Selective endothelial dysfunction in conscious dogs after cardiopulmonary bypass

Zanaboni, Paul, Paul A. Murray, Brett A. Simon, Kenton Zehr,Kirk Fleischer, Elaine Tseng, and Daniel P. Nyhan. Selective endothelial dysfunction in conscious dogs after cardiopulmonary bypass.J. Appl. Physiol. 82(6):1776-1784, 1997.It has previously been demonstrated thatcardiopulmonary bypass (CPB) causes prolonged pulmonary vascularhyperreactivity (D. P. Nyhan, J. M. Redmond, A. M. Gillinov, K. Nishiwaki, and P. A. Murray. J. Appl.Physiol. 77: 1584-1590, 1994). Thisstudy investigated the effects of CPB on endothelium-dependent(acetylcholine and bradykinin) and endothelium-independent (sodiumnitroprusside) pulmonary vasodilation in conscious dogs. Continuousleft pulmonary vascular pressure-flow (LP-) plots were generated in conscious dogs before CPB and again in the same animals 3-4 days post-CPB. The dose of U-46619 used to acutely preconstrict the pulmonary circulation to similar levels pre- andpost-CPB was decreased (0.13 ± 0.01 vs. 0.10 ± 0.01 mg · kg¹ · min¹,P < 0.01) after CPB. Acetylcholine,bradykinin, and sodium nitroprusside all caused dose-dependentpulmonary vasodilation pre-CPB. The pulmonary vasodilator response toacetylcholine was completely abolished post-CPB. For example, at leftpulmonary blood flow of 80 ml · kg¹ · min¹acetylcholine (10 µg · kg¹ · min¹)resulted in 72 ± 15% reversal (P < 0.01) of U-46619 preconstriction pre-CPB but caused no changepost-CPB. However, the responses to bradykinin and sodium nitroprussidewere unchanged post-CPB. The impaired pulmonary vasodilator response toacetylcholine, but not to bradykinin, suggests a selective endothelialdefect post-CPB. The normal response to sodium nitroprusside indicates that cGMP-mediated vasodilation is unchanged post-CPB.

     

Baroreflex modulation of ultradian oscillations of blood pressure and heart rate in unanesthetized dogs

Telemetered, free-running dogs were studied to determine the role of cardiovascular control systems in modulation of ultradian oscillations of arterial pressure (MAP) and heart rate (HR). Data, aquired (2 Hz) by a stable telemetry system, was stored on a digital computer and analyzed for its harmonic content by a Fast Fourier Transform (FFT) algorithm. Both AP and HR consistently demonstrated rhythms having a period of from 0.6 to 1.0 h. Modulation of these rhythms by arterial pressure control systems was assessed in dogs studied before and carotid sinus baroreceptor denervation, before and after denervation of the aortic arch baroreceptors and before and after a combination of both these procedures. The data indicate the power spectral density (PSD) of MAP, but not HR, is increased (p less than 0.05) after denervation of the carotid sinuses alone, while the primary frequency of the oscillations was unchanged. On the other hand, denervation of the aortic arch baroreceptors alone was without effect on either the frequency or PSD of these oscillations. A combination of both carotid sinus and aortic arch denervation resulted in an increased (p less than 0.05) PSD of MAP oscillations but not in their frequency. These data indicate that the carotid sinuses modulate rhythmic behavior of MAP by buffering the magnitude, but not frequency, of the oscillations. Moreover, since oscillations were present in dogs after denervation of both the carotid sinus and aortic arch baroreceptors, these ultradian oscillations are not a result of a non-linear negative feedback mechanisms arising from these pressure sensitive regions.     

Manufacturing and <Emphasis Type="Italic">in vivo</Emphasis> inner ear visualization of MRI traceable liposome nanoparticles encapsulating gadolinium

Background  

Treatment of inner ear diseases remains a problem because of limited passage through the blood-inner ear barriers and lack of control with the delivery of treatment agents by intravenous or oral administration. As a minimally-invasive approach, intratympanic delivery of multifunctional nanoparticles (MFNPs) carrying genes or drugs to the inner ear is a future therapy for treating inner ear diseases, including sensorineural hearing loss (SNHL) and Meniere's disease. In an attempt to track the dynamics and distribution of nanoparticles in vivo, here we describe manufacturing MRI traceable liposome nanoparticles by encapsulating gadolinium-tetra-azacyclo-dodecane-tetra-acetic acid (Gd-DOTA) (abbreviated as LPS+Gd-DOTA) and their distribution in the inner ear after either intratympanic or intracochlear administration.     

Modelling the vertical distribution of Prochlorococcus and Synechococcus in the North Pacific Subtropical Ocean

A simple model was developed to examine the vertical distribution of Prochlorococcus and Synechococcus ecotypes in the water column, based on their adaptation to light intensity. Model simulations were compared with a 14-year time series of Prochlorococcus and Synechococcus cell abundances at Station ALOHA in the North Pacific Subtropical Gyre. Data were analysed to examine spatial and temporal patterns in abundances and their ranges of variability in the euphotic zone, the surface mixed layer and the layer in the euphotic zone but below the base of the mixed layer. Model simulations show that the apparent occupation of the whole euphotic zone by a genus can be the result of a co-occurrence of different ecotypes that segregate vertically. The segregation of ecotypes can result simply from differences in light response. A sensitivity analysis of the model, performed on the parameter alpha (initial slope of the light-response curve) and the DIN concentration in the upper water column, demonstrates that the model successfully reproduces the observed range of vertical distributions. Results support the idea that intermittent mixing events may have important ecological and geochemical impacts on the phytoplankton community at Station ALOHA.     

Nitrogenase gene expression in the Chesapeake Bay Estuary

Like many estuaries, the Chesapeake Bay has pronounced gradients in salinity and nutrients. Previous studies have shown that there is a high diversity of nitrogenase (nifH) genes in the estuary, and that there are specific distributions of individual nifH phylotypes. In contrast to previous work that revealed the remarkable diversity of nifH phylotypes in the Chesapeake estuary, in this study of nifH expression we only detected two phylotypes, and both were phylogenetically related to cyanobacterial nifH genes. One of the phylotypes was closely related to a nifH sequence from the filamentous, heterocystous cyanobacterium Anabaena cylindrica, and was found at the head of the estuary. The other phylotype was found in a sample collected near the mouth of the estuary and was closely related to nifH sequences from Group A unicellular cyanobacteria, which has previously been reported in oceanic waters only. These nifH phylotypes had distinct patterns of expression that were restricted to different regions of the Chesapeake Bay. This study provides the first evidence of nifH expression in the Chesapeake Bay, and suggests that diazotrophic unicellular cyanobacteria have a broader distribution and activity than previously recognized.     

Additional Hosts for the Ring Nematode,Criconemella xenoplax

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.     

Ecogenomic sensor reveals controls on N2-fixing microorganisms in the North Pacific Ocean

Nitrogen-fixing microorganisms (diazotrophs) are keystone species that reduce atmospheric dinitrogen (N₂) gas to fixed nitrogen (N), thereby accounting for much of N-based new production annually in the oligotrophic North Pacific. However, current approaches to study N₂ fixation provide relatively limited spatiotemporal sampling resolution; hence, little is known about the ecological controls on these microorganisms or the scales over which they change. In the present study, we used a drifting robotic gene sensor to obtain high-resolution data on the distributions and abundances of N₂-fixing populations over small spatiotemporal scales. The resulting measurements demonstrate that concentrations of N₂ fixers can be highly variable, changing in abundance by nearly three orders of magnitude in less than 2 days and 30 km. Concurrent shipboard measurements and long-term time-series sampling uncovered a striking and previously unrecognized correlation between phosphate, which is undergoing long-term change in the region, and N₂-fixing cyanobacterial abundances. These results underscore the value of high-resolution sampling and its applications for modeling the effects of global change.