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Colloid osmotic pressure in interstitial fluid and lymph from rabbit subcutaneous tissue
MICROVASCULAR
Colloid
RESEARCH
Osmotic
21, 390-392 (1981)
Pressure in Interstitial Rabbit Subcutaneous HANS OLAV
Fluid and Lymph from Tissue
FADNES’
Institute of Physiology, University of Bergen, 5000 Bergen, Norway Received December 3, 1980
Interstitial fluid collected from rat subcutaneous tissue by a wick method shows a protein concentration estimated at about 50% of plasma concentration (Aukland and Fadnes, 1973). This concentration represents a colloid osmotic pressure (COP) of 10 mm Hg (Johnsen, 1974). With this method the importance of the interstitial fluid COP in transcapillary fluid balance and edema prevention in experimental hypoproteinemia (Fadnes, 1975) and increased venous pressure (Fadnes, 1976) is demonstrated. In earlier articles (Fadnes and Aukland, 1977; Fadnes et al., 1977) the reliability of the wick method for measuring interstitial fluid colloid osmotic and hydrostatic pressure was discussed. We concluded that if sufficient protein is taken up by the implanted wick, the wick fluid of 9- 10 mm Hg and wick hydrostatic pressure of - 1 mm Hg reflects the condition in normal interstitial fluid. If less protein is available, the wick fluid COP is less than interstitial fluid COP. This results in water absorption from the wick and more negative wick pressure. These wicks look stiff and dry and show a lower fluid content than control wicks. These observations suggest that the implanted wick can behave as a colloid osmometer. In an attempt to examine further the reliability of the wick method for transcapillary fluid studies, we have compared the COP in wick fluid and local lymph in control conditions and under increased venous pressure. Eleven rabbits (body wt 2.7-4.2 kg) are anesthetized with pentobarbital (20-25 mg/kg iv). In six of the rabbits the venous pressure of the hindlimbs is increased by ligating the caval vein and both iliac veins the day before testing. Interstitial fluid is collected from subcutaneous tissue on the hindlimb by two nylon wicks (each 3-4 cm long and 1 mm thick) implanted for 1 hr (Fadnes and Aukland, 1977). After implantation the wicks are transferred to tubes containing liquid paraffin and centrifuged to isolate the wick fluid (Johnsen, 1974), usually about 10 ~1. A skin incision is then made on the lateral aspects of the leg, distal to the knee. A lymph vessel, superficial to the muscle fascia and distal to the popliteal node is cannulated with a steel cannula (o.d. 0.4 mm) connected to a PE 10 catheter. To prevent evaporation, lymph is sampled under liquid paraffin. About lo-20 ,ul of lymph is ’ Present address: Medical Department, 9012 Regionsykehuset i Tromso, Norway. 390 00262862/81/030390-03$02.WO Copyright @I 1981 by Academic Press, Inc. AU rights of reproduction in any form reserved. Printed in U.S.A.
BRIEF
391
COMMUNICATIONS
wick
0
4
8
12 venous
16 0 4 pressurqmm
fluid
8 Hg
12
16
FIG. 1. The effect of increased venous pressure on the colloid osmotic pressure (COP) in lymph (left panel) and in wick fluid (right panel).
collected in the course of 2-3 min by gentle massage over the lymph vessel. The COP in plasma, wick fluid, and lymph is measured on a membrane osmometer constructed in this laboratory (Aukland and Johnsen, 1974). The femoral venous pressure is measured by cannulating a superficial branch in the groin. In control animals (five measurements on five rabbits) the COP in wick fluid was 6.5 mm Hg (range: 5.5-7.5) and in lymph, 6.8 mm Hg (range: 5.5-8.0), the difference being statistically not significant (P > 0.05, Wilcoxon paired test). This figure is close to COP calculated from rabbit subcutaneous interstitial fluid protein concentration sampled by a micropuncture technique (Haljamae and Freden, 1970) and that found in capsular fluid from implanted capsules in the same tissue (Taylor and Gibson, 1975). Plasma COP average is 19.1 mm Hg (SD = 2.5). When the venous pressure is increased by vein ligatures, a fall in COP is observed both in lymph and wick fluid (Fig. 1). At venous pressure of 12-16 mm Hg, COP in wick fluid and lymph is reduced to 2-4 mm Hg, similar to that observed in rat subcutaneous tissue (Fadnes, 1976). Corresponding COPS in wick fluid and in lymph showed fairly good correlation (r = 0.79), and are not significantly different (P > 0.05, Wilcoxon paired test) (Fig. 2). 8-
.
. . .
6 -
.
I” E n0
. .
.
4-
cE 02
. .
.
/
2 -
COPL (rs0.79) = 1.02 COPw
.
.
0 0
2 wick
4 fluid
- 0.46
1 8
6 COP,mm
Hg
2. Corresponding colloid osmotic pressures (COP) in wick fluid and in lymph. The solid line represents the calculated regression line. FIG.
392
BRIEF COMMUNICATIONS
If the COPS in interstitial fluid and lymph are equal, the present results support our earlier conclusion that wick fluid represents interstitial fluid COP. Alternatively, the COP both in wick fluid and lymph could be higher than that of undisturbed interstitial fluid, for example in lymph because of a concentrating process in the lymphatics. If so, additional assumptions would be needed to explain how COPS of these fluids vary proportionately over a wide range. The most straight forward conclusion is, therefore, that both wick fluid and lymph have COPS similar to that of interstitial fluid. REFERENCES AUKLAND, K., AND FADNES, H. 0. (1973). Protein concentration of interstitial fluid collected from rat
skin by a wick method. Acta Physiol. &and. 88, 350-358. K., AND JOHNSEN, H. M. (1974). A colloid osmometer for small fluid samples. Acta Physiol. &and. 90, 485-490. FADNES, H. 0. (1975). Protein concentration and hydrostatic pressure in subcutaneous tissue of rats in hypoproteinemia. Stand. J. Clin. Lab. Invest. 35, 441-446. FADNES, H. 0. (1976). Effect of increased venous pressure on the hydrostatic and colloid osmotic pressure in subcutaneous interstitial fluid in rats: Edema preventing mechanisms. Stand. J. Clin. Lab. Invest. 36, 371-377. FADNES, H. O., AND AUKLAND, K. (1977). Protein concentration and colloid osmotic pressure of interstitial fluid collected by the wick technique. Analysis and evaluation of the method. Microvasc. Res. 14, 11-25. FADNES, H. O., REED, R. K., AND AUKLAND, K. (1977). Interstitial fluid pressure in rats measured with a modified wick technique. Microvasc. Res. 14, 27-36. HALJAMAE, H., AND FREDEN, H. (1970). Comparative analysis of the protein content of local subcutaneous tissue fluid and plasma. Microvasc. Res. 2, 163-171. JOHNSEN,H. M. (1974). Measurement of colloid osmotic pressure of interstitial fluid. Acta Physiol. Stand. 91, 142-144. TAYLOR, A. E., AND GIBSON,W. H. (1975). Concentrating ability of the lymphatic vessels. Lymphology 8, 43-49. AUKLAND,
Colloid
RESEARCH
Osmotic
21, 390-392 (1981)
Pressure in Interstitial Rabbit Subcutaneous HANS OLAV
Fluid and Lymph from Tissue
FADNES’
Institute of Physiology, University of Bergen, 5000 Bergen, Norway Received December 3, 1980
Interstitial fluid collected from rat subcutaneous tissue by a wick method shows a protein concentration estimated at about 50% of plasma concentration (Aukland and Fadnes, 1973). This concentration represents a colloid osmotic pressure (COP) of 10 mm Hg (Johnsen, 1974). With this method the importance of the interstitial fluid COP in transcapillary fluid balance and edema prevention in experimental hypoproteinemia (Fadnes, 1975) and increased venous pressure (Fadnes, 1976) is demonstrated. In earlier articles (Fadnes and Aukland, 1977; Fadnes et al., 1977) the reliability of the wick method for measuring interstitial fluid colloid osmotic and hydrostatic pressure was discussed. We concluded that if sufficient protein is taken up by the implanted wick, the wick fluid of 9- 10 mm Hg and wick hydrostatic pressure of - 1 mm Hg reflects the condition in normal interstitial fluid. If less protein is available, the wick fluid COP is less than interstitial fluid COP. This results in water absorption from the wick and more negative wick pressure. These wicks look stiff and dry and show a lower fluid content than control wicks. These observations suggest that the implanted wick can behave as a colloid osmometer. In an attempt to examine further the reliability of the wick method for transcapillary fluid studies, we have compared the COP in wick fluid and local lymph in control conditions and under increased venous pressure. Eleven rabbits (body wt 2.7-4.2 kg) are anesthetized with pentobarbital (20-25 mg/kg iv). In six of the rabbits the venous pressure of the hindlimbs is increased by ligating the caval vein and both iliac veins the day before testing. Interstitial fluid is collected from subcutaneous tissue on the hindlimb by two nylon wicks (each 3-4 cm long and 1 mm thick) implanted for 1 hr (Fadnes and Aukland, 1977). After implantation the wicks are transferred to tubes containing liquid paraffin and centrifuged to isolate the wick fluid (Johnsen, 1974), usually about 10 ~1. A skin incision is then made on the lateral aspects of the leg, distal to the knee. A lymph vessel, superficial to the muscle fascia and distal to the popliteal node is cannulated with a steel cannula (o.d. 0.4 mm) connected to a PE 10 catheter. To prevent evaporation, lymph is sampled under liquid paraffin. About lo-20 ,ul of lymph is ’ Present address: Medical Department, 9012 Regionsykehuset i Tromso, Norway. 390 00262862/81/030390-03$02.WO Copyright @I 1981 by Academic Press, Inc. AU rights of reproduction in any form reserved. Printed in U.S.A.
BRIEF
391
COMMUNICATIONS
wick
0
4
8
12 venous
16 0 4 pressurqmm
fluid
8 Hg
12
16
FIG. 1. The effect of increased venous pressure on the colloid osmotic pressure (COP) in lymph (left panel) and in wick fluid (right panel).
collected in the course of 2-3 min by gentle massage over the lymph vessel. The COP in plasma, wick fluid, and lymph is measured on a membrane osmometer constructed in this laboratory (Aukland and Johnsen, 1974). The femoral venous pressure is measured by cannulating a superficial branch in the groin. In control animals (five measurements on five rabbits) the COP in wick fluid was 6.5 mm Hg (range: 5.5-7.5) and in lymph, 6.8 mm Hg (range: 5.5-8.0), the difference being statistically not significant (P > 0.05, Wilcoxon paired test). This figure is close to COP calculated from rabbit subcutaneous interstitial fluid protein concentration sampled by a micropuncture technique (Haljamae and Freden, 1970) and that found in capsular fluid from implanted capsules in the same tissue (Taylor and Gibson, 1975). Plasma COP average is 19.1 mm Hg (SD = 2.5). When the venous pressure is increased by vein ligatures, a fall in COP is observed both in lymph and wick fluid (Fig. 1). At venous pressure of 12-16 mm Hg, COP in wick fluid and lymph is reduced to 2-4 mm Hg, similar to that observed in rat subcutaneous tissue (Fadnes, 1976). Corresponding COPS in wick fluid and in lymph showed fairly good correlation (r = 0.79), and are not significantly different (P > 0.05, Wilcoxon paired test) (Fig. 2). 8-
.
. . .
6 -
.
I” E n0
. .
.
4-
cE 02
. .
.
/
2 -
COPL (rs0.79) = 1.02 COPw
.
.
0 0
2 wick
4 fluid
- 0.46
1 8
6 COP,mm
Hg
2. Corresponding colloid osmotic pressures (COP) in wick fluid and in lymph. The solid line represents the calculated regression line. FIG.
392
BRIEF COMMUNICATIONS
If the COPS in interstitial fluid and lymph are equal, the present results support our earlier conclusion that wick fluid represents interstitial fluid COP. Alternatively, the COP both in wick fluid and lymph could be higher than that of undisturbed interstitial fluid, for example in lymph because of a concentrating process in the lymphatics. If so, additional assumptions would be needed to explain how COPS of these fluids vary proportionately over a wide range. The most straight forward conclusion is, therefore, that both wick fluid and lymph have COPS similar to that of interstitial fluid. REFERENCES AUKLAND, K., AND FADNES, H. 0. (1973). Protein concentration of interstitial fluid collected from rat
skin by a wick method. Acta Physiol. &and. 88, 350-358. K., AND JOHNSEN, H. M. (1974). A colloid osmometer for small fluid samples. Acta Physiol. &and. 90, 485-490. FADNES, H. 0. (1975). Protein concentration and hydrostatic pressure in subcutaneous tissue of rats in hypoproteinemia. Stand. J. Clin. Lab. Invest. 35, 441-446. FADNES, H. 0. (1976). Effect of increased venous pressure on the hydrostatic and colloid osmotic pressure in subcutaneous interstitial fluid in rats: Edema preventing mechanisms. Stand. J. Clin. Lab. Invest. 36, 371-377. FADNES, H. O., AND AUKLAND, K. (1977). Protein concentration and colloid osmotic pressure of interstitial fluid collected by the wick technique. Analysis and evaluation of the method. Microvasc. Res. 14, 11-25. FADNES, H. O., REED, R. K., AND AUKLAND, K. (1977). Interstitial fluid pressure in rats measured with a modified wick technique. Microvasc. Res. 14, 27-36. HALJAMAE, H., AND FREDEN, H. (1970). Comparative analysis of the protein content of local subcutaneous tissue fluid and plasma. Microvasc. Res. 2, 163-171. JOHNSEN,H. M. (1974). Measurement of colloid osmotic pressure of interstitial fluid. Acta Physiol. Stand. 91, 142-144. TAYLOR, A. E., AND GIBSON,W. H. (1975). Concentrating ability of the lymphatic vessels. Lymphology 8, 43-49. AUKLAND,