Effects of isoprenaline and phenylephrine on energy-rich phosphate compounds and glucose-6-phosphate in smooth and cardiac muscle.

1. Tension changes produced by phenylephrine and isoprenaline have been examined in four tissues-the guinea-pig taenia coli, the longitudinal muscle strip of rabbit duodenum, the abdominal aorta of the rabbit and the rat heart.2. Changes in the amounts of adenosine triphosphate (ATP), creatine phosphate (CP) and glucose-6-phosphate (G-6-P) associated with the addition of phenylephrine and isoprenaline have been measured in the four tissues using enzymatic fluorimetric analysis.3. An alpha-adrenoceptor-mediated increase in tension (phenylephrine; rabbit aorta) was associated with no change in the amounts of ATP, CP or G-6-P.4. An alpha-adrenoceptor-mediated decrease in tension (phenylephrine; guineapig taenia coli and rabbit duodenum) was associated with no change in the amounts of ATP, CP or G-6-P.5. A beta-adrenoceptor-mediated increase in force of contraction (phenylephrine and isoprenaline; rat heart) was associated with a reduction in the amounts of ATP and CP and an increase in the amount of G-6-P.6. A beta-adrenoceptor-mediated decrease in tension (isoprenaline; guinea-pig taenia coli and rabbit duodenum) was associated with an increase in the amounts of ATP and CP and no change in the amount of G-6-P.7. beta-Adrenoceptor-mediated metabolic changes were antagonized by propranolol.