Capillary filtration coefficient is independent of number of perfused capillaries in cat skeletal muscle

The capillary filtration coefficient (CFC) is assumed to reflect both microvascular hydraulic conductivity and the number of perfused capillaries at a given moment (precapillary sphincter activity). Estimation of hydraulic conductivity in vivo with the CFC method has therefore been performed under conditions of unchanged vascular tone and metabolic influence. There are studies, however, that did not show any change in CFC after changes in vascular tone and metabolic influence, and these studies indicate that CFC may not be influenced by alteration in the number of perfused capillaries. The present study reexamined to what extent CFC in a pressure-controlled preparation depends on the vascular tone and number of perfused capillaries by analyzing how CFC is influenced by 1) vasoconstriction, 2) increase in metabolic influence by decrease in arterial blood pressure, and 3) occlusion of precapillary microvessels by arterial infusion of microspheres. CFC was calculated from the filtration rate induced by a fixed decrease in tissue pressure. Vascular tone was increased in two steps by norepinephrine (n = 7) or angiotensin II (n = 6), causing a blood flow reduction from 7.2 +/- 0.8 to at most 2.7 +/- 0.2 ml x min(-1) x 100 g(-1) (P < 0.05). The decrease in arterial pressure reduced blood flow from 4.8 +/- 0.4 to 1.40 +/- 0.1 ml x min(-1) x 100 g(-1) (n = 6). Vascular resistance increased to 990 +/- 260% of control after the infusion of microspheres (n = 6). CFC was not significantly altered from control after any of the experimental interventions. We conclude that CFC under these conditions is independent of the vascular tone and number of perfused capillaries and that variation in CFC reflects variation in microvascular hydraulic conductivity.     

NEM and filipin increase albumin transport in lung microvessels

This study was undertaken to evaluate the role of transcytosis as a bulk transfer mechanism for the passage of albumin from blood to tissue. Isolated rat lungs were continuously weighed and perfused with an albumin-serum buffer solution under strictly controlled hemodynamic conditions, which allowed measurements of microvascular pressure and of the capillary filtration coefficient (L(p)S). With the use of a tissue uptake technique, it was possible to determine lung albumin clearance under isogravimetric conditions (Cl(iso)), or at elevated filtration rates, to obtain an "apparent albumin reflection coefficient" (sigma(alb)). Experiments were performed during control and after reducing lung temperature from 35 degrees to 22 degrees C and after infusions of the transcytosis inhibitors N-ethylmaleimide (NEM) or filipin. Cooling moderately increased vascular resistance and reduced L(p)S and Cl(iso) largely in proportion to the induced increases in viscosity. At 35 degrees C, NEM (0.13 mM) caused a marked increase in L(p)5 and in Cl(150) and also caused a reduction in sigma(alb.) Furthermore, Cl(iso) increased for the highest dose of filipin tested (1.8 microg/ml). The demonstrated relative cooling insensitivity of the transfer of albumin across the endothelium in rat lungs does not support the contention of transcytosis of proteins across the endothelium. Furthermore, neither NEM nor filipin inhibited lung microvascular albumin transport, but actually increased lung endothelial permeability.     

Pulmonary transvascular flux of transferrin

We compared the pulmonary transvascular fluxes of transferrin and albumin in the intact sheep lung. Anesthetized sheep were prepared with lung lymph fistulas. The vascular blood pool was marked with 99mTc-erythrocytes, autologous transferrin was labeled with 113mIn, and albumin was labeled with 125I. Samples of blood, plasma, lymph, and lung were obtained up to 180 min after tracer infusion. Lymph tissue radioactivities were corrected for the intravascular component and expressed as extravascular-to-plasma concentration ratios. Clearance of transferrin and albumin from the plasma space followed a two-compartment model. The clearance rate constant was 2.1 +/- 0.1 x 10(-3) min for albumin and 2.4 +/- 0.1 x 10(-3) min for transferrin (P less than 0.05). Lymph-to-plasma ratios for albumin and transferrin were not different. However, the extravascular-to-plasma ratio for albumin was greater than transferrin (P less than 0.05). The lymph and lung data were deconvoluted for the plasma input function and fit to a two-compartment model. The results indicate that albumin and transferrin have similar permeabilities across the vascular barrier but have different pulmonary circulation to lymph kinetics because the extravascular volume of distribution of albumin is greater than transferrin.     

Transvascular protein transport in mice lacking endothelial caveolae

Caveolae are Omega-shaped vesicular structures postulated to play a role in transvascular protein transport. Studies on mice lacking endothelial caveolae, caveolin-1 knockout (Cav-1-KO) mice, indicate increased macromolecular transport rates. This was postulated to be due to the appearance of an alternative pathway. The present study tested whether an alternative pathway had appeared in Cav-1-KO mice. Male Cav-1-KO (n=12) and male control mice (n=13) were intubated and anesthetized using 2% isoflurane. 125I-labeled albumin, 131I-labeled immunoglobulin M (IgM), and polydisperse FITC-Ficoll were administered intravenously. During tracer administration, a 90-min peritoneal dialysis dwell was performed. Clearance of tracers to dialysate and permeability-surface area product for glucose were assessed. Transvascular protein transport was higher in Cav-1-KO compared with control mice. Albumin clearance from plasma to peritoneum was 0.088+/-0.008 microl/min in control and 0.179+/-0.012 microl/min in Cav-1-KO (P=0.001) mice. IgM clearance was 0.049+/-0.003 and 0.083+/-0.010 microl/min in control and Cav-1-KO mice, respectively (P=0.016). Ficoll clearance was increased in Cav-1-KO mice. In conclusion, the lack of caveolae in Cav-1-KO mice resulted in a marked increase in macromolecular transport. A two-pore analysis of the Ficoll clearance data revealed that the higher transport rate in Cav-1-KO mice was not compatible with the appearance of an alternative pathway for macromolecular transport. In contrast, the higher transperitoneal protein and Ficoll clearance is consistent with passive porous transport through an unperturbed two-pore system, presumably at an elevated capillary hydraulic pressure. Alternatively, the data may be explained by reductions in the selectivity of the endothelial glycocalyx, leading to an increased capillary hydraulic conductivity and large solute filtration.     

Estrogen and progesterone effects on transcapillary fluid dynamics

The purpose of this study was to determine estrogen (E(2)) and progesterone (P(4)) effects on atrial natriuretic peptide (ANP) control of plasma volume (PV) and transcapillary fluid dynamics. To this end, we suppressed reproductive function in 12 women (age 21-35 yr) using a gonadotropin releasing-hormone (GnRH) analog (leuprolide acetate) for 5 wk. During the 5th week, the women either received 4 days of E(2) administration (17beta-estradiol, transdermal patch, 0.1 mg/day) or 4 days of E(2) with P(4) administration (vaginal gel, 90 mg P(4) twice per day). At the end of the 4th and 5th week of GnRH analog and hormone administration, we determined PV (Evans blue dye) and changes in PV and forearm capillary filtration coefficient (CFC) during a 120-min infusion of ANP (5 ng x kg body wt(-1) x min(-1)). Preinfusion PV was estimated from Evans blue dye measurement taken over the last 30 min of infusion based on changes in hematocrit. E(2) treatment did not affect preinfusion PV relative to GnRH analog alone (45.3 +/- 3.1 vs. 45.4 +/- 3.1 ml/kg). During ANP infusion CFC was greater during E(2) treatment compared with GnRH analog alone (6.5 +/- 1.4 vs. 4.9 +/- 1.4 microl. 100 g(-1) x min(-1) mmHg(-1), P < 0.05). The %PV loss during ANP infusion was similar for E(2) and GnRH analog-alone treatments (-0.8 +/- 0.2 and -1.0 +/- 0.2 ml/kg, respectively), indicating the change in CFC had little systemic effect on ANP-related changes in PV. Estimated baseline PV was reduced by E(2)-P(4) treatment. During ANP infusion CFC was approximately 30% lower during E(2)-P(4) (6.0 +/- 0.5 vs. 4.3 +/- 4.3 microl. 100 g(-1) x min(-1) mm Hg(-1), P < 0.05), and the PV loss during ANP infusion was attenuated (-0.9 +/- 0.2 and -0.2 +/- 0.2 ml/kg for GnRH analog-alone and E(2)-P(4) treatments, respectively). Thus the E(2)-P(4) treatment lowered CFC and reduced PV loss during ANP infusion.     

Whole-body systemic transcapillary filtration rates, coefficients, and isogravimetric capillary pressures in Bufo marinus and Rana catesbeiana

Whole-body and organ-level transcapillary filtration rates and coefficients are virtually unexamined in ectothermal vertebrates. These filtration rates appear to be greater than in mammals when plasma volume shifts and lymphatic function are analyzed. Gravimetric techniques monitoring whole-body mass changes were used to estimate net systemic filtration in Bufo marinus and Rana catesbeiana while perfusing with low-protein Ringer's and manipulating venous pressure. Capillary pressures were estimated from arterial and venous pressures after measuring the venous to arterial resistance ratio of 0.23. The capillary filtration coefficient (CFC) for the two species was 25.2+/-1.47 mL min-1 kg-1 kPa-1. Isogravimetric capillary pressure (Pci), the pressure at which net fluid is neither filtered nor reabsorbed, was 1.12+/-0.054 kPa and was confirmed by an independent method. None of these variables showed a significant interspecific difference. The anuran CFC and Pci are significantly higher than those found using the same method on rats (7.6+/-2.04 mL min-1 kg-1 kPa-1 and 0.3+/-0.37 kPa, respectively) and those commonly reported in mammals. Despite the high CFC, the high Pci predicts that little net filtration will occur at resting in vivo capillary pressures.     

Decreased capillary filtration but maintained venous compliance in the lower limb of aging women

There are sex-related differences in venous compliance and capillary filtration in the lower limbs, which to some extent can explain the susceptibility to orthostatic intolerance in young women. With age, venous compliance and capacitance are reduced in men. This study was designed to evaluate age-related changes in venous compliance and capillary filtration in the lower limbs of healthy women. Included in this study were 22 young and 12 elderly women (23.1 +/- 0.4 and 66.4 +/- 1.4 yr). Lower body negative pressure (LBNP) of 11, 22, and 44 mmHg created defined transmural pressure gradients in the lower limbs. A plethysmographic technique was used on the calf to assess venous capacitance and net capillary filtration. Venous compliance was calculated with the aid of a quadratic regression equation. No age-related differences in venous compliance and capacitance were found. Net capillary filtration and capillary filtration coefficient (CFC) were lower in elderly women at a LBNP of 11 and 22 mmHg (0.0032 vs. 0.0044 and 0.0030 vs. 0.0041 ml.100 ml(-1).min(-1).mmHg(-1), P < 0.001). At higher transmural pressure (LBNP, 44 mmHg), CFC increased by approximately 1/3 (0.010 ml.100 ml(-1).min(-1).mmHg(-1)) in the elderly (P < 0.001) but remained unchanged in the young women. In conclusion, no age-related decrease in venous compliance and capacitance was seen in women. However, a decreased CFC was found with age, implying reduced capillary function. Increasing transmural pressure increased CFC in the elderly women, indicating an increased capillary susceptibility to transmural pressure load in dependent regions. These findings differ from earlier studies on age-related effects in men, indicating sex-specific vascular aging both in the venous section and microcirculation.     

Comparison of cerebrospinal fluid transport in fetal and adult sheep

We quantified cerebrospinal fluid (CSF) transport (conductance) and CSF outflow resistance in late-gestation fetal and adult sheep using two methods, a constant pressure infusion method and a bolus injection technique into the lateral ventricles. No significant differences in CSF conductance (fetus 0.013 +/- 0.002, adult 0.014 +/- 0.003 ml x min(-1) x cm H(2)O(-1)) or CSF outflow resistance (fetus 83.7 +/- 9.8, adult 84.7 +/- 19.7 cm H(2)O x ml(-1) x min) were observed. To confirm CSF transport to plasma in fetal animals, (125)I- or (131)I-labeled human serum albumin (HSA) was injected into the lateral ventricles. The tracer entered fetal plasma with an average mass transport rate of 1.91 +/- 0.47% injected/h (n = 9). In two fetuses, we monitored the tracer appearance in plasma and cervical and thoracic duct lymph after injection of radioactive HSA into the ventricular CSF. As was the case in adult animals, fetal tracer concentrations increased in all three compartments over time, with the highest concentrations measured in lymph collected from the cervical lymphatics. These results 1) indicate that global CSF transport parameters in the late-gestation fetus and adult sheep are similar and 2) suggest an important role for extracranial lymphatic vessels in CSF transport before birth.     

Early fluid and protein shifts in men during water immersion

High precision blood and plasma densitometry was used to measure transvascular fluid shifts during water immersion to the neck. Six men (28-49 years) undertook 30 min of standing immersion in water at 35.0 +/- 0.2 degrees C; immersion was preceded by 30 min control standing in air at 28 +/- 1 degrees C. Blood was sampled from an antecubital catheter for determination of blood density (BD), plasma density (PD), haematocrit (Ht), total plasma protein concentration (PPC), and plasma albumin concentration (PAC). Compared to control, significant decreases (p less than 0.01) in all these measures were observed after 20 min immersion. At 30 min, plasma volume had increased by 11.0 +/- 2.8%; the average density of the fluid shifted from extravascular fluid into the vascular compartment was 1006.3 g.l-1; albumin moved with the fluid and its albumin concentration was about one-third of the plasma protein concentration during early immersion. These calculations are based on the assumption that the F-cell ratio remained unchanged. No changes in erythrocyte water content during immersion were found. Thus, immersion-induced haemodilution is probably accompanied by protein (mainly albumin) augmentation which accompanies the intravascular fluid shift.     

Heterogeneous responses of human limbs to infused adrenergic agonists: a gravitational effect?

Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this "dependent hypertension" would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng x 100 ml limb volume-1 x min-1) and phenylephrine (0.025-0.8 microg x 100 ml limb volume-1 x min-1) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 +/- 2.5 vs. 26.9 +/- 2.0 mmHg x 100 ml x min x ml-1; P < 0.001) and maximal conductance was lower (46.1 +/- 11.9 vs. 59.4 +/- 13.4 ml x ml-1 x min-1 x mmHg-1; P < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions (P < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm (P < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that alpha1- but not beta-adrenergic-receptor responsiveness in human limbs is nonuniform. The relatively greater response to alpha1-adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing.     

Effect of high transcapillary pressures on capillary ultrastructure and permeability coefficients in dog lung.

To determine the correlation between ultrastructural and physiological changes in blood-gas barrier function in lungs transiently exposed to very high vascular pressures, we increased capillary transmural pressure (Ptm) of 6 canine isolated perfused left lower lung lobe preparations (high-pressure group) to 80.3 Torr for 3.8 min and then determined the capillary filtration (K(fc)) and osmotic reflection (sigma(d)) coefficients at a Ptm of 19.1 Torr in the ventilated lung lobes. This was followed by perfusion fixation of the lobes at a Ptm of 20.5 Torr for ultrastructural analysis. These data were compared with those obtained in six lobes in which Ptm was not transiently elevated before K(fc), sigma(d), and ultrastructural evaluation. K(fc) was higher [0.249 +/- 0.042 (SE) vs. 0.054 +/- 0.009 g. min(-1). Torr(-1). 100 g(-1); P < 0.01] and sigma(d) was lower (0.52 +/- 0.07 vs. 0.85 +/- 0.08; P < 0.01) in the high-pressure group. In contrast, although endothelial and epithelial breaks were occasionally observed in some experiments, their incidence was not increased in the high-pressure group. These data suggest that the increased transvascular water and protein flux occurred through pathways of a size not resolvable by electron microscopy after vascular perfusion-fixation at a Ptm of 20.5 Torr.     

Sex-related effects on venous compliance and capillary filtration in the lower limb

Recent studies in humans have suggested sex differences in venous compliance of the lower limb, with lower compliance in women. Capillary fluid filtration could, however, be a confounder in the evaluation of venous compliance. The venous capacitance and capillary filtration response in the calves of 12 women (23.2 +/- 0.5 years) and 16 men (22.9 +/- 0.5 years) were studied during 8 min lower body negative pressure (LBNP) of 11, 22, and 44 mmHg. Calf venous compliance is dependent on pressure and was determined using the first derivative of a quadratic regression equation that described the capacitance-pressure relationship [compliance = beta1 + (2 x beta2 x transmural pressure)]. We found a lower venous compliance in women at low transmural pressures, and the venous capacitance in men was increased (P < 0.05). However, the difference in compliance between sexes was reduced and not seen at higher transmural pressures. Net capillary fluid filtration and capillary filtration coefficient (CFC) were greater in women than in men during LBNP (P < 0.05). Furthermore, calf volume increase (capacitance response + total capillary filtration) during LBNP was equivalent in both sexes. When total capillary filtration was not subtracted from the calf capacitance response in the calculation of venous compliance, the sex differences disappeared, emphasizing that venous compliance measurement should be corrected for the contribution of CFC.     

Compounds that increase cAMP prevent ischemia-reperfusion pulmonary capillary injury.

This study evaluated the physiological effects of compounds that increase adenosine 3',5'-cyclic monophosphate (cAMP) on changes in pulmonary capillary permeability and vascular resistance induced by ischemia-reperfusion (I-R) in isolated blood-perfused rabbit lungs. cAMP was elevated by 1) beta-adrenergic stimulation with isoproterenol (ISO, 10(-5) M), 2) post-beta-receptor stimulation of adenylate cyclase with forskolin (FSK, 10(-5) M), 3) and dibutyryl cAMP (DBcAMP, 1 mM), a cAMP analogue. Vascular permeability was assessed by determining the capillary filtration coefficient (Kf,c), and capillary pressure was measured using the double occlusion technique. The total, arterial, and venous vascular resistances were calculated from measured pulmonary arterial, venous, and capillary pressures and blood flow. Reperfusion after 2 h of ischemia significantly (P less than 0.05) increased Kf,c (from 0.115 +/- 0.028 to 0.224 +/- 0.040 ml.min-1.cmH2O-1.100 g-1). These I-R-induced changes in capillary permeability were prevented when ISO, FSK, or DBcAMP was added to the perfusate at reperfusion (0.110 +/- 0.022 and 0.103 +/- 0.021, 0.123 +/- 0.029 and 0.164 +/- 0.024, and 0.153 +/- 0.030 and 0.170 +/- 0.027 ml.min-1.cmH2O-1.100 g-1, respectively). I-R significantly increased total, arterial, and venous vascular resistances. These increases in vascular resistance were also blocked by ISO, FSK, and DBcAMP. These data suggest that beta-adrenergic stimulation, post-beta-receptor activation of adenylate cyclase, and DBcAMP prevent the changes in pulmonary vascular permeability and vascular resistances caused by I-R in isolated rabbit lungs through a mechanism involving an increase in intracellular levels of cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hemodynamic and sympathoadrenal responses to mental stress during nitric oxide synthesis inhibition

Cardiovascular and sympathoadrenal responses to a reproducible mental stress test were investigated in eight healthy young men before and during intravenous infusion of the nitric oxide (NO) synthesis inhibitor N-monomethyl-L-arginine (L-NMMA). Before L-NMMA, stress responses included significant increases in heart rate, mean arterial pressure, and cardiac output (CO) and decreases in systemic and forearm vascular resistance. Arterial plasma norepinephrine (NE) increased. At rest after 30 min of infusion of L-NMMA (0.3 mg.kg(-1).min(-1) iv), mean arterial pressure increased from 98 +/- 4 to 108 +/- 3 mmHg (P <0.001) because of an increase in systemic vascular resistance from 12.9 +/- 0.5 to 18.5 +/- 0.9 units (P <0.001). CO decreased from 7.7 +/- 0.4 to 5.9 +/- 0.3 l/min (P <0.01). Arterial plasma NE decreased from 2.08 +/- 0.16 to 1.47 +/- 0.14 nmol/l. Repeated mental stress during continued infusion of L-NMMA (0.15 mg.kg(-1).min(-1)) induced qualitatively similar cardiovascular responses, but there was a marked attenuation of the increase in mean arterial blood pressure, resulting in similar "steady-state" blood pressures during mental stress without and with NO blockade. Increases in heart rate and CO were attenuated, but stress-induced decreases in systemic and forearm vascular resistance were essentially unchanged. Arterial plasma NE increased less than during the first stress test. Thus the increased arterial tone at rest during L-NMMA infusion is compensated for by attenuated increases in blood pressure during mental stress, mainly through a markedly attenuated CO response and suppressed sympathetic nerve activity.     

Vascular resistance and Kf in normal and PMA-injured rabbit lungs: effects of adenosine

The effects of adenosine (ADO) on pulmonary vascular resistance (PVR) distribution, vascular compliance (C), and permeability were determined in normal and PMA-injured isolated rabbit lungs perfused with a 1:1 mixture of 6% albumin in Krebs-Henseleit buffer and autologous blood. ADO or vehicle was continuously infused into the reservoir at 1,4, or 5 mumol/min after a 1-mumol bolus of ADO or vehicle. The capillary filtration coefficient (Kf) and arterial, venous, and double occlusion pressures were measured at baseline and 30 min after phorbol myristate acetate (PMA; 4 x 10(-8) M) or vehicle. Perfusate differential and total leukocyte counts as well as adenine nucleotides, 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), and thromboxane B2 (TxB2) concentrations were determined at each measurement period. ADO was recovered as hypoxanthine and inosine in the perfusate. ADO alone did not alter PVR, C, Kf, or TxB2 but reduced 6-keto-PGF1 alpha levels. PMA induced an increase in Kf (0.024 +/- 0.002 to 0.040 +/- 0.006 g.cmH2O-1.min-1, P less than 0.05) that was completely blocked by 4 or 5 mumol/min ADO. PVR increased by 63 +/- 11% after PMA, primarily in the arteries and arterial and venous microvessels. The postcapillary resistance increase was blunted by 4 mumol/min ADO; 5 mumol/min ADO prevented the PVR increase in all segments. ADO did not affect the initial adherence of neutrophils in the lung or the PMA-induced 87 +/- 2% decrease in circulating leukocytes (greater than 98% lymphocytes) or threefold increase in TxB2 levels. These results suggest that protection by ADO is not mediated by the altering of cyclooxygenase products or by leukocyte adherence.     

Hemodynamics of orthostatic intolerance: implications for gender differences

Women have a greater incidence of orthostatic intolerance than men. We hypothesized that this difference is related to hemodynamic effects on regulation of cardiac filling rather than to reduced responsiveness of vascular resistance during orthostatic stress. We constructed Frank-Starling curves from pulmonary capillary wedge pressure (PCWP), stroke volume (SV), and stroke index (SI) during lower body negative pressure (LBNP) and saline infusion in 10 healthy young women and 13 men. Orthostatic tolerance was determined by progressive LBNP to presyncope. LBNP tolerance was significantly lower in women than in men (626.8 +/- 55.0 vs. 927.7 +/- 53.0 mmHg x min, P < 0.01). Women had steeper maximal slopes of Starling curves than men whether expressed as SV (12.5 +/- 2.0 vs. 7.1 +/- 1.5 ml/mmHg, P < 0.05) or normalized as SI (6.31 +/- 0.8 vs. 4.29 +/- 0.6 ml.m-2.mmHg-1, P < 0.05). During progressive LBNP, PCWP dropped quickly at low levels, and reached a plateau at high levels of LBNP near presyncope in all subjects. SV was 35% and SI was 29% lower in women at presyncope (both P < 0.05). Coincident with the smaller SV, women had higher heart rates but similar mean arterial pressures compared with men at presyncope. Vascular resistance and plasma norepinephrine concentration were similar between genders. We conclude that lower orthostatic tolerance in women is associated with decreased cardiac filling rather than reduced responsiveness of vascular resistance during orthostatic challenges. Thus cardiac mechanics and Frank-Starling relationship may be important mechanisms underlying the gender difference in orthostatic tolerance.     

Stimulation of platelet serotonin and Rb uptake by N-ethylmaleimide

The effects of N-ethylmaleimide (NEM) on mouse platelet serotonin (5-HT) and ⁸⁶Rb⁺ uptake were studied. The 5-HT transport system showed a biphasic response to increasing concentrations of NEM, with low concentrations (25–50 μM) stimulating and high concentrations (200–400 μM) inhibiting 5-HT transport. Fluoxetine, an inhibitor of the platelet 5-HT transporter, blocked NEM-induced stimulation of 5-HT transport. The kinetics of 5-HT uptake indicated that NEM (50 μM) markedly increased the maximal rate of 5-HT transport (V_max control = 28.4±1.4 pmol/10⁸ platelets/4 min vs V_max NEM = 64.5±9.5 pmol/10⁸ platelets/4 min but had no significant effect on the K_m value. Platelet Na⁺ K⁺ ATPase activity was determined by measuring ⁸⁶Rb⁺ uptake. Platelet ⁸⁶Rb⁺ uptake showed a biphasic response to NEM, with low concentrations (25–100 μM) significantly stimulating and high concentrations (400 μM) inhibiting uptake. These changes in platelet ⁸⁶Rb⁺ uptake paralleled the biphasic changes in 5-HT transport. In the presence of fluoxetine, 5-HT transport was markedly inhibited but no change in the ability of NEM to stimulate ⁸⁶Rb⁺ uptake was observed. These data suggest that low concentrations of NEM activate plasma membrane Na⁺ K⁺ ATPase which results in a marked stimulation of platelet 5-HT transport.     

Impaired endothelium-mediated vasodilation is not the principal cause of vasoconstriction in heart failure

The extent to which abnormal endothelium-dependent vasodilator mechanisms contribute to abnormal resting vasoconstriction and blunted reflex vasodilation seen in heart failure is unknown. The purpose of this study was to test the hypothesis that the resting and reflex abnormalities in vascular tone that characterize heart failure are mediated by abnormal endothelium-mediated mechanisms. Thirteen advanced heart-failure patients (New York Heart Association III-IV) and 13 age-matched normal controls were studied. Saline, acetylcholine (20 microg/min), or L-arginine (10 mg/min) was infused into the brachial artery, and forearm blood flow was measured by venous plethysmography at rest and during mental stress. At rest, acetylcholine decreased forearm vascular resistance in normal subjects, but this response was blunted in heart failure. During mental stress with intra-arterial acetylcholine or L-arginine, the decrease in forearm vascular resistance was not greater than during saline control in heart failure [saline control vs. acetylcholine (7 +/- 3 vs. 6 +/- 3, P = NS) or vs. L-arginine (9 +/- 2 units, P = NS)]. The increase in forearm blood flow was not greater than during saline control in heart failure [saline control vs. acetylcholine (1. 2 +/- 0.3 vs. 1.3 +/- 0.3, P = NS), or vs. L-arginine (1.2 +/- 0.2 ml x min(-1) x 100 ml(-1), P = NS)]. Furthermore, during mental stress with nitroprusside, the decrease in forearm vascular resistance was not greater than during saline control [saline control vs. nitroprusside (7 +/- 3 vs. 5 +/- 4 ml x min(-1) x 100 g(-1), P = NS)], and the increase in forearm blood flow was not greater than during saline control [saline control vs. nitroprusside (1.2 +/- 0.3 vs. 1.3 +/- 0.5 ml x min(-1) x 100 g(-1), P = NS)]. Because the endothelial-independent agent nitroprusside was unable to restore resting and reflex vasodilation to normal in heart failure, we conclude that impaired endothelium-mediated vasodilation with acetylholine-nitric oxide cannot be the principal cause of the attenuated resting- or reflex-mediated vasodilation in heart failure.     

Vascular perfusability and capillary macromolecular permeability in the mechanically induced rabbit hydrosalpinx

The mechanically induced rabbit hydrosalpinx, a frequently studied animal model of human hydrosalpinges, was examined to determine the variations, in vascular perfusion and capillary albumin permeability, which occur in hydrosalpinges. At laparotomy, 4 adult female virgin rabbits underwent isthmic and ampullary occlusion with small tantalum clips. 4 weeks later, fluorescein isothiocyanate-labelled bovine serum albumin (FITC BSA: molecular weight 67,000) was injected intravenously 5 min before oviduct excision. Examination of tubal sections by incident light fluorescent microscopy demonstrated poor interplical vascular perfusability and markedly reduced interplical capillary permeability to FITC BSA in both isthmic and ampullary segments of hydrosalpinx. These observations imply that, in the experimental rabbit hydrosalpinx, interplical deciliation is probably vascular in origin; furthermore the marked decrease in capillary macromolecule permeability may explain the serous fluid collection within the hydrosalpinx. Poor fecundity following microsurgical restoration of tubal patency in hydrosalpinges is possibly due to the failure of this decrease in submucosal capillary perfusability and macromolecular permeability to resolve.     

Peripheral vascular resistance increases after termination of obstructive apneas.

The mechanisms by which obstructive apneas produce intermittent surges in arterial pressure remain poorly defined. To determine whether termination of obstructive apneas produce peripheral vasoconstriction, we assessed forearm blood flow during and after obstructive events in sleeping patients experiencing spontaneous upper airway obstructions. In all subjects, heart rate was monitored with an electrocardiogram and blood pressure was monitored continuously with digital plethysmography. In 10 patients (protocol 1), we used forearm plethysmography to assess forearm blood flow, from which we calculated forearm vascular resistance by performing venous occlusions during and after obstructive episodes. In an additional four subjects, we used simultaneous Doppler and B-mode images of the brachial artery to measure blood velocity and arterial diameter, from which we calculated brachial flow continuously during spontaneous apneas (protocol 2). In protocol 1, forearm vascular resistance increased 71% after apnea termination (29.3 +/- 15.4 to 49.8 +/- 26.5 resistance units, P < 0.05) with all patients showing an increase in resistance. In protocol 2, brachial resistance increased at apnea termination in all subjects (219.8 +/- 22.2 to 358.3 +/- 46.1 mmHg x l(-1) x min; P = 0.01). We conclude that termination of obstructive apneas is associated with peripheral vasoconstriction.