259 BRAIN NATRIURETIC PEPTIDE AT NON HYPOTENSIVE DOSES RAISES CARDIAC SYMPATHETIC NERVE ACTIVITY IN SHEEP

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Background: The reported effects of atrial natriuretic peptide (ANP) on sympathetic nerve activity (SNA) are variable, dependent on concomitant haemodynamic actions and likely to be regionally differentiated. There are few reports of the effect of B-type natriuretic peptide (BNP) on SNA and none have measured cardiac SNA (CSNA) by direct microneurography. Methods: We measured the effects of low dose (2.4pmol/kg/min infused for 120 min) ANP and BNP on CSNA and hemodynamics in conscious sheep (n=8). Results: Whilst there was a trend for arterial pressure and cardiac output to fall with both ANP and BNP changes were not significant compared with vehicle control. Heart rate rose in response to BNP (p=0.044), but not ANP, to be 10–12 bpm above control levels. ANP had no significant effect on any CSNA parameters measured. By contrast, BNP induced a rise in CSNA burst frequency (∼20 bursts/min higher than control, p=0.011) and burst area (∼40% higher than control, p=0.013). However, BNP induced rises in burst incidence (bursts/100beats) and burst area/100 beats were not significant. Conclusions: BNP infused at doses below the threshold to induce significant hypotension increased CSNA burst frequency and burst area/min. This increase in CSNA is in large part secondary to an increase in heart rate as CSNA burst incidence and burst area/100 beats were not significantly increased. This study provides no evidence for inhibition of sympathetic traffic directed to the heart by either ANP or BNP.

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