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Biomedical subjects

D H Smyth

Publications and source records attributed to D H Smyth.

At least 37 records · Page 2Linked to original sources
PubMed1970

The effect of adenosine triphosphate on the transmural potential in rat small intestine.

1. ATP either in the mucosal or serosal fluid caused a transient increase in the potential difference and short-circuit current across the wall of rat jejunum in vitro, the serosal solution becoming more positive.2. Similar responses were observed in the ileum and colon, and in in vivo preparations of small intestine.3. The response is relatively specific for ATP.4. The transient nature of the response is not due to rapid hydrolysis of extracellular ATP.5. High concentrations of K(+) in the mucosal medium, serosal ouabain or mucosal 2,4-dinitrophenol all inhibit the response without altering the time course.6. Significant inhibition was not observed in the presence of ADP or in Mg(2+)-free salines.7. The results are consistent with an intracellular action of ATP in the epithelium to stimulate net ion transport. The results do not demonstrate whether or not extracellular ATP can act as an energy donor for an electrogenic ion pump.8. Theophylline prolongs the time course of the response, and the involvement of the adenyl cyclase system cannot be excluded as an explanation for the findings.

Adenine Nucleotides↗
PubMed1970

Intracellular hydrolysis of short chain glycerides by rat small intestine in vitro and transfer of glycerol.

1. When triacetin, tripropionin and tributyrin are incubated with sacs of rat everted intestine, they enter the epithelial cells and are completely hydrolysed to free fatty acids and glycerol.2. The distribution between the mucosal and serosal fluids of the glycerol released is very different from that of the fatty acid. Although both hydrolytic products are accumulated in the serosal fluid, a much higher fraction of the fatty acid appears in this compartment.3. When glycerol is initially present in the mucosal fluid there is no evidence of its movement against a concentration gradient.4. The results confirm the existence of a transport mechanism for fatty acids released intracellularly but do not require the hypothesis of a special mechanism for glycerol transfer.

Animals↗
PubMed1970

Effects of fasting on intestinal transfer of sugars and amino acids in vitro.

1. Transfer of sugars, amino acids and fluid and metabolism of glucose were studied with everted sacs of small intestine prepared from fed and 3-day fasted rats.2. In the absence of glucose there was some evidence for increased intestinal transfer of sugars and amino acids in fasted animals. In the presence of glucose there was in general decrease in transfer of amino acids and fluid.3. In fasted animals glucose transfer was reduced except in the lower ileum, and there was a general reduction in glucose metabolism.4. Because of the large reduction in gut weight in fasted animals, expressing transfer on a weight basis is considered not to be a valid procedure in studying the effects of fasting on intestinal transfer.5. The results have been discussed in relation to effects of fasting on energy availability, efficiency of transfer mechanisms, permeability of the intestine and the value of in vitro methods in the study of physiological absorption.

Amino Acids↗
PubMed1970

The relation between L-methionine uptake and sodium in rat small intestine in vitro.

1. Uptakes of L-methionine and mannitol by rat jejunum in vitro were measured over test periods from 5 to 120 sec after 30 min pre-test periods in the presence or absence of Na.2. The initial stage in methionine uptake was dependent on the presence of Na(+) and to a lesser extent on the K(+) concentration. In contrast mannitol uptake was independent of Na and K.3. The initial stage in methionine uptake can be reactivated 30-60% within 5 sec by replacing an Na-deficient intestine into an Na-containing medium.4. Initial methionine uptake was greater with a normal intracellular and low medium Na concentration than with a high medium and low intracellular Na concentration. It is suggested that the intracellular Na concentration is a critical factor, more important than the Na gradient, in determining the rate of amino acid transfer across the luminal membrane.

Animals↗
PubMed1969

Sodium pumps in the rat small intestine in relation to hexose transfer and metabolism.

1. The nature of Na transfer across rat jejunum was studied by measuring the Na and fluid transfers and the electrical potential in the presence of galactose, mannose and glucose.2. Galactose, actively transferred but not metabolized, caused an increase in the potential but no change in Na transfer or tissue resistance.3. Mannose, not actively transferred but metabolized, caused a large increase in Na and fluid transfer without affecting the potential or tissue resistance. Similar results were obtained with glucose in the presence of phlorrhizin.4. Galactose in the presence of mannose increased fluid and Na transfer to the level found with glucose, which is both actively transferred and metabolized.5. These results are consistent with the view that there are two Na pumps associated with hexoses in rat jejunum, both moving Na towards the serosal side. One is an electrogenic pump, stimulated by hexose transfer, and which results in a rise in potential, and the other is a neutral pump which is stimulated by hexose metabolism and which does not affect the potential.

Animals↗
PubMed1968

Some effects of ouabain and potassium on transport and metabolism in rat small intestine.

1. Ouabain (10(-3)M) inhibited the transfer of glucose, proline, methionine and fluid but not of galactose and 3-O-methyl glucose by sacs of rat everted intestine.2. Ouabain (10(-3)M) inhibited both glucose and mannose metabolism. Hexose metabolism was also reduced by varying the [K] from 4.8 m-equiv/l.3. Ouabain (10(-3)M) or absence of K reduced the stimulation of amino acid, hexose and fluid transfer by mannose. Although presence of ouabain or absence of K did not inhibit endogenous galactose transfer, these conditions prevented mannose from stimulating this transfer.4. Ouabain (10(-3)M) exerted greater effects on hexose and amino acid transfer when K was omitted from the saline and its inhibitory effects were partially overcome by increased serosal [K].5. Ouabain (10(-2)M) caused further inhibition of amino acid and glucose transfer and also reduced the transfer of galactose and 3-O-methyl glucose.6. The implications of these results are discussed with respect to the relationships between cations and hexose and amino acid transfer.

Amino Acids↗