Active relaxation of unstriated muscle produced by epinephrine

Abstract

The frog's stomach muscle and the guinea pig's uterus relax without application of any external force when treated with epinephrine; this relaxation is accompanied by increased oxygen consumption, hence it is postulated that relaxation produced by epinephrine is an active process. Ultimately the oxygen consumption decreases with relaxation, suggesting that contraction is also an active process. It is postulated, therefore, that unstriated muscle contains two contractile mechanisms, one that relaxes actively and the other passively.