text: [The contraction curve of the isolated intestine produced by medium-high doses of drugs. The depressive effects of sodium].
  The contraction-curve of guinea-pig ileum, in response to carbamylcholine has been analysed. The curve is characterized by three phases: a rapid contraction, the clonus (C), immediately followed by a partial relaxation; thereafter the curve goes up again and finally, there is a tonic phase (T) characterized by a low and steady contraction (fade). The effects due to different experimental conditions have been investigated: increasing doses of carbamylcholine, ageing of the specimen, atropine application on the tonic phase; moreover the most notable experimental condition was Na reduction in the medium. This decrement, produces a decrease of C and an increases of T. On the basis of the results it has been concluded that: a) Na+ which enters the cell under muscarinic stimulation mobilizes Ca++ from deposits and causes contractile effects; thereafter, Na++ also moves Ca++ from actomyosine and produces a relaxing effect; b) spare receptors complete the action of the drug; when these receptors are activated by high doses of the muscarinic agent, they increase the amount of Na+ which enters the cell to negatively modulate the contraction.