The Accumulation of Adenosine in Rabbit Intestinal Muscle

Abstract

Strips of longitudinal muscle from rabbit intestine accumulated radioactivity when exposed to [3H]‐adenosine. Accumulation of radioactivity was not sodium‐dependent or ouabain‐sensitive, but was reduced by cooling, zero glucose plus bubbling with N2, 2,4, dinitrophenol, dipyridamole, hexobendine and lidoflazine. After 7 min exposure to [3H]‐adenosine, the tissue was found to contain radioactive adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and adenosine itself in the approximate ratio 13: 6: 4: 1. In the presence of dipyridamole, hexobendine or lidoflazine (each 1 μm), the amounts of radioactive ATP, ADP, AMP and adenosine were reduced with the concentration of adenosine not significantly different from controls. It is concluded that energy‐dependent uptake of adenosine does not occur in the longitudinal muscle of rabbit intestine. Adenosine enters the tissue by a passive process and rapidly becomes phosphorylated giving rise to apparently high tissue: medium ratios. The drugs dipyridamole, hexobendine and lidoflazine appear to reduce the accumulation of radioactivity by preventing the formation of adenosine phosphate derivatives.

Identification of Separate Receptors for Adenosine and Adenosine 5′‐triphosphate in Causing Relaxations of the Isolated Taenia of the Guinea‐pig Caecum

“…Consequently, the experiments were repeated with dipyridamole in the McEwen's solution. Dipyridamole reduces adenosine uptake, probably by inhibiting the intracellular phosphorylation of adenosine to ATP (Hopkins & Goldie, 1971;Hopkins, 1973;Hulme & Weston, 1974). Thus, when Hulme & Weston exposed rabbit intestine to adenosine in the presence of dipyridamole, the intracellular level of adenosine was normal or slightly elevated, but the amount of ATP was much less than in the control group.…”

Some Effects of Dipyridamole, Hexobendine and Lidoflazine on Inhibitory Processes in Rabbit Duodenum

“…The present experiments have been performed using the intramural inhibitory pathway in rabbit duodenum (Weston, 1973) mole, hexobendine and lidoflazine. In this tissue, these drugs seem to reduce adenosine accumulation by preventing the transformation of adenosine into its phosphate derivatives (Hulme & Weston, 1974).…”

“…were chosen from a parallel study (Hulme & Weston, 1974). In separate experiments, the agonist activity of dipyridamole, hexobendine and lidoflazine was assessed using the 4 min dose cycle described above.…”

“…At least six experiments were performed for each concentration of dipyridamole, hexobendine and lidoflazine and the significance of the mean log shifts was assessed by paired Student's t test. The concentrations of dipyridamole, hexobendine and lidoflazine used (10-8, 10-7, 10-6 M) were chosen from a parallel study (Hulme & Weston, 1974). In separate experiments, the agonist activity of dipyridamole, hexobendine and lidoflazine was assessed using the 4 min dose cycle described above.…”