| Abstract: | Increases in plasma vasopressin and renin activity that occur in response to haemorrhage have been attributed in part to reflex effects from cardiac receptors and sinoaortic baroreceptors, but the relative importance of these different receptors in causing humoral changes during haemorrhage in conscious dogs has not been reported. We investigated this question by hemorrhaging 6 sham-operated (SO), 6 cardiac-denervated (CD), 4 sinoaortic-denervated (SAD), and 4 combined sinoaortic and cardiac-denervated (SACD), conscious dogs. Blood was removed at a rate of 0.9 ml/kg X min. Plasma vasopressin and renin samples were taken during a control period and after 10, 20, and 30 ml/kg of blood had been removed. Results (mean +/- SE) are shown in the tables below. (table; see text) These experiments illustrate that: resting plasma levels of vasopressin and renin in conscious dogs are unaffected by the denervation procedures used in these experiments, the increase in plasma vasopressin that occurs during haemorrhage is mediated largely via cardiac receptors, with a considerably smaller contribution from the sinoaortic baroreceptors, during moderately severe haemorrhage (30 ml/kg) vasopressin secretion can be increased by a mechanism independent of sinoaortic and cardiac reflexes, the increase in plasma renin activity that occurs during haemorrhage is not dependent upon either cardiac or sinoaortic reflexes. |
