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Biomedical subjects

J Vanĕcek

Publications and source records attributed to J Vanĕcek.

At least 37 records · Page 2Linked to original sources
PubMed1987

Entrainment of the circadian rhythm in the rat pineal N-acetyltransferase activity by prolonged periods of light.

Entertainment of the circadian rhythm in the pineal N-acetyltranferase activity by prolonged periods of light was studied in rats synchronized with a light:dark regime of 12:12 h by observing phase-shifts in rhythm after delays in switching off the light in the evening or after bringing forward of the morning onset of light. When rats were subjected to delays in switching off the light of up to 10 h and then were released into darkness, phase-delays of the evening N-acetyltransferase rise during the same night corresponded roughly to delays in the light switch off. However, phase-delays of the morning decline were much smaller. After a delay in the evening switch off of 11 h, no N-acetyltransferase rhythm was found in the subsequent darkness. The evening N-acetyltransferase rise was phase-delayed by 6.2 h at most 1 day after delays. Phase-delays of the morning N-acetyltransferase decline were shorter than phase-delays of the N-acetyltransferase rise by only 0.7 h to 0.9 h at most. Hence, 1 day after delays in the evening switch off, the period of the high night N-acetyltransferase activity may be shortened only slightly. The N-acetyltransferase rhythm was abolished only after a 12 h delay in switching off the light. Rats were subjected to a bringing forward of the morning light onset and then were released into darkness 4 h before the usual switch off of light. In the following night, the morning N-acetyltransferase decline, but not the evening rise, was phase advanced considerably. Moreover, when the onset of light was brought forward to before midnight, the N-acetyltransferase rise was even phase-delayed. Hence, 1 day after bringing forward the morning onset of light, the period of the high night N-acetyltransferase activity may be drastically reduced. When rats were subjected to a 4 h light pulse around midnight and then released into darkness, the N-acetyltransferase rhythm in the next night was abolished. The data are discussed in terms of a two-component pacemaker controlling the N-acetyltransferase rhythm. It is suggested that delays in the evening switch off of light may disturb the N-acetyltransferase rhythm the next day only a little, as the morning component may adjust to phase-delays of the evening component almost within one cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetyltransferases↗
PubMed1987

Dynamics of discrete entrainment of the circadian rhythm in the rat pineal N-acetyltransferase activity during transient cycles.

To elucidate entrainment of a pacemaker controlling the N-acetyltransferase (NAT) rhythm in the rat pineal gland, we studied the phase response curves (PRCs) of this rhythm. We exposed 50- to 60-day-old male Wistar rats maintained in a light-dark cycle (LD 12:12) to a 1-min light pulse at different times before midnight or at various times throughout the whole night. We then released them into constant darkness and studied the morning NAT decline during the night when rats were pulsed before midnight, as well as the evening NAT rise and the morning decline after 4 days following the pulses. The PRC for the first NAT decline and the PRCs for the NAT rise and decline after 4 days were compared with published transient PRCs (Illnerová and Vanĕcek, 1982b), in order to obtain a complete picture of the dynamics of the NAT rhythm entrainment during the transient cycles. Phase delays in the NAT rise due to a pulse before midnight were complete (i.e., identical to those of day 4) on day 1. Phase delays in the NAT decline were almost complete on day 1, while incomplete phase delays were observed on day 0. Phase advances in the NAT rise and decline due to a pulse past midnight had different dynamics: Advances in the decline were complete on day 1, while advances in the rise were absent on day 1 and much smaller than in the decline on day 4. The results are discussed in terms of a two-component (E-M) pacemaker controlling the NAT rhythm. The NAT rise may reflect the phase of the E-component, while the decline reflects the M-component. Phase delays of the E-component are accomplished within one cycle, and so are phase advances of the M-component. However, although delays of E already result in delays of M one cycle after the pulse, it takes several transient cycles before advances of M begin to induce advances of E.

Acetyltransferases↗
PubMed1987

Bacterial pyrogens of different origin and pharmacokinetics of rifampicin.

Changes of pharmacokinetics of rifampicin (RFP, Rifadin were investigated on endotoxin pretreated still not ruminant calves. The animals served as their own controls and drug administration twice in a 1-week interval gave the same results. Endotoxin 0.02 micrograms kg-1 given intravenously 1 h prior to the oral administration of RFP (20 mg kg-1) induced considerable pharmacokinetic changes. The serum levels of the total drug were significantly lower after the endotoxin administration. The pharmacokinetic analysis revealed significant changes mainly in the distribution phase. When both toxin and drug were administered intravenously, the drug levels were higher. The results are discussed with reference to the pathophysiological endotoxin changes. After the toxin administration the bioavailability of oral RFP was 4-fold lower.

Administration, Oral↗
PubMed1986

Change in duration of the nighttime melatonin peak may be a signal driving photoperiodic responses in the Djungarian hamster (Phodopus sungorus).

A regime of 14 h of light and 10 h of darkness (LD 14:10) induced regression of testes and accessory glands in adult Djungarian hamsters maintained originally in LD 16:8, but recrudescence of these organs in hamsters maintained originally in LD 8:16. Duration of the period of elevated nighttime melatonin levels in LD 14:10 was the same irrespective of whether hamsters had come from LD 16:8 or from LD 8:16. It is suggested that a change in duration of the nighttime melatonin peak and its direction rather than absolute duration of the melatonin peak may be a hormonal signal driving photoperiodic responses in adult Djungarian hamsters.

Animals↗
PubMed1986

Adjustment of the rat pineal N-acetyltransferase rhythm to change from long to short photoperiod depends on the direction of the extension of the dark period.

Extension of the rat pineal N-acetyltransferase rhythm after transition from LD 16:8 to LD 8:16 proceeded more rapidly when the transition was accomplished by prolongation of the dark period into the morning than into the evening hours. After symmetrical or evening prolongation of the dark period, adjustment of the rhythm to the LD 8:16 regimen was almost completed within 6 days. After prolongation of darkness into the morning hours, a temporal overextension of the rhythm occurred.

Acetyltransferases↗
PubMed1985

Comparison of pineal melatonin rhythms in young adult and old Djungarian hamsters (Phodopus sungorus) under long and short photoperiods.

The pattern of the pineal melatonin rhythm was studied in 3-6- and 17-22-month-old female Djungarian hamsters under light-dark (LD) schedules, LD 16:8 and LD 8:16. Under both photoperiods, the amplitude of the melatonin rhythm was 2.5 times higher in young adult hamsters than in old ones. Two weeks after the change from LD 16:8 to LD 8:16, the period of elevated nocturnal melatonin levels lengthened by about 3 h in both age groups. It is suggested that old Djungarian hamsters, as well as young adults, might be able to recognize the length of a photoperiod and its change.

Age Factors↗
PubMed1985

The circadian rhythm in plasma melatonin concentration of the urbanized man: the effect of summer and winter time.

Plasma melatonin rhythms were measured in healthy urbanized persons between July 4 and 5 and between January 13 and 14. In contrast to findings in other mammals studied thus far, no difference in the duration of elevated night melatonin concentration was observed between summer and winter. In winter, melatonin rhythms were phase-delayed by about 1.5 h as compared with summer patterns.

Adult↗
PubMed1985

Endotoxin and pharmacokinetics of rifampicin.

Changes of pharmacokinetics of rifampicin (20 mg . kg-1 orally) were seen in rabbits pretreated with 0.02, 0.2 and 2.0 micrograms . kg-1 of endotoxin S. typhimurium given intravenously. The animals served as their own controls. The two higher endotoxin doses induced significantly lower plasma levels and changes in the absorption and elimination phase. After the lowest endotoxin dose the results were variable. Tolerance to pyrogenicity of endotoxin, produced by daily toxin administration abolished the otherwise induced changes in rifampicin pharmacokinetics.

Animals↗
PubMed1985

Arrest of the circadian pacemaker driving the pineal melatonin rhythm in hibernating golden hamsters, Mesocricetus auratus.

Pineal melatonin rhythm in golden hamsters was abolished during hibernation. After arousal in darkness, pineal melatonin increased rapidly regardless of whether the arousal was induced during the day or at night. Rapid increase of pineal melatonin after arousal was markedly diminished in animals exposed to light. In hamsters aroused at midnight, the melatonin rhythm in constant darkness ran with the reversed phase relative to hamsters aroused at noon. Since after arousal the melatonin rhythm obviously starts anew from the same phase, we conclude that the circadian pacemaker driving the rhythm might be arrested during hibernation at the day-time phase.

Animals↗
PubMed1985

The effect of intermittent treatment with sulphadimidine on coccidiosis in preruminant calves.

Preruminant calves excreted coccidia oocysts in their faeces after 3 weeks of group housing. Two weeks of oral sulphadimidine (SDM) administration, 50 mg/kg on the first day of treatment followed by daily administration of 37.5 mg/kg, under the same housing conditions kept the faeces free of oocysts. Three weeks later, these calves excreted oocysts again. Repetition of the same treatment for 2 weeks controlled the infection again, but a second treatment for 5 days did not suffice. The repeated long treatment affected immunoglobulin levels adversely. SDM given repeatedly at a lower dose rate (30 mg/kg) for 1-week periods with medication-free intervals of 1 week controlled the infection and no adverse effects were noted. In comparison with controls, weight gains were greater in treated calves.

Animals↗
PubMed1985

Entrainment of the circadian rhythm in rat pineal N-acetyltransferase activity under extremely long and short photoperiods.

Entrainment of a pacemaker driving the circadian rhythm in rat pineal N-acetyltransferase activity was studied under extremely long and short photoperiods. Adult male rats maintained under the light-dark regime (LD) 18:6 or under the regime LD 6:18 were exposed to a 1-min light pulse at different times at night, then they were released into darkness, and the next night phase-shifts of the evening N-acetyltransferase rise and of the morning N-acetyltransferase decline caused by light pulses were determined. The evening rise was phase-delayed by at most 0.5 h under LD 18:6, but by as much as 2.8 h under LD 6:18. The morning decline was phase-advanced by at most 1.9 h under LD 18:6, but by as much as 3.5 h under LD 6:18. Hence, the magnitude of phase-shifts and consequently patterns of phase-response curves, which show possibilities of discrete entrainment, depend on the photoperiods under which animals are maintained. A 1-min light pulse applied within 1 h before the end of the dark period phase-advanced the morning N-acetyltransferase decline under LD 18:6 as well as under LD 6:18, while a pulse applied within 1 h after the beginning of the dark period phase-delayed the evening N-acetyltransferase rise only in rats maintained under LD 18:6, but not in those kept under LD 6:18. It seems that under very long photoperiods, the N-acetyltransferase rhythm may be entrained by evening as well as by the morning light, while under very short photoperiods the rhythm may be synchronized by morning light only.

Acetyltransferases↗
PubMed1985

Effect of short and long photoperiods on pineal N-acetyltransferase rhythm and on growth of testes and brown adipose tissue in developing rats.

The effect of photoperiod on the rhythm in pineal N-acetyltransferase activity and on the growth of testes and of brown adipose tissue was studied in infant rats at the age of 5-15 days. After exposure to light at night, high N-acetyltransferase activity declined in 6-, 7-, and 8-day-old intact rats, but not in 5-day-old intact rats or in 8-day-old blinded rats. Hence, light might penetrate under closed eyelids and might be perceived by retinal photoreceptors in rats older than 6 days. In 15-day-old animals, the amplitude of the N-acetyltransferase rhythm was ten times higher than in 5-day-old rats. The pattern of the N-acetyltransferase rhythm, namely the duration of elevated nocturnal activity, was different under long and short photoperiod at least 1 week before opening of eyes. Photoperiod affected the growth of testes and of interscapular brown adipose tissue already in the preweaning period. In 15-day-old rats, immediately after opening of eyes, the weight of testes was significantly higher and the weight of brown fat lower under long than under short photoperiod. Photoperiodic regulation thus occurs before rats open their eyelids.

Acetyltransferases↗
PubMed1985

Regulation of the circadian rhythm in pineal melatonin production.

The pineal gland exhibits a circadian rhythm in the activity of N-acetyltransferase, the enzyme responsible for the rhythmic production of melatonin. Our data are consistent with the hypothesis that the N-acetyltransferase rhythm is regulated by a two-oscillator pacemaker. The evening N-acetyltransferase rise is controlled by an evening oscillator coupled to dusk, the morning decline by a morning oscillator coupled to dawn. The phase-relationship between both oscillators may determine the period of high night N-acetyltransferase activity and hence the period of elevated melatonin level. This period is different during long and short days and it may provide animals with information about environmental day duration.

Animals↗
PubMed1984

Pineal melatonin in hibernating and aroused golden hamsters (Mesocricetus auratus).

Daily changes of pineal melatonin content were determined in warm-adapted nonhibernating and cold-adapted hibernating golden hamsters (Mesocricetus auratus). Pineal melatonin in nonhibernating golden hamsters showed marked daily rhythm with the night values about 20 times higher than the daytime ones. In hamsters hibernating for 2 and 3 days the melatonin rhythm was abolished, since no increase of pineal melatonin over basal levels occurred throughout 24 hr period. After arousal from hibernation melatonin increased rapidly regardless whether the hamsters were provoked to arousal during day or night.

Animals↗
PubMed1984

Adjustment of pineal melatonin and N-acetyltransferase rhythms to change from long to short photoperiod in the Djungarian hamster Phodopus sungorus.

In the Djungarian hamster Phodopus sungorus, the daily temporal pattern of synthesis and release of pineal hormone melatonin, mainly the length of the period of elevated melatonin levels, may be involved in transferring the information on day length to the neuroendocrine-gonadal axis. The present study investigated the time course of adjustment of the rhythm in melatonin production and concentration to the change from long to short photoperiods. Adult female Djungarian hamsters, maintained on a regime of 16 h of light and 8 h of darkness per day (LD 16:8) were transferred to the LD regime 8:16 and the daily rhythms in the pineal melatonin concentration and in the pineal N-acetyltransferase activity, as an indicator of melatonin formation, were studied at various intervals following the transfer. Under LD 16:8, the nocturnal melatonin concentration was elevated for 4.8 h. After 3 days on LD 8:16, no extension of the period of high melatonin levels occurred. 2, 4 and 6 weeks after the transfer to LD 8:16, the period of elevated melatonin levels lasted for 8.1, 9.3 and 11.5 h, respectively. Extension of the melatonin pattern proceeded first predominantly into the morning hours. Only after this extension was completed, a considerable extension into the evening hours began. Extension of the N-acetyltransferase rhythm on short photoperiods proceeded in the same way as that of the melatonin rhythm. The data show that while a change in the photoperiod might be seen by hamsters within 2 weeks after the transfer to LD 8:16, the full shortening of the photoperiod might be recognized only within 6 weeks or later.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗