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Biomedical subjects

I T Johnson

Publications and source records attributed to I T Johnson.

115 records · Page 7Linked to original sources
PubMed1974

Absorption of folic acid by everted segments of rat jejunum.

1. Everted rings of rat intestine were used to study the initial uptake rate of folic acid at various concentrations and incubation temperatures in vitro.2. Folic acid was accumulated linearly for periods of at least 30 min.3. The initial uptake rate was found to reach a constant value as the concentration of folic acid in the incubation medium was increased above 5 x 10(-6)M.4. Reducing the temperature of incubation from 37 to 27 degrees C gave small Q(10) values at either end of the concentration range.5. Transfer of folic acid into the serosal compartment of everted sacs was shown to undergo a rate reduction in the same concentration range.6. A mechanism for folic acid transport is suggested in which folic acid is converted to the neutral species at the mucosal surface in an acid microclimate.

Animals↗
PubMedDate not supplied

The clastogenic and mutagenic effects of ascorbigen and 1'-methylascorbigen.

Ascorbigen, which occurs naturally in the human diet, and a synthetic analogue (1'-methylascorbigen), were assayed for cytotoxic and clastogenic activities in a SV40-transformed Indian Muntjac cell line (SVM), and for mutagenic activity in the Ames test using Salmonella typhimurium strains TA98 and TA100. Ascorbigen had no effect upon the clonal survival of SVM at concentrations below 0.21 mg/ml and did not induce either chromosome aberrations or sister-chromatid exchanges (SCEs) at any concentration tested up to the maximum compatible with the assay conditions; nor did it induce mutations in either Salmonella strain. In contrast, 1'-methylascorbigen was an order of magnitude more cytotoxic, demonstrating a Dq of 0.03 mg/ml, and whilst it too was not found to induce chromosome aberrations it did induce SCEs in SVM (although only at highly cytotoxic doses) and mutations in the Ames test.

Animals↗
PubMedDate not supplied

Cytotoxicity and genotoxicity of diallyl sulfide and diallyl disulfide towards Chinese hamster ovary cells.

Two compounds found in garlic, diallyl sulfide (DAS) and diallyl disulfide (DDS), were tested for cytotoxic and genotoxic effects in a Chinese hamster ovary cell line. DDS was found to be more cytotoxic than DAS (showing a Dq of 1.6 micrograms/ml and a D0 of 0.6 microgram/ml as opposed to values of 295 and 90 micrograms/ml, respectively). Both compounds were found to induce both chromosome aberrations and sister chromatid exchanges (SCEs) with DDS again being more active on a weight-for-weight basis, exhibiting activity at concentrations below 10 micrograms/ml compared with the levels of 300 micrograms/ml and above required for DAS to show any effect. The addition of rat liver S-9 activation fraction to the assays modified the effects of the two compounds in a non-consistent manner. It reduced the induction of SCEs by both compounds, enhanced the generation of aberrations by DDS (but not by DAS) and radically altered the parameters of both survival curves, reducing the Dq values almost to zero but increasing the D0 values.

Allyl Compounds↗