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Biomedical subjects

D Mayer

Publications and source records attributed to D Mayer.

At least 217 records · Page 12Linked to original sources
PubMed1979

A double-labelling radioassay for the determination of 5'-nucleotidase activity.

For the determination of 5'-ribonucleotide phosphohydrolase (EC 3.1.3.5;5'-Nase) in rat liver, a radiochemical double-labelling assay was developed. [14C]-labelled AMP which is hydrolyzed to [14C]-adenosine by 5'-Nase activity is added to crude liver homogenates. After 30 min, the process is stopped and [2-3H]-adenosine added to estimate the loss of [14C]-adenosine during separation by ion exchange column chromatography. The enzymatic reaction was found to be linear in correlation with the enzyme content and the incubation time. The specificity of the reaction was evaluated by addition of beta-glycerophosphate which acts as a competitive inhibitor to eliminate the catalytic effect of non-specific phosphatases, and addition of alpha, beta-methylene adenosine 5'-diphosphate, a specific inhibitor of 5'-Nase; both cause an almost complete suppression of enzyme activity.

Adenosine↗
PubMed1979

[Circadian fluctuations of pharmacokinetic parameters after oral administration of hexobarbital (author's transl)].

To 4 male and 2 female subjects hexobarbital was applied orally at different times of the day: 2, 10, 18 h. Serum concentrations of hexobarbital were determined by HPLC procedure and the resulting pharmacokinetic parameters in a rotating iterative program. Application at 18 h resulted in a shorter invasion time, a higher maximum concentration and a delayed elimination; in addition, the AUC was elevated in relation to application at 2 or 10 h. In the 2 female subjects a different pattern was observed. The results lead to the assumption that application of hexobarbital is more effective in the evening than in the morning.

Adult↗
PubMed1978

Cardiopulmonary adjustment and metabolic response to maximal and submaximal physical exercise of boys and girls at different stages of maturity.

Cardiopulmonary and metabolic variables were investigated at maximal and submaximal bicycle ergometer exercises in 41 swimmers of both sexes, 8--18 years old. VO2 max and VO2 max . HR-1 were higher in boys than in girls and increased with maturity, while VO2 max. kg-1 and HVE were not influenced by this. The HV increased clearly during this growth period, the pubertal and postpubertal subjects showing 16 and 17% higher values for HV and HV . kg-1 than those reported in normal schoolchildren populations. During the submaximal exercise at 70% VO2 max the highest HR values were found in the prepubertal group, whilst the lowest were observed in the postpubertal subjects. These findings suggest that a given percentage of VO2 max as a reference unit, is more reliable than a certain HR to obtain comparable results in subjects with different ages. Blood samples were collected before, during, and after the submaximal exercise. Blood glucose and FFA did not differ in relation to the stages of maturity. During exercise, insulin decreased in prepubertal children, did not alter in pubertal adolescents, and increased in postpubertal subjects. The lactate concentration, during exercise, increased in relation to maturity. The same results were found for HGH, but no differences were found with regard to sex. Since the pattern of HGH secretion during exercise is similar to that found after arginine and insulin administration it is assumed that the same mechanism (i.e., sex hormones) triggers the HGH release.

Adolescent↗
PubMed1978

[On the development of an oral preparation of meproscillarin (author's transl)].

Analytical methods of determination, investigations of stability and the behaviour of the substance in artificial gastric and intestinal fluids are the bases for the formulation of an oral preparation of 14-hydroxy-3beta-[4-O-methyl-alpha-L-rhamnopyranosyl)oxy]-14beta-bufa-4,20,22-trienolide (meproscillarin, Clift). The problems of developing a stable form, the maintenance of uniform content and the bioavailability are discussed.

Administration, Oral↗
PubMed1976

The circadian rhythm of synthesis and catabolism of cholesterol.

The circadian rhythms of HMG-CoA reductase and cholesterol-7 alpha-hydroxylase (low values, during light, rising in the evening with maximum at 12.00 p.m.) are investigated in rats under diverse conditions. Intragastral administration of cholestyramine (bile acid-absorbing resin) leads to an increased rhythm of both enzymes. Feeding of cholic acid (or cholesterol) reduces the activity of both enzymes (of HMG-CoA reductase and cholesterol-7 alpha-hydroxylase, respectively). In starved rats enzyme activity and time of day is proportional to the metabolism of a substrate.ies are lowered, too; a damped rhythm reappears after 24 h. A 20% fat diet (containing saturated fatty acids predominantly) markedly reduces the high values. Enzyme activities inhabited after thyroidectomy can be normalized by thyroxin substitution. Thyroxin administration in the normal remains without effect. Four-day insulin treatment of the normal inhibits cholesterol-7 alpha-hydroxylase, has no effect on HMG-CoA reductase. In the untreated diabetic rat cholesterol-7 alpha-hydroxylase is increased, HMG-CoA reductase significantly inhibited. Insulin treatment of the diabetic animal results in normalized values of HMG-CoA reductase whilst cholesterol-7 alpha-hydroxylase is nearly completely suppressed. The rate-limiting enzymes of cholesterol turnover are peripherally regulated by their products via a negative feedback. In contrast, hormones may have synergistic or opposite effects; thus they may represent means of higher regulation. All regulative possibilities discussed (except hypophysectomy) do modifiy the circadian rhythms. This cannot be demonstrated after hypophysectomy. After hypophysectomy circadian rhythms are not detectable any more. To get valid data about biochemical or pharmacological effects on these enzymes the circadian viriations have to be considered by measuring at different times of day (e.g. fat diet); for only the area of enzyme activit

Alcohol Oxidoreductases↗
PubMed1975

[Development of an oral retard preparation of verapamil and absorption study in the anesthetized dog].

1. An oral retard preparation of verapamil (Isoptin retard) is described. The sustained release of the active compound from verapamil retard is obtained by mixing and pressing verapamil hydrochloride with sodium alginate. The proportion of active compound and physiologically indifferent additive may range between 1:1 and 1:2. 2. The determination of the in vitro release according to the half-change method shows that verapamil is completely released from the retard preparation only after 6 to 7 h; with conventional dragées more than 90% of the compound is dissolved already after 10 min. 3. In artificial gastric and intestinal juice (pH 1.4 and 7.5) similar times of release are found. 4. The in vitro results are supported by tests on the intestinal absorption in the anesthetized dog. In a ligated duodenum section verapamil is, 3 to 8 h after application, markedly more slowly released and absorbed from the retard preparation than from conventional dragées.

Alginates↗