Changes in the Physiology and Pharmacology of the Uterine Muscle of the Cow in Relation to the Estrous Cycle

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Abstract
Studies were made upon excised uterine muscle of cattle killed at known stages of the estrous cycle. Spontaneous motility is greatest during proestrum and estrus, becomes irregular during metestrum and dies down during diestrum. The motility consists of two types of waves, strong contractions of great amplitude at intervals of 1½ to 2 minutes and small contractions at 20 to 30 second intervals. The latter increase in importance during metestrum and are a large factor in the production of the irregularity. In early diestrum long rhythmic changes of tone also occur. Pituitrin, arecolin and lentin produce strong tonic contractions at all stages of the cycle. Eserine, gynergen and pilocarpine have very irregular effects and are mainly inert. Atropine rarely produces an inhibitory effect. Epinephrin is inhibitory during and shortly after the estrogenic phase, and motor during the progestational phase. The cow thus falls into group III, the ‘cat’ group in respect to this effect. The muscle cells of the uterus grow in length during the estrogenic phase and decrease in length during the rest of the cycle. The growth impulse starts at the apices of the uterine horns and travels caudally. It is over at the apices earlier than it is in the rest of the tract.

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