Venous Tone in the Developmental Stages of Spontaneous Hypertension

Abstract—The initial stages of hypertension in the spontaneously hypertensive rat (SHR) are characterized by an increase in cardiac output. Venous capacitance plays an important role in the control of cardiac output. This study tested the hypothesis that venous tone is elevated in the developmental stages of spontaneous hypertension. Male SHR or normotensive Wistar-Kyoto (WKY) rats were instrumented for the measurement of arterial pressure (FAP) and intrathoracic vena caval pressure (FVP). A latex-tipped catheter was advanced into the right atrium via the jugular vein. Mean circulatory filling pressure (MCFP), an index of integrated venomotor tone, was calculated as MCFP5FVP1(FAP2FVP)/VAR. FAP and FVP were recorded after 5 seconds of right atrial balloon inflation. The venous to arterial compliance ratio (VAR) was estimated as 76 for WKY and 106 for SHR. Mean arterial pressure (MAP), heart rate, and MCFP were recorded in conscious rats of 4 to 6 and 8 to 10 weeks of age. In 4- to 6-week-old rats, both MAP and MCFP were significantly elevated in the SHR (MAP, 12966 mm Hg; MCFP, 6.660.4 mm Hg) compared with the age-matched WKY (MAP, 9166 mm Hg; MCFP, 5.460.4 mm Hg), whereas heart rate was not significantl