Vitamin C and E supplementation alters protein signalling after a strength training session, but not muscle growth during 10 weeks of training.

This study investigated the effects of vitamin C and E supplementation on acute responses and adaptations to strength training. Thirty-two recreationally strength-trained men and women were randomly allocated to receive a vitamin C and E supplement (1000 mg day(-1) and 235 mg day(-1), respectively), or a placebo, for 10 weeks. During this period the participants' training involved heavy-load resistance exercise four times per week. Muscle biopsies from m. vastus lateralis were collected, and 1 repetition maximum (1RM) and maximal isometric voluntary contraction force, body composition (dual-energy X-ray absorptiometry), and muscle cross-sectional area (magnetic resonance imaging) were measured before and after the intervention. Furthermore, the cellular responses to a single exercise session were assessed midway in the training period by measurements of muscle protein fractional synthetic rate and phosphorylation of several hypertrophic signalling proteins. Muscle biopsies were obtained from m. vastus lateralis twice before, and 100 and 150 min after, the exercise session (4 × 8RM, leg press and knee-extension). The supplementation did not affect the increase in muscle mass or the acute change in protein synthesis, but it hampered certain strength increases (biceps curl). Moreover, increased phosphorylation of p38 mitogen-activated protein kinase, Extracellular signal-regulated protein kinases 1 and 2 and p70S6 kinase after the exercise session was blunted by vitamin C and E supplementation. The total ubiquitination levels after the exercise session, however, were lower with vitamin C and E than placebo. We concluded that vitamin C and E supplementation interfered with the acute cellular response to heavy-load resistance exercise and demonstrated tentative long-term negative effects on adaptation to strength training.

Increased interstitial protein because of impaired lymph drainage does not induce fibrosis and inflammation in lymphedema.

OBJECTIVE: The pathophysiology of lymphedema is incompletely understood. We asked how transcapillary fluid balance parameters and lymph flow are affected in a transgenic mouse model of primary lymphedema, which due to an inhibition of vascular endothelial growth factor receptor-3 (VEGFR-3) signaling lacks dermal lymphatics, and whether protein accumulation in the interstitium occurring in lymphedema results in inflammation. METHODS AND RESULTS: As estimated using a new optical-imaging technique, we found that this signaling defect resulted in lymph drainage in hind limb skin of K14-VEGFR-3-Ig mice that was 34% of the corresponding value in wild-type. The interstitial fluid pressure and tissue fluid volumes were significantly increased in the areas of visible swelling only, whereas the colloid osmotic pressure in plasma, and thus the colloid osmotic pressure gradient, was reduced compared to wild-type mice. An acute volume load resulted in an exaggerated interstitial fluid pressure response in transgenic mice. There was no accumulation of collagen or lipid in skin, suggesting that chronic edema presented in the K14-VEGFR-3-Ig mouse was not sufficient to induce changes in tissue composition. Proinflammatory cytokines (interleukin-2, interleukin-6, interleukin-12) in subcutaneous interstitial fluid and macrophage infiltration in skin of the paw were lower, whereas the monocyte/macrophage cell fraction in blood and spleen was higher in transgenic compared with wild-type mice. CONCLUSIONS: Our data suggest that a high interstitial protein concentration and longstanding edema is not sufficient to induce fibrosis and inflammation characteristic for the human condition and may have implications for our understanding of the pathophysiology of this condition.

Isolation of interstitial fluid in skin during volume expansion: evaluation of a method in pigs.

The ability to isolate interstitial fluid (IF) from skin would make it possible to study the microcirculation and proteins in this environment both during normal and pathophysiological conditions. Traditional IF sampling using implanted wicks suffer from low volumes with risk of contamination by local inflammatory, intracellular, and vascular proteins. To sample larger volumes of true IF, a recently described tissue centrifugation method was compared with dry and wet wicks from porcine skin under normal conditions and following volume expansion. With all three methods, volume expansion caused a significant lowering of interstitial colloid osmotic pressure as expected, and the fluid was similar to plasma when compared using size-exclusion HPLC. The centrifugation method was superior with respect to isolating larger amounts of true IF for further studies. Mass spectrometry of IF sampled with centrifugation showed that most of the proteins reflected the major plasma proteins with some tissue-specific proteins like decorin, gelsolin, and orosomucoid-1. Lumican, pigment epithelium-derived factor, and fatty acid-binding protein 4 were only identified in IF after volume expansion, possibly reflecting a local response to increased fluid filtration. Tissue centrifugation to collect IF from skin should be applicable to both clinical and experimental studies on IF balance during different pathophysiological conditions and interventions.

The alpha11beta1 integrin has a mechanistic role in control of interstitial fluid pressure and edema formation in inflammation.

OBJECTIVE: Collagen-binding integrins may be involved in controlling interstitial fluid pressure (Pif), transcapillary fluid flux, and tissue fluid volume. Our aim was to explore whether the newly discovered collagen binding alpha11beta1 integrin has a mechanistic role in inflammatory edema formation. METHODS AND RESULTS: In collagen matrices seeded with a mixture of mast cells and fibroblasts, fibroblasts lacking the alpha11 integrin subunit (alpha11(-/-)) contracted collagen gels less efficiently than control fibroblasts, suggesting that the alpha11beta1 integrin is able to mediate tensile force in connective tissues. In alpha11(-/-) mice, control Pif in skin did not differ from the pressure found in wild-type mice. Whereas a reduction in Pif was found in control mice after inducing inflammation, thereby contributing to fluid extravasation and edema formation, such a reduction was not seen in alpha11(-/-) mice. That this effect is mediated through the extracellular compartment is suggested by a similar plasma protein extravasation ratio in alpha11(-/-) and wild-type mice. CONCLUSIONS: Our data suggest that alpha11beta1 integrins on dermal fibroblasts mediate collagen lattice remodeling and have a mechanistic role in controlling Pif in inflammation and thereby fluid extravasation and edema formation in vivo.

The interstitium conducts extrarenal storage of sodium and represents a third compartment essential for extracellular volume and blood pressure homeostasis.

The role of salt in the pathogenesis of arterial hypertension is not well understood. According to the current understanding, the central mechanism for blood pressure (BP) regulation relies on classical studies linking BP and Na+ balance, placing the kidney at the very centre of long-term BP regulation. To maintain BP homeostasis, the effective circulating fluid volume and thereby body Na+ content has to be maintained within very narrow limits. From recent work in humans and rats, the notion has emerged that Na+ could be stored somewhere in the body without commensurate water retention to buffer free extracellular Na+ and that previously unidentified extrarenal, tissue-specific regulatory mechanisms are operative regulating the release and storage of Na+ from a kidney-independent reservoir. Moreover, immune cells from the mononuclear phagocyte system not only function as local on-site sensors of interstitial electrolyte concentration, but also, together with lymphatics, act as systemic regulators of body fluid volume and BP. These studies have established new and unexpected targets in studies of BP control and thus the pathophysiology of hypertension: the interstitium/extracellular matrix of the skin, its inherent interstitial fluid and the lymphatic vasculature forming a vessel network in the interstitium. Aspects of the interstitium in relation to Na+ balance and hypertension are the focus of this review. Taken together, observations of salt storage in the skin to buffer free extracellular Na+ and macrophage modulation of the extracellular matrix and lymphatics suggest that electrolyte homeostasis in the body cannot be achieved by renal excretion alone, but also relies on extrarenal regulatory mechanisms.

Role of Hyperplasia of Gingival Lymphatics in Periodontal Inflammation.

Lymphatic vessels are important for maintenance of tissue fluid homeostasis and afferent antigen transport. In chronic inflammation, lymphangiogenesis takes place and is characterized by lymphatic endothelial cell proliferation and lymphatic hyperplasia. Vascular endothelial growth factor C (VEGFC) is the main known lymphangiogenic growth factor, and its expression is increased in periodontitis, a common chronic infectious disease that results in tissue destruction and alveolar bone loss. The role of lymphangiogenesis during development of periodontitis is unknown. Here, we test if transgenic overexpression of epithelial VEGFC in a murine model is followed by hyperplasia of lymphatic vessels in oral mucosa and if the lymphatic drainage capacity is altered. We also test if lymphatic hyperplasia protects against periodontal disease development. Transgenic keratin 14 (K14)-VEGFC mice had significant hyperplasia of lymphatics in oral mucosa, including gingiva, without changes in blood vessel vasculature. The basal lymph flow was normal but slightly lower than in wild-type mice when oral mucosa was challenged with lipopolysaccharide from Porphyromonas gingivalis. Under normal conditions, K14-VEGFC mice exhibited an increased number of neutrophils in gingiva, demonstrated enhanced phagocyte recruitment in the cervical lymph nodes, and had more alveolar bone when compared with their wild-type littermates. After induction of periodontitis, no strain differences were observed in the periodontal tissues with respect to granulocyte recruitment, bone resorption, angiogenesis, cytokines, and bone-related protein expressions or in draining lymph node immune cell proportions and vascularization. We conclude that overexpression of VEGFC results in hyperplastic lymphatics, which do not enhance lymphatic drainage capacity but facilitate phagocyte transport to draining lymph nodes. Hyperplasia of lymphatics does not protect against development of ligature-induced periodontitis.

Blood-tissue transport of exogenous albumin and immunoglobulin G in genetically analbuminemic rats.

Tracer uptake studies were carried out in adult female Nagase (NA) strain analbuminemic rats [derived from Sprague-Dawley (SD) stock] and in adult female SD controls to determine the extent to which capillary permeability to plasma proteins is altered in the absence of endogenous albumin. Accessory measurements (arterial pressure, central venous pressure, plasma and interstitial fluid protein concentrations and oncotic pressures, plasma volume, and interstitial fluid volume) confirm the report of Joles et al. [Am. J. Physiol. 257 (Renal Fluid Electrolyte Physiol. 26): F23-F28, 1989] that shows elevated plasma volumes, normal interstitial fluid volumes, nearly normal plasma oncotic pressures (due to elevated globulin concentrations), and lower interstitial fluid oncotic pressures. In skin, skeletal muscles, and heart muscle, clearances of exogenous heterologous (bovine) albumin were 20-40% higher in NA than in SD controls. In intestine, albumin clearances were 20-30% lower. In NA rats blood-to-tissue clearances of heterologous (bovine) immunoglobulin G in skin and heart were higher and in the intestine they were lower than in SD controls; however, clearances in skeletal muscles were not elevated. The differences between NA and SD are small compared with the large increases in macromolecular permeabilities reported by others for organs and single microvessels perfused with albumin-free fluids.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood flow and interstitial fluid pressure in the rat submandibular gland during changes in perfusion.

The submandibular gland is a cell-rich encapsulated organ with high transport of fluid through the interstitial space during salivation. We hypothesized that the gland is a low-compliant tissue, i.e., that a modest increase in fluid volume will produce a rise in interstitial fluid pressure (IFP) counteracting fluid filtration into the interstitium. To test this hypothesis, we measured IFP with micropipettes and glandular blood flow (GBF) with a laser-Doppler flowmeter during changes in perfusion. Clamping of the carotid artery or the jugular vein, or electrical stimulation of the sympathetic or parasympathetic nerve to the gland, induced changes in perfusion. Baseline IFP averaged 3.5 +/- 0.5 mm Hg. Clamping of the artery reduced IFP and GBF (-56.5 +/- 8.4% and -53.1 +/- 6.4%, respectively), whereas clamping of the vein decreased GBF (-21.6 +/- 14.3%) and increased IFP (141.2 +/- 27.4%). Sympathetic nerve stimulation reduced both parameters (-86.9 +/- 16.5% and -74.4 +/- 7.0%, respectively). In contrast, stimulation of the parasympathetic nerve elicited an increase in GBF (133.2 +/- 5.9%) and in IFP (173.3 +/- 41.4%). Thus, changes in vascular volume led to concomitant changes in IFP consistent with low tissue compliance, a phenomenon of importance for fluid volume regulation.

Evaluation of methodologies for measurement of interstitial fluid pressure (Pi): physiological implications of recent Pi data.

As one of the determinants of net transcapillary filtration, filling of initial lymphatics and interstitial compliance, interstitial fluid pressure (Pi) is of great physiological interest. Several methods have been developed to measure Pi, all measuring the fluid equilibration pressure, i.e., the pressure in a saline-filled tube brought into contact with the interstitium. The methods designed to establish such contact may be characterized as acute and chronic. With acute methods, i.e., needle without infusion, wick catheters, WIN, and micropipettes, measurements are made within minutes to a few hours after insertion of the device. The chronic methods are various capsules (perforated, porous, or Teflon rings) implanted into the tissue 4 to 6 weeks before measurements. A general finding in previous studies from different laboratories and in different species have been that the chronic methods give more strongly negative (subatmospheric) Pi than the acute methods, and that the chronic methods give much greater pressure responses to changes in IFV. By direct comparison of acute and chronic methods in the same tissue and site, all give similar Pi in steady state conditions, while an acute over- and dehydration results in far more pronounced pressure changes recorded with chronic than with acute devices. It is proposed that these transient pressure differences recorded by acute vs. chronic methods result from different physical properties of the capsule lining compared with that of the surrounding skin, in addition to a possible osmometer effect of the capsule lining. Recent data show that such methodological problems have resulted in great variation in the estimation of compliance of the interstitium and have overemphasized the importance of Pi as an edema-preventing mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

High dose vitamin C counteracts the negative interstitial fluid hydrostatic pressure and early edema generation in thermally injured rats.

BACKGROUND AND OBJECTIVE: edema formation after thermal injury is rapid and fulminant within the first hour after injury and increased microvascular permeability has been claimed to be the main responsible mechanism. An acute decrease in interstitial fluid hydrostatic pressure (P(if)) down to -150 mm Hg has recently been reported in dermal burns. This strong negative tissue pressure creates a 'suction' on the fluid in the capillaries. Furthermore, high dose vitamin C (VC) has been shown to reduce postburn edema and fluid requirements following major burn injuries. This led to the present study, aimed at investigating whether VC administered after thermal injury in rats, could attenuate the strongly negative P(if). Edema volume was measured by total tissue water content (TTW) and extravasation of albumin (Ealb). STUDY DESIGN: a prospective, open experimental study. MATERIALS AND METHODS: pentobarbital-anesthetized rats received either a full-thickness burn injury covering 10% of total body surface area, or a sham burn. The rats were given VC or equal volumes normal saline (NS) either before the burn, 5 or 30 min after the injury. VC (25 mg/ml in NS, osmolality 272 mOsm/l) was administered as a bolus (66 mg/kg) followed by infusion (33 mg/kg/h). The animals were divided into 7 groups (6 animals in each) according to the timing of VC/NS administration: (1) VC-preburn, (2) VC-5 min postburn, (3) VC-30 min postburn, (4) NS-preburn, (5) NS-5 min postburn, (6) NS-30 min postburn and (7) VC-pre sham burn group. All groups were duplicated for series I and II. MEASUREMENTS: in series I; P(if) was measured using a sharpened glass micropipette connected to a servo-controlled counter pressure system. Measurements were averaged in the following time periods: preburn, 5-20, 21-40, 41-60 and 61-90 min postburn. In series II; Ealb and TTW were measured in burned and non-burned skin by radio-labelled albumin and wet-dry weights, respectively. RESULTS: in the sham control group (VC-pre-sham burn), P(if) ranged between -1 and -2 mm Hg and did not change throughout the experimental period. In the NS group (placebo), P(if) fell to -46.8 +/- 10.1 (1 S.D.) mm Hg at 5-20 min after the injury and were -23.1 +/- 13.4 and -11.6 +/- 4.1 mm Hg at 21-40 and 41-60 min postburn. P(if) returned to preburn values at 61-90 min post injury. In the VC groups, there was a marked attenuation of the negative P(if) to average -10.1 +/- 11.8 mm Hg at 5-20 min, -2 +/- 1.7 and -0.6 +/- 1.2 mm Hg at 21-40 and 41-60 min after injury, respectively (all p < 0.01 compared to NS). TTW in burned skin of the NS-5 min groups was 3.12 +/- 0.28, VC5-min group was 2.57+/-0.69 and VC sham was 1.77+/-0.19 ml/g DW, respectively (p < 0.01 compared to sham control for all values). In all the VC-groups TTW values were higher than sham control and lower than in the corresponding NS-groups (p > 0.05 both ways). No statistical significant differences were found between Ealb-values in the VC- and NS-groups. CONCLUSION: high-dose vitamin C attenuates the development of strongly negative P(if) in burned dermis and reduces the edema as measured by TTW. No significant change in Ealb was found. Vitamin C was thus found to have potential beneficial effects on the acute postburn edema generation.

Lymphangiogenesis and lymphatic function in periodontal disease.

Lymphatic vessels return extravasated fluid, proteins, and cells back into the circulation and are important in immune cell trafficking. In the gingiva, lymphatic vessels are located in the lamina propria and travel over the external surface of the alveolar bone. The gingival lymphatics are important for fluid drainage, since lack of lymphatics has been shown to increase interstitial fluid pressure and fluid volume. Maintenance of gingival lymphatic vessels requires continuous signaling by the growth factors VEGF-C and -D via their receptor VEGFR-3. The growth factors are expressed in the gingival epithelium and also in immune cells in the lamina propria. VEGF-C seems to be crucial for lymphangiogenesis induced during periodontal disease development. The lymphatic vessels protect against periodontitis in mice, probably by clearing bacteria and bacterial products and by promoting humoral immune responses. Down-regulation of CCL21, a ligand important for dendritic cell migration, has been demonstrated in lymphatics from patients with periodontitis. High enzymatic activity in the gingiva of these patients may also contribute to impaired lymphatic function, due to the loss of structural components in the interstitium influencing lymphatic function. So far, knowledge is limited in this field because of the dearth of studies on the role of lymphatic vessels in periodontal disease.

High-salt diet increases hormonal sensitivity in skin pre-capillary resistance vessels.

AIMS: Recent data indicate that the skin of rats on a high-salt diet is able to accumulate Na(+) without commensurate water. This extrarenal mechanism of Na(+) homoeostasis could affect skin vasoregulation. We hypothesized that the major resistance vessel of rat skin, the pre-capillary arterioles, has increased vasoreactivity within the physiological range of circulating ANG II, a hormone relevant to salt-sensitive hypertension. METHODS AND RESULTS: Skin arterioles from skin and muscle were isolated using the agar-infusion technique. Vessels from rats fed high-salt and low-salt diet had similar lumen diameter and media area/lumen area ratio. Contractile sensitivity to ANG II was increased in skin vessels from high-salt vessels at all doses tested starting at 10(-10) m (P < 0.01). Pre-capillary arterioles from muscle displayed similar contractions to ANG II, independent of the diet. As ANG II and the renin-angiotensin system are strongly involved in salt conservation, we explored whether vasoreactivity for noradrenaline was increased as well, because this is a functionally unrelated hormone. At low doses, contractions were similar, but at 10(-5) and 10(-4) m, noradrenaline produced stronger contractions in skin vessels from high-salt compared with low-salt rats (P < 0.01). CONCLUSIONS: Our data demonstrate significantly increased hormonal vasoreactivity of skin vessels from rats on a high-salt diet, which could increase peripheral resistance in many situations and contribute to higher pressure in salt-sensitive hypertension. As vessels from adjacent muscle were unaffected, we raise the interesting possibility that increased vasoreactivity in the skin could be linked to osmotically inactive Na(+) accumulation.

Physiology and pathology of collagen receptors.

Just before the transition from pre-genomic to the post-genomic era, the two latest members of the mammalian integrin family were identified. These integrins, which were named alpha10beta1 and alpha11beta1, are both collagen receptors and are related. Rather than being twins, they can be regarded as close cousins. They both belong to the subfamily of integrins that contain an I-domain in the alpha subunit. This domain is also the part that endows these integrins with the capacity to bind the GFOGER sequence in collagens. In the current review, we summarize and update the current knowledge about the in vitro and in vivo functions of these integrins.

Microvascular pressures in DMBA-induced rat mammary tumours.

Microvascular pressures have been measured in the superficial layers of DMBA-induced mammary tumours in rats. The vessels were punctured with glass micropipettes (tip diameter 1-3 micron), and pressure measured with a modified Wiederhielm servo-controlled counter-pressure technique. After measurement the microvascular tree in some tumours was visualized by silicone rubber injections. The mean arteriolar pressures were 44.5 and 38.9 mmHg in arterioles with diameters of 46-80 and 15-45 micron respectively. Mean capillary pressure was 23.8 mmHg, while mean pressures of 13.3 and 9.7 mmHg were obtained in vennules of 15-45 and 46-100 micron respectively. The 'local perfusion pressure' (arteriolar pressure minus venous pressure, where the local venous pressure almost equals the tissue pressure) in central areas of tumours of more than 5.5 g can be calculated to be maximally one half of that in skin. This may well contribute to tumour hypoxia and subsequent necrosis.

Cornea fluid dynamics. II. Evidence for transport of radiolabelled albumin in rabbits by bulk flow.

Transport of radiolabelled albumin in vivo has been measured in cornea. In anaesthetized rabbits, a 1-10 nl mixture of either 125I- or 131I-labelled human serum albumin and fluorescinthiocarbamoyldextran was injected with micropipettes under guidance of a fluorescent microscope. The injection sites were a spot 3 mm from limbus and the cornea centre, and the sites were localized by a template fitting the cornea exactly. Four, 12, 20 and 30 hr after the injection, the rabbits were reanaesthetized, and enucleated after being killed with an overdose of anaesthetic. The bulbi were frozen, and dissection of cornea performed in the cold room using the template described above and a stereomicroscope. Numbered samples were obtained, and isotope distribution measured. In the experiments lasting for 20 hr, about 55% of the isotope was recovered, giving a transfer coefficient of 0.4-0.5 per day. A common pattern of isotope distribution was observed independent of duration of isotope equilibration; peripherally injected isotope moved preferentially in central direction, indicating that fluid is transported by bulk flow and diffusion from peripheral to central cornea. Centrally injected isotope moved symmetrically from the injection point, as expected from transport by diffusion alone. Data from experiments with isotope injection in the cornea centre allowed the calculation of a diffusion coefficient for albumin along cornea of 2.19 x 10(-7) cm2 sec-1.

Cornea fluid dynamics. I: measurement of hydrostatic and colloid osmotic pressure in rabbits.

Interstitial fluid pressure (Pi) has been measured in vivo in ocular tissues of rats and rabbits, and in vitro in corneas of cows and humans with micropipettes connected to a servocontrolled counterpressure system. The in vivo measurements were performed after anaesthesia and careful immobilization of the head. In all species Pi became gradually more negative from the limbus to the cornea centre; in rabbits the change was from -17.8 mmHg 0.5 mm centrally to the limbus to -42.7 mmHg in central cornea. Cornea and sclera interstitial fluid was isolated by centrifugation, and was used for analysis of colloid osmotic pressure (both tissues) and Na(+)-concentration and electrophoresis (cornea only). During low speed centrifugation (3000 rpm), a wet weight fraction of 2-4% was isolated from cornea, having a colloid osmotic pressure not significantly different from that of plasma (18.9 mmHg). Na+ analysis suggested that the isolated fluid did not derive from corneal cells. Electrophoresis showed a protein pattern in cornea fluid similar to that of plasma except for a band with MW corresponding to 39,000 found in cornea only. The present study demonstrates a pressure gradient from sclera to cornea, and along cornea from periphery to centre, and suggests that proteins in cornea fluid contribute significantly to swelling pressure.

Comparison of methods for measurement of interstitial fluid pressure in cat skin/subcutis and muscle.

Interstitial fluid pressure (IFP) in cats was measured with four techniques, i.e., hollow perforated and porous polyethylene capsules, wick in needle (WIN), and micropipettes. During control conditions, skin IFP of -1.5 +/- 0.4 (SD) mmHg (n = 53) was obtained with micropipettes, whereas pressures recorded in subcutis with perforated and porous capsules were -1.6 +/- 0.9 (n = 26) and -1.6 +/- 0.8 mmHg (n = 13), respectively. These were all significantly different from the -1.2 +/- 0.5 mmHg (n = 50) obtained in subcutis with WIN. In skeletal muscle, control IFP of -0.5, -0.5, and -1.1 mmHg was measured with micropipettes, WIN, and porous capsules, respectively. During peritoneal dialysis skin and muscle IFP recorded with micropipettes and WIN was reduced by 3-3.5 mmHg, whereas pressure in porous and perforated capsules fell by 7 and 10 mmHg, respectively. Intravenous Ringer infusion caused a marked transient rise in capsular pressures, not reflected by micropipettes and WIN, but similar pressures were obtained 210 min after infusion. In conclusion, all techniques reflect true IFP under steady-state conditions. Both capsules apparently act like osmometers in acute overhydration or dehydration and are, in addition, sensitive to pressure changes in local veins and are therefore not suitable for measurement of changes in IFP that take place in less than a few hours.

Subcutaneous interstitial fluid colloid osmotic pressure in dehydrated rats.

We collected interstitial fluid for measurement of colloid osmotic pressure (COPi) of normally hydrated and dehydrated rats with two methods: (1) saline-soaked nylon-wicks implanted in vivo for 1 h; and (2) the crossover method, i.e. titration with wicks pre-loaded with serial dilutions of rat plasma implanted post mortem for 15-20 min. All wicks were implanted in subcutis on the back. Dehydration was induced by injection of 40 mg furosemide followed by 24 h water deprivation. The saline-soaked wick method gave an average control COPi of 10.8 mmHg, 2-3 mmHg lower than the corresponding pressure obtained with the crossover method. This discrepancy between the methods increased to 10-11 mmHg in dehydrated animals, indicating that the saline-soaked wick method underestimates COPi even more during dehydration than during control conditions. The mean COPi of 22.8 mmHg (SD = 3.7, n = 9) obtained in dehydrated rats using the crossover method corresponds well with what is to be expected from the reduction in interstitial fluid volume. The present study suggests that the frequently used implantation period for saline-soaked wicks of 60 min should be prolonged to 90-120 min. It further shows that the rise in COPi is about 3 times more important than the fall in interstitial fluid hydrostatic pressure in restricting mobilization of interstitial fluid during dehydration.