The American journal of physiology
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To examine the influence of the various frequency components of renal sympathetic nerve activity (RSNA) on renal blood flow (RBF) dynamics, a Doppler flow probe and renal nerve electrode were implanted on the left renal artery of 10 rabbits. Experiments were performed 4-9 days after surgery. Physiological changes in RSNA were induced by subjecting the rabbits to periods of breathing hypoxic gas mixtures. ⋯ Thus the renal vasculature was able to follow relatively low-frequency (< 0.5-Hz) fluctuations of RSNA and responded with corresponding oscillations in RBF. In contrast, the renal vasculature responded with increased constriction at the high-frequency (> 0.5-Hz) fluctuations of RSNA. These findings suggest that, in conscious rabbits, high-frequency oscillations of RSNA contribute to the vasoconstrictor tone, whereas the lower frequencies of RSNA contribute to the variability of RBF.
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Near-infrared spectrophotometry (NIRS) potentially provides a tool for noninvasive tissue oxygenation and blood volume monitoring. Cerebral monitoring could be useful in the prevention of hypoxic ischemic brain injury in newborns. This study sought to validate such NIRS measurements in normoventilated, hypocapnic, and hypoxemic states in the brain of newborn piglets vs. arterial (SaO2) and sagittal sinus blood hemoglobin saturation (SssO2) and blood volume measurements with 99mTc-labeled erythrocytes. ⋯ NIRS measurements of oxygenation, however, correlated well with a weighted mean value of SaO2 and SssO2 (r = 0.90; P < 0.0001). Multiple linear regression of the oxygenation index (i.e., oxyhemoglobin - deoxyhemoglobin) on SaO2 and SssO2 suggested that NIRS sees hemoglobin in tissue in a venous-to-arterial ratio of 2:1. Therefore, in this study, NIRS reliably monitored changes in cerebral tissue oxygenation but not in CBV.
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In bilateral ureteral obstruction, both aquaporin-2 (AQP2) levels and urinary concentrating capacity are markedly reduced. However, the mechanisms involved in AQP2 downregulation are unknown. In rats with unilateral ureteral obstruction (UUO) the relative role of intrarenal and systemic factors can be evaluated. ⋯ Immunocytochemistry confirmed the marked decrease in AQP2 expression in obstructed kidneys. In nonobstructed kidneys AQP2 was predominantly found in intracellular vesicles, which together with the reduced expression and elevated free water clearance strongly suggests a role of AQP2 in the observed compensatory diuresis from nonobstructed kidneys. The much lower AQP2 protein and mRNA levels in obstructed vs. nonobstructed kidneys are consistent with intrarenal factors playing a major role for downregulation of AQP2.