Hydrostatic pressure on vagal effects and heart contraction

Abstract

Vagal inhibitory effects are readily observed in isolated vagal heart preparations of Rana pipiens. The normal effect was partially blocked by raising the hydrostatic pressure to about 2,000 psi. There was a complete block of vagal effects at about 5,000 psi or more. When the preparation was subjected to low pressure, the vagal inhibitory effect again occurred. This process could be repeated several times. Physostigmine raised the critical pressure limit by about 2,000 psi. The observed phenomena are discussed in particular with respect to the kinetics of acetylcholinesterase under the high pressure. Work done per contraction of the heart is increased under high pressure by about 25%. The total work done, however, in a definite period, e.g., 1 min, is decreased because the rate of the contraction is decreased.