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Biomedical subjects

M G Johnston

Publications and source records attributed to M G Johnston.

At least 19 recordsLinked to original sources
PubMed2002

Blocking cerebrospinal fluid absorption through the cribriform plate increases resting intracranial pressure.

Cerebrospinal fluid (CSF) drains through the cribriform plate (CP) in association with the olfactory nerves. From this location, CSF is absorbed into nasal mucosal lymphatics. Recent data suggest that this pathway plays an important role in global CSF transport in sheep. In this report, we tested the hypothesis that blocking CSF transport through this pathway would elevate resting intracranial pressure (ICP). ICP was measured continuously from the cisterna magna of sheep before and after CP obstruction in the same animal. To block CSF transport through the CP, an external ethmoidectomy was performed. The olfactory and adjacent mucosa were removed, and the bone surface was sealed with tissue glue. To restrict our analysis to the cranial CSF system, CSF transport into the spinal subarachnoid compartment was prevented with a ligature tightened around the thecal sac between C1 and C2. Sham surgical procedures had no significant effects, but in the experimental group CP obstruction elevated ICP significantly. Mean postobstruction steady-state pressures (18.0 +/- 3.8 cmH(2)O) were approximately double the preobstruction values (9.2 +/- 0.9 cmH(2)O). These data support the concept that the olfactory pathway represents a major site for CSF drainage.

Absorption↗
PubMed2001

Spinal and cranial contributions to total cerebrospinal fluid transport.

In this study, we quantified cerebrospinal fluid (CSF) transport from the cranial and spinal subarachnoid spaces separately in sheep and determined the relative proportion of total CSF drainage that occurred from both CSF compartments. Cranial and spinal CSF systems were separated by placement of an extradural ligature over the spinal cord between C(1) and C(2). In one approach, two different radiolabeled human serum albumins (HSA) were introduced into the appropriate CSF compartment by a perfusion system (method 1) or as a bolus injection (method 2). Plasma tracer recoveries in conjunction with a mass balance equation were used to estimate CSF transport. In method 3, catheters connected to reservoirs filled with artificial CSF were introduced into the cranial and spinal CSF compartments. Incremental CSF pressures were established in each CSF system, and the corresponding steady-state flow rates were measured. Total CSF drainage ranged from 0.51 to 0.75 ml. h(-1). cmH(2)O(-1). Expressed as a percentage of the total CSF transport, the ratios of cranial-to-spinal clearance estimated from methods 1, 2, and 3 were 75:25, 88:12, and 75:25, respectively. Primarily on the basis of the data derived from methods 1 and 3, we conclude that the spinal subarachnoid compartment has an important role in CSF clearance and is responsible for approximately one-fourth of total CSF transport.

Animals↗
PubMed1998

The relationship of blood lymphocytes to the recirculating lymphocyte pool.

Lymphocyte recirculation facilitates the detection and elimination of pathogens and the dissemination of immunologic memory. It is generally assumed that all small lymphocytes in the blood are actively recirculating, yet there is little quantitative data directly comparing the migration of this population with actively recirculating, lymph-derived lymphocytes. In this study blood lymphocytes were labeled with fluorescein isothiocyanate (FITC), and lymph lymphocytes were labeled with CM-DiI, reinfused intravenously, and monitored in blood and lymph. After equilibration the concentration of blood lymphocytes was several times higher in blood than in lymph, whereas lymph lymphocytes displayed the opposite behavior. This suggested that blood lymphocytes did not recirculate as efficiently as lymph lymphocytes, so we examined the following blood lymphocyte subsets in greater detail: B cells, CD4+, CD8+, and gammadelta T cells. Within 4 hours postinjection the percentage of FITC+ CD8+ and CD4+ lymphocytes fell in the blood and remained significantly lower than the injected sample. In contrast, the concentration of FITC+ gammadelta T cells did not change, and the percentage of FITC+ B cells increased. These data suggest that subpopulations of B and perhaps gammadelta T lymphocytes in the blood do not recirculate efficiently through lymph nodes.

Animals↗
PubMed1998

Pressure-volume relationships in sheep mesenteric lymphatic vessels in situ: response to hypovolemia.

We applied the principles of cardiac mechanics to study the contraction cycles of postnodal sheep mesenteric lymphatic vessels in an in situ preparation. A segment of intestinal lymphatic was isolated from lymph input and provided with Krebs solution from a reservoir. Pressure-volume relationships were assessed under various transmural pressure conditions using videomicroscopic techniques to measure diameter changes and a miniature catheter pressure transducer to monitor intralymphangion pressure. The contraction cycles were quite variable but, on average, exhibited three phases of systole and three phases of diastole with periods of isovolumetric contraction and relaxation. Elevations of transmural pressure up to 4 cm H2O resulted in significant increases in stroke volume, ejection fraction, pulse pressure, and output/minute but not contraction frequency. Regression analysis of the end systolic (ESPVR) and end diastolic pressure-volume relations (EDPVR) revealed a linear ESPVR (r2 = 0.83 +/- 0.03) and exponential EDPVR (r2 = 0.83 +/- 0.02), a result that is similar to that observed in cardiac contraction cycles. Following a 25% whole blood volume bleed (a stimulus known to enhance lymphatic pumping), significant increases in stroke volume, ejection fraction, and output/minute were observed up to transmural pressures of 4 cm H2O. While an index used to assess cardiac contractility (end systolic elastance-Ees) was not observed to change after the bleed, a shift to the left of the end-systolic pressure-volume relations compared with the sham-bled group (significant shift of regression lines for ESPVR) suggested that hemorrhage exerted a positive inotropic effect on mesenteric lymphatics.

Animals↗
PubMed1998

Role of protein kinase C in the regulation of pumping activity in bovine mesenteric lymphatic vessels.

We investigated the role of protein kinase C (PKC) in regulating the lymphatic myogenic response. Bovine mesenteric lymphatics were suspended in an organ bath with inflow and outflow ends cannulated. Input was provided from a reservoir filled with Krebs solution. The PKC activator phorbol 12-myristate 13-acetate (PMA) inhibited pumping significantly whether tested at a fixed pressure or as pressures were raised in 2 cm H2O increments (50% inhibition achieved at 4.6 x 10(-8)M. The inactive phorbol ester (4-alpha-PMA) had no effect. The specific PKC inhibitors calphostin (10(-9) to 10(-7)M) or chelerythrine (10(-8) to 10(-6)M) had no significant effect on pumping. However, chelerythrine (10(-6)M) was capable of reversing the inhibitory effects of PMA (5 x 10(-8)M). PKC activation is believed to inhibit nitric oxide (NO) production in some blood vessels, and previous work from our laboratory has demonstrated that NO is important in facilitating pumping activity in bovine lymphatics. We observed that sodium nitroprusside (sNP, 10(-7)M) or L-arginine (10(-4)M), reversed the depressor effects of PMA. These results suggest that PKC may not be involved in regulating the vessel's contractile response to pressure-induced stretch. However, the data with PMA suggest that these ducts contain PKC. PKC activation depresses lymphatic pumping and this effect may be mediated in part, by inhibition of NO.

Alkaloids↗
PubMed1998

Intracellular calcium stores modulation in lymph vessels depends on wall stretch.

We studied the effect of intracellular calcium stores modulation on the ability of lymph vessels to propel fluid in a preparation of actively contracting isolated bovine mesenteric lymph vessels. Vessels were cannulated at each end, placed in a temperature-controlled organ bath, and circulated with oxygenated Krebs solution. Vessel wall tension (transmural pressure) was changed by raising the height of the fluid-filled reservoir and outflow catheters appropriately. When transmural pressure was set and maintained at 6 cmH2O (1 cmH2O = 98.1 Pa), caffeine (10(-3) M), ryanodine (10(-7) M), and cyclopiazonic acid (CPA; 7 x 10(-6) M) inhibited lymphatic pumping. We also studied the effect of these agents on the relationship between lymph pump activity and transmural pressure, a relationship normally described by a bell-shaped curve. When transmural pressure was increased at 5-min intervals, the magnitude of inhibition by caffeine (10(-3) M) and CPA (7 x 10(-6) M) was greater than when transmural pressure was held constant. Ryanodine, on the other hand, had no effect on lymphatic contractility when transmural pressure was manipulated. The ryanodine results suggest the existence of an interaction between vessel wall stretch and intracellular calcium stores modulation that is not seen with caffeine or CPA.

Animals↗
PubMed1997

Role of extra- and intracellular Ca2+ in the lymphatic myogenic response.

We used an actively contracting in vitro preparation of bovine mesenteric lymph vessels to study the effect of selected calcium channel modulators on the ability of these vessels to propel fluid. We found that blocking the dihydropyridine receptor with nifedipine and diltiazem inhibited pumping at concentrations within the range used clinically (10(-7) and 10(-6) M, respectively). Intracellular calcium modulation using ryanodine (10(-6) M) also inhibited pumping. Furthermore, we studied the effect of these agents on the relationship between lymph flow and transmural pressure, a relationship normally described by a bell-shaped curve. Diltiazem, 10(-6) M, attenuated pumping over the range of pressures studied. On the other hand, ryanodine at 10(-7) M, a concentration capable of inhibiting pumping at a constant transmural pressure, had no effect on the pressure-flow relationship when transmural pressure was manipulated. Thus we have determined that calcium movement via the L-type channel contributes significantly to the regulation of lymph pump activity and that intracellular calcium flux plays a less significant role that may be modified by transmural pressure.

Animals↗
PubMed1996

The use of the lipophilic fluorochrome CM-DiI for tracking the migration of lymphocytes.

In this study we examined the new cell dye CM-DiI for tracking the migration of lymphocytes from blood to lymph. This lipophilic marker intercalates in the plasma membrane like the PKH dyes and older DiI derivatives. The stability and intensity of staining achieved with these dyes is better than most other fluorochromes or radioisotopes, yet they are poorly soluble in aqueous solutions, which can make staining difficult, and they are not fixable in tissue sections. CM-DiI is reported to have increased water solubility and it can be fixed using traditional aldehyde fixatives, making it feasible to detect labeled cells in histological sections. To determine the suitability of CM-DiI as a lymphocyte marker, a labeling protocol was developed. We tested the ability of stained cells to recirculate in vivo. Following the intravenous injection of CM-DiI positive cells, their recovery in lymph over 40 h was comparable to that of cells labeled with other fluorochromes or radioisotopes. The kinetics of recirculation were also very similar, as labeled cells were detectable in lymph within 4 h of injection, and the peak percentage of labeled cells in lymph was generally observed between 20-30 h. We also confirmed that CM-DiI is retained in the lymphocyte membrane following routine paraffin processing. Thus CM-DiI does not appear to alter the process of lymphocyte recirculation, and it should be a useful marker for tracking these cells.

Animals↗
PubMed1996

Atrial natriuretic peptide attenuates flow in an isolated lymph duct preparation.

We investigated the hypothesis that atrial natriuretic peptide (ANP) attenuates lymph vessel pumping. In the present experiments, isolated bovine lymphatic vessels were cannulated at each end to create inflow and outlfow ports for the administration of Krebs' solution (vehicle) or ANP and for the measurement of fluid pumped by the vessel respectively. Once cannulated, the vessels were placed in a temperature-regulated bath circulated with oxygenated vehicle. Transmural pressure was regulated by the height of a fluid-filled reservoir. Lymph pump activity was assessed by measuring the volume of outlfow every ten minutes, ANP was administered at concentrations of 0 (control), 0.1, 1.0, 10 and 100 nM. Data were expressed as a percentage of the value in the control period. When compared with vehicle, ANP produced a significant inhibition of lymph pump activity by 7.7% at 0.1 nM, 24.2% at 10 nM and 38.26% at 100 nM averaged over the hour for which the vessels were exposed to each concentration. Thus ANP inhibits lymph pumping concentration dependently. This may be yet another mechanism by which ANP exerts its haemodynamic effects.

Animals↗
PubMed1996

The exit of lymphocytes and RBCs from the peritoneal cavity of sheep.

The purpose of this study was to compare the exit rates and migration pathways of 51Cr-labeled lymphocytes from the peritoneal cavity into the blood with those of a non-motile cell population, 111In-RBCs, in order to determine whether lymphocytes actively migrate from the peritoneal cavity. Radiolabeled cells were infused into the peritoneal cavity and multiple samples of lymph draining from the peritoneal cavity and/or blood were obtained, then the animal was sacrificed and various tissues were harvested and assayed for radioactivity. The recovery of 51Cr-lymphocytes from the mesenteric nodes was not significantly different from that of nodes anatomically distant from the cavity, so it is unlikely that large numbers of lymphocytes migrate across the mesothelial lining of the cavity and into the mesenteric lymphatics. However, the caudal mediastinal node contained about 18-fold more 51Cr-lymphocytes and 473 times as many 111In-RBCs, confirming the importance of this node in the drainage of cells and fluid from the cavity. The hepatic node also appears to receive cells directly from the peritoneal cavity. We also calculated the recovery of labeled cells at the end of the experiment (T = 40 h), and found that the recovery of 51Cr-lymphocytes (3.87 +/- 1.29% ID) in the blood was much lower than that of 111In-RBCs (35.28 +/- 5.02% ID). This difference can be attributed mainly to the traffic of labeled lymphocytes out of the blood rather than the selective retention of lymphocytes within the peritoneal cavity. Cannulation of the caudal mediastinal efferent lymphatic and the thoracic duct, which drain the peritoneal cavity, revealed approximately a 3-fold higher cumulative recovery of 111In-RBCs than 51Cr-lymphocytes over 6 h. However, by 40 h the percentage of labeled RBCs and lymphocytes remaining in the cavity was not significantly different. While 51Cr-lymphocytes may leave the peritoneal cavity at a slower rate than 111In-RBCs, both cell populations appear to exit solely via lymphatic vessels.

Animals↗
PubMed1996

The lymphatic circulation plays a dynamic role in blood volume and plasma protein restitution after hemorrhage.

The purpose of this study was to determine the contribution of the lymphatic circulation to blood volume and plasma protein restitution after hemorrhage. Splenectomized sheep were prepared with thoracic duct and vascular catheters. The day after surgery, thoracic duct lymph flow, thoracic duct lymph protein, plasma protein, mean arterial pressure, and blood volume were measured. After 12 h, awake sheep were either bled 25% of blood volume over 5 min (HEM; n = 6) or observed (SHAM; n = 5) and measurements were recorded for 48 h. In HEM, the thoracic duct protein return rate and thoracic duct lymph flow transiently decreased (0-.5 h) but were then equal to or greater than that in SHAM. In HEM, there was restitution of both blood volume and plasma protein mass approximately 12 h after hemorrhage. Both thoracic duct lymph flow and protein return rate are significant contributors to blood volume and plasma protein restitution after hemorrhage. These findings and the prior demonstration by the authors that lymphatic vessel pumping is increased after hemorrhage suggest a dynamic role for the lymphatic circulation in blood volume homeostasis after hemorrhage.

Analysis of Variance↗
PubMed1995

Importance of valves and lymphangion contractions in determining pressure gradients in isolated lymphatics exposed to elevations in outflow pressure.

Lymphatic pressures were measured at several locations along an isolated lymphatic system exposed to elevations in outflow pressure. The objective of this study was to determine the contributions of lymphangion contractions and valve function to the observed pressure gradients. In each experiment, five bovine mesenteric lymphatic vessels (each with four to nine lymphangions) were joined in series by t-pieces connected to pressure transducers. The vessels were placed in an organ bath with input provided by a reservoir filled with Krebs solution. With a constant inflow pressure of 4 cm H2O, outflow pressures were elevated in 2- or 5-cm H2O increments. Except for inflow and outflow pressures which were fixed, the pressures measured at four other locations along the system were pulsatile due to lymphatic contractions. The mean pressures increased as outflow pressures were raised. While mean pressures were highest at the outflow end, estimates of the net pressure generated by each segment suggested that all segments, including those at the most upstream locations, increased their contractile activity. In addition, diastolic pressure gradients formed across the system. These did not appear to be due to valve failure (endurance limit of valves was 168 +/- 32 cm H2O) but rather, appeared to relate to the progressive inability of lymphangions to empty which, for a given lymphangion, began to occur at a mean outflow pressure of 9.8 +/- 1.1 cm H2O.

Animals↗
PubMed1995

Evidence that the L-arginine pathway plays a role in the regulation of pumping activity in bovine mesenteric lymphatic vessels.

The objective of this study was to investigate the role of the L-arginine pathway in the regulation of lymphatic pumping. Bovine mesenteric lymphatic vessels (8 to 12 cm in length containing four to six lymphangions) were immersed in an organ bath with input provided by a reservoir filled with Krebs solution. The vessels were stimulated to pump by applying a 6 cm H2O transmural pressure. The addition of 10(-7)-10(-4) M oxyhemoglobin, NG-monomethyl-L-arginine (L-NMMA), or methylene blue to the reservoir resulted in a reduction in lymphatic pumping. L-Arginine (10(-7)-10(-4) M) had no effect on spontaneous pumping activity. However, L-arginine reversed the inhibition caused by oxyhemoglobin and L-NMMA. When tested between 10(-7) and 10(-6) M, sodium nitroprusside (sNP) had variable effects on lymphatics. sNP depressed pumping in approximately 2/3 of the vessels and increased pumping in the remaining 1/3 of ducts. When the results were meaned, sNP caused a significant depression in activity. However, the lower concentration of sNP (10(-7) M) was able to reverse the inhibitory effects of oxyhemoglobin, L-NMMA, and methylene blue whereas the higher concentration (10(-6) M) caused further reductions in pumping activity. These results suggest that bovine lymphatic vessels produce nitric oxide or a related compound. L-Arginine metabolites appear to facilitate the pumping response by an as yet undefined mechanism.

Animals↗
PubMed1994

Effect of phosphatidylcholine on lymphatic drainage and fluid loss from the peritoneal cavity of sheep.

The purpose of this investigation was to test the hypothesis that phosphatidylcholine enhances net ultrafiltration by decreasing lymphatic drainage of the peritoneal cavity. Twelve sheep were used in this study. Six animals received 50 ml/kg intraperitoneal infusions of Dianeal 4.25% (490 mOsm/liter) and six received similar volumes of premixed phosphatidylcholine-Dianeal (510 mOsm/liter). Labeled albumin (25 microCi 125I-human serum albumin) was added to the dialysate as a lymph flow marker. Lymph drainage of the peritoneal cavity was estimated from the appearance of the intraperitoneally administered tracer in the blood. Net ultrafiltration was significantly enhanced by phosphatidylcholine at each hour up to 6 hours post-infusion, and over this period reached 30.3 +/- 3.8 ml/kg in the phosphatidylcholine animals compared to 12.2 +/- 2.1 ml/kg in the control group. Phosphatidylcholine treatment decreased the volume removed by lymphatics; by six hours 5.5 +/- 1.1 ml/kg in the animals receiving phosphatidylcholine, and 10.3 +/- 1.0 ml/kg in the control group was drained as lymph. Fluid loss (estimated from the tracer disappearance from the peritoneal cavity) was slightly less in the phosphatidylcholine-treated animals, averaging 15.8 +/- 1.6 in this group versus 16.8 +/- 1.7 ml/kg in the control sheep. However, these differences were not significant. Phosphatidylcholine significantly increased transcapillary ultrafiltration (estimate of volume movement into peritoneal cavity without fluid loss) from 27.6 +/- 1.5 ml/kg in the controls to 43.8 +/- 3.4 ml/kg in the animals receiving phosphatidylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Pressure-flow relationships in isolated sheep prenodal lymphatic vessels.

The objective of this study was to determine how isolated sheep prenodal popliteal lymphatic vessels responded to transmural and outflow pressure changes. Afferent lymphatics (0.5-1.0 mm diameter) were suspended in an organ bath with both inflow and outflow ends cannulated. Input to the duct was provided from a reservoir filled with Krebs solution. Two types of experiments were performed. In one group, a transmural pressure was applied to the ducts. In a second group of studies, the inflow pressure was fixed (at 2, 4, or 6 cmH2O) and the outflow pressure was increased in 4-cmH2O increments. The transmural pressure-flow relationship was expressed as a bell-shaped curve with pumping increasing up to 18-26 cmH2O and declining at higher pressures. Maximum flow rates averaged 1.4 +/- 0.6 ml/10 min. Greater than 50% of maximum pumping activity was available between approximately 12 and 43 cmH2O. In response to outflow pressures, variable responses were observed. In some vessels, elevations of outflow pressure had little impact on flow rates, until high outflow pressures were attained. In other ducts, pumping declined in response to outflow pressure challenge. With lower inflow pressures (2 or 4 cmH2O), flow rates occasionally increased with elevations of the outflow catheter. In ducts preset with inflow pressures of 6 cmH2O, the mean stop-flow pressure was 60 +/- 4.6 cmH2O. In comparison with previously published data on the pressure-flow relationships in postnodal lymphatics, prenodal vessels pumped over a larger range of transmural or outflow pressures.

Animals↗
PubMed1994

51Cr-RBCs and 125I-albumin as markers to estimate lymph drainage of the peritoneal cavity in sheep.

The purpose of this study was to compare the use of 125I-labeled human serum albumin (125I-HSA) and autologous 51Cr-labeled red blood cells (51Cr-RBCs) as lymph flow markers to estimate lymph drainage of the peritoneal cavity in conscious sheep. In one group, we assessed lymph drainage from the appearance of intraperitoneally administered tracer in the bloodstream. To determine distribution of drainage into discrete lymph compartments, in a second group of studies, lymph was collected from the caudal mediastinal lymph node and the thoracic duct, both of which are involved in lymphatic drainage of the ovine peritoneal cavity. Ringer lactate solution (50 ml/kg) containing 8-10 microCi each of 125I-HSA and 51Cr-RBCs was infused into the peritoneal cavity. Lymph drainage was calculated by dividing the change in mass of tracer in the blood or lymph compartments by the average intraperitoneal tracer concentration. In noncannulated animals, lymph drainage averaged over 6 h was higher with 125I-HSA as tracer (1.35 +/- 0.12 vs. 0.62 +/- 0.19 ml.h-1.kg-1 with 51Cr-RBCs). A similar pattern was noted in terms of drainage into the caudal lymphatic (0.89 +/- 0.23 and 0.52 +/- 0.19 ml.h-1.kg-1 with 125I-HSA and 51Cr-RBCs, respectively) and thoracic duct (0.16 +/- 0.06 and 0.05 +/- 0.02 ml.h-1.kg-1 with 125I-HSA and 51Cr-RBCs, respectively). Analysis of 125I-HSA and 51Cr-RBC concentrations in lymph and intraperitoneal fluid suggested sieving of RBCs at the diaphragmatic stomata or lymph nodes. Using 125I-HSA as tracer and combining data from noncannulated and cannulated sheep, we estimated peritoneal lymph drainage to be 1.35 ml.h-1.kg-1, with 66% of this flow drained by the caudal vessel, 22% by the parasternal pathway (right lymph duct), and 12% by the thoracic duct.

Animals↗
PubMed1994

Lymph flow and lymphatic drainage of inflammatory cells from the peritoneal cavity in a casein-peritonitis model in sheep.

The purpose of this study was to characterize the cellular responses in the peritoneal cavity and draining lymph in a sterile peritonitis model in conscious sheep. Lymph was collected from lymphatics that drained the peritoneal space (caudal mediastinal and thoracic ducts) as well as from lymph vessels that drained peripheral tissues (prescapular). Casein was used as the inflammatory agent. Dialysis solution (Dianeal 4.25%) containing 1g% casein and 25 microCi 125I-human serum albumin was infused into the peritoneal cavity in 50 ml/kg volumes. Peritoneal volumes increased from a mean infused volume of 1572 +/- 51 ml to a maximum of 2119 +/- 77 ml at 3 hours. Over 6 hours, the number of macrophages and lymphocytes in the peritoneal cavity remained relatively constant but the number of neutrophils increased from 9.9 +/- 4.2 x 10(7) to 9.2 +/- 1.9 x 10(9) total cells. Caudal lymph which drains directly from the peritoneal cavity through diaphragmatic stomata, demonstrated a 5 fold increase in flow rate over 6 hours following the Dianeal-casein infusion. Thoracic duct and prescapular flows declined approximately 70% and 50% respectively in the same time period. the concentration of lymphocytes and the lymphocyte outputs (product of volume and concentration) declined in all lymph compartments. No elevations in neutrophil numbers in the thoracic and prescapular lymph compartments were observed but neutrophil output in the caudal lymph increased steadily from 3.1 +/- 1.5 x 10(6) to 4.6 +/- 1.3 x 10(7)/hr at the 6 hour mark. We conclude that the major route of removal of inflammatory cells and fluid from the peritoneal cavity is through diaphragmatic lymphatics.

Animals↗