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Biomedical subjects

M Schmidt

Publications and source records attributed to M Schmidt.

At least 829 records · Page 46Linked to original sources
PubMed1984

Modulation of renal ATPase activities by cyclic AMP.

A possible link between cellular cyclic AMP content and Na+K+ATPase activity was investigated in homogenates of rat kidney. Enzyme kinetics of Mg2+ and Na+K+ATPase were run in the presence of cyclic AMP, dibutyryl cAMP and compounds expected to elevate cyclic AMP levels such as forskolin, a potent adenylate cyclase activator, IBMX, an inhibitor of phosphodiesterases, and the beta-agonist isoproterenol. Medullary Na+K+ATPase is strongly inhibited by cyclic AMP whereas cortical Na+K+ATPase was stimulated in the same conditions. The correlation between ATPase activity and cellular cyclic AMP content supports the concept of a possible regulation of the enzyme by cyclic AMP.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Evidence for mobility of a new family of mouse middle repetitive DNA elements (LTR-IS).

Locus variation and sequence conservation of mouse LTR-IS elements, a new family of middle repetitive DNA sequences was studied. It is shown that LTR-IS sequences are present in all the inbred strains and subspecies of M. musculus tested and in M. cooki and M. caroli. Their arrangement in mouse genomes is polymorphic. Southern blot analysis and DNA sequencing revealed the existence of homologous DNA sequences with and without LTR-IS element insertion. LTR-IS sequences therefore appear to have arisen in early mouse ancestors and have, at least at some point, been mobile.

Animals↗
PubMed1984

Vascular effects of apomorphine and related compounds in the perfused rat kidney.

The renal vascular effects of aporphines and related compounds were studied on the isolated perfused rat kidney in the presence of 10(-5) M phenoxybenzamine and 10(-5) M sotalol and after contraction of the vascular bed with prostaglandin F2 alpha (10(-7) -3 X 10(-6) M). Under these conditions, (R)-(-)-apomorphine showed renal dopaminomimetic activity, i.e. renal vasodilation competitively inhibited by (+)-butaclamol (10(-8) M) but not by (-)-butaclamol (3 X 10(-8) M). It had an apparent affinity 25 times higher but a markedly lower intrinsic activity than dopamine. N-n-Propyl and trihydroxylated aporphines were less potent and the mono-10-hydroxylated aporphine was completely inactive. (S)-(+)-Bulbocapnine also showed weak dopaminomimetic activity but tetrahydropapaveroline was devoid of such an effect. (-)-N-(2-Chloroethyl)-norapomorphine (10(-5) M) irreversibly antagonised dopamine-induced renal vasodilation. At concentrations above 3 X 10(-6) M, most aporphines and tetrahydropapaveroline induced additional non-dopamine receptor related renal vasodilation.

Animals↗
PubMed1984

Are the funnel-canal organs the 'campaniform sensilla' of the shore crab, Carcinus maenas (Decapoda, Crustacea)? II. Ultrastructure.

The funnel-canal organs on the dactyls of the shore crab, Carcinus maenas, are innervated by 3-24 sensory cells with unbranched dendrites, which attain a length of 500-1400 micron. The outer dendritic segments are enclosed in a dendritic sheath and pass through the cuticle within a canal. Two dendrite types can be distinguished according to ultrastructural criteria: Type I has a long ciliary segment, A-tubules with an osmiophilic core and arms, and a thick ciliary rootlet. Type II possesses only a short ciliary segment and a thin ciliary rootlet. Each funnel-canal organ contains two type-I dendrites. Their ciliary bases appear a few micron distal to those of the type-II dendrites (1 to 22 in number). Two inner and two to eight outer enveloping cells belong to a sensillum. The innermost enveloping cell contains a large scolopale. In the second enveloping cell single scolopale rods are present. Thus, the funnel-canal organs are characterized by structural features typical for mechanosensitive scolopidia, on the one hand, and for chemoreceptors, on the other. Therefore, the funnel-canal organs are very likely bimodal sensilla (contact chemoreceptors). A comparison with other arthropod sensilla shows that cuticular mechanoreceptors of aquatic crustaceans generally exhibit a 'scolopidial' organization.

Animals↗
PubMed1984

Replication variants of the human inactive X chromosome. II. Frequency and replication rate relative to the other chromosomes of the complement.

Replication variants of the inactive X chromosome were investigated in lymphocytes from six donors by means of terminal BrdU or thymidine incorporation. There were interindividual differences in the incidence of particular variants. In endoreduplicated and tetraploid cells both allocyclic X chromosomes showed the same replication sequence. The Xp22 band of the allocyclic X chromosome seemed to replicate later than the homologous material in some cells. Initiation time of DNA synthesis within the inactive X chromosome was found to be stable; termination time, however, varied greatly relative to the other chromosomes. Early completion of replication within the heterochromatic X chromosome could be demonstrated preferentially for the Xq25-27 terminal sequence, but other variants expressed the phenomenon also. A variable replication rate of the inactive X chromosome is believed to be responsible for its asynchronous, independent replication. The biological significance of the phenomenon is discussed with respect to cell differentiation.

Chromosome Aberrations↗
PubMed1984

The tumor-inhibiting effect of isomeric dichloro(diphenylethylenediamine)platinum(II) complexes.

Ring unsubstituted dichloro(diphenylethylenediamine)platinum(II) complexes show a dependence of their antitumor activity on the configuration and position of phenyl rings in ethylenediamine ligand. Dichloro(1,1-diphenylethylenediamine)platinum(II) (1d) and meso-dichloro(1,2-diphenylethylenediamine)-platinum(II) (meso-2d) have a weaker effect on the human breast-cancer cell line MDA-MB 231 and on rat leukemia L 5222 than (+/-)-dichloro(1,2-diphenylethylenediamine)platinum(II)((+)-2d) and its enantiomers (+)-2d and (-)-2d which cause marked and comparable inhibition of both tumors; (+/-)-2d is also active on ADJ/PC 6 plasmacytoma of the mouse and on cisplatin-, daunomycin-, and cisplatin/daunomycin-resistant Ehrlich ascites tumors of the mouse. The differences in activity of the diastereomers (+/-)-2d and meso-2d, for which distinct influences on the DNA secondary structure can be demonstrated CD spectroscopically may be explained by a steric hindrance of the drug-DNA interaction.

Animals↗
PubMed1984

Evidence that a major class of mouse endogenous long terminal repeats (LTRs) resulted from recombination between exogenous retroviral LTRs and similar LTR-like elements (LTR-IS).

Two endogenous retroviral long terminal repeats (LTRs) were sequenced and compared to LTR-IS (a family of insertion-element-like sequences with structural features of solitary retroviral LTRs) and to Moloney murine leukemia virus DNA. The sequence comparisons revealed that the major difference between these two endogenous LTRs is a 190-base-pair segment which is also present in LTR-IS elements. Hybridization analysis of DNAs from several mouse species using specific probes shows linkage of the 190-base-pair segment to a LTR-IS specific fragment. It is concluded that the major class of endogenous LTRs has been generated by recombination between exogenous retroviral LTRs and LTR-IS sequences.

Animals↗
PubMed1984

Passive/active immunization against hepatitis B.

No differences in eventual immune-response rates were found between 325 subjects immunized passively/actively against hepatitis B and a control group of 108 subjects vaccinated only actively. The geometric mean titers of antibodies to hepatitis B surface antigen were nearly identical in controls and in a group of 87 individuals immunized passively/actively with the same vaccine lot. Lower geometric mean titers of antibodies to hepatitis B surface antigen were seen in 238 individuals who were vaccinated passively/actively with a different vaccine lot, a difference that may be explained by a somewhat lower immunogenicity in this particular lot. The mean half-life of hepatitis B immunoglobulin was calculated as 24.8 days, and in approximately 90% of vaccines 300,000 mIU of hepatitis B immunoglobulin provided protection until an active immune response had developed.

Adult↗
PubMed1984

The sympathetic nervous system and renal sodium handling: is dopamine involved?

The presence of vascular dopamine receptors and dopaminergic nervous fibers in the kidney suggests that dopamine plays a role in the control of renal function by the autonomic nervous system. Dopamine and norepinephrine have contrary effects in the kidney. This is particularly apparent at the level of efferent glomerular arterioles. Variations in postglomerular vascular resistance may induce variations in the filtration fraction and in peritubular oncotic pressure, thus influencing proximal tubule sodium reabsorption. We propose that the sympathetic innervation of the kidney controls the postglomerular vascular resistance; this control can be achieved through a balance between the vascular effects of dopamine and norepinephrine.

Animals↗
PubMed1984

[Characterization of the alpha adrenoreceptors in the vascular bed of the isolated rat kidney].

The vasoconstrictive effect of alpha-adrenoceptor agonists was studied on isolated perfused kidney from normal Wistar rats. Methoxamine (ED50 = 1.61 +/- 0.16 X 10(-6) M; m +/- SEM), phenylephrine (2.33 +/- 0.16 X 10(-6) M) and alpha-methylnoradrenaline (1.60 +/- 0.40 X 10(-6) M) acted as full agonists. Dopamine (9.5 +/- 1.08 X 10(-5) M) had a partial agonistic effect. Clonidine and B-HT 920 were inactive up to the concentration of 10(-4) M. Prazosin, but not yohimbine (10(-6) M) antagonized the response to phenylephrine (pA2 = 8.48 +/- 0.12) and to alpha-methylnoradrenaline (8.02 +/- 0.10). Our results suggest that the postsynaptic alpha-adrenoceptors which when stimulated increases vascular resistance of isolated rat kidney, belong exclusively to the alpha 1-subtype.

Adrenergic alpha-Agonists↗
PubMed1984

[Short-term irradiation of glioblastomas with high-dose single fractions].

Compared to surgery alone, postoperative radiotherapy leads with glioblastomas (grade IV gliomas) to a significant improvement of the therapeutic results. The prolongation of survival time, however, is to a large extent compensated by the therapy itself (it normally implicates hospitalisation). Therefore, we tested the efficiency of rapid course irradiation with high fractions. 70 patients were treated daily with individual fractions of 3.5 Gy, 4 to 6 fractions per week. The entire dose amounted to 31.5 to 38.5 Gy. The average survival time was 33.5 weeks corresponding to the survival time known from the combined surgical and radiotherapy treatment of glioblastomas. An effective increase in therapy-free survival time seems possible, especially when the entire focal dose does not exceed 35 Gy. It is remarkable that the patients with the maximum exposure did not have the longest survival times and rates. Living conditions for the patients were similar to those with conventional fractionation , or even better. Rapid course irradiation with high fractions and a limited total dose (35 Gy) presently is - apart from the accelerated superfractionation - a successful measure to prolong the therapy-free survival time for patients with grade IV gliomas.

Adolescent↗
PubMed1984

Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.

Angiotensin II↗
PubMed1984

[Intramural pseudodiverticulosis of the esophagus].

Description of a case of rare endoluminal pseudodiverticulosis--only 49 cases have been reported to date--presenting the characteristic x-ray morphology and clinical course. Aetiological factors and the pathogenesis of the dilatation of the submucous oesophageal gland as a morphological substrate of pseudodiverticulosis are discussed.

Aged↗