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Biomedical subjects

R J Levin

Publications and source records attributed to R J Levin.

At least 109 records · Page 6Linked to original sources
PubMed1977

Electrical assessment of functional lactase activity in conscious man.

Using an electrical technique for measuring transjejunal potential differences (PDs) in conscious man, we have estimated the electrogenic absorption of the hexoses liberated by hydrolysis of lactose which was infused into the jejunum of one normal control and 21 patients with diarrhoea. The results were compared with jejunal lactase levels determined from biopsy specimens taken from the recording site immediately after infusion. The PD evoked by 100 mM lactose was very significantly lower in patients with lactase levels below 4 units (lactase deficient) compared with subjects with normal lactase levels. There was also a significant correlation (r = 0.87, P less than 0.005) between the magnitude of the lactose potential (expressed as the ratio of the maximum glucose transfer potential) and the mucosal lactase level in the hypolactasic subjects but not in patients with normal lactase levels. Thus, in the subjects with lactase deficiency, the electrogenic transfer of hexose is clearly limited by the rate of lactose hydrolysis. Unlike other assessments of functional lactase activity, the electrical test provides a specific index of jejunal function and, moreover, can be adapted to investigate the possible disorders of small intestinal motility and secretion associated with hypolactasia.

Adolescent↗
PubMed1976

Influence of specific dietary sugars on the jejunal mechanisms for glucose, galactose, and alpha-methyl glucoside absorption: evidence for multiple sugar carriers.

The effects of feeding glucose, galactose, and alpha-methyl glucoside on the kinetics of absorption of these sugars in the jejunum of the fasting rat were assessed by recently developed chemical and electrical methods for characterizing the electrogenic active transfer mechanisms in vivo. The parameters of 'apparent Km' (an index of carrier affinity) and Vmax (an index of the maximum jejunal transfer capacity) were obtained from the kinetic data to describe quantitatively the active transport mechanisms in rats fed their normal solid diet, in rats deprived of solid food for three days, and in rats deprived of solid food but allowed ad libitum access to isotonic solutions of glucose, galactose, or alpha-methyl glucoside for up to three days. Feeding the sugars to fasting rats produced complex differential effects on the 'apparent Km's' and Vmax's of the various transport mechanisms. The changes, although complex, can best be explained by alterations in the transport mechanisms per se rather than by non-specific changes in intestinal morphology or metabolism. The differential effects induced by the feeding sugars are further evidence for the concept that jejunal enterocytes possess multiple carriers or mechansims for the absorption of actively transported sugars in vivo. The multiple forms of the sugar carriers (isocarriers?) MAY BE INVOLVED IN THE FACULTATIVE RESPONSES OF THE ENTEROCYTES TO CHANGES IN THE DIETARY LEVELS OF SUGAR AND MAY BE IMPORTANT IN UNDERSTANDING THE INFLUENCES OF DISEASE AND NUTRITIONAL STATUS ON ABSORPTION PROCESSES IN MAN.

Animals↗
PubMed1976

Electrogenic glucose absorption in untreated and treated coeliac disease.

Using a method for measuring changes in transmural potential difference across the human jejunum in vivo, the operational kinetic parameters of 'Apparent Km' and PD max for the active electrogenic component of glucose absorption were estimated in a group of healthy volunteers and in patients with coeliac disease. Both the 'Apparent Km' (17+/2mM; mean +/SEM) and the PD max (8.6+/0.7 mV) in nine patients with untreated coeliac disease were significantly lower (p less than 0.005) than in the control group ('Apparent Km' = 74+/5mM; PD max 12.8+/0.9mV, n=20). Treatment of five coeliac patients by gluten withdrawal for less than three months increased significantly the values of both the "Apparent Km (35+/6mM) and the TPD max (11.4+/1.2mV). Treatment of five patients for more than six months caused a further increase in the values of both kinetic parameters ('Apparent Km' = 108+/13mM; PD max =15.6+/2.7mV) to levels which exceeded those in healthy subjects. The possible interpretations of the differences in the kinetic characteristics of electrogenic glucose transport between coeliac patients and healthy subjects are discussed.

Celiac Disease↗
PubMed1975

An experimental method of identifying and quantifying the active transfer electrogenic component from the diffusive component during sugar absorption measured in vivo.

1. The kinetics of absorption of glucose, galactose and alpha-methyl glucoside have been measured in rat jejunum in vivo using a chemical method and a new electrical technique. 2. Sugar absorption estimated by chemical methods exhibited two components. One component was phlorrhizin-sensitive, saturable and generated electrical potential differences (electrogenic active component) while the other was phlorrhizin-insensitive, non-saturable and did not generate electrical potentials (diffusive component). 3. The diffusive component of the actively transported sugars was indentical to the absorption behaviour of sorbose, a hexose that is not actively transferred. 4. A method for correcting the data obtained from chemical absorption studies for the diffusive component was developed. The corrected, operational kinetic constants for 'apparent Km' obtained by this method were not significantly different to values obtained electrically. The identity between the values obtained by both methods supports the concept that they represent a measure of the same rate-limiting step in the absorption process. 5. The application and significance of the techniques is discussed in relation to the clinical assessment of intestinal sugar absorption.

Animals↗
PubMed1975

The bioelectric parameters of the vagina during the oestrous cycle of the rat.

1. A new in vitro preparation of the rat vagina was devised to allow the measurement of the electrical potential difference (p.d.), short-circuit current (s-c.c.) and tissue resistance. 2. In vivo and in vitro, the magnitude of the transvaginal p.d. (adventitia positive to lumen) was greatest at oestrus and smallest at dioestrus and metoestrus. The p.d. at pro-oestrus was not significantly different from the latter values. 3. The s-c.c. was significantly greater at oestrus than at metoestrus, dioestrus and pro-oestrus. 4. The vaginal resistance was maximal at pro-oestrus and was significantly greater than that at metoestrus, dioestrus and oestrus. The value at oestrus was significantly greater than that at metoestrus and dioestrus. These changes in resistance correlate well with known changes in vaginal morphology during the oestrous cycle. 5. It is proposed that the cellular site for the generation of vaginal bioelectric activity is the basal cell layer of the vagina and that the variations of the transvaginal p.d. measured in vivo are caused by the changes in vaginal current and tissue resistance.

Activity Cycles↗
PubMed1975

Effects of fasting and semistarvation on the kinetics of active and passive sugar absorption across the small intestine in vivo.

The effects of dietary restriction on the kinetics of absorption in vivo of glucose, galactose and alpha-methyl glucoside were assessed by electrical and chemical methods in the rat jejunum. 2. The 'apparent Km', maximum absorption or Vmax (mu-mole/10 cm. 15 min) and maximum potential difference (p.d.max) were obtained for the jejunal electrogenic active transfer mechanism from the transfer p.d.s and the chemical absorption data corrected for diffusion using various graphical kinetic plots. 3. Fasting for 3 days greatly decreased the 'apparent Kms', obtained from electrical or chemical data, for all the sugars but had no effect on those for L-valine or L-methionine. Semistarvation caused a less pronounced reduction of the 'apparent Kms' for the sugars. The dietary-induced change in 'apparent Km' for glucose was also observed in the fasted hamster. One interpretation of these changes is that the affinity of the carriers for sugars increases during dietary restriction; the greater the level of restriction the greater the increase. 4. Fasting and semistarvation caused large reductions in the Vmax. These reductions were correlated with a reduced enterocyte population estimated by changes in enterocyte column size. 5. The reduction in the Vmax for galactose was mainly accounted for by the decrease in enterocyte population. In the case of glucose, other factors such as reduced enterocyte metabolism or changes in the carriers must be involved to explain the discrepancy between the large decrease in Vmax and the enterocyte column size. 6. Fasting and semi-starvation had complex, differential actions on the p.d.max for glucose, galactose and alpha-methyl glucoside. These changes did not correlate with those observed in the Vmax measured chemically. 7. A standard diet obtained from two commercial sources was found to differ greatly in its effect on the electrogenic transfer system for alpha-methyl glucoside but had no effect on those for galactose and glucose.

Animals↗