PROSTAGLANDINSLEUK~S ANDESSENTIALFATTYACDS Prostaglandms Leukotrienes and Esw~tral Fatty Acidr (1992) 46. 277-W 0 Longman Group UK Ltd 1992
Effect of Sodium and Chloride Depletion on Urinary Prostaglandin Fzcr Excretion in Potassium Loaded Rats M. Rathaus, J. Bernheim,
D. Katz, J. Green and E. Podjamy
Department of Nephrology, Meir Hospital, 44281 Kfar Saha, Israel and Sackler School of Medicine, Unil>ersity. Israel (Reprint requests to h4R)
Previous studies have shown that the urinary excretion of prostaglandin (PC) F,, is stimulated by potassium (K) loading. Because changes of sodium chloride (NaCI) intake also affect renal PG production, in this study we investigated the interaction between the effect of K and that of concomitant reduction of Na and Cl intake. The urinary excretion of PGFzu and PGE, was measured in 12 groups of female rats on normal, high or low K intake. Na and Cl intake were adjusted so that rats had normal intake (controls, C), were selectively Cl depleted (CD), selectively Na depleted (ND) or Na and Cl depleted (NCD). In rats with normal K intake, urinary PGF,, was not modified by changes of Na or Cl intake, whereas PGE, was increased in by Cl depletion (in both NCD ar CD groups). Potassium chloride loading increased urinary PGF,,and selective Na depletion (ND group) induced a further increase. On the other hand, PGF,, was not stimulated when K load was associated with Cl depletion. Urine PGF,, was directly correlated with plasma aldosterone and urinary kallikrein. Urinary PGEz did not change with K-loading. The results suggest that PGF,, participates in the renal adaptation to KCl-loading but not when K is accompanied by non-Cl anions.
INTRODUCTION A considerable number of studies has addressed the influence of electrolyte intake on the renal synthesis of prostaglandins (PGs). Sodium chloride (NaCl) loading (1) or deprivation (2) elicit changes PG production. This, taken together with the stimulation of PG synthesis by some hormones (3) and the influence of PGs on tubular transport (4). suggests that these substances play a definite role in renal NaCl handling. Variations of potassium (K) intake also influence renal PG synthesis, but the results of different studies have been conflicting. K depletion increased the urinary excretion of PGE, (5, 6) and its synthesis in vitro (7), and this has been proposed as the mechanism of the concentrating defect of K depletion (6). The effects of K loading have been the object of few studies. The urinary excretion of PGF,, was increased in rats after K- loading (8, 9). Potassium loading stimulated the glomerular synthesis of PGE, and induced a relative increase of PGF,, vs PGE, in medullary and papillary slices ( 10). Recently, we observed that medullary PGF,,, synthesis and its urinary excretion are stimulated by KC1 but not by a comparable load of other K salts (Rathaus et al. unpublished data). Because the role Date received 12 November Date accepted 73 December
1YY I I YY I
of PGF,, in renal physiology is presently unknown (11). the meaning of its relationship with K and Cl balance has not been elucidated. To our knowledge, the effects of Cl on renal PG synthesis have not been studied, nor could we find studies addressing the issue of concomitant changes of electrolyte intake on it. We therefore designed the present investigations to measure the urinary excretion of PGF,, and PGE, during combined changes of Na and Cl intake, and after K loading.
MATERIALS AND METHODS Protocols Female Charles-River rats, weighing between 159 and 270 g (mean 218 g) were studied. All rats received the same basic food (Assia Maabaroth. Israel) containing: sodium (Na): 3; potassium (K): 13: chloride (Cl): 35; magnesium (Mg): 13; calcium: 1030; phosphorus: 7.50 mg/lOO g. MgSO, (770 mg/lOO g) was added. Different combinations of electrolyte intake were obtained as outlined in Table 1. Potassium intake was either normal (NK) or high (HK). In addition, rats had normal NaCl intake (controls, C) , selective chloride depletion (CD), selective Na depletion (ND) or NaCl depletion (NCD). The 8 groups consisted of: C-NK (n = 28). CDNK (n = 12). ND-HK (n = 8) and NCD-NK (n = 12); and
and Essential Fatty Acids
Table 1 Electrolyte content of the different diets used (g/kg). In all protocols, the same special food was used, containing virtually no Na, K or Cl. MgS04 was added to all groups (7.7 g/kg). Electrolytes were added to the food and rats drank distilled water. Each diet was given for 15 days Diet
8.8 14.0 _
Normal K NaCl KC1 K-citrate High K NaCl KC1 KzSO, KH,PO, K-citrate Na-citrate
8.8 112.0 _ _ _
_ 40.0 40.0 80.0 14.7
_ 112.0 _ _ _
according to the method described in detail by Bertani et al (13). Urinary kallikrein was measured as previously described by an esterolytic assay using CBS 23.41 (2 AcOH, H-D-Val-CHA-Arg-pNA) as substrate (Diagnostica Stago, France) (12). Plasma aldosterone was measured by RIA using a commercial kit ( 14).
_ 40.0 40.0 80.0
C = control, CD = selective Cl depletion, ND = selective Na depletion, NCD = NaCl deplation
C-HK (n = 15), CD-HK (n = lo), ND-HK (n = 5) and NCD-HK (n = 5). Rats received the chosen diet for 15 days. Body weight was measured before and at the end of the diet period. Thereafter rats were housed for 24 h in individual metabolic cages to obtain urine collections. On the following day, the animals were anesthetized with penthotal(50 mg/kg i.p.) and arterial blood was obtained after laparotomy and cannulation of the abdominal aorta.
Laboratory methods K and Na were measured by flame photometry. Cl was measured with a Cl titrator (Radiometer, Copenhagen: model CM TlO). Blood pH and bicarbonate concentration were measured with an acid base analyzer (Radiometer, Copenhagen; model ABL3). Urinary PGs were measured by radioimmunoassay (RIA) as reported previously (12) after silicic acid column chromatography
Materials Kallikrein (porcine pancreas) was from Sigma. Aprotinin (Trasylol) was from Bayer. [3H]PGE, (30-50 Ci/mmol) and [3H]PGF,, (30-50 Ci/mmol) were from Amersham, UK. Antisera for PGE? and PGF?, were from Bio-Yeda, Rehovoth, Israel.
Statistics Results are expressed as mean f SEM. Differences between groups were studied by one-way analysis of variance and multiple comparisons using the method of protected least significant difference (LSD).
RESULTS Animals with normal normal K intake Body weight, fluid intake and urinary output changed only sligthly and not significantly with the different changes in Na and Cl intake. Urine Na was low, as expected, in the Na depleted groups. The Cl depleted group had urinary Na excretion lower than controls, but this was not significant. Urine K and Cl excretion varied according to the protocols (Table 2). Serum Na was lower in the NCD. ND and CD groups than in controls, but remained normal. Serum K and Cl were in the normal range in all groups. Opposite changes of acidbase balance were observed with Cl or Na depletion: CD
Table 2 Balance and urinary electrolytes
Change of body weight (%) Normal K High K Fluid intake (ml/day) Normal K High K Urine volume (ml/day) Normal K High K Urine Na (mmol/day) Normal K High K Urine K (mmol/day) Normal K High K Urine Cl (mmol/day) Normal K High K
a.7 + 2.0 +I.0 * 1.0
-3.9 f 0.7 -0.6 f 1.2
Xl.9 f 0.8 -8.9 + 1.7”.b
-4.3 f 1.4 4.9 + 3.8
20.0 f 1.0 44.0 * 3.0d
18.0 f 4.0 38.0 + 2.0d
17.0 f 1.0 37.0 f 6.0d
12.0+ 1.0” 29.0 f 5.0 a.d
14.0 * 1.0 36.0 f 3.0”
7.0 f 1.0 27.0 + 2.0”.d
6.0 f 1.0 29.0 + 5.0”.d
4.0 * 1.0 19.0 * 4.0”.”
1.1 + 0.2 1.2 * 0.1
0.5 zho.1 1.4 f 0.2d
1.5 * 0.2 10.8 + O.gd
1.2 f 0.3 13.5 * 0.9”,d
2.5 ?c 0.3 10.9 f 0.9d
0.1 kO.1” 0.1 fO.1”
0.1 * 0.1a.d 0.2 * O.I”JJ 2.3 f 0. I 11.7f 1.3d 2.3 ? 0.1 11.5 * 1.4d.h
0.1 * O.l”.b 0.1 + 0.1 ah 0.8 + 0.1 12.2 f 2.1” 0.1 f O.l”,’ 0.1 * 0.1”
C = control, CD = selective Cl depletion, ND = selective Na depletion, NCD = NaCl depletion. Statistical analysis was done with one-way ANOVA and the LSD procedure: p values of