Changes in plasma levels of vasopressin and renin in response to haemorrhage in dogs.

1. The rabbit rectum superfused with blood or Krebs solution was used to assay vasopressin in circulating blood and in plasma extracts respectively.2. Vasopressin was released by a rapid fall in diastolic pressure of as little as 5 mmHg, and the amount of vasopressin released was proportional to the magnitude of the fall in diastolic pressure in the range studied. These results would indicate that vasopressin release follows the magnitude of the fall in diastolic pressure more closely than the actual decrease in blood volume in haemorrhagic hypotension.3. It was shown that the time required to induce an increase in circulating vasopressin is inversely proportional to the severity of the fall in diastolic pressure; this suggested that the stimulation of neurosecretory reflex arc varies with the intensity of the stimulus.4. The slight changes in plasma renin activity as well as the pattern of renin release suggested the unlikeliness of the influence of renin upon vasopressin secretion under these circumstances. On the contrary, the results suggested that the secretion of large amounts of vasopressin tended to inhibit renin release.