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Biomedical subjects

J Vanĕcek

Publications and source records attributed to J Vanĕcek.

At least 19 recordsLinked to original sources
PubMed1992

Localization of 2-[125I]iodomelatonin binding sites in the brain of the Atlantic salmon, Salmo salar L.

The photosensory pineal organ of teleost fish shows a circadian rhythm in melatonin synthesis, and melatonin is known to influence a number of physiological functions. However, the target sites for melatonin are not known. We have investigated the distribution of melatonin binding sites in the brain of the salmon, Salmo salar. Brains were collected for receptor binding assay and autoradiography at each of three time points: just after lights on, just before lights off, and in the dark at midnight (photoperiod light-dark 12:12, lights on at 08.00 h, lights off at 20.00 h). Specific binding of 2-[125I]iodomelatonin was observed in several brain areas. High densities were associated with (1) the optic tectum, (2) the preoptic area, (3) an area encompassing the magnocellular superficial pretectal nucleus ('nucleus rotundus') and the glomerular complex, (4) the inferior lobes of the hypothalamus, (5) the lateral mesencephalic tegmentum including the torus semicircularis, and (6) the molecular layer of the cerebellum. No binding was observed in the pineal organ or in the pituitary. We observed no differences in labeling between brains collected at different time points, except in the preoptic area where binding was high at 20.00 and 24.00 h, but low at 08.00 h, and in the corpus cerebelli, where labeling in the molecular layer was higher at 24.00 and 08.00 h than at 20.00 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Melatonin inhibitory effect on luteinizing hormone release is potentiated after long pretreatment with the indole.

The effect of melatonin on luteinizing-hormone releasing-hormone stimulation of cyclic AMP accumulation and luteinizing hormone (LH) release from neonatal rat hemipituitaries was studied in vitro. Melatonin inhibited LH-release from pituitaries of animals kept previously on long but not on short photoperiods; cyclic AMP accumulation was, however, inhibited on both photoperiods. There were no daily changes in the melatonin effect. Inhibition of LH-release was strongly potentiated after 6 h preincubation with melatonin as compared with 20 min preincubation; cyclic AMP was not significantly affected by the length of preincubation.

Animals↗
PubMed1991

Mechanism of melatonin action.

Melatonin transduces the effect of photoperiod on the neuroendocrine system. Synthesis of melatonin in the pineal gland is well described, but the location of its target(s) and the mechanism of its action are little known. In attempt to localize melatonin target(s), the presence of high affinity binding sites in rat brain was determined. Such sites were detected in discrete brain areas, including the hypothalamus and anterior pituitary. Subcellular analysis indicated these binding sites were on plasma membranes, which suggests that melatonin modulates cell functions through intracellular second messengers. The effects of melatonin on second messengers were studied using the neonatal anterior pituitary, in which melatonin is known to inhibit the LHRH-induced release of LH. Studies on the effects of melatonin on second messenger indicated [corrected] that melatonin inhibits accumulation of cAMP and cGMP as well as synthesis of diacylglycerol and release of arachidonic acid. Time-course analysis indicates that inhibition by melatonin of the LHRH-induced release of LH increases following long preincubation. Since the effect of melatonin on LHRH-induced release of LH is prevented by dibutyryl cAMP, we conclude that melatonin might act by inhibiting production of cAMP.

Animals↗
PubMed1979

Ontogenic drug studies in calves. II. Changes in salicylate levels and metabolism in calves with diarrhoea.

Acetylsalicylic acid (ASA) was administered by oral route to calves and mice. A comparison of plasma levels of salicylates and salicyluric acid was performed in healthy and diarrhoic calves. The calves were infected with E. coli enterotoxin producing strains. During the 6 h observation period increased levels of salicylates were found in all age groups of calves (1-60 days). There were no significant differences in salicyluric acid plasma levels between controls and diarrhoic animals. Intravenous injection of cholera toxin in mice caused lower levels of total salicylates, but increased levels of salicylic acid and salicyluric acid. The importance of adequate animal model is discussed.

Animals↗
PubMed1979

Ontogenic drug studies in calves. I. Age dependent salicylate levels and metabolism.

Acetylsalicylic acid (ASA) was administered to 52 Friesian calves 1--60 days old by oral route in the field, 63.5 mg/kg body weight constantly between 9 and 10 a.m., i.e., 3--4 h after morning feeding. The animals were divided according to age into groups. Total salicylate levels, salicylic acid and salicyluric acid plasma levels were determined up to 6 h after administration. The older the animals, the lower were the total salicylate and salicylic acid levels and the higher the salicyluric acid levels. The age dependence is highly significant during the first two weeks of life. Glucuronides could not be detected in quantitatively measurable amounts.

Aging↗
PubMed1978

Immunoglobulin levels in large calf agglomerations.

The zinc sulphate turbidity test was used to establish the total immunoglobulin levels of calves from birth to 4 months of age. Colostral immunity fell rapidly and the lowest levels were found in the third and fourth week of life. During the fifth week there was a significant increase. 25% of animals were hypogammaglobulinaemic in the first week of life. This ratio increased to 50% in the third week of life. At the age of two months the lowest immunoglobulin levels almost vanished. These findings are discussed as basic information for the appropriate management of calf agglomerations. Animals should be agglomerated only after the first months of life. When this is not possible, the pens for large agglomerations should have individual housing for the newly admitted calves. The importance of appropriate epizootological measures to reduce infections are pointed out.

Age Factors↗
PubMed1976

Effect of dihydroxyphenylalanine, imipramine and coffeine on the light induced decrease in nocturnal serotonin N-acetyltransferase in the rat pineal gland.

The s.c. administration of 150mg L-dihydroxphyenylalaine/kg b.w. 15 min before the decapitation prevents the light induced decrease in nocturnal serotonin N-acetyltransferase activity in the rat pineal gland. The s.c. administration of 50mg imipramine/kg b.w., resp. 100mg/kg b.w., 15 min before the decapitation, slows down, or prevents the light induced fall in the activity. The maintenance of a sufficient level of active norepinephrine on beta-receptors, either by displacement of norepinephrine in the nerve endings by dopamine, or by the inhibition of norepinephrine reuptake by imipramine, thus slows down or prevents the decrease in serotonin N-acetyltransferase activity after exposure to light during the night. The i.p. administration of a phosphodiesterase inhibitor coffeine citrate in a dose 200mg/kg 90 min after switching off the light for the night stimulated serotonin N-acetyltransferase activity 270 min after the light and been switched off, but did not influence the abrupt decrease induced in nocturnal activity by exposure to light.

Acetyltransferases↗
PubMed1976

Pregnancy interrupting effects of some bacterial toxins.

Embryotoxic properties of Shigella dysenteriae and Clostridium perfringens toxins, of E. coli endotoxin, V. cholerase and E. coli enterotoxins were compared in mice. E. coli endotoxin has embryotoxic effects at all stages of pregnancy. E. coli enterotoxin V. cholerae enterotoxin and Shigella dysenteriae toxin are most effective mainly at earlier stages of pregnancy. Clostridium perfringens toxin has no embryotoxic effect.

Abortifacient Agents, Nonsteroidal↗