Atrial natriuretic factor and volume expansion-induced natriuresis in the spontaneously hypertensive rat.

The implication of atrial natriuretic factor (ANF) during acute volume expansion in the spontaneously hypertensive rat (SHR) was evaluated. The effect of short-term afterload relief was also investigated. Fourteen- to 15-week-old SHR and Wistar-Kyoto (WKY) rats were treated with hydralazine for 5 days. The systolic blood pressure (BP) of SHR decreased to normotensive levels but cardiac hypertrophy was not reduced. Isotonic, iso-oncotic volume expansion (equivalent to 10% of total blood volume) was performed 3 times at 15-min intervals on conscious animals. The effect of volume expansion on central venous pressure was identical among the groups. Changes in left ventricular end-diastolic pressure (LVEDP) induced by volume expansion were greater in SHR than in WKY rats and were not affected by treatment. The increases in plasma N-terminal ANF (ANF-(1-98)) concentrations were larger in both treated and untreated SHR verses WKY rats. Despite enhanced ANF release in SHR, the overall magnitude of the diuretic and natriuretic responses to volume expansion was similar in all groups. The natriuretic response was strongly correlated with plasma ANF in WKY rats, this relationship was weak in control SHR, and restored by treatment. It is suggested that ANF release is not impaired in SHR at a 10% volume load; however, there seems to be a lower renal responsiveness to ANF in SHR.