Concentrations of β-endorphin and oxytocin were measured in plasma of cows before, during and after parturition. The effect of the PGF2α analogue cloprostenol on β-endorphin and oxytocin release was investigated. During parturition, there were marked, parallel increases in β-endorphin and oxytocin concentrations. Both hormones were released in an episodic manner in conjunction with uterine and abdominal contractions. It is therefore likely that factors stimulating oxytocin release also enhance β-endorphin secretion. This suggests a role of labour or labour-associated hormones in stimulating peripheral β-endorphin release. Cloprostenol caused an immediate, pronounced increase in plasma β-endorphin and oxytocin concentrations.
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