The release of vasopressin without oxytocin in response to haemorrhage

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Abstract
Blood samples wen-collected from anaesthetized cats during haemorrhage or stimulation of the peripheral end of the vagus. Vasopressin and oxytocin were estimated in the samples by assaying alcohol extracts for antidturetic activity in the water loaded rat and for milk-ejecting activity in the lactating guineapig. Haemorrhage caused vasopressin to be released into the blood without detectable amounts of oxytocin. A similar result was obtained with vagal stimulation provided that the fall of blood pressure which it produced exceeded a critical value of about 80 mmHG. Failure to detect oxytocin in blood samples containing vasopressin was not due to the presence of adrenaline [epinephrine] or any inhibitory substance in the extracts blocking the response of the mammary gland to oxytocin. The stimulus for the independent release of vasopressin by haemorrhage appears to be the associated fall in arterial blood pressure.