CARDIAC-FUNCTION IN A RAT MODEL OF CHRONIC AORTIC STIFFNESS

Cardiac function was investigated in conscious normotensive rats in wh ich increased aortic stiffness was produced as a result of vascular ca lcium overload after treatment with vitamin Dg plus nicotine (VDN rats , n = 16; controls, n = 17). Baseline stroke volume, cardiac output, a nd cardiac response to a venous volume overload were unchanged after 1 mo of exposure to increased aortic stiffness, as were baseline venous return and total vascular capacitance. The latter was estimated from the change in mean circulatory filling pressure after modification of circulatory volume. Cardiovascular reflexes were modified in VDN rats. Bradycardia evoked by an increase in arterial P-CO2 (Pa-CO2) or hypot ensive hemorrhage was more pronounced. The Pa-CO2-induced bradycardia was accompanied by a fall in cardiac output in VDN rats but not in con trols. In VDN rats, the attenuation of sympathetic reflexes may explai n the slower recovery of blood pressure after hypotensive hemorrhage. In conclusion, a chronic increase in aortic stiffness does not comprom ise cardiac performance, but cardiovascular reflexes are impaired in V DN rats. Whether this is because of the increase in aortic stiffness o r the effect of VDN treatment on the baroreceptors or other components of the reflex are remains to be elucidated.