The site of action of phlorrhizin in inhibiting intestinal absorption of glucose

Abstract

The effect of phlorrhizin in inhibiting glucose absorption from the intestine both in vivo and in vitro is well established, but the mode of action is still un-known. The present work was undertaken in an attempt to locate the site of action of phlorrhizin in the intestine. It was done concurrently with the experiments using a different technique recently reported by Parsons, Smyth & Taylor (1958) and supports theif conclusion that one action of phlorrhizin is to prevent the entry of glucose into the epithelial cells from the mucosal side. A preliminary account has been given by Newey, Parsons & Smyth (1957). METHODSThe general principle of the experiments was to incubate segments of intestine aerobically in solutions containing 14C-uniformly-labelled glucose, to examine the radioactivity of the metabolic C02, and hence to determine whether glucose had penetrated into the cells. The intestinal preparation used was that of Wiseman (1953) as modified by Smyth & Whaler (1953). White rats weighing 200-300 g were anaesthetized with pentobarbitone sodium. The intestine was removed, and three segments of small intestine, each approximately 16 cm in length, taken from the jejunal end were fixed to the apparatus. The intestine was suspended in 25 ml. Ringer-phosphate solution (Krebs, 1933) containing 200 mg glucose/100 ml., and 40 ml. of the same solution was also circulated through the lumen of the intestinal segments. These solutions are referred to as the serosal and mucosal fluids respectively. Samples of the mucosal and serosal fluids were taken for analysis at the end of the experiments. In the radioactive experiments 14C-labelled glucose was added to either the mucosal or serosal fluid and in some cases to both. During the experiment the metabolic C02 was collected as BaCO3 as described by Smyth & Whaler (1953), the total amount of C02 was measured and also the radioactivity of the BaCO3. The activity of the glucose was determined by combustion and conversion to BaCO.. From the total amount of CO2 produced, the activity of the BaCO3 obtained from this, and the activity of the BaCO2 from the labelled glucose used, the amount of 14CO2 was calculated. Determinations were thus made of the metabolic C02derived from the glucose in the mucosal or serosal fluids. Further experiments were done in which phlorrhizin was added in various concentrations to the mucosal or serosal fluids, and the effect of this on the production of 14CO2 was measured. In order to allow time for the inhibitor to act the phlorrhizin was added 15 min before the labelled glucose, and therefore in the control experiments without phlorrhizin the preparation was incubated for 15 min before the labelled glucose was added.6-2

Proceedings of the Physiological Society

“…If the potential in our experiments is due to sodium, a more rapid transfer of cations from the lumen is suggested. Newey, Parsons & Smyth (1959) have shown that the entry of glucose into the mucosal cells is prevented by phlorrhizin, and the present findings would suggest that phlorrhizin affects sodium entry, not necessarily directly, but possibly by preventing glucose entry. This is of interest in relation to the suggestion of Crane, Miller & Bihler (1961) that there is a direct relationship between sodium transfer and glucose transfer by the intestine.…”

Electrical potentials associated with intestinal sugar transfer

“…Parsons et al (1958) found that phlorrhizin in concentrations of less than 5 x 10-4 M had little effect on oxygen consumption of the intestine, and Newey, Parsons & Smyth (1959) showed that at these concentrations phlorrhizin inhibited the entry of glucose into the cell from the luminal side, with only a small effect on metabolism. These findings showed that phlorrhizin had effects on cellular processes involved in glucose transfer, quite apart from its effect on glucose metabolism.…”

The effect of uranyl nitrate on intestinal transfer of hexoses

“…Ponz (1952) suggested that uranyl ions function as nonpenetrating inhibitors of glucose absorption in the rat intestine and Ponz & Lluch (1958), using an in vivo technique, observed that the intestinal transfer of glucose and galactose was diminished in the presence of uranyl ions while transfer of fructose and arabinose was unaffected. Since at least part of the hexose transfer mechanism is close to the luminal border of the cell (Newey, Parsons & Smyth, 1959) it was of interest to investigate the effect of uranyl ions on hexose transfer by an in vitro technique.…”