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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.

Piperidine is a biogenic alicyclic amine possessing potent pharmacological activity. Interest has recently been focussed on its possible role as an endogenous hypnogenic substance. Using a mass fragmentographic technique with deuterium-labelled piperidine as an internal standard, the time relations of the change in brain levels of piperidine and the anesthetic activity of urethane were determined in mice. The brain piperidine level increased prior to the loss of the righting reflex and the elevated level declined prior to the reappearance of the reflex. The change in brain piperidine level correlated with neither that in spontaneous motility nor that in body temperature. The findings favor the idea that piperidine might at least partly regulate the level of consciousness.