REFLEX VASOPRESSIN AND RENIN MODULATION BY CARDIAC RECEPTORS IN HUMANS

Animal studies have shown that vasopressin secretion is modulated by arterial baroreceptors and cardiopulmonary volume receptors. Whether this is the case also in humans is controversial, however. To determine whether vasopressin is reflexly modulated by cardiac volume receptors, we studied the effect on plasma vasopressin (venous blood, radioimmunoassay) of reducing venous return and left ventricular end-diastolic diameter (echocardiography) by producing a 20-minute lower body negative pressure in 14 healthy subjects (aged 49.3+/-3.8 years, mean+/-SEM). The data were compared with those of 14 age-matched heart-transplant recipients, i.e., subjects with cardiac denervation. In healthy subjects, lower body negative pressure at - 15 mm Hg caused a modest reduction in left ventricular end-diastolic diameter (-5+/-3.4%) and no change in vasopressin, whereas lower body negative pressure at -37.5 mm Hg caused a more marked reduction in left ventricular end-diastolic diameter (-12+/-2.5%) and a small, variable, but overall statistically significant (p<0.05) increase in vasopressin (+145+/-46%, p<0.01). The left ventricular end-diastolic diameter changes induced by the two lower body negative pressure stimuli were similar in heart-transplant recipients, but the vasopressin increase seen with the lower body negative pressure at -37.5 mm Hg was abolished. The marked increase in plasma renin activity and forearm vascular resistance induced by lower body negative pressure in healthy subjects was also abolished or drastically attenuated in heart-transplant recipients. The abolition of the responses was not due to a generalized hyporeactivity because, in heart-transplant recipients, vasopressin, plasma renin activity, and forearm vascular resistance increased normally when stimulated by hyperosmolarity, angiotensin converting enzyme inhibition, and cold, respectively. Thus, in humans vasopressin is modulated reflexly by cardiac volume receptors, although to a limited degree and only for large changes in central blood volume. The reflex influence of cardiac receptors extends to plasma renin activity and vascular resistance, indicating a role of these receptors in both blood volume and blood pressure control.