Neurohumoral regulation of arterial pressure in hemorrhage and heart failure

Hydrogen sulfide upregulates KATP channel expression in vascular smooth muscle cells of spontaneously hypertensive rats

The study was designed to investigate whether H2S could upregulate expression of KATP channels in vascular smooth muscle cells (VSMCs), and by this mechanism enhances vasorelaxation in spontaneously hypertensive rats (SHR). Blood pressure, vascular structure, and vasorelaxation were analyzed. Plasma H2S was detected using polarographic sensor. SUR2B and Kir6.1 expressions were detected in VSMCs of SHR and in A7r5 cells as well as primarily cultured ASMCs using real-time PCR, western blot, immunofluorescence, and confocal imaging. Nuclear translocation of forkhead transcription factors FOXO1 and FOXO3a in ASMCs was detected using laser confocal microscopy, and their binding activity with SUR2B and Kir6.1 promoters was examined by chromatin immunoprecipitation. SHR developed hypertension at 18 weeks. They showed downregulated vascular SUR2B and Kir6.1 expressions in association with a decreased plasma H2S level. H2S donor, however, could upregulate vascular SUR2B and Kir6.1 expressions, causing a left shift of the vasorelaxation curve to pinacidil and lowered tail artery pressure in the SHR. Also, H2S antagonized endothelin-1 (ET-1)-inhibited KATP expression in A7r5 cells and cultured ASMCs. Mechanistically, H2S inhibited ET-1-stimulated p-FOXO1 and p-FOXO3a expressions (inactivated forms), but increased their nuclear translocation and the ET-1-inhibited binding of FOXO1 and FOXO3a with Kir6.1 and SUR2B promoters in ASMCs. Hence, H2S promotes vasorelaxation of SHR, at least in part, through upregulating the expression of KATP subunits by inhibiting phosphorylation of FOXO1 and FOXO3a, and stimulating FOXO1 and FOXO3a nuclear translocation and their binding activity with SUR2B and Kir6.1 promoters.

KEY MESSAGES

H2S increased vascular SUR2B and Kir6.1 expression of SHR, promoting vasorelaxation. H2S antagonized ET-1-inhibited KATP expression in A7r5 cells and cultured ASMCs. H2S inhibited ET-1-induced FOXO1 and FOXO3a phosphorylation in ASMCs. H2S promoted FOXO1 and FOXO3a nuclear translocation and binding with target gene promoters.

Atrial natriuretic peptide serum concentration decreases in donors undergoing discontinuous plasmapheresis involving a large extracorporeal blood volume

BACKGROUND

In donor plasmapheresis, circulatory reactions occur at a similar frequency as in whole-blood donation although the large extracorporeal blood volume (ECV) occurring during discontinuous plasmapheresis might predispose donors to hypovolemic reactions. The regulatory mechanisms compensating for this intradonation blood volume (BV) deficit are not well understood. It was the aim of this study to delineate whether atrial natriuretic peptide (ANP) is involved in the BV regulation of plasmapheresis donors. Because ANP regulates volume overload, it might decrease during BV decrease in plasmapheresis.

STUDY DESIGN AND METHODS

ANP serum concentrations were determined in 60 donors undergoing discontinuous plasmapheresis. Samples were taken before the start of the procedure and when maximum ECV (ECV(max)) was reached at the end of the last withdrawal. Donors were randomly selected after stratification for sex and BV. In a control investigation, the same donors were kept in a reclined position for the duration of a plasmapheresis session without plasma withdrawal. ANP plasma concentration changes were correlated with changes of hemodynamic variables, which were recorded noninvasively with bioelectrical impedance cardiography.

RESULTS

Median ANP concentration decreased from 13.0 to 8.4 pg per mL during donation and from 11.6 to 10.5 pg per mL during the control session. The mean control-adjusted ANP change due to plasma withdrawal was -2.62 pg per mL (p = 0.006). This decrease was not attributable to a dilution effect. ANP change did not correlate with changes of recorded hemodynamic variables.

CONCLUSION

The decrease of the ANP serum concentration during plasmapheresis demonstrates that the ECV(max) constitutes a hypovolemic challenge of the donors, which elicits a neurohormonal regulatory mechanism aimed at maintaining cardiovascular homeostasis.

Routine blood pressure measurements do not predict adverse events in hospitalized patients

PURPOSE

Countless blood pressure measurements are performed every day for almost every hospitalized patient. We analyzed the value of routine blood pressure measurements on patient care in an unselected group of hospitalized patients.

METHODS

The study included 639 patients who were admitted to the hospital with a broad range of medical conditions. Two independent investigators reviewed the medical charts of the patients. Routine blood pressure values were abstracted from the patient charts and evaluated with respect to the occurrence of adverse clinical events in the study group. Changes in blood pressure between the last measurement just before adverse clinical events and the mean blood pressure values 72 hours before the adverse events were calculated and compared with mean normal day-to-day variations in blood pressure.

RESULTS

In every patient, a mean of 1.6 +/- 0.6 routine blood pressure measurements per day were performed. Of the 639 patients in the study, 122 (19%) had clinical complications. The most commonly occurring complications were gastrointestinal bleeding (n = 15), falls (n = 13), other bleeding (n = 12) and pneumonia (n = 8). In patients who experienced clinical complications, pre-event systolic and diastolic blood pressure changes of at least 10 mm Hg occurred in 41% and 24% of the group, respectively, but this was not different from the normal day-to-day variations observed in patients who had no clinical complications. The results also were similar for patients who died or who had a severe adverse event that required admission to an intensive care unit.

CONCLUSION

Routine blood pressure measurements in a general hospital patient population do not predict clinical adverse events.

Lower body negative pressure as a model to study progression to acute hemorrhagic shock in humans

Hemorrhage is a leading cause of death in both civilian and battlefield trauma. Survival rates increase when victims requiring immediate intervention are correctly identified in a mass-casualty situation, but methods of prioritizing casualties based on current triage algorithms are severely limited. Development of effective procedures to predict the magnitude of hemorrhage and the likelihood for progression to hemorrhagic shock must necessarily be based on carefully controlled human experimentation, but controlled study of severe hemorrhage in humans is not possible. It may be possible to simulate hemorrhage, as many of the physiological compensations to acute hemorrhage can be mimicked in the laboratory by applying negative pressure to the lower extremities. Lower body negative pressure (LBNP) sequesters blood from the thorax into dependent regions of the pelvis and legs, effectively decreasing central blood volume in a similar fashion as acute hemorrhage. In this review, we compare physiological responses to hemorrhage and LBNP with particular emphasis on cardiovascular compensations that both share in common. Through evaluation of animal and human data, we present evidence that supports the hypothesis that LBNP, and resulting volume sequestration, is an effective technique to study physiological responses and mechanisms associated with acute hemorrhage in humans. Such experiments could lead to clinical algorithms that identify bleeding victims who will likely progress to hemorrhagic shock and require lifesaving intervention(s).

Angiotensin potentiates excitatory sensory synaptic transmission to medial solitary tract nucleus neurons

Femtomole doses of angiotensin (ANG) II microinjected into nucleus tractus solitarii (nTS) decrease blood pressure and heart rate, mimicking activation of the baroreflex, whereas higher doses depress this reflex. ANG II might generate cardioinhibitory responses by augmenting cardiovascular afferent synaptic transmission onto nTS neurons. Intracellular recordings were obtained from 99 dorsal medial nTS region neurons in rat medulla horizontal slices to investigate whether ANG II modulated short-latency excitatory postsynaptic potentials (EPSPs) evoked by solitary tract (TS) stimulation. ANG II (200 fmol) increased TS-evoked EPSP amplitudes 20-200% with minimal membrane depolarization in 12 neurons excited by ANG II and glutamate, but not substance P (group A). Blockade of non-N-methyl-d-aspartate receptors eliminated TS-evoked EPSPs and responses to ANG II. ANG II did not alter TS-evoked EPSPs in 14 other neurons depolarized substantially by ANG II and substance P (group B). ANG II appeared to selectively augment presynaptic sensory transmission in one class of nTS neurons but had only postsynaptic effects on another group of cells. Thus ANG II is likely to modulate cardiovascular function by more than one nTS neuronal pathway.