Pflfigers Archiv
Pfltigers Arch. 381, 165-169 (1979)
EuropeanJournal of Physiology 9 by Springer-Verlag 1979
Renal Blood Flow after Bilateral Ureteral Ligation in the Rat Samaisukh Sophasan and Buarong Saraggananda PhysiologyDepartment, Faculty of Science, Mahidol University,Rama VI Road, Bangkok 4, Thailand
Abstract. Renal blood flow (RBF) in rat was measured' by using a noncannulating electromagnetic flowmeter. In the sham control rats, anesthetized with Inactin, R B F averaged 7 ml/min/g K W when arterial blood pressure was above 110 m m Hg. Autoregulation of RBF was observed when the arterial blood pressure was in the range of 1 1 0 - 1 5 0 m m Hg. Glomerular filtration rate (GFR), measured by polyfructosan clearance, averaged 1.08ml/min/g KW. In experimental rats with 24 h of bilateral ureteral ligation (BUL), R B F averaged 38 % of control value. During 1/2 - 3 h following release of the left ureteral occlusion, RBF increased to 60 % of control value. The autoregulatory ability of the damaged kidney was reduced during B U L and did not improve after releasing occlusion. During the postobstructive period arterial blood pressure remained stable. Thus, a high total renal vascular resistance was responsible for the depressed RBF. G F R in these rats averaged only 9 % of control value. The reduction in R B F alone does not explain the drastic reduction in G F R in this model of renal failure.
Key words: obstruction.
Kidney
blood
supply
-
Ureteral
Introduction
Functional defects after 24 h of bilateral ureteral ligation (BUL) in the rat have been studied by several investigators [4, 9 - 1 2 , 20]. After the release of the occlusion, glomerular filtration rate ( G F R ) was reduced to 1 0 - 2 0 % of control value [11, 12]. Several factors may contribute to this reduction in G F R . Leakage of inulin across the damaged kidney tubule has been suggested to account for 24 % of this reduction [12]. In the presence of near normal proximal tubular pressure [20], 28 % of the surface nephrons were not functioning as indicated by the absence of tubular fluid flow [11]. Moreover, the single nephron glomerular filtration rate ( S N G F R ) of the remaining nephrons was
3 4 - 4 0 % of the control value [11, 20]. These data suggest that renal blood flow (RBF) through the damaged kidney may be depressed. Measurements of RBF using p-aminohippuran clearance and extraction during the post-obstructive period were found to be conflicting. Yarger et al. [20] found renal plasma flow to be severely depressed while Jaenike [1l] observed a normal RBF. It is the purpose of this study to measure RBF in rats before and after the release of 24 h of bilateral ureteral ligation. Since R B F may vary with arterial blood pressure, especially after acute ureteral obstruction in dogs [8, 15], we also investigated the autoregulatory ability of the damaged kidney. Using a noncannulating electromagnetic flowmeter, RBF was measured in rats while mean arterial blood pressure (mABP) was varied stepwise by the method of Arendshorst et al. [2]. In sham-operated nondiuretic rats, anesthetized with Inactin, autoregulation of RBF was observed when arterial blood pressure was in the range of 1 1 0 - 1 5 0 m m Hg. Before and after the release of left ureteral occlusion after 24 h of BUL, RBF was respectively only 38 and 60 % of control values. The autoregulatory ability of the damaged kidney during both periods was not completely abolished.
Methods
A total of 14 male, Wistar rats weighing 150 - 300 g weredividedinto 2 groups, sham-control group (7 rats) and BUL experimental group (7 rats). Each animal was fasted overnightwhilewater was allowed ad libitum. On the followingday the rat was anesthetizedwith ether, and placed on a thermoregulatedboard to maintain its rectal temperature at approximately37~C. Through a mid line abdominal incision, small segments of both ureters were cleared from the surrounding tissue and silk threads were looped around them. In control rats, the silk threads were removed, but in experimental rats, both ureters were completely occluded by tying securely the silk threads. The abdominal incision was closedby suture of the muscleand skin separately. The animal was returned to its cage where food was withheld but water was allowed. On the followingday, the rat was anesthetized by intraperitoneal injection of Inactin, [sodium salt of ethyl-(1-methyl-propyl)-
0031-6768/79/0381/0165/$ 01. O0
166
Pflfigers Arch. 381 (1979)
malonylthiourea], 10 rag/100 g body weight (BW). It was then placed on a thermoregulated board. The rectal temperature, measured with a Yellow-springs telethermometer, was maintained close to 37~ C. Surgical procedures included a tracheotomy, and femoral artery and vein cannulations. The left kidney was exposed by an abdominal incision and was cleared from perirenal fat. The abdominal aorta above both renal arteries was cleared for application of a constrictor clamp. The left renal artery was carefully cleared of surrounding tissue for application of a flow probe. The left ureter was cannulated with PE50 tubing. Arterial blood pressure was monitored with a Statham P 23 AC pressure transducer connected to a Beckman Dynograph recorder. To estimate GFR, in the control group, polyfructosan (PFS, Laevosan, Linz, Austria), 10% in normal saline (0.9% NaC1) solution was continuously infused at the rate of 34 lal/min. Urine collection was not started until 1 h after the infusion had begun. Urine was collected for periods of 3 0 - 50 min under light mineral oil in preweighed vials. Urine volume was estimated by weighing. An arterial blood sample (0.2 ml) was taken at the mid-period of each urine collection, through the arterial cannula. The removed blood was replaced by an equal volume of 6 g/100 ml bovine serum albumin (Fraction V, Sigma Chem. Co.) in normal saline intra-arterially. Left renal blood flow was measured by the method of Arendshorst et al. [2]. Briefly, a small-diameter flow transducer (EP 401.5, 1.5 mm circumference lumen size) was positioned around the renal artery as close as possible to its origin from the aorta. Renal blood flow was registered by a square-wave electromagnetic flowmeter (Model 501 D, Carolina Medical Electronics, Inc.) and recorded on a Beckman recorder. Zero flow through the renal artery was determined at the beginning and the end of each experiment, by completely occluding the renal artery distal to the flow probe for 2 3 s. Baseline drift was negligible. The flowmeter system was calibrated periodically by infusing heparinized rat blood through an excised segment of a rat carotid artery immersed in normal saline. The coefficient of variation was about 15 % between calibration runs. Several factors, i.e., properties of the artery, sensitivity of the probe etc., may have caused these variations. In each experiment 2 to 4 urine samples were collected. At the end of each urine collection, an autoregulatory tracing of left RBF and ABP, Fig. 1, was recorded in the following way. Arterial blood pressure was raised by occluding both carotid arteries. Blood pressure below the constrictor clamp was then successively reduced from 150 to 50 mm Hg at a step of 10 mm Hg and maintained stable at each level for about 20 s. The degree of constriction of the clamp was determined by an electronic servosystem [17]. Then the constriction was removed and both carotid occlusions were released. Urine collection was resumed a few minutes after these procedures. In the experimental animal, before the release of the left ureteral occlusion, normal saline without polyfructose was infused intravenously at the rate of 17 pl/min, and an autoregulatory tracing was recorded. One half hour before the release a prime dose of polyfructosan was given intravenously, followed by continuous infusion of 2 % PFS in normal saline solution at the rate of 17 pl/min, in order not to overhydrate the animal. Only the left ureteral occlusion was released after 24 h of BUL. One half hour later 2 to 4 urine samples were collected as described. The experiment was terminated about 3 h afterward. Both kidneys were then removed, decapsulated and weighed. The concentration ofpolyfructosan in plasma and urine samples was analyzed by an anthrone method [6]. Renal blood flow was expressed in ml/m[n/g kidney weight (KW). Renal venous pressure was assumed to be constant and equal to 5 mm Hg. Renal vascular resistance (RVR) was calculated as follows: RVR =
mABP - 5 mm Hg RBF
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Pfltigers Arch. 381, 165-169 (1979)
EuropeanJournal of Physiology 9 by Springer-Verlag 1979
Renal Blood Flow after Bilateral Ureteral Ligation in the Rat Samaisukh Sophasan and Buarong Saraggananda PhysiologyDepartment, Faculty of Science, Mahidol University,Rama VI Road, Bangkok 4, Thailand
Abstract. Renal blood flow (RBF) in rat was measured' by using a noncannulating electromagnetic flowmeter. In the sham control rats, anesthetized with Inactin, R B F averaged 7 ml/min/g K W when arterial blood pressure was above 110 m m Hg. Autoregulation of RBF was observed when the arterial blood pressure was in the range of 1 1 0 - 1 5 0 m m Hg. Glomerular filtration rate (GFR), measured by polyfructosan clearance, averaged 1.08ml/min/g KW. In experimental rats with 24 h of bilateral ureteral ligation (BUL), R B F averaged 38 % of control value. During 1/2 - 3 h following release of the left ureteral occlusion, RBF increased to 60 % of control value. The autoregulatory ability of the damaged kidney was reduced during B U L and did not improve after releasing occlusion. During the postobstructive period arterial blood pressure remained stable. Thus, a high total renal vascular resistance was responsible for the depressed RBF. G F R in these rats averaged only 9 % of control value. The reduction in R B F alone does not explain the drastic reduction in G F R in this model of renal failure.
Key words: obstruction.
Kidney
blood
supply
-
Ureteral
Introduction
Functional defects after 24 h of bilateral ureteral ligation (BUL) in the rat have been studied by several investigators [4, 9 - 1 2 , 20]. After the release of the occlusion, glomerular filtration rate ( G F R ) was reduced to 1 0 - 2 0 % of control value [11, 12]. Several factors may contribute to this reduction in G F R . Leakage of inulin across the damaged kidney tubule has been suggested to account for 24 % of this reduction [12]. In the presence of near normal proximal tubular pressure [20], 28 % of the surface nephrons were not functioning as indicated by the absence of tubular fluid flow [11]. Moreover, the single nephron glomerular filtration rate ( S N G F R ) of the remaining nephrons was
3 4 - 4 0 % of the control value [11, 20]. These data suggest that renal blood flow (RBF) through the damaged kidney may be depressed. Measurements of RBF using p-aminohippuran clearance and extraction during the post-obstructive period were found to be conflicting. Yarger et al. [20] found renal plasma flow to be severely depressed while Jaenike [1l] observed a normal RBF. It is the purpose of this study to measure RBF in rats before and after the release of 24 h of bilateral ureteral ligation. Since R B F may vary with arterial blood pressure, especially after acute ureteral obstruction in dogs [8, 15], we also investigated the autoregulatory ability of the damaged kidney. Using a noncannulating electromagnetic flowmeter, RBF was measured in rats while mean arterial blood pressure (mABP) was varied stepwise by the method of Arendshorst et al. [2]. In sham-operated nondiuretic rats, anesthetized with Inactin, autoregulation of RBF was observed when arterial blood pressure was in the range of 1 1 0 - 1 5 0 m m Hg. Before and after the release of left ureteral occlusion after 24 h of BUL, RBF was respectively only 38 and 60 % of control values. The autoregulatory ability of the damaged kidney during both periods was not completely abolished.
Methods
A total of 14 male, Wistar rats weighing 150 - 300 g weredividedinto 2 groups, sham-control group (7 rats) and BUL experimental group (7 rats). Each animal was fasted overnightwhilewater was allowed ad libitum. On the followingday the rat was anesthetizedwith ether, and placed on a thermoregulatedboard to maintain its rectal temperature at approximately37~C. Through a mid line abdominal incision, small segments of both ureters were cleared from the surrounding tissue and silk threads were looped around them. In control rats, the silk threads were removed, but in experimental rats, both ureters were completely occluded by tying securely the silk threads. The abdominal incision was closedby suture of the muscleand skin separately. The animal was returned to its cage where food was withheld but water was allowed. On the followingday, the rat was anesthetized by intraperitoneal injection of Inactin, [sodium salt of ethyl-(1-methyl-propyl)-
0031-6768/79/0381/0165/$ 01. O0
166
Pflfigers Arch. 381 (1979)
malonylthiourea], 10 rag/100 g body weight (BW). It was then placed on a thermoregulated board. The rectal temperature, measured with a Yellow-springs telethermometer, was maintained close to 37~ C. Surgical procedures included a tracheotomy, and femoral artery and vein cannulations. The left kidney was exposed by an abdominal incision and was cleared from perirenal fat. The abdominal aorta above both renal arteries was cleared for application of a constrictor clamp. The left renal artery was carefully cleared of surrounding tissue for application of a flow probe. The left ureter was cannulated with PE50 tubing. Arterial blood pressure was monitored with a Statham P 23 AC pressure transducer connected to a Beckman Dynograph recorder. To estimate GFR, in the control group, polyfructosan (PFS, Laevosan, Linz, Austria), 10% in normal saline (0.9% NaC1) solution was continuously infused at the rate of 34 lal/min. Urine collection was not started until 1 h after the infusion had begun. Urine was collected for periods of 3 0 - 50 min under light mineral oil in preweighed vials. Urine volume was estimated by weighing. An arterial blood sample (0.2 ml) was taken at the mid-period of each urine collection, through the arterial cannula. The removed blood was replaced by an equal volume of 6 g/100 ml bovine serum albumin (Fraction V, Sigma Chem. Co.) in normal saline intra-arterially. Left renal blood flow was measured by the method of Arendshorst et al. [2]. Briefly, a small-diameter flow transducer (EP 401.5, 1.5 mm circumference lumen size) was positioned around the renal artery as close as possible to its origin from the aorta. Renal blood flow was registered by a square-wave electromagnetic flowmeter (Model 501 D, Carolina Medical Electronics, Inc.) and recorded on a Beckman recorder. Zero flow through the renal artery was determined at the beginning and the end of each experiment, by completely occluding the renal artery distal to the flow probe for 2 3 s. Baseline drift was negligible. The flowmeter system was calibrated periodically by infusing heparinized rat blood through an excised segment of a rat carotid artery immersed in normal saline. The coefficient of variation was about 15 % between calibration runs. Several factors, i.e., properties of the artery, sensitivity of the probe etc., may have caused these variations. In each experiment 2 to 4 urine samples were collected. At the end of each urine collection, an autoregulatory tracing of left RBF and ABP, Fig. 1, was recorded in the following way. Arterial blood pressure was raised by occluding both carotid arteries. Blood pressure below the constrictor clamp was then successively reduced from 150 to 50 mm Hg at a step of 10 mm Hg and maintained stable at each level for about 20 s. The degree of constriction of the clamp was determined by an electronic servosystem [17]. Then the constriction was removed and both carotid occlusions were released. Urine collection was resumed a few minutes after these procedures. In the experimental animal, before the release of the left ureteral occlusion, normal saline without polyfructose was infused intravenously at the rate of 17 pl/min, and an autoregulatory tracing was recorded. One half hour before the release a prime dose of polyfructosan was given intravenously, followed by continuous infusion of 2 % PFS in normal saline solution at the rate of 17 pl/min, in order not to overhydrate the animal. Only the left ureteral occlusion was released after 24 h of BUL. One half hour later 2 to 4 urine samples were collected as described. The experiment was terminated about 3 h afterward. Both kidneys were then removed, decapsulated and weighed. The concentration ofpolyfructosan in plasma and urine samples was analyzed by an anthrone method [6]. Renal blood flow was expressed in ml/m[n/g kidney weight (KW). Renal venous pressure was assumed to be constant and equal to 5 mm Hg. Renal vascular resistance (RVR) was calculated as follows: RVR =
mABP - 5 mm Hg RBF
0 .J u. 0
v
6
q
4
~
_5,8 5,6
2
0
hl eW
........
f
.............
. --:~---_.-]--.---
'150 re
741
t32
150 r if')
~ < --
.j ~"
-
90
~^82
-
,-- k,~, /
70re
