Baroregulation of Vasopressin Secretion	

An acute fall in blood pressure or blood volume causes release of vasopressin. Whether hypertension or hypervolaemia affect vasopressin secretion is not known. The exponential rise in plasma vasopressin concentrations in response to progressive hypotension induced in healthy normal subjects by the infusion of the ganglion- blocking drug trimetaphan, over periods of fifteen to thirty minutes, is shown in Fig. 5.12. Similar large increases in the concentration of plasma vasopressin have been demonstrated in normal humans who have been rendered hypotensive after tilting, or hypovolaemic after phlebotomy.