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Biomedical subjects

J Vanĕcek

Publications and source records attributed to J Vanĕcek.

At least 55 records · Page 3Linked to original sources
PubMed1984

Effect of blinding on the growth of reproductive organs in male rats treated neonatally with testosterone propionate.

Prepubertal blinding slightly retards the growth of seminal vesicles and prostate in male Wistar rats. Neonatal administration of testosterone propionate (TP) increases the susceptibility of rats to light deprivation. The growth of testes, seminal vesicles and prostate is markedly retarded in TP-treated rats blinded at 30 days of age. However, prepubertal blinding does not inhibit the tissue growth completely since even in TP-treated animals steady growth of reproductive organs occurs. Blinding of TP-treated adult rats induces involution of seminal vesicles and prostate although it has no effect on testis weight. The weight of testes can thus be influenced by light deprivation only during its growth in maturing animals, whereas the weights of seminal vesicles and prostate may be affected even in adult animals.

Age Factors↗
PubMed1983

The evening rise in the rat pineal N-acetyltransferase activity under various photoperiods.

The evening rise in the rat pineal N-acetyltransferase (NAT) activity was studied under various photoperiods. After the onset of darkness, NAT increased more rapidly under longer than under shorter photoperiods. Since following the evening administration of isoproterenol the rates of NAT induction and NAT responses to various doses were similar in short and in long photoperiods, it is suggested that the different times courses of the NAT increase may be due to the time of noradrenaline release from pineal nerve endings and to the quantity of the released noradrenaline.

Acetyltransferases↗
PubMed1983

Regulation of the pineal melatonin concentration in the rat (Rattus norvegicus) and in the Djungarian hamster (Phodopus sungorus).

1. Rapid changes of melatonin concentration in pineals of rats (Rattus norvegicus) after isoproterenol administration or in the course of a day were accompanied by parallel changes of N-acetyltransferase but not of hydroxyindole-O-methyltransferase activity. 2. In pineals of Djungarian hamsters (Phodopus sungorus) the evening and morning melatonin changes were also parallel with N-acetyltransferase changes. 3. In both species, melatonin concentration during its rise had approached the maximum earlier than N-acetyltransferase reached its highest activity. 4. It is proposed that the N-acetyltransferase rhythm drives the melatonin rhythm both in rats and in Djungarian hamsters; the maximum melatonin production may, however, depend also on hydroxyindole-O-methyltransferase activity and substrate concentration.

Acetylserotonin O-Methyltransferase↗
PubMed1982

Effect of light at night on the pineal rhythm in N-acetyltransferase activity in the Syrian hamster Mesocricetus auratus.

Pineal N-acetyltransferase activity in the male Syrian hamster exhibited a daily rhythm; the maximal night-time value was 3.5-fold higher than the day-time value. When hamsters were exposed to light at night N-acetyltransferase declined within 30 min to 1/5 of its former activity. These results indicate that the Syrian hamster the pineal melatonin rhythm may be regulated at least partly via changes in N-acetyltransferase activity.

Acetyltransferases↗
PubMed1982

Effect of photoperiod on the growth of reproductive organs and on pineal N-acetyltransferase rhythm in male rats treated neonatally with testosterone propionate.

Neonatal administration of testosterone propionate (TP) sensitized male Wistar rats to photoperiodic regulation of reproduction. Testicular, seminal vesicle and prostate weights in 105-day-old TP-treated rats housed under natural photoperiodic conditions were lower during autumn and winter than during spring and summer. The reproductive organ weights in 75-day-old TP-treated rats kept under artificial lighting regimens were smaller under photoperiods shorter than 10 h per day than under photoperiods of 10 h per day or longer. In TP-treated males, pinealectomy prevented the decrease in reproductive organ weights induced by short days. The pineal involvement in the photoperiodic regulation of reproduction might be mediated by the rhythm in melatonin. Under a 8L:16D regimen, when reproductive organ weights were decreased, the period of high night N-acetyltransferase activity, which determines the period of the increased melatonin production, lasted about 1 h longer than under 12L:12D.

Acetyltransferases↗
PubMed1981

Posttetanic inhibition in the guinea - pig ileum by endogenous opiate ligands; effects of cold storage of the preparations and of the age of experimental animals.

Naloxone-sensitive inhibition of neurogenic twitch contractions was induced by tetanic stimulation of the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum. In preparations stored in the cold for more than 2 days, the inhibition disappeared and in some preparations posttetanic potentiation was manifested, instead. Thus enkephalinergic neurones are more sensitive to the effect of cold storage than cholinergic neurones. The naloxone-sensitive posttetanic inhibition was developed in newborn animals but in animals older than 3 years a naloxone-resistent component appeared.

Acetylcholine↗
PubMed1980

Some characteristics of the night N-acetyltransferase in the rat pineal gland.

Following light on at night experiments, N-acetyltransferase level declines, at first rapidly and after 20 min more slowly. We partly characterised the night N-acetyltransferase and the residual N-acetyltransferase 20 min after light on. Both enzymes had pH optimum 6.8 and were inactivated thermally in vitro with a half time of 8 min. Pre-treatment with cycloheximide or puromycin did not block the rise in N-acetyltransferase following isoproterenol administration shortly after light on. We propose that night N-acetyltransferase is one enzyme. After light on, the enzyme rapidly deactivates to a less active form. Isoproterenol applied within a short time may partly reactivate the enzyme.

Acetyltransferases↗
PubMed1980

Pineal rhythm in N-acetyltransferase activity in rats under different artificial photoperiods and in natural daylight in the course of a year.

The rhythm in melatonin formation was studied in rats kept in natural daylight throughout the year and in rats housed under different artificial photoperiods. N-acetyltransferase activity was chosen as the indicator of melatonin formation. The period of the high night N-acetyltransferase was shortest in rats kept under LD 16:8 and longest in rats under LD 8:16. A short, 1-day adaptation to longer days, from LD 12:12 to LD 16:8, involved the induction of the morning decline in N-acetyltransferase by an earlier 'light on'. Following long-term adaptation to LD 16:8, N-acetyltransferase declined spontaneously 1 h before the morning 'light on'. A short, 1-day adaptation to shorter days, from LD 12:12 to LD 8:16, involved an earlier evening rise in N-acetyltransferase and a spontaneous morning decline at approximately the same time as in LD 12:12. Following long-term adaptation to LD 8:16, the period of high N-acetyltransferase shifted towards the later part of the night and the activity declined 2 h before the 'light on'. In natural daylight, the period of the high night N-acetyltransferase was shortest in June and longest in December. The morning decline in N-acetyltransferase was probably induced by dawn on April 19 and June 20, but was spontaneous on December 19. The existence of differences in the N-acetyltransferase rhythm and consequently in the rhythm of melatonin formation in natural daylight throughout the year and under different artificial photoperiods supports the hypothesis that the changing rhythmic pattern of melatonin release might be a mechanism by means of which a photic information is transformed into a humoral one.

Acetyltransferases↗