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.     

Administration-time differences in the pharmacokinetics of gentamicin intravenously delivered to human beings

Administration-time differences of gentamicin pharmacokinetics were studied by crossover design after a single intravenous administration of gentamicin (80 mg) to 10 human subjects at 09:00 (morning time) and 22:00 (nighttime). The profiles of serum gentamicin concentration showed a significant statistical difference between 09:00 and 22:00, suggesting circadian variations of pharmacokinetic behaviors. A significant circadian rhythm of pharmacokinetic parameters as a function of time of day was noted in human subjects, showing lower total body clearance Clt and higher serum area under the curve (AUC) when given at nighttime. The half-life t1/2 was shorter in the morning (2.82 h +/- 0.43 h) when compared to the nighttime (2.97 h +/- 0.36 h), but the difference was not statistically significant. The AUC was significantly greater in the morning (23.4 +/- 3.84 micrograms-h/mL) than that in the nighttime (26.3 +/- 5.79 micrograms-h/mL) (p < .05), most likely because the Clt was significantly higher when gentamicin was given in the morning (3.51 +/- 0.57 L/h) versus in the nighttime (3.18 +/- 0.65 L/h). Although the volume of distribution Vd decreased when given at nighttime, it was independent of the dosing time. From this study, there was an administration-time difference of gentamicin pharmacokinetics in human beings. The optimized dosing regimen of gentamicin can be decided by considering circadian rhythm and rest-activity routine so that minimized toxicity and effective therapy are established for patients. The current findings also can be applied to other drugs with circadian rhythms of pharmacokinetics and narrow therapeutic windows in clinical chronotherapeutics.     

Diurnal variations in plasma ACTH, cortisol and beta-endorphin levels in cocaine addicts.

In order to establish possible alterations in the hypothalamic pituitary-adrenal axis and in ACTH-related opioids in cocaine addicts, plasma ACTH, cortisol and beta-endorphin levels were measured throughout the day in 9 cocaine addicts [age: 27 +/- 5 years (mean +/- SE); weight: 72 +/- 6.1 kg, duration of cocaine addiction: at least 2 years] on the day of their admission to a recovery community for drug abusers (first test) and after 15 days of abstinence (second test). Nine normal controls (age: 28 +/- 6 years; weight: 73 +/- 3.2 kg) were tested only once in a similar manner. Blood samples were taken at 06:00, 08:00, 10:00, 12:00, 18:00 and 20:00 h and served for hormonal assays. Urine samples were taken from cocaine addicts at 08:00 h on the experimental day and on the following day. Results of both urine assays were positive for cocaine catabolites, indicating cocaine administration during the day before the experimental test. From the day of their admission in the community (1st experimental day), the patients were forbidden to use cocaine. For 4 days after admission, they were treated with symptomatics to attenuate withdrawal symptoms. Thereafter, the patients underwent a washout period of pharmacological treatments for 10 days before being retested (second test). Urine samples taken at 08:00 h on this second experimental day and on the next day were negative for the presence of drug catabolites. During the first test, cocaine addicts showed higher plasma ACTH, cortisol and beta-endorphin levels than normal controls at all examined time points.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 microg/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 microg/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.     

The effect of oral ethanol ingestion on the diurnal neurotensin secretion in man.

Neurotensin is a tridecapeptide, present in the central nervous system and the gastrointestinal tract in man and animals. The affect of orally administered ethanol (1 g/kg body weight) on the neurotensin secretion over 24 hr period was studied in eight young healthy men. No significant circadian rhythm of neurotensin secretion was detected in the eight subjects studied. Ethanol produced a progressive rise in the plasma level of neurotensin reaching a maximum at 12:00 (13.8 +/- 8.6 pmol/l). At 12:00 and 14:00, the neurotensin concentrations were significantly higher than on the placebo day (p < 0.05). The secretion rate of neurotensin was determined approximately using the area under the curve method. Ethanol produced a transient rise in neurotensin secretion over the first 12 hrs period (08:00-20:00 h) after its administration (p < 0.02). The observation that ethanol increases transiently the neurotensin secretion in man supports the hypothesis that neurotensin may be involved in the biological effect of ethanol. The source of its secretion remains to be elucidated.     

Circadian time-effect of orally administered loratadine on plasma pharmacokinetics in mice

Little is known about the chronopharmacokinetics of loratadine, a long-acting tricyclic antihistamine H(1) widely used in the treatment of allergic diseases. Hence, the pharmacokinetics of loratadine and its major metabolite, desloratadine, were investigated after a 20 mg/kg dose of loratadine had been orally administered to comparable groups of mice (n=33), synchronized for three weeks to 12 h light (rest span)/12 h dark (activity span). The drug was administered at three different circadian times (1, 9, and 17 h after light onset [HALO]). Multiple blood samples were collected over 48 h, and plasma concentrations of loratadine and desloratadine were determined by high performance liquid chromatography. There were no significant differences in T(max) of loratadine and desloratadine between treatment-time different groups. However, the elimination half-life (t1/2) of the parent compound and its metabolite was significantly longer (p<0.01) following administration at 9 HALO (t1/2 loratadine and desloratadine 5.62 and 4.08 h at 9 HALO vs. 4.29 and 2.6 h at 17 HALO vs. 3.26 and 3.27 at 1 HALO). There were relevant (p<0.05) differences in C(max) between the three treated groups for loratadine and desloratadine; 133.05+/-3.55 and 258.07+/-14.45 ng/mL at 9 HALO vs. 104.5+/-2.61 and 188.62+/-7.20 ng/mL at 1 HALO vs. 94.33+/-20 and 187.75+/-10.79 ng/mL at 17 HALO. Drug dosing at 17 HALO resulted in highest loratadine and desloratadine total apparent clearance values: 61.46 and 15.97 L/h/kg, respectively, whereas loratadine and desloratadine clearances (CL) were significantly slower (p<0.05) at the other administration times (loratadine and desloratadine CL was 57.3 and 14.22 L/h/kg at 1 HALO vs. 43.79 and 12.89 L/h/kg at 9 HALO, respectively). The area under the concentration-time curve (AUC) of loratadine and desloratadine was significantly (p<0.05) greater following drug administration at 9 HALO (456.75 and 1550.57 (ng/mL) . h, respectively); it was lowest following treatment at 17 HALO (325.39 and 1252.53 (ng/mL) . h, respectively). These pharmacokinetic data indicate that the administration time of loratadine significantly affected its pharmacokinetics: the elimination of loratadine and its major metabolite desloratadine.     

CHRONOKINETICS OF CEFTAZIDIME AFTER INTRAMUSCULAR ADMINISTRATION TO DOGS

Ceftazidime, a third-generation cephalosporin, is widely used for the treatment of Pseudomonas aeruginosa infections. The aims of the present study were to characterize the pharmacokinetics of ceftazidime and to estimate the T?>?MIC against P. aeruginosa, after its intramuscular (im) administration at two different dosing times (08:30?h and 20:30?h) to dogs, in order to determine whether time-of-day administration modifies ceftazidime pharmacokinetics and/or predicted clinical antipseudomonal efficacy. Six female healthy beagle dogs were administered ceftazidime pentahydrate by the intramuscular route in a single dose of 25?mg/kg at both 08:30 and 20:30?h, two weeks apart. Plasma ceftazidime concentrations were determined by microbiological assay. Pharmacokinetic parameters and time above the minimum inhibitory concentration (T?>?MIC) and 4xMIC for Pseudomonas aeruginosa were calculated from the disposition curve of each dog. No differences between the daytime and nighttime administrations were found for the main pharmacokinetic parameters, including C_max, t_max, t_{½ λ}, AUC, and MRT; however, the high interindividual variability shown by these values and the small number of individuals may account for this lack of difference. Rate of absorption (k_a) was significantly higher after the 20:30?h than 08:30?h administration. No significant differences between T?>?MIC were found when comparing the 08:30?h and 20:30?h administrations. Mean T?>?MIC values predicted a favorable bacteriostatic effect for all susceptible strains of P. aeruginosa for the 12?h dosing interval at both dosing times. Our results suggest that similar antipseudomonal activity may be expected when ceftazidime is administered at 8:30 and 20:30?h; however, as only two timepoints of drug administration were explored, we are unable to draw any conclusions for other treatment times during the 24?h. (Author correspondence: rebuelto@fvet.uba.ar).     

Influence of time of day on propofol pharmacokinetics and pharmacodynamics in rabbits

This study evaluates the administration time-of-day effects on propofol pharmacokinetics and sedative response in rabbits. Nine rabbits were sedated with 5?mg/kg propofol at three local clock times: 10:00, 16:00, and 22:00?h. Each rabbit served as its own control by being given a single infusion at the three different times of day on three separate occasions. Ten arterial blood samples were collected during each clock-time experiment for propofol assay. A two-compartment model was used to describe propofol pharmacokinetics, and the pedal withdrawal reflex was used as the sedation pharmacodynamic response. The categorical data comprising the presence or absence of pedal withdrawal reflex was described by a logistic model. The typical volume of the central compartment equaled 7.67?L and depended on rabbit body weight. The elimination rate constant depended on drug administration time; it was lowest at 10:00?h, highest at 16:00?h, and intermediate at 22:00?h. Delay of the anesthetic effect, with respect to plasma concentrations, was described by the effect compartment, with the rate constant for the distribution to the effector compartment equal to 0.335?min(-1). Drug concentration had a large effect on the probability of anesthesia. The degree of anesthesia was largest at 10:00?h, lowest at 16:00?h, and intermediate at 22:00?h. In summary, both the pharmacokinetics and pharmacodynamics of propofol in rabbits depended on administration time. The developed population approach may be used to assess chronopharmacokinetics and chronopharmacodynamics of medications in animals and humans.     

Administration-Time Differences in the Pharmacokinetics of Gentamicin Intravenously Delivered to Human Beings

Administration-time differences of gentamicin pharmacokinetics were studied by crossover design after a single intravenous administration of gentamicin (80 mg) to 10 human subjects at 09:00 (morning time) and 22:00 (nighttime). The profiles of serum gentamicin concentration showed a significant statistical difference between 09:00 and 22:00, suggesting circadian variations of pharmacokinetic behaviors. A significant circadian rhythm of pharmacokinetic parameters as a function of time of day was noted in human subjects, showing lower total body clearance Cl_t and higher serum area under the curve (AUC) when given at nighttime. The half-life t_1/2 was shorter in the morning (2.82h ± 0.43h) when compared to the nighttime (2.97h ± 0.36h), but the difference was not statistically significant. The AUC was significantly greater in the morning (23.4 ± 3.84 μg-h/mL) than that in the nighttime (26.3 ± 5.79 μg-h/mL) (p<. 05), most likely because the Cl_t, was significantly higher when gentamicin was given in the morning (3.51 ± 0.57 L/h) versus in the nighttime (3.18 ± 0.65 L/h). Although the volume of distribution V_d decreased when given at nighttime, it was independent of the dosing time. From this study, there was an administration-time difference of gentamicin pharmacokinetics in human beings. The optimized dosing regimen of gentamicin can be decided by considering circadian rhythm and rest-activity routine so that minimized toxicity and effective therapy are established for patients. The current findings also can be applied to other drugs with circadian rhythms of pharmacokinetics and narrow therapeutic windows in clinical chronotherapeutics.     

Superovulatory response of Sistani cattle to three different doses of FSH during winter and summer

Objective of the present study was to investigate the effect of season and dose of FSH on superovulatory responses in Iranian Bos indicus beef cattle (Sistani). Cyclic cows, in summer (n=16) and winter (n=16), were assigned randomly to three dose-treatment groups of 120 (n=10), 160 (n=12) and 200 (n=10) total mg of Folltropin-V with injections given twice daily for 4 days in decreasing doses. Estrous cycles were synchronized with two prostaglandin F2alpha injections given 14 days apart. From day 5 after the ensuing cycle, daily ovarian ultrasonography was conducted to determine emergence of the second follicular wave at which time superovulation was initiated. Relative humidity, environmental and rectal temperatures were measured at 08:00, 14:00 and 20:00 h for the 3 days before and 2 days after the estrus of superovulation. Non-surgical embryo recovery was performed on day 7 after estrus. The effects of season, dose, time of estrous expression and all two-way interactions were evaluated on superovulatory responses: total numbers of CL, unovulated follicles (10 mm), ova/embryo, transferable and non-transferable embryos. Season (summer or winter), doses of Folltropin-V (120, 160 or 200 mg NIH) and time of estrous expression (08:00, 14:00 or 20:00 h) did not affect the number of transferable embryos (3.1+/-0.58). When superovulatory estrus was detected at 08:00, a FSH dose effect was detected with the greatest numbers of CL (12.2+/-0.87) and total ova/embryos (12.2+/-1.46) occurring with 200 mg FSH (dosextime of estrous expression; P<0.01).     

MORNING-EVENING ADMINISTRATION TIME DIFFERENCES IN DIGOXIN KINETICS IN HEALTHY YOUNG SUBJECTS

Digoxin, frequently used in the treatment of congestive heart failure, has a very narrow therapeutic index. We studied the differences in digoxin pharmacokinetics when ingested in the morning versus evening. A single digoxin (0.25 mg) dose was given orally to the same group of 10 diurnally active healthy (6 male and 4 female) volunteers in the morning at 08:00 and evening at 20:00 in separate experiments scheduled 2 weeks apart. Blood samples were collected at specific times for 48h after each timed dose; digoxin was determined by radioimmunoassay (RIA). Maximum plasma concentration C_max; T_max, the time to reach C_max; area under plasma concentration curve AUC; and elimination half-time T_1/2 of digoxin were determined. T_max was statistically significantly shorter (54 min) following 08:00 dosing compared to 20:00 dosing (96 min). Although the C_max was higher after morning than evening dosing, it was not significantly so. No other parameter of digoxin pharmacokinetics except T_max exhibited administration time dependency. (Chronobiology International, 18(5), 841-849, 2001)     

Control of birth in rats by RU 486, an antiprogesterone compound

Rats, isolated at mating (Day 1 of pregnancy), were submitted to either 8 h (8L:16D, Exp. I) or 14 h (14L:10D, Exp. II) of light daily with lights on from 12:00 h to 20:00 h and from 06:00 to 20:00 h respectively. In Exp. I, a single dose of RU 486 (10 mg in 0.2 ml ethanol) was given cutaneously at 08:00 h (Group A1), 12:00 h (Group B1), 19:00 h (Group C1) on Day 21 and at 08:00 h (Group D1) and 12:00 h (Group E1) on Day 22. In Exp. II, the same dose of RU 486 was given at 08:00 h (Group A2), 12:00 h (Group B2) and 19:00 h (Group C2) on Day 21. The solvent was given once at each of the preceding times to the control groups (T1 and T2) in both experiments. Groups T1 and T2 gave birth at two periods, the first on Day 22, the second on Day 23; the proportion of births during each of these periods depended on the light regimen (66.3% in 8L:16D; 50% in 14L:10D on Day 22). The distribution of births in Groups D1 and E1 treated on Day 22 were similar to their controls (T1). Rats treated on Day 21 (Groups A1, A2, B1, B2, C1, C2) gave birth over single periods on Day 22 after an interval correlated with the time of RU 486 administration. The earlier the treatment was given, the higher was the number of dead young and the lower the weight of live young 1 day after birth. These effects of prematurity did not impair further survival rates or weight at weaning.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Influence of Time of Day on Propofol Pharmacokinetics and Pharmacodynamics in Rabbits

This study evaluates the administration time-of-day effects on propofol pharmacokinetics and sedative response in rabbits. Nine rabbits were sedated with 5?mg/kg propofol at three local clock times: 10:00, 16:00, and 22:00?h. Each rabbit served as its own control by being given a single infusion at the three different times of day on three separate occasions. Ten arterial blood samples were collected during each clock-time experiment for propofol assay. A two-compartment model was used to describe propofol pharmacokinetics, and the pedal withdrawal reflex was used as the sedation pharmacodynamic response. The categorical data comprising the presence or absence of pedal withdrawal reflex was described by a logistic model. The typical volume of the central compartment equaled 7.67?L and depended on rabbit body weight. The elimination rate constant depended on drug administration time; it was lowest at 10:00?h, highest at 16:00?h, and intermediate at 22:00?h. Delay of the anesthetic effect, with respect to plasma concentrations, was described by the effect compartment, with the rate constant for the distribution to the effector compartment equal to 0.335?min^?1. Drug concentration had a large effect on the probability of anesthesia. The degree of anesthesia was largest at 10:00?h, lowest at 16:00?h, and intermediate at 22:00?h. In summary, both the pharmacokinetics and pharmacodynamics of propofol in rabbits depended on administration time. The developed population approach may be used to assess chronopharmacokinetics and chronopharmacodynamics of medications in animals and humans. (Author correspondence: agnbienert@op.pl)     

MORNING-EVENING ADMINISTRATION TIME DIFFERENCES IN DIGOXIN KINETICS IN HEALTHY YOUNG SUBJECTS

Digoxin, frequently used in the treatment of congestive heart failure, has a very narrow therapeutic index. We studied the differences in digoxin pharmacokinetics when ingested in the morning versus evening. A single digoxin (0.25 mg) dose was given orally to the same group of 10 diurnally active healthy (6 male and 4 female) volunteers in the morning at 08:00 and evening at 20:00 in separate experiments scheduled 2 weeks apart. Blood samples were collected at specific times for 48h after each timed dose; digoxin was determined by radioimmunoassay (RIA). Maximum plasma concentration C_max; T_max, the time to reach C_max; area under plasma concentration curve AUC; and elimination half-time T_1/2 of digoxin were determined. T_max was statistically significantly shorter (54 min) following 08:00 dosing compared to 20:00 dosing (96 min). Although the C_max was higher after morning than evening dosing, it was not significantly so. No other parameter of digoxin pharmacokinetics except T_max exhibited administration time dependency. (Chronobiology International, 18(5), 841–849, 2001)     

Influence of Feeding Schedule on Chronopharmacological Aspects of Gentamicin in Mice

The effects of the time of day of drug administration on the subchronic toxicity and pharmacokinetics of gentamicin, as well as the role of feeding schedule on circadian rhythms, were investigated in mice. ICR male mice were housed in a light-dark (LD) cycle (12:12) with food and water ad libitum (ALF) or under a time-restricted feeding (TRF) schedule (feeding time: 8 h during the light phase) for 1 day or 14 days before drug administration. The animals were given a single subcutaneous dose of gentamicin 180 mg/kg for the kinetic studies and subcutaneous doses of gentamicin 180 mg/kg/day for 14 days or 220 mg/kg/day for 18 days for the subchronic toxicity studies. A significant dosing-time dependency was shown for mortality and body weight loss, with higher values at midlight and lower ones at the middark (p > 0.05). A significant circadian rhythm was also found for gentamicin kinetics in ALF mice, with the highest clearance at middark and the lowest one at midlight (p > 0.01). The kinetic rhythm of gentamicin coincided well with the toxicity rhythm of the drug. The TRF schedule had a marked influence on the rhythms of gentamicin kinetics and toxicity, showing lowest clearance and higher toxicity at middark. The rhythm of subchronic toxicity of gentamicin seems to be due, at least in part, to the rhythm in kinetics and is strongly influenced by the feeding schedule. Thus, the timing of dosing is an important factor in the kinetics and the subchronic toxicity of gentamicin administration in mice, and the manipulation of feeding schedule can modify the rhythm of the toxicity by changing the rhythm of gentamicin kinetics.     

Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer)

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p<0.0005), choice reaction time (p<0.05), self-rated alertness (p<0.0005), fatigue (p<0.05), forward (sit-and-reach) flexibility (p<0.02), and right-hand grip strength (p<0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p<0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p<0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p>0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p<0.01) and spinal hyper-extension (p<0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p<0.001, peak at 20:00 h) and chip test performance (p<0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.     

Diurnal variations of serum GM-CSF levels

We aimed to investigate the daily variations of serum granulocyte-macrophage colony-stimulating factor (GM-CSF) levels and to correlate them with peripheral blood cells counts. Venous blood samples from eleven healthy volunteers were taken four times a day, being at 08:00, 14:00, 20:00 and 02:00h and serum GM-CSF levels measured by ELISA. We could not find a significant overall difference among GM-CSF levels at four different times of the day using the Friedman test. On the other hand, serum GM-CSF levels at night (20:00h) were found to be significantly increased when compared to the morning levels (08:00h) using the Wilcoxon test (P=0. 022). The levels of lymphocytes and white blood cells (WBCs) at 20:00h were also higher than the morning levels (08:00h) as expected. While there was a strong relationship between the morning levels of GM-CSF (08:00h) and all measurements of peripheral blood cells during the day, the levels of GM-CSF measured at 02:00, 14:00 and 20:00h were found to be significantly correlated with only the WBC levels. It was concluded that there may be a significant difference between morning and night levels of GM-CSF and morning levels of GM-CSF may be more important in the regulation of WBC counts during the day. These variations warrant further studies about diurnal rhythms of haematopoiesis chronotherapy with CSFs.     

Human chorionic gonadotropin and luteinizing hormone-releasing hormone reverse the blockade of ovulation in pregnant mare's serum gonadotropin-primed immature rats by the anti-androgenic drug, hydroxyflutamide

The present study was designed to examine mechanism(s) of the anti-ovulatory action of the anti-androgen, hydroxyflutamide (OH-F). Prepubertal rats were treated with 4 IU pregnant mare's serum gonadotropin (PMSG) (day -2) to induce first estrus and ovulation. They received OH-F in sesame oil or oil alone at 08:00 and 20:00 h on day 0 (the day of proestrus) and ovulations were assessed on the morning of day 1. Eighty-three percent of control animals ovulated with a mean of 7.7 +/- 1.1 corpora lutea per rat. Hydroxyflutamide blocked ovulation in all but 2 of the 12 rats receiving this drug alone. All of OH-F treated rats that received 5 and 25 IU human chorionic gonadotropin (hCG) ovulated with means +/- SEM of 9.1 +/- 0.1 and 7.3 +/- 1.4 corpora lutea per rat, respectively. The dose of 0.2 IU hCG was essentially ineffective, while the effect of 1.0 IU hCG was intermediate. At the dose of 20 ng and above (100 and 500 ng) luteining hormone-releasing hormone (LHRH) completely overcame the ovulation blockade in the OH-F treated animals, while a 4-ng dose was ineffective. At 18:00 h on the day of proestrus, serum LH levels in control animals were 17.56 +/- 2.60 ng/mL, which were 920% above basal levels (1.90 +/- 0.13) indicating a spontaneous LH surge. This surge was suppressed in OH-F treated rats. Injection of LHRH, at the dose of 20 ng and above, reinstated the LH release in OH-F treated animals. Thus, the anti-androgen, OH-F, inhibits ovulation in PMSG-treated immature rats through its interference with the preovulatory LH surge; the inhibition can be reversed by hCG or LHRH. Hydroxyflutamide does not appear to interfere at the level of the pituitary, but may have direct action at the hypothalamic and (or) extrahypothalamic sites involved in the generation of positive feedback signals that control LH release.     

Orcadian Variation in Amikacin Clearance and Its Effects on Efficacy and Toxicity in Mice with and Without Immunosuppression

A once-daily dosage regimen has been recently recommended in the use of aminoglycoside antibiotics since they induce a postantibiotic effect. In choosing this regimen, one must determine the most appropriate time of day for administration of the drug. We investigated the effects of the timing of amikacin (AMK) administration on the kinetics, the efficacy against intraperitoneal infection with Pseudomonas aeruginosa, and the toxicity of AMK in mice with and without immijnosuppression. We found circadian variations in the kinetics, efficacy, and toxicity of the drug in mice. Male and female ICR mice, which were housed under a light-dark (12:12 h) cycle with free food and water intake, were injected subcutaneously with AMK sulfate 50 mg/kg body wt. There was a circadian variation in AMK clearance for both sexes with the maximum value in the dark phase and the minimum in the light phase after a single administration. When AMK 500 mg/kg/day was repeatedly administered once daily for 30 days, higher toxicity was demonstrated in mice injected with the drug at the time of day with lower AMK clearance, although no difference was demonstrated in the toxicity between the two time points with different AMK clearance when AMK 1,500 mg/kg was administered in a single dose. The ED₅₀ of AMK to cure the infected mice in the midlight phase (13:00 h) with lower clearance was significantly lower than that in the middark phase (01:00 h) with higher clearance. In contrast, the ED₅₀ in the early light phase (09:00 h) was significantly lower than that in the early dark phase (21:00 h), although AMK clearance was not different between these two different time points. In mice premedicated with cyclophosphamide to suppress immune functions, the difference in the ED₅₀ of AMK was still demonstrated between 13:00 and 01:00 h, but not between 09:00 and 21:00 h. The present study shows not only that there were circadian variations in both AMK clearance and toxicity after repeated administration, but also that there was a circadian variation in the efficacy of AMK in mice infected with P. aeruginosa. These results suggest that the timing of drug administration should be considered in pharmacotherapy with AMK and that the most appropriate time of administration in mice and nocturnal animals may be in the midlight (resting) phase. They also suggest that the ED₅₀ of AMK. against P. aeniginosa infection may be influenced not only by the circadian variation in pharmacokinetics but also by the variations in immune systems suppressed by cyclophosphamide.