Search PubMed⌕ Search

Biomedical subjects

C Chen

Publications and source records attributed to C Chen.

At least 1,315 records · Page 73Linked to original sources
PubMed1976

Combined effects of rate membrane potential, and drugs on maximum rate of rise (Vmax) of action potential upstroke of guinea pig papillary muscle.

We studied the effect of increasing the rate of stimulation on the maximum rate of rise of the action potential upstroke (Vmax) in guinea pig papillary muscles at various resting membrane potentials and after the addition of quinidine and lidocaine to the perfusate. Increasing rate caused a decrease in Vmax due to interaction of three factors: (1) a metabolic factor, presumably resetting of the Na-K pump, which caused a decrease in Vmax at all levels of resting potential between -90 and -60 mV, (2) a transient decrease in resting potential which influenced Vmax when the resting potential was less negative than approximately -80 mV, and (3) the recovery characteristics of Vmax which contributed to the decrease in this variable when rate was faster than 5/sec. As a result of these factors the steady state curve relating membrane potential to Vmax was itself rate-dependent. Lidocaine and quinidine exaggerated the rate-dependent decrease in Vmax; however, their effects differed. The effect of quinidine was consistent with its known depressant effect on the Na-K pump. The lidocaine effect was consistent with a slowing of recovery of Vmax. Our results help to explain the effects of an increase in rate on Vmax and conduction velocity in normal, partially depolarized, and drug-treated fibers

Action Potentials↗
PubMed1975

Biosynthesis and cytokinin activity of 8-hydroxy and 2,8-dihydroxy derivatives of zeatin and N-6(increment-2-isopentenyl)adenine.

8-Hydroxy and 2,8-dihydroxy derivatives of the cytokinins, 6-(4-hydroxy-3-methyl-trans-2-butenylamino)purine and N-6-(increment -2-isopentenyl)adenine, have been biosynthesized by xanthine oxidase oxidation. 8-Hydroxy derivatives have been shown to be the major intermdeiates. These compounds were tested for cytokinin activity in the tobacco bioassay. The results suggest that substitution of the 8 position with a hydroxyl group causes less decrease of cytokinin activity than substitution of both the 2 and 8 positions with hydroxyl groups.

Adenine↗
PubMed1975

Culdoscopic ligation as an outpatient procedure.

The increasing demand for abortion and sexual sterilization has caused the need to perform such operations on an outpatient basis. The University Department of Obstetrics and Gynaecology, Singapore, started a prospective study of culdoscopic ligation as an outpatient procedure in November, 1972. To date, over 600 operations have been performed. Analysis of the first 405 cases showed a low complication rate of 2.4 per cent. This study showed that culdoscopic ligation performed in the hospital outpatient is safe and feasible.

Adult↗
PubMed1975

Neonatal thyroxine administration, behavioral maturation, and brain growth in mice of different brain weight.

L-thyroxine in amounts of .5, 1, and 2 mug was injected daily from age 5 through 14 days in 3 lines of mice selected for high (H), medium (M), or low (L) brain weight. Controls (injected with vehicle only) of these lines differed in ages of eye-opening, first auditory startle, and perfection of a surface-righting response. Thyroxine at .5 mug/day accelerated the maturation of eye-opening, auditory startle, and aerial-righting response, but had no effect on a grasping response or open-field activity. Brain weights were depressed significantly in all thyroxine treated groups except in the 9k-mug dosage in H mice.

Age Factors↗
PubMed1975

Interaction of cholera enterotoxin with cultured adrenal tumor cells.

In the adrenal tumor cell system ganglioside Gm1 inhibited cholera enterotoxin (CT)-induced steroidogenesis if it was preincubated with the toxin or added to adrenal cells 10 min before CT. In the preincubation studies a molar ratio of Gm1 to toxin of 3:1 was necessary for half-maximal inhibition of steroidogenesis. On the other hand, horse serum anticholeragenoid neutralized the steroidogenic response to cell-bound CT by 50% if it was added to adrenal monolayer cultures 15 min after the toxin. Specific antiserum was able to neutralized 20% of the toxin-induced activity even if it was added to adrenal cultures 2 h after CT. Phase contrast microscopy demonstrated that partial neutralization of the biochemical effect of CT by horse serum anticholeragenoid was accompanied by partial prevention of toxin-induced rounding of adrenal cells. Further studies showed that pretreatment of cultured adrenal cells with a maximal dose of CT increased cyclic adenosine 3'-5'-monophosphate formation in response to a maximal stimulating dose of adrenocorticotropin. This result suggested potentiation of hormonal activation of adenylate cyclase in intact adrenal tumor cells in response to CT.

Adrenal Gland Neoplasms↗
PubMed1975

In vitro interaction of estrogen and prolactin on hormone-dependent rat mammory tumors (38511).

Hormone-dependent, regressing mammary tumors in rats were incubated in a chemically defined culture medium containing tritium labeled leucine at 37 degrees for 2 hr. The rate of tritium incorporation into the protein fraction by these tissues was measured with and without the addition of 17beta-estradiol and/or ovine prolactin into the medium. Tumor tissue responded to either estrogen or porlactin by a 6-7% increase in the rate of 3-H-leucine incorporation. When the incubation medium contained both the hormones, the increase in the rate of 3-H leucine incorporation was 19% which was significantly greater than the sum of the effect of each single hormone measured independelntly. These results demonstrate a synergistic effect between estrogen and prolactin on rat mammary tumors.

Animals↗
PubMed1974

Cyclic metabolic pathway of a butylated hydroxytoluene by rat liver microsomal fractions.

A cyclic metabolic pathway was obtained when 3,5-di-t-butyl-4-hydroxytoluene (BHT) was incubated with a rat liver microsomal preparation. The pathway is as follows: BHT --> 4-hydroperoxy-4-methyl-2,6-di-t-butylcyclohexa-2,5-dienone (BHT-OOH) --> 4-hydroxy-4-methyl-2,6-di-t-butylcyclohexa-2,5-dienone (BHT-3(0)OH) --> BHT. This metabolic pathway suggests that antioxidants such as BHT owe their high efficacy, at least in part, to their metabolic regeneration.

Animals↗
PubMed1972

The effects of mercaptoethanol and of peritoneal macrophages on the antibody-forming capacity of nonadherent mouse spleen cells in vitro.

Nonadherent mouse spleen cells exhibited poor viability and little or no capacity to form antibodies to sheep red cells in the Mishell-Dutton culture system. Viability and antibody-forming capacity could be restored by addition to these cultures of low concentrations of mercaptoethanol (10(-4)-10(-5)M), or by addition of appropriate numbers of mouse peritoneal macrophages. Macrophage concentrations lower than optimal resulted in lower lymphoid cell viability and correspondingly fewer plaque-forming cells, whereas excess macrophages resulted in marked inhibition of antibody formation despite good viability of the lymphocytes. Restoration of the nonadherent cells with mercaptoethanol was thus much simpler and more reproducible than it was with macrophages; furthermore, the number of plaque-forming cells developed in cultures restored with mercaptoethanol was approximately fourfold higher than it was in cultures restored with optimal numbers of macrophages. In the presence of mercaptoethanol, the plaque-forming capacity of the nonadherent spleen cells was not increased when small numbers of macrophages were added to the system, nor was it decreased when the few macrophages present in the nonadherent cells were further reduced or eliminated. Excess macrophages inhibited antibody formation in the cultures containing mercaptoethanol as they did in control cultures. Optimal restoration of plaque-forming capacity to the nonadherent spleen cells with mercaptoethanol required the reducing agent to be present throughout the 4 or 5 day culture period. Addition of mercaptoethanol 1 or more days after initiation of culture, or transfer of the cells to a medium free of mercaptoethanol before completion of the culture resulted in a reduction in the numbers of plaque-forming cells. The results suggest that mouse lymphoid cells do not require macrophages in order to form antibodies to sheep red cells in vitro, provided mercaptoethanol is present in the culture medium. The mechanism of action of mercaptoethanol under these conditions is not completely clear, but one of its effects is to promote the viability of lymphoid cells in the cultures.

Animals↗
PubMed1972

Restoration of antibody-forming capacity in cultures of nonadherent spleen cells by mercaptoethanol.

Populations of mouse spleen cells, without those cells that adhere to glass or plastic, exhibit little or no capacity for formation of antibody to sheep erythrocytes in the Mishell-Dutton culture system. When 5 x 10(-5)M mercaptoethanol is added to the culture medium, the antibody-forming capacity of these nonadherent spleen cells is restored to that of unfractionated spleen cells.

Animals↗