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Biomedical subjects

R Schmid

Publications and source records attributed to R Schmid.

At least 289 records · Page 16Linked to original sources
PubMed1981

Formation and disposition of newly synthesized heme in adult rat hepatocytes in primary culture.

Studies with the intact liver have suggested that newly synthesized heme exists transiently in a small pool before its incorporation into tissue heme proteins. The same or a closely related pool may regulate synthesis of heme and serve as the precursor of "early peak" bilirubin. To delineate this postulated pool by a direct approach, we have utilized primary cultures of adult rat hepatocytes. Cultures pulse-labeled with delta-amino[3H]levulinic acid at various time points were fractionated into 105,000 X g supernatant and pellet. Labeled heme appeared within 1 to 2 min in the cytosol fraction, followed by transfer to the pellet. The kinetics of heme formation and transfer and of labeled bilirubin production were analyzed by computer simulation utilizing the least squares method. The experimental findings conformed best to a four-compartment model that includes a second cytosolic heme compartment exchanging with the initially labeled compartment but not serving as a direct precursor of bilirubin. Calculation of apparent rate coefficients indicated that, in cultured hepatocytes, 20% of newly formed heme is converted directly to bile pigment, whereas 80% is utilized for formation of cellular heme proteins (64% in the pellet, 16% in the second cytosol compartment). This experimental approach has provided direct evidence for a rapidly formed cytosolic heme fraction which appears to be identical with the previously postulated regulatory or "unassigned" heme pool of the liver.

Aminolevulinic Acid↗
PubMed1981

[Hypophyseal reaction state during oral contraceptiva (author's transl)].

In 5 normocyclic women, firstly taking a conventional oral contraceptive, Neogynon (50 mcg EE + 250 mcg levo-norgestrel) for 6 months, the levels of LH, 17 beta-E2 and progesterone did not rise after changeover to a dose-reduced pill, Microgynon 30 (30 mcg EE + 150 mcg levo-norgestrel). This fact indicates maintained central suppression. Examination of the hypothalamic-hypophyseal axis by the Gn-RH test (50 mcg) with Microgynon 30 showed negative results during the first treatment cycle in 13 out of 18 women. In the 6th treatment cycle only 7 Gn-RH non-reactive women were observed and after stimulation with 100 mcg Gn-RH only 5 women remained with negative Gn-RH tests. Of the 20 women who took conventional oral contraceptives over a period of 6 months to 6 years (7 took Eugynon: 50 mcg EE + 500 mcg D,L-norgestrel, 5 Lyndiol: 75 mcg mestranol + 2.5 mg lynoestrenol, 8 Neogynon, only one from the Neogynon group showed a positive result. On the other hand there was a positive reaction in 4 out of 7 women using the two step dose-reduced preparation Sequilar (11 tablets of 50 mcg EE + 50 mct levo-norgestrel and 10 tablets of 50 mcg EE + 125 mcg levo-norgestrel).

Adult↗
PubMed1981

[The efficacy of gestoden (delta 15-d-norgestrel) as ovulation inhibitor (author's transl)].

Two single-phase combined low-dosage oral contraceptive preparations were tested with respect to their effects on functional parameters of the menstrual cycle. Twenty young women with a normal biphasic menstrual cycle took part in this random study. Evaluation of cervical function, consistency and crystallisation ability of the cervical mucous and of the karyopyknosis index as well as radioimmunoassay of the serum levels of LH, FSH, HPRL, 17-beta-oestradiol and progesterone were carried out consecutively as from the 8th day over the duration of one control cycle and one in which contraceptive as administered. Preparation I (SH D 356 A) contained 75 micrograms delta 15-d-norgestrel (Gestoden) + 30 micrograms ethinyloestradiol. Whilst preparation II (SH D 356 B) contained 75 micrograms d-norgestrel + 30 micrograms ethinyloestradiol. Both substances successfully inhibited ovulation, whereby the former achieved a markedly greater suppression of function with regard to all parameters and, yet good menstrual cycle control was maintained. Hence, gestoden enables the content of active components in oral contraceptives to be reduced even further without detracting from the safety of the technique.

Adult↗
PubMed1981

Cytochrome P-450 heme moiety. The specific target in drug-induced heme alkylation.

Exogenously administered heme is incorporated into rat hepatic cytochrome P-450 in vivo (Correia, M. A., Farrell, G. C. Schmid, R. S., Ortiz de Montellano, P. R., Yost, G. S., and Mico, B. A. (1979) J. Biol. Chem. 254, 15-17). This was demonstrated in allylisopropylacetamide (AIA)-treated rats by the formation of a radioactive adduct derived from the porphyrin of the administered [3H]heme and AIA. Formation of such adducts requires catalytic participation of cytochrome P-450 in oxidative metabolism of AIA to an active species which subsequently alkylates the prosthetic heme moiety of the cytochrome. These results suggested that the exogenous heme had been incorporated prosthetically into cytochrome P-450 prior to generation of the adduct. However, the possibility remained that a minute portion of the inactivating AIA-species escaped the catalytic site of the generating hemoprotein and alkylated the nonprosthetically bound isotopic heme. To examine this critical possibility, we have employed a chemical derivative of heme which binds to the microsomal membrane. Although this heme derivative is a structurally suitable target for attack by the inactivating drug species, we found that it was unsuitable for incorporation into the prosthetic site of cytochrome P-450. The findings of this study provide irrefutable evidence that the label recovered in drug-porphyrin adducts is derived exclusively from radioactive heme incorporated prosthetically into cytochrome P-450. Drug-porphyrin adducts can therefore be used as reliable probes to follow the transfer of heme from the hepatic "free" heme pool into cytochrome P-450.

Alkylation↗
PubMed1981

Reduction of biliverdin and placental transfer of bilirubin and biliverdin in the pregnant guinea pig.

Biliverdin was reduced to bilirubin in pregnant and foetal guinea pigs, and the 100000 g supernatant from homogenates of foetal liver, placenta and maternal liver showed high biliverdin reductase activity. The placental transport of unconjugated bilirubin and biliverdin was compared by injecting unlabelled and radiolabelled pigments into the foetal or maternal circulation and analysing blood collected from the opposite side of the placenta. Injected bilirubin crossed the placenta from foetus to mother and vice versa, but injected biliverdin did not appear to cross without prior reduction to bilirubin. The guinea-pig placenta is apparently more permeable to bilirubin than biliverdin. Reduction of biliverdin to bilirubin in the foetus may, therefore, be essential for efficient elimination of haem catabolites from the foetus in placental mammals.

Animals↗
PubMed1981

Unidirectional habituation of vestibulo-ocular responses by repeated rotational or optokinetic stimulations in the cat.

1. Unilateral habituation of the vestibulo-ocular reflex was produced in adult cats stimulated by repeated unidirectional velocity steps (vestibular training) or by a continuously moving visual surround (optokinetic training). -- 2. Unidirectional vestibular training produced a strong asymmetry of vestibulo-ocular responses (VOR). Responses to velocity steps applied to the "trained" labyrinth were decreased both in gain and in time-constant. This effect generalized to responses to sinusoidal oscillations (0.03 Hz to 0.1 Hz), i.e. to a stimulus not used during training. -- No spontaneous nystagmus was ever observed in spite of the dynamic VOR asymmetry. -- 3. Unilateral vestibular habituation produced by vestibular training appeared to be a long-lasting phenomenon. It was still present 10 days after the end of training. -- 4. Optokinetic responses were not affected by vestibular training. -- 5. Unidirectional optokinetic training produced an increase in the slow phase velocity of optokinetic nystagmus (OKN) by about 25% in both directions. This effect did not persist for more than a few minutes. A marked spontaneous nystagmus was recorded in the dark after each session of optokinetic training, with a slow phase in the direction opposite to the previous OKN. -- 6. VOR in response to velocity steps and to sinusoidal oscillations were decreased unilaterally after optokinetic training. This effect was of short duration, however, and disappeared within the interval between training sessions. This lack of retention contrasted with the prolonged effect of vestibular training.

Acoustic Stimulation↗
PubMed1981

Endogenous inhibitors of Na+-independent [3H]GABA binding to crude synaptic membranes.

The characteristics of the Na+-independent high-affinity binding of [3H]GABA to various types of crude synaptic membranes (CSM) prepared from rat brain cortex were studied. In freshly prepared CSM the content of GABA was so high that the high-affinity [3H]GABA binding could not be determined. In contrast when the frozen-thawed CSM were incubated at 37 degrees for 30 min with or without Triton X-100 or phospholipase C and then washed repeatedly, there was a virtual disappearance of GABA from the supernatant extracts and the binding constants of [3H]GABA to CSM could be determined. Two apparent populations of [3H]GABA binding sites, one with a low- and the other with a high-affinity constant, were detected. The ratio of the number of high- to low-affinity binding sites varies with the method used to prepare the membranes. The lowest value of this ratio was observed with membranes incubated at 37 degrees for 30 min. However, when frozen-thawed CSM were treated with 0.05% Triton X-100 repeatedly, the ratio of the number of high- to low-affinity binding sites increased progressively. This increase in ratio is due to a selective increase in the number of the high-affinity sites without significant changes in the number of the low-affinity sites. The extent of the increase in the number of sites that bind [3H]GABA with high affinity after repeated Triton X-100 treatments was paralleled by a decrease of an endogenous protein which inhibits GABA binding. The reapplication of this endogenous material to membranes repeatedly treated with Triton X-100 reduces the number of high-affinity binding sites for [3H]GABA to values similar to those measured in membranes that were not treated with Triton X-100. The inhibitory preparation extracted from CSM incubated with Triton X-100 was shown to be free of GABA or phospholipids. The gel filtration chromatography reveals the presence of two molecular forms of the inhibitor; of these, the high-molecular-weight material fails to bind GABA, whereas the low-molecular-weight material appears to bind GABA. The high-molecular-weight endogenous inhibitor has been termed GABA modulin.

Amino Acids↗
PubMed1981

Alveolar bone loss in rats after immunization with Actinomyces viscosus.

We investigated a possible cause-and-effect relationship between sensitization against Actinomyces viscosus Nyl and destructive periodontal disease in RIC-Sprague-Dawley rats. Germfree rats (66) were either immunized with A. viscosus Nyl (day 20) or orally infected with A. viscosus Nyl (days 38 and 39) or both. We measured alveolar bone loss in maxillary and mandibular molars, in vitro T-lymphocyte responsiveness, and serum antibody titers. In immunized and monoassociated rats bone loss in both jaws progressed rapidly between days 37 and 72, whereas the rate of further resorption decreased until day 100. In monoassociated rats, development of bone loss was much slower, and the maximum resorption measured was, at best, half of the bone loss compared with the former group. However, no amplification of bone loss by immunization was observed in a second experiment using 63 conventional rats kept in relative gnotobiosis. Antibody titers to A. viscosus Nyl in gnotobiotic monoassociated rats were higher in immunized animals, whereas no difference was found in the respective groups of the relative gnotobiotic experiment. The fact that immunization more than doubled alveolar bone loss in gnotobiotic monoassociated rats confirms the allergic nature of the disease. The lack of such an effect under conventional conditions points to suppressor mechanisms whose decrease might convert stable periodontal lesions into progressive ones.

Actinomyces↗
PubMed1981

Bilirubin kinetics in intact rats and isolated perfused liver. Evidence for hepatic deconjugation of bilirubin glucuronides.

Most previous compartmental models describing bilirubin transport and metabolism in the liver have been validated solely by analysis of the plasma disappearance of radiolabeled bilirubin in human subjects. We now have determined the transport kinetics of a bilirubin tracer pulse by analysis of plasma, liver, and bile radioactivity data from 30 intact rats. Plasma [3H]bilirubin disappearance was best described by the sum of three exponentials, and a six-compartment model, derived by simulation analysis, was necessary and adequate to describe all experimental data. Examination of the injected radiolabeled bilirubin by extraction with hexadecyltrimethylammonium bromide and thin-layer chromatography revealed that 6.6% (mean) of the original pigment had been degraded to labeled nonbilirubin derivatives during preparation of the tracer dose. This material exhibited a significantly longer half-life (mean 50.6 min) of the plasma terminal exponential than that of authentic radiobilirubin (20.6 min). In isolated perfused rat liver, the kinetics of [3H]bilirubin in perfusate and bile readily fitted the proposed model. Compatibility of the model with the data obtained, both in the isolated liver and in vivo, required that a fraction of bilirubin conjugated in the liver be deconjugated and returned to the plasma. Deconjugation of bilirubin glucuronides was evaluated directly by infusion of bilirubin monoglucuronides, containing 14C in the glucuronosyl group, into rats with an external bile fistula. Since metabolic degradation of hydrolyzed 14C-labeled glucuronic acid yields 14CO2, this was measured in expired air. Whereas 86% of the administered labeled pigment was recovered in bile, 7% of the label appeared in 14CO2. These findings directly validate a portion of the proposed kinetic model and suggest that hepatic deconjugation of a small fraction of bilirubin glucuronides is a physiological event. Deconjugation may also account, at least in part, for the presence of increased concentrations of unconjugated bilirubin in the plasma of patients with cholestasis.

Animals↗
PubMed1981

Heme enhances hexobarbital metabolism in perfused rat liver after drug-mediated destruction of cytochrome P-450.

During mixed-function oxidation of allylisopropylacetamide (AIA), autocatalytic destruction of hepatic cytochrome P-450 leads to retarded elimination of this agent. After AIA-mediated destruction of cytochrome P-450, exogenously administered heme that has entered liver cells is directly incorporated into cytochrome P-450. This raises the hepatic content of this hemoprotein, enhances the activity of mixed-function oxidases and accelerates hepatic clearance of the inactivating agent, AIA. We have studied the metabolic consequences of these phenomena for the disposition of hexobarbital coadministered with AIA in the isolated perfused rat liver. AIA decreased perfusate fractional disappearance of hexobarbital by approximately 80%. This was attributable to destruction of cytochrome P-450 rather than to competitive inhibition of hexobarbital metabolism, since by increasing the molar ratio of hexobarbital to AIA in perfusate, hexobarbital elimination was not enhanced. Heme administered after AIA significantly accelerated hexobarbital disappearance from the perfusate, reflecting increased hexobarbital metabolism by reconstituted cytochrome P-450. In the absence of prior destruction of cytochrome P-450 by AIA, heme failed to alter the rate of hexobarbital elimination. These findings demonstrate that drug-mediated destruction of cytochrome P-450 results in impaired hexobarbital metabolism, which is reversible by administration of heme. Heme infusion may be useful in treatment of patients poisoned with drugs that destroy hepatic cytochrome P-450.

Allylisopropylacetamide↗
PubMed1980

The effect of kainic acid on the hippocampal content of putative transmitter amino acids.

The time courses of the changes in the contents of GABA (gamma-aminobutyric acid), glutamate, aspartate, taurine, glycine and alanine were measured in both hippocampi of rats which were rejected in one hippocampus with kainic acid (KA). The contents of these amino acids were measured with high performance liquid chromatography. The hippocampal contents of GABA, glutamate, aspartate and taurine were reduced homolaterally to the KA injection; in contrast, the contents of glycine and alanine failed to change. The extent of the reductions of GABA, glutamate, aspartate and taurine was dependent on the size of the lesion caused by KA. The greatest decrease occurred after two simultaneous injections of KA, in dorsal and ventral hippocampus. An analysis of the amino acids at different levels of the hippocampus after dorsal injections of KA showed that in the hippocampus the amino acidergic axons do not travel longitudinally. This study suggests that GABA, glutamate, aspartate and taurine are preferentially located in intrinsic hippocampal neurons with short axons.

Amino Acids↗
PubMed1980

[Timing of ovulation in clomiphene-induced cycles (author's transl)].

214 menstrual cycles, induced by clomiphene in 121 women desiring a family but manifesting disturbances of cycle, type WHO II (1976) were investigated with regard to pattern of cervical function. 184 were ovulatory cycles. The time of ovulation was predictable within a range of two days in 58.7% of cases by means of the cervical score, consisting of the dilatation of the cervical os, the degree of transparency, the quantity and the consistency of the cervical mucus. The occurence of the "LH peak" and the rise in basal body temperature (BBT) were set in relation to this. In 41.3% of cycles the cervical score, influenced by the antioestrogenic effect of clomiphene, gave only insufficient evidence. In subsequent treatment cycles the cervical function, in relation to the individual case and the inducible quality of the cycle, showed a similar response rate as in the first treatment cycle. Our results suggest that, after examination of the first clomiphene-induced cycle by the combined means of cervical score and hormoneanalytic methods, patients with a positive cervical response, can be investigated by any interested doctor, even if he doesn't have a laboratory at his disposal, in order to assess the timing of ovulation for therapeutic measures.

Body Temperature↗