Atrial natriuretic peptide participates in the regulation of vestibular blood flow.

Atrial natriuretic peptide (ANP) is a cardiac hormone which exerts natriuretic, diuretic and vasorelaxant effects. Among the many organs and vascular beds populated with ANP receptors (Genest and Cantin, 1988) are the vestibular and auditory organs of the inner ear (Lamprecht and Meyer zum Gottesberge, 1988). The purpose of the current study was to assess the potential influence of ANP on vestibular blood flow in the guinea pig. The inner ear was exposed with a posterior-lateral approach medially through the mastoid cortex. The laser Doppler probe was placed adjacent to the ampulla of the posterior semicircular canal. Baseline measurements of mean blood pressure (BP), heart rate (HR) and vestibular blood flow were established. ANP dissolved in physiologic saline was infused intravenously at concentrations of 15, 150 or 300 ng/kg/min at 10 microliters/min for 30 min. Measurements were recorded during the infusion and for a recovery period of 65 min. The control group was treated equivalently and infused with 0.15 M NaCl. Baseline BP and HR for all animals were 40.1 +/- 6.67 and 190 +/- 15.7, respectively. BP, HR and vestibular blood flow remained stable during the baseline, control and recovery conditions of saline infused subjects. Infusion of ANP (15 ng/kg/min) induced a mild elevation of BP followed by a small decrease in pressure during the post-infusion period. Vestibular blood flow showed a decrease to approximately 20% below baseline during infusion and stabilized at this level during the recovery period. Infusion of higher concentrations of ANP (150 and 300 ng/kg/min) induced a similar pattern of BP change in a dose-dependent manner. Vestibular blood flow, however, evidenced significant elevations during the post-infusion periods for both concentrations. These increases (22% and 26%, for 150 and 300 ng/kg/min, respectively) were significantly different from vestibular blood flow changes in the saline and low dose groups. The HR remained stable for baseline, infusion and recovery periods for each of the ANP infused subjects. This investigation demonstrates the systemic and local effects of ANP suggest a possible role for ANP in local regulation of vestibular blood flow.