± 2.3 ml/min/kg p > 0.05). Renal clearance of methotrexate tended to decrease at night and unbound renal clearance decreased significantly (from 17.5 ± 1.7 ml/min/kg to 8.5 ± 3.6 ml/min/kg p > 0.05). Creatinine clearance did not exhibit diurnal variation, when comparing two 12-h collections, but there was a significant decrease in the nonglomerular clearance of methotrexate (from 14.8 ± 5.2 to 6 ± 4 ml/min/kg). Because it is a weak organic acid, the tubular secretion of methotrexate depends on urinary pH. At night urinary pH is more acidic. This may result in more reabsorption and hence reduced renal clearance.     

Effects of Amlodipine on Orcadian Rhythms in Blood Pressure, Heart Rate, and Motility: A Telemetric Study in Rats

In male Wistar rats [light (L): 07:00-19:00 h, dark (D): 19:00-07:00 h], the effects of the calcium channel blocker amlodipine (1, 3, 10 mg/kg i.p.) on blood pressure, heart rate, and motor activity were studied by telemetric monitoring. Amlodipine was injected either at 07:00 h or at 19:00 h. Systolic and diastolic blood pressure were dose-dependently decreased with more pronounced effects in the dark span, ED₅₀ values in D were about seven times lower than in L. In contrast, the dose-dependent increase in heart rate was more pronounced in L than in D. No significant effects of amlodipine were found on motor activity. The study gives evidence for a circadian phase-dependency in the cardiovascular effects amlodipine in rats.     

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Dosing‐time–dependent changes in the effect and toxicity of morphine were examined in mice housed under alternating 12 h light (07:00 to 19:00 h) and dark (19:00 to 07:00 h) cycles. Morphine (0.5 mg/kg) was injected intraperitoneally (i.p.) in animals to assess its beneficial effect (i.e., protection against the kaolin‐induced, bradykinin‐mediated, writhing reaction) and its toxicity (i.e., alteration of the hepatic enzymes of aspartate aminotransferase [AST] alanine aminotransferase [ALT], and glutathione [GSH] in separate experiments). The magnitude of the analgesic effect of morphine depended on dosing time, with minimum effect at 02:00 h and maximum effect at 14:00 h. The serum hepatic enzyme levels of AST and ALT increased after dosing morphine (100 mg/kg) at 02:00 and 14:00 h. Time courses of these enzymes did not differ between the two trials. However, hepatic GSH, which is involved in the detoxification of chemical compounds, significantly decreased after i.p. morphine injection at 02:00 but not at 14:00 h. Overall, the results suggest that the analgesic effect of morphine is greater after dosing during the resting than during the activity phase of mice that have been induced with bradykinin‐mediated pain. Drug‐induced hepatic damage as inferred by GSH alteration, however, may be greater after dosing during the active phase.     

Effects of Amlodipine on Orcadian Rhythms in Blood Pressure,Heart Rate,and Motility: A Telemetric Study in Rats

In male Wistar rats [light (L): 07:00–19:00 h, dark (D): 19:00–07:00 h], the effects of the calcium channel blocker amlodipine (1, 3, 10 mg/kg i.p.) on blood pressure, heart rate, and motor activity were studied by telemetric monitoring. Amlodipine was injected either at 07:00 h or at 19:00 h. Systolic and diastolic blood pressure were dose-dependently decreased with more pronounced effects in the dark span, ED₅₀ values in D were about seven times lower than in L. In contrast, the dose-dependent increase in heart rate was more pronounced in L than in D. No significant effects of amlodipine were found on motor activity. The study gives evidence for a circadian phase-dependency in the cardiovascular effects amlodipine in rats.     

Chronopharmacology of morphine in mice

Dosing-time-dependent changes in the effect and toxicity of morphine were examined in mice housed under alternating 12 h light (07:00 to 19:00 h) and dark (19:00 to 07:00 h) cycles. Morphine (0.5 mg/kg) was injected intraperitoneally (i.p.) in animals to assess its beneficial effect (i.e., protection against the kaolin-induced, bradykinin-mediated, writhing reaction) and its toxicity (i.e., alteration of the hepatic enzymes of aspartate aminotransferase [AST] alanine aminotransferase [ALT], and glutathione [GSH] in separate experiments). The magnitude of the analgesic effect of morphine depended on dosing time, with minimum effect at 02:00 h and maximum effect at 14:00 h. The serum hepatic enzyme levels of AST and ALT increased after dosing morphine (100 mg/kg) at 02:00 and 14:00 h. Time courses of these enzymes did not differ between the two trials. However, hepatic GSH, which is involved in the detoxification of chemical compounds, significantly decreased after i.p. morphine injection at 02:00 but not at 14:00 h. Overall, the results suggest that the analgesic effect of morphine is greater after dosing during the resting than during the activity phase of mice that have been induced with bradykinin-mediated pain. Drug-induced hepatic damage as inferred by GSH alteration, however, may be greater after dosing during the active phase.     

Mechanism of the stimulatory action of antisteroid RU486 on follicle-stimulating hormone secretion in the cyclic Rat

These experiments explored the mechanism underlying FSH hypersecretion on estrous afternoon in rats injected with RU486 (RU) on proestrus. Four-day cyclic rats were injected with RU at 12:00 h on proestrus (1 or 4 mg/0.2 ml oil; s.c.), and its effects on LH and FSH secretion at 18:30 h on estrus were compared with those of antiprogestagens ZK299 (ZK) (1 or 4 mg/0.2 ml oil; s.c.) and Org31806 (OR) (2 or 8 mg/0.2 ml oil; s.c.). Additionally, rats treated with RU or nembutal (PB) (60 mg/kg; i.p. at 13:00 h on proestrus) were injected with an LHRH antagonist (LHRHa) at 10:00 h on estrus (1 mg/0.2 ml saline; s.c.) or progesterone (P) (7.7, 15.5 or 30.9 mg/0.2 ml oil; s.c.) on proestrus at 10:00 h in RU-injected rats and at 14:00 h in PB-injected rats. Animals were killed by decapitation at 18:30 h on estrus and serum LH and FSH concentrations were determined. Rats treated with 1 or 4 mg of RU or Org or 4 mg of ZK recorded increased serum FSH on estrous afternoon, while 1 mg ZK had no effect. PB increased mainly serum LH levels and, to a lesser extent, FSH levels. P decreased serum FSH concentrations in both RU- and PB-injected rats. LHRHa reversed the effects of PB on FSH secretions, but reduced FSH hypersecretion induced by RU only. These results are interpreted to mean that, in the absence of proestrous afternoon P-inhibitory action of the neural stimulus controlling LHRH release, FSH secretion on estrous afternoon involves two components: one is LHRH dependent while, in contrast to LH secretion, the other is LHRH independent, and only expressed in a low estrogen background.     

Differences in Sleep,Light, and Circadian Phase in Offshore 18:00–06:00 h and 19:00–07:00 h Shift Workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep‐wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00–06:00 h and 19:00–07:00 h schedules during summer (May–August). Ten men, aged 46±10 yrs (mean±SD), worked the 19:00–07:00 h shift schedule for two or three weeks offshore (58°N). Seven men, mean age 41±12 yrs, worked the 18:00–06:00 h shift schedule for two weeks offshore (61°N). Circadian phase was assessed by calculating the peak (acrophase) of the 6‐sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00–06:00 h had a 6‐sulphatoxymelatonin acrophase of 11.7±0.77 h (mean±SEM, decimal hours), whereas it was significantly later, 14.6±0.55 h (p=0.01), for adapted subjects working 19:00–07:00 h. Two subjects did not adapt to the 19:00–07:00 h night shift (6‐sulphatoxymelatonin acrophases being 4.3±0.22 and 5.3±0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00–07:00 h of 5.71±0.31 h compared to those working 18:00–06:00 h whose mean sleep duration was 6.64±0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00–07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00–07:00 h than the 18:00–06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

Chronopharmacology of methotrexate pharmacokinetics in childhood leukemia.

Survival has been shown to improve when maintenance therapy for acute lymphocytic leukemia in children is given at night rather during the day. We examined the possibility that diurnal variation in methotrexate pharmacokinetics may contribute to this improvement. In a crossover study, we determined the pharmacokinetics of intravenous methotrexate at 10:00 and 21:00 h in six children with standard or high-risk leukemia. During the study, children refrained from concomitant drugs (6-mercaptopurine and trimethoprim sulfamethoxazole). There was a significant fall in methotrexate plasma clearance at night (from 5.6 +/- 3 ml/min/kg to 4.7 +/- 2.3 ml/min/kg p < 0.05). Renal clearance of methotrexate tended to decrease at night and unbound renal clearance decreased significantly (from 17.5 +/- 1.7 ml/min/kg to 8.5 +/- 3.6 ml/min/kg p < 0.05). Creatinine clearance did not exhibit diurnal variation, when comparing two 12-h collections, but there was a significant decrease in the nonglomerular clearance of methotrexate (from 14.8 +/- 5.2 to 6 +/- 4 ml/min/kg). Because it is a weak organic acid, the tubular secretion of methotrexate depends on urinary pH. At night urinary pH is more acidic. This may result in more reabsorption and hence reduced renal clearance.     

Chronopharmacokinetic Study of Gentamicin in Dogs

The purpose of this experiment was to determine whether the time of day of single intravenous doses of gentamicin affects the drug's pharmacokinetics in dogs maintained under a 12 h light (08:00 to 20:00 h), 12 h dark (20:00 to 08:00 h) cycle. Using a crossover design, 6 mixed‐breed male dogs received a single dose of 2 mg/kg of gentamicin at 8:00 or 20:00 h. Serial blood samples were collected and pharmacokinetic parameters were calculated following each timed dose. The concentration of the antibiotic was lower following the 08:00 h compared to the 20:00 h administration. When gentamicin was administered at 20:00 h, the initial concentration, mean residence time, and area under the disposition curve were significantly higher (p<0.05) and the apparent volume of distribution of the central compartment, apparent volume of distribution, apparent volume of distribution at steady‐state, and total body clearance (1.73±0.55 at 20:00 h versus 3.31±0.67 L/min/kg at 08:00 h) were significantly lower than for the 08:00 h administration (p<0.05). Our results show that the pharmacokinetics of gentamicin exhibits significant temporal variation when administered to dogs at different times of day.     

Chronopharmacological Study of Cephalexin in Dogs

Recent studies have identified a 24 h rhythm in the expression and function of PEPT1 in rats, with significantly higher levels during the nighttime than daytime. Similarly, temporal variations have been described in glomerular filtration rate and renal blood flow, both being maximal during the activity phase and minimal during the rest phase in laboratory rodents. The aim of this study was to assess the hypothesis that the absorption of the first‐generation cephalosporin antibiotic cephalexin by dogs would be less and the elimination would be slower after evening (rest span) compared to morning (activity span) administration, and whether such administration‐time changes could impair the medication's predicted clinical efficacy. Six (3 male, 3 female; age 4.83±3.12 years) healthy beagle dogs were studied. Each dog received a single dose of 25 mg/kg of cephalexin monohydrate per os at 10∶00 and 22∶00 h, with a two‐week interval of time between the two clock‐time experiments. Plasma cephalexin concentrations were determined by microbiological assay. Cephalexin peak plasma concentration was significantly reduced to almost 77% of its value after the evening compared to morning (14.52±2.7 vs. 18.77±2.8 µg/mL) administration. The elimination half‐life was prolonged 1.5‐fold after the 22∶00 h compared to the 10∶00 h administration (2.69±0.9 vs. 1.79±0.2 h). The area under the curve and time to reach peak plasma concentration did not show significant administration‐time differences. The duration of time that cephalexin concentrations remained above the minimal inhibitory concentrations (MIC) for staphylococci susceptiblity (MIC=0.5 µg/mL) was>70% of each of the 12 h dosing intervals (i.e., 10∶00 and 22∶00 h). It can be concluded that cephalexin pharmacokinetics vary with time of day administration. The findings of this acute single‐dose study require confirmation by future steady‐state, multiple‐dose studies. If such studies are confirmatory, no administration‐time dose adjustment is required to ensure drug efficacy in dogs receiving an oral suspension of cephalexin in a dosage of 25 mg/kg at 12 h intervals.     

Opuntia ficus-indica juice supplementation: what role it plays on diurnal variation of short-term maximal exercise?

The aim of this study was to investigate the effect of natural Opuntia ficus-indica juice (OFIJ) supplementation on anaerobic performance at two times of day. Twenty-two healthy male subjects (20.91 ± 1.22; 21.00 ± 0.84 years) divided into two groups: Experimental group (EG: n = 11) and a control group (CG: n = 11) performed two tests-sessions (30-s of Wingate test (i.e. Peak power (PP), Mean power (MP)), Sargent jump test (SJT), sprint 10 m), before and after natural OFIJ supplementation at 07:00 h and 17:00 h. T-test showed that the OFIJ has a potent antioxidant capacity for capturing free radicals following the 22-diphenyl-1-picrylhydrazyl (DPPH^●) test (p < 0.05). Likewise, the ANOVA revealed that anaerobic performances were significantly higher at 17:00 h compared to 07:00 h around the peak of the temperature (p < 0.05) in both EG and CG before supplementation. Moreover, OFIJ lead an improvement of performances with (+2.09% at 07:00 h vs.+9.36% 17:00 h) for PP, (+11.29% at 07:00 h vs.+11.77% 17:00 h) for MP, (+9.42% at 07:00 h vs.+7.63% 17:00 h) for SJT in EG. The RPE scores on response to the Wingate test decrease after OFIJ supplementation (p < 0.01). For the sprint values, a significant improvement was after OFIJ (?7.10% at 07:00 h vs. ?6.45% 17:00 h). However, no change was observed for CG after supplementation. In conclusion, the natural OFIJ supplementation for two weeks appears to ameliorate the performance upon two times of day with great improvement observed in the evening during short-term maximal exercise given the higher muscle damage, inflammatory, and oxidative responses at this time of day. Thus, it’s necessary that athletes, coaches, and medical staff consider the positive effects of Opuntia ficus-indica to improve anaerobic performance.     

Pharmacokinetics of ketoprofen enantiomers in monkeys following single and multiple oral administration

Pharmacokinetic studies are reported after single oral administration of 3 mg/kg of stereochemically pure (S)-ketoprofen [(S)-KP] and (R)-ketoprofen [(R)-KP] to three male Cynomolgus monkeys and after repeated administration for 6 months of 3, 15 and 75 mg/kg/day of (S)-KP to both male and female monkeys. A high-performance liquid chromatographic (HPLC) analysis was performed without derivatization of the samples, using a chiral column. The pharmacokinetic parameters for (S)-KP after administration of (S)-KP and for (R)-KP after administration of (R)-KP were, respectively, elimination half-life 2.32 ± 0.36 and 1.64 ± 0.40 h; oral clearance 3.50 ± 0.66 and 7.50 ± 3.20 ml/min/kg; apparent volume of distribution 0.74 ± 0.24 and 1.16 ± 0.76 liter/kg; mean residence time 1.79 ± 0.77 and 1.41 ± 0.65 h; area under the concentration/time curve 14.16 ± 2.93 and 7.31 ± 2.98 μg·h/ml. Forty-nine percent unidirectional bioinversion of (R)-KP to (S)-KP was observed in this species and the pharmacokinetic parameters for the (S)-KP resulting from this inversion were also calculated. In the study of 6-month repeated administration of (S)-KP, linear pharmacokinetic behavior and no evidence of drug accumulation were observed at the three dose levels. © 1994 Wiley-Liss, Inc.     

Timing Light Treatment for Eastward and Westward Travel Preparation

Jet lag degrades performance and operational readiness of recently deployed military personnel and other travelers. The objective of the studies reported here was to determine, using a narrow bandwidth light tower (500 nm), the optimum timing of light treatment to hasten adaptive circadian phase advance and delay. Three counterbalanced treatment order, repeated measures studies were conducted to compare melatonin suppression and phase shift across multiple light treatment timings. In Experiment 1, 14 normal healthy volunteers (8 men/6 women) aged 34.9±8.2 yrs (mean±SD) underwent light treatment at the following times: A) 06:00 to 07:00 h, B) 05:30 to 07:30 h, and C) 09:00 to 10:00 h (active control). In Experiment 2, 13 normal healthy subjects (7 men/6 women) aged 35.6±6.9 yrs, underwent light treatment at each of the following times: A) 06:00 to 07:00 h, B) 07:00 to 08:00 h, C) 08:00 to 09:00 h, and a no-light control session (D) from 07:00 to 08:00 h. In Experiment 3, 10 normal healthy subjects (6 men/4 women) aged 37.0±7.7 yrs underwent light treatment at the following times: A) 02:00 to 03:00 h, B) 02:30 to 03:30 h, and C) 03:00 to 04:00 h, with a no-light control (D) from 02:30 to 03:30 h. Dim light melatonin onset (DLMO) was established by two methods: when salivary melatonin levels exceeded a 1.0 pg/ml threshold, and when salivary melatonin levels exceeded three times the 0.9 pg/ml sensitivity of the radioimmunoasssy. Using the 1.0 pg/ml DLMO, significant phase advances were found in Experiment 1 for conditions A (p?<?.028) and B (p?<?0.004). Experiment 2 showed significant phase advances in conditions A (p?<?0.018) and B (p?<?0.003) but not C (p?<?0.23), relative to condition D. In Experiment 3, only condition B (p?<?0.035) provided a significant phase delay relative to condition D. Similar but generally smaller phase shifts were found with the 2.7 pg/ml DLMO method. This threshold was used to analyze phase shifts against circadian time of the start of light treatment for all three experiments. The best fit curve applied to these data (R²?=?0.94) provided a partial phase-response curve with maximum advance at approximately 9–11 h and maximum delay at approximately 5–6 h following DLMO. These data suggest largest phase advances will result when light treatment is started between 06:00 and 08:00 h, and greatest phase delays will result from light treatment started between 02:00 to 03:00 h in entrained subjects with a regular sleep wake cycle (23:00 to 07:00 h).     

Ring the Bell for Matins: Circadian Adaptation to Split Sleep by Cloistered Monks and Nuns

Cloistered monks and nuns adhere to a 10-century-old strict schedule with a common zeitgeber of a night split by a 2- to 3-h-long Office (Matins). The authors evaluated how the circadian core body temperature rhythm and sleep adapt in cloistered monks and nuns in two monasteries. Five monks and five nuns following the split-sleep night schedule for 5 to 46 yrs without interruption and 10 controls underwent interviews, sleep scales, and physical examination and produced a week-long sleep diary and actigraphy, plus 48-h recordings of core body temperature. The circadian rhythm of temperature was described by partial Fourier time-series analysis (with 12- and 24-h harmonics). The temperature peak and trough values and clock times did not differ between groups. However, the temperature rhythm was biphasic in monks and nuns, with an early decrease at 19:39?±?4:30?h (median?±?95% interval), plateau or rise of temperature at 22:35?±?00:23?h (while asleep) lasting 296?±?39?min, followed by a second decrease after the Matins Office, and a classical morning rise. Although they required alarm clocks to wake-up for Matins at midnight, the body temperature rise anticipated the nocturnal awakening by 85?±?15?min. Compared to the controls, the monks and nuns had an earlier sleep onset (20:05?±?00:59?h vs. 00:00?±?00:54?h, median?±?95% confidence interval, p?=?.0001) and offset (06:27?±?0:22?h, vs. 07:37?±?0:33?h, p?=?.0001), as well as a shorter sleep time (6.5?±?0.6 vs. 7.6?±?0.7?h, p?=?.05). They reported difficulties with sleep latency, sleep duration, and daytime function, and more frequent hypnagogic hallucinations. In contrast to their daytime silence, they experienced conversations (and occasionally prayers) in dreams. The biphasic temperature profile in monks and nuns suggests the human clock adapts to and even anticipates nocturnal awakenings. It resembles the biphasic sleep and rhythm of healthy volunteers transferred to a short (10-h) photoperiod and provides a living glance into the sleep pattern of medieval time. (Author correspondence: isabelle.arnulf@psl.aphp.fr)     

Chronotoxicity of Nedaplatin in Rats

Chronotoxicologic profiles of nedaplatin, a platinum compound, were evaluated in rats maintained under a 12 light/12 dark cycle with light from 07:00 h to 19:00 h. Nedaplatin (5 mg/kg) was injected intravenously, once a week for 5 weeks at 08:00 h or 20:00 h. The suppression of body weight gain and reduction of creatinine clearance were significantly greater with the 20:00 h than 08:00 h treatment. Accumulation of nedaplatin in the renal cortex and bone marrow were also greater with 20:00 h treatment. There were significant relationships between the nedaplatin content in the kidney and bone marrow and degree of injury to each. These results suggest that the nedaplatin-induced toxicity depends on its dosing-time, and it is greater with treatment at 20:00 h, during the active phase. The dosing-time dependency in the accumulation of nedaplatin in the tissue of the organs might be involved in this chronotoxicologic phenomenon.     

Chronotoxicity of nedaplatin in rats

Chronotoxicologic profiles of nedaplatin, a platinum compound, were evaluated in rats maintained under a 12 light/12 dark cycle with light from 07:00h to 19:00 h. Nedaplatin (5 mg/kg) was injected intravenously, once a week for 5 weeks at 08:00h or 20:00h. The suppression of body weight gain and reduction of creatinine clearance were significantly greater with the 20:00h than 08:00h treatment. Accumulation of nedaplatin in the renal cortex and bone marrow were also greater with 20:00 h treatment. There were significant relationships between the nedaplatin content in the kidney and bone marrow and degree of injury to each. These results suggest that the nedaplatin-induced toxicity depends on its dosing-time, and it is greater with treatment at 20:00 h, during the active phase. The dosing-time dependency in the accumulation of nedaplatin in the tissue of the organs might be involved in this chronotoxicologic phenomenon.     

Chronotoxicity of Nedaplatin in Rats

Chronotoxicologic profiles of nedaplatin, a platinum compound, were evaluated in rats maintained under a 12 light/12 dark cycle with light from 07:00 h to 19:00 h. Nedaplatin (5 mg/kg) was injected intravenously, once a week for 5 weeks at 08:00 h or 20:00 h. The suppression of body weight gain and reduction of creatinine clearance were significantly greater with the 20:00 h than 08:00 h treatment. Accumulation of nedaplatin in the renal cortex and bone marrow were also greater with 20:00 h treatment. There were significant relationships between the nedaplatin content in the kidney and bone marrow and degree of injury to each. These results suggest that the nedaplatin-induced toxicity depends on its dosing-time, and it is greater with treatment at 20:00 h, during the active phase. The dosing-time dependency in the accumulation of nedaplatin in the tissue of the organs might be involved in this chronotoxicologic phenomenon.     

Chronopharmacokinetics of Imipramine and Desipramine in Rat Forebrain and Plasma After Single and Chronic Treatment with Imipramine

Daily variations in the pharmacokinetics of imipramine (IMI) could contribute to circadian phase-dependent effects of the drug. Therefore, the chronopharmacokinetics of IMI and its metabolite, desipramine (DMI), were studied after single and chronic application. Male rats were synchronized to a 12:12 hour lightdark (L:D) regimen with lights on from 07:00 to 19:00 (dark, 19:00-07:00). In single-dose experiments rats were injected with IMI (10 mg/kg) i.p. or i.v. at 07:30 or 19:30 and groups of rats were killed 0-22 hours thereafter. After chronic application of IMI in drinking water (≈ 15 mg/kg/d) groups of rats were killed during the 14th day of treatment at 02:00, 08:00, 14:00, and 20:00, respectively. Brain and plasma concentrations of IMI and DMI were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection. After single i.p. application of IMI, maximal brain concentrations (C_max) of IMI and DMI were nearly twofold higher in darkness (IMI, 4.8 μg/g; DMI, 1.8 μg/g) than in light (IMI, 2.85 Mg/g; DMI, 0.85 Mg/g). Also, the area under the curve (AUC) (0-22 hours) was about 1.6-fold greater in darkness than in light for IMI and DMI; half-lives were not circadian phase dependent. After i.v. injection of IMI, the AUC in brain was also about 30% greater in darkness than in light. After chronic application of IMI in drinking water, brain concentrations of IMI and DMI varied more than threefold within 24 hours. The data demonstrate that the pharmacokinetics of IMI and DMI are circadian phase dependent. It is assumed that circadian variations in drug distribution are more likely to contribute to the drug's chronopharmacokinetics than variations in the drug's metabolism. The 24-hour variations in the drug's concentrations after chronic IMI application in drinking water can be explained by the drinking behavior of the rats, which by itself is altered by IMI.     

Differential effects of chloral hydrate and pentobarbital sodium on cocaine-induced electroencephalographic desynchronization at the medial prefrontal cortex in rats

We evaluated the effects of two anesthetics on the cocaine-induced electroencephalographic (EEG) desynchronization in male, Sprague-Dawley rats. One group was anesthetized with chloral hydrate (400 mg/kg, i.p., 80 mg/kg/h i.v. supplement; group A). The other group was anesthetized with pentobarbital sodium (50 mg/kg, i.p., 10 mg/kg/h i.v. supplement; group B). The degree of EEG desynchronization after cocaine administration (1.5 mg/kg, i.v.) was expressed as an increase in the mean power frequency (MPF) and a decreasa in the root mean square (RMS). These maximal increases and decreases were observed to be larger in group A (MPF: 43.3 ± 7.0% increase; RMS: 47.4 ± 5.0% decrese) than in group B (MPF: 17.8 ± 3.6% increase; RMS: 19.2 ± 2.5% decrease). Our laboratory previously proved that dopaminergic neurotransmission at the medial prefrontal cortex (mPFC) participated in the cocaine-induced EEG desynchronization and that both D-1 and D-2 receptors were involved in the process. Therefore, in vivo microdialysis coupled with high performance liquid chromatography was used to quantify the changes of extracellular dopamine (DA) concentrations at the mPFC for 90 minutes at 10 minute intervals after 1.5 mg/kg cocaine i.v. injection. The extracellular DA increases in both groups was rapid and reached the maximal peak within 10 min. There was no significant difference in the maximal increase of DA between groups (group A : 375.2 ± 35.77% versus group B: 332.2 ± 16.69% over basal value). These results suggest that different anesthetics may differentially affect cocaine-induced EEG desynchronization and this difference has no bearing on the DA response in the mPFC.     

Chronopharmacokinetics of imipramine and desipramine in rat forebrain and plasma after single and chronic treatment with imipramine.

Daily variations in the pharmacokinetics of imipramine (IMI) could contribute to circadian phase-dependent effects of the drug. Therefore, the chronopharmacokinetics of IMI and its metabolite, desipramine (DMI), were studied after single and chronic application. Male rats were synchronized to a 12:12 hour light:dark (L:D) regimen with lights on from 07:00 to 19:00 (dark, 19:00-07:00). In single-dose experiments rats were injected with IMI (10 mg/kg) i.p. or i.v. at 07:30 or 19:30 and groups of rats were killed 0-22 hours thereafter. After chronic application of IMI in drinking water (approximately 15 mg/kg/d) groups of rats were killed during the 14th day of treatment at 02:00, 08:00, 14:00, and 20:00, respectively. Brain and plasma concentrations of IMI and DMI were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection. After single i.p. application of IMI, maximal brain concentrations (Cmax) of IMI and DMI were nearly twofold higher in darkness (IMI, 4.8 micrograms/g; DMI, 1.8 micrograms/g) than in light (IMI, 2.85 micrograms/g; DMI, 0.85 microgram/g). Also, the area under the curve (AUC) (0-22 hours) was about 1.6-fold greater in darkness than in light for IMI and DMI; half-lives were not circadian phase dependent. After i.v. injection of IMI, the AUC in brain was also about 30% greater in darkness than in light. After chronic application of IMI in drinking water, brain concentrations of IMI and DMI varied more than threefold within 24 hours. The data demonstrate that the pharmacokinetics of IMI and DMI are circadian phase dependent. It is assumed that circadian variations in drug distribution are more likely to contribute to the drug's chronopharmacokinetics than variations in the drug's metabolism. The 24-hour variations in the drug's concentrations after chronic IMI application in drinking water can be explained by the drinking behavior of the rats, which by itself is altered by IMI.