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1 Department of Nephrology, Johann Wolfgang Goethe-University, Med. Clinic IV, Frankfurt, Germany
2 Department of Nephrology, Friedrich-Alexander-University, Med. Clinic IV, Erlangen, Germany
3 Department of Pharmacology and Experimental Therapeutics, Loyola University Chicago, Stritch School of Medicine, Chicago, Illinois, USA
* To whom correspondence should be addressed. E-mail: mfm431{at}rzmail.uni-erlangen.de.
Increase of left ventricular end-diastolic pressure (LVEDP) due to volume expansion (VExp) enhances activity of mechanosensitive vagal cardiac afferent C-fibers (CNFA) thus decreasing renal sympathetic nerve activity (RSNA). Hypotensive hemorrhage (hHem) attenuates RSNA despite decreased LVEDP. We hypothesized that CNFA increases with any change in LVEDP. Coronary perfusion pressure (CPP) supposably affected in both conditions might be a putative stimulus of CNFA as well. VExp and hHem was performed in anesthetized male Sprague-Dawley rats while measuring blood pressure, heart rate and RSNA. Cervical vagotomy abolished RSNA response in both reflex responses. Single unit CNFA was recorded while changing LVEDP: Rapid changes (±4, ±6, ±8 mmHg) were obtained by graded occlusion of the caval vein (ocCav) and descending aorta (ocAo). Prolonged changes were obtained by VExp and hHem. Furthermore CNFA was recorded in a modified Langendorff heart while CPP was changed (70, 100, 40 mmHg).
Rapid LVEDP changes increased CNFA (ocCav: +16±3 Hz [
+602%]; ocAo: +15±3 Hz [ +553%]; 70 units; p<0.05). VExp and hHem (n=6) increased CNFA (VExp: +10±4 Hz [ +1033%]; hHem: +10±2 Hz [ +1225%]; p<0.05). Increase in CPP increased CNFA (+2±1 Hz [ +225%], p<0.05) whereas decrease in CPP decreased CNFA (-0.8±0.4 Hz [ -50%], p<0.05). All C-fibers recorded originated from the left ventricle. CNFA increased with any LVEDP change but changed equidirectional with CPP. Thus, neither LVEDP nor CPP fully account directly for afferent C-fiber and reflex sympathetic responses. The intrinsic afferent stimuli and receptive fields to account for reflex sympathoinhibition still remain cryptical.
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