Effects of papaverine on the rabbit ileum under the influence of altered temperature and extracellular Ca2+

Effects of temperature and variations of the extracellular Ca 2+ content on the activity of rabbit ileum were investigated. The spasmolytic efficacy of papaverine was also studied. A rise of temperature from 25 to 42°C significantly increased the spontaneous pendular movements, whereas the contraction amplitude was not significantly altered. Reduction of the extracellular Ca 2+ to one half did not affect spontaneous motility or the tension developed at a bath temperature of 25°C. At 42°C, however, lowering of the extracellular Ca 2+ decreased the frequency of motility but increased the contraction amplitude. At the high temperature the pD 2 value of papaverine was higher than at the low temperature. This effect was partly abolished after exposure to iodoacetic acid (IAA). Ca 2+ reduction had the same effect as a temperature rise: at a low extracellular Ca 2+ content the pD 2 of papaverine increased. It is concluded, therefore, that high temperatures stimulate the energy-requiring Ca 2+ pump mechanism thus leading to a lowered concentration of free intracellular Ca 2+ . As a consequence, the concentration of papaverine required to produce relaxation is less at the higher temperature than at the lower temperature.