Enhancement of active tension during release phase of slow stretch-release cycle of quail oviduct

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Abstract
There occur strong spontaneous contractions in the avian oviduct. These contractions are considered to effect the locus of the ovum during ovum transport. It is not known how these contractions are regulated and no comprehensive description of the contractions exists. When a transversal strip cut from the magnum part of the oviduct was first stretched to a length of .apprx. 275% Lo (Lo = length in situ) and then released to a length of Lo at a rate of 1.7 mm/min, it was found that contractions were different during release from those during stretch. The rate of stretch and release, and the change in length, were physiological, i.e., they can be recorded under normal transport circumstances in vitro. The amplitude of active tension was usually larger during release than during stretch at comparable lengths. The duration of a single contraction was significantly longer during stretch than during release, but the number of contractions was smaller. The total area of active tension was 1.34 times greater during release than during stretch. Passive tension always increased with stretching, while during release passive tension was smaller. It is discussed whether the changes are of membranous origin or if they result directly from the contractile apparatus.