Search PubMed⌕ Search

Biomedical subjects

C Ritter

Publications and source records attributed to C Ritter.

At least 91 records · Page 5Linked to original sources
PubMed1981

Relative muscarinic synaptic activation by anionic, neutral or cationic liposomes.

Liposomes made of dipalmitoyl phosphatidyl choline (DPC) and safflower oil fatty acids produce a contraction of the guinea pig ileum longitudinal muscle myenteric plexus preparation (LMMP). Stimulating the LMMP while liposomes are present yielded greater than control contractions, an effect which remained for many minutes after liposomes had been washed out. Neutral (DPC) liposomes produced a direct transitory decrease in basal tension and phasic activity. Stimulation in the presence of neutral liposomes resulted in slower attainment of maximal contraction. Cationic liposomes(DPC + oleylamine) had little direct effect, but slightly decreased stimulus evoked maximal contraction.

Acetylcholine↗
PubMed1981

Differential enhancement of antitumor effectiveness by phospholipid vesicles (liposomes).

The simultaneous administration of dipalmitoylphosphatidylcholine liposomes and methyl-bis(beta-chloroethyl)amine (HN2) to Ehrlich ascites tumor-bearing mice results in prolongation of survival, reduction of toxicity, and increase in chemotherapeutic index when compared to HN2 alone. Delay for as little as 10 min in the administration of HN2 following the liposomes eliminates this enhancement of activity and, in fact, abolishes much of the chemotherapeutic activity of the alkylating agent itself. The enhancement phase of liposomal action correlates with a significant increase in HN2 uptake by tumor cells which cannot be due to entrapment of drug in the liposomes, while the reduced toxicity could reflect subsequent HN2 transport. Persistent membrane alteration is also seen in the contrasting case of the lipid-soluble alkylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea where advanced administration of the liposome preparation significantly increases the chemotherapeutic activity. The observed effects are also shown to be influenced by liposome composition. The hypothesis is advanced that, under the given experimental conditions, liposomes can cause persistent reorganization of cell membranes which follow a characteristic course and have specific features.

Animals↗
PubMed1981

Alterations of muscarinic synaptic activity by anionic liposomes.

Liposomes made of phosphatidyl serine and dioleylphosphatidic acid have two effects on contraction of the guinea pig ileum longitudinal muscle-myenteric plexus preparation. First, the liposomes directly stimulate contraction, apparently through acetylcholine release. Second, after the liposomes are removed from the Tyrode solution bathing the preparation, electrical field stimulation or acetylcholine addition produce contractions which are significantly less than control. The acetylcholine release effect is presynaptic, on the nerve terminal, while the decreased responsiveness effect is postsynaptic, at the level of the muscarinic receptor.

Acetylcholine↗
PubMed1981

Calcium antagonism of anionic liposome actions at a muscarinic synapse.

Addition of 0.5 mM Ca++ to guinea pig ileum longitudinal muscle-myenteric plexus preparation, which is contracted under the influence of anionic liposomes, is followed by a rapid, temporary, relaxation. Such Ca++ addition produces no change in the field-stimulated preparation, eliminating direct Ca++ effects or neuronal acetylcholine release nor in the preparation stimulated by added acetylcholine, eliminating direct Ca++ effects on muscle. These eliminations leave the Ca++ interaction with liposomes, probably causing self-fusion, and loss from interaction with cholinergic neurons, as the mechanism for Ca++-induced relaxation.

Animals↗
PubMed1980

Relative enhancement by various liposomes of BCNU effectiveness against L-1210 leukemia in vivo.

When maximal effective dose (MED) of BCNU is injected together with liposomes to mice with L-1210 leukemia, the effectiveness of the drug is decreased. But when half the MED is injected with liposomes into such mice, survival is increased compared to mice injected with BCNU alone. Study of liposome composition on BCNU anti-leukemic effect revealed that negatively charged liposomes made of dioleylphosphadyl choline plus phosphatidyl serine given with half the MED of BCNU increased both long-term survival and mean survival time. This enhancement was not produced with negatively charged liposomes made of dioleylphosphatidic acid alone or in liposomes in which phosphatidyl serine plus dioleylphosphatidic acid was diluted with the neutral phospholipid, dioleylphosphatidyl choline.

Animals↗
PubMed1978

[Cytogenetic studies on women during and following the use of hormonal contraceptives].

The object of our investigations was the assessment of chromosomal changes in lymphocyte cultures of 33 women after long-term application of Ovosiston and Non-Ovlon (Group I), of 10 women with discontinued use of hormonal contraceptives at intervals of at least two month (Group II), cytogenetic investigations of 20 untreated healthy persons (Group III). We did not find an increase of numerical or structural aberrations in all cases. Our study of anomalies in the position of acrocentric chromosomes in the metaphase indicates a significantly increasing rate of associations after long-term use of hormonal contraceptives in lymphocyte culture. Origin connexion and importance of associations were discussed.

Cells, Cultured↗
PubMed1977

Hexose shunt dehydrogenase activity in leukocytes isolated from bovine milk.

A spectrophotometric method for measuring small changes in light absorption at specific wavelengths from highly turbid suspensions of biological material (dual-beam spectrophotometry) has been used to measure glucose-6-phosphate oxidation and nicotinamide adenine dinucleotide phosphate (oxidized) reduction catalyzed by lysates of milk leukocytes. This reduction was correlated .84 with cellular protein concentration and, therefore, with cell concentration.

Animals↗
PubMed1976

Influence of prostaglandins upon adenosine release and of adenosine upon prostaglandin release in the isolated rabbit heart.

Prostaglandin (PG) E1 with its high effect of coronary dilation causes a distinct increase in the adenosine release from the isolated rabbit heart (Langendorff technique). Compared to this, an equal dose of PGF2alpha increases the release of adenosine only to a small extent. Conversely, application of adenosine results in a considerable release of PG-like substances from the rabbit heart in vitro. The present investigations support the hypothesis that, apart from adenosine, PG's too, are involved in coronary regulation as modulators.

Adenosine↗
PubMed1976

[The effect of oxyfedrine, prenylamine and dipyridamole on heart hypertrophy and collagen concentration of pressure loaded rat hearts].

Rats were subjected to constriction of the abdominal aorta and two days later to nephrectomy. The maximum left ventricular hypertrophy was reached on the seventh day following the nephrectomy. During one month the animals were treated, six days per week with i.p. dipyridamole, prenylamine or oxyphedrine. The drugs studied suppressed the increase in hydroxyproline concentration of the left ventricle whereas the development of heart hypertrophy was not influenced.

Animals↗
PubMed1976

Comparison of the effects of nitrogen mustard on the functional properties of mitochondria from sensitive and resistant strains of Ehrlich ascites tumors.

In vivo treatment of sensitive tumor cells with nitrogen mustard (HN2) results in marked inhibitions of protein and nucleic acid synthesis by mitochondria subsequently isolated from these cells. This inhibition occurs at doses of drug which produce no apparent inhibition of total RNA synthesis. The inhibition gradually reverses itself in sensitive cells and is less severe and more rapidly reversed in resistant cells. The in vivo sensitivity of the mitochondria is in striking contrast to their in vitro behavior; isolated mitochondria resist 50 times the in vivo ID50 level of the drug. The sensitivity of protein and RNA synthesis in mitochondria is presumed to be related to the differences in organization between the nucleocytoplasmic processes and the mitochondrial. But the data also suggest that the in vivo effects on mitochondria are indirect, either acting via the cytoplasm or nucleus or via a carrier mechanism having mitochondrial affinity.

Animals↗
PubMed1975

[Variation of mechanical and biochemical parameters of pressure-loaded rabbit hearts following chronic administration of dipyridamole].

After constricting the aorta ascendens of rabbits, the influence of chronic administration of dipyridamole (8 mg/kg i.m. on 6 out of 7 days of the week for 3 months) upon heart hypertrophy, hemodynamics and the hydroxyproline content in the right and left ventricles, the incorporation rate of 2-[14C]-glycine into the actomyosin and soluble protein of the left ventricle was studied. The dipyridamole treatment had no effect on the increase in systolic pressure, the contractility index of the aorta-stenosed animals and heart rate. In contrast, the hypertrophic development, and consequently the increase in hydroxyproline concentration and the increased incorporation rate of 2-[14C]-glycine into the soluble protein were inhibited. The possible mechanism of action of dipyridamole on the development of heart hypertrophy in the rabbit is discussed.

Animals↗