Toxicology, 3 (1975) 29--32 © Elsevier/North-Holland, Amsterdam -- Printed in The Netherlands
THE INFLUENCE OF DIETARY CHLORIDE ON BROMIDE EXCRETION IN THE RAT
A.G. RAUWS and M.J. VAN LOGTEN
Laboratories o f Pharmacology and Toxicology, National Institute o f Public Health, P.O. Box 1, Bilthoven (The Netherlands) (Received April 8th, 1974) (Accepted April 22nd, 1974)
SUMMARY
The influence of graded doses of chloride in drinking water on the excretion rate of bromide was investigated in the rat. Bromide half-life varies from 2.5 days during high chloride intake to 25 days during low chloride intake. It is concluded that chloride will have a marked influence on the no-effect level of bromide.
INTRODUCTION
Bromide ions, after absorption into an organism, replace an equivalent a m o u n t of chloride ions in the extracellular fluid. Just like chloride, bromide is excreted predominantly by the kidneys. The greater part of both halogen ions is reabsorbed in the kidney tubules after glomerular filtration. Bromide is reabsorbed to a greater extent than chloride [ 1 ]. As a result bromide has a biological half-life in the order of days. If chloride intake is increased, bromide reabsorption decreases, due to competition by chloride: consequently the excretion rate of bromide increases [2]. In this investigation the relation between bromide half-life and chloride intake is studied because of its implications for the toxicity of bromide when administered daily. MATERIAL AND METHODS
Animals Female Wistar-SPF rats of approx. 120 g were used. They were housed under conventional conditions. After 3 weeks, during which bromide was administered, their mean weight was approximately 160 g; two weeks later -at the end of the experiment -- it was approximately 180 g.
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Diet Muracon SSP-Tox, Muracon SSP-Tox-Br with 2000 ppm sodium bromide a d d e d , a n d M u r a c o n S S P - T o x - Z (salt-free, n o salt m i x t u r e a d d e d ) w e r e obt a i n e d f r o m T r o u w a n d Co., P u t t e n , T h e N e t h e r l a n d s . T h e c h l o r i d e c o n t e n t s o f M u r a c o n S S P - T o x a n d M u r a c o n S S P - T o x - Z w e r e 8.25 m g / g a n d 0.95 m g / g respectively. T h e f o o d was s u p p l i e d ad libitum. T a p w a t e r or s o d i u m c h l o r i d e s o l u t i o n s c o n t a i n i n g 0.02, 0.05 or 0.15 mole/1 w e r e s u p p l i e d ad libitum. Design (1) Five g r o u p s o f 6 rats received M u r a c o n S S P - T o x - B r f o r 3 weeks, until t h e i r p l a s m a b r o m i d e level was a p p r o x i m a t e l y 10 mmole/1. (2) T h e n t h e f o l l o w i n g r e g i m e n s o f f o o d a n d d r i n k i n g w a t e r w e r e instituted: g r o u p 1: M u r a c o n S S P - T o x + t a p w a t e r ; g r o u p 2: M u r a c o n S S P - T o x - Z + t a p w a t e r ; g r o u p 3: M u r a c o n S S P - T o x - Z + 0.02 mole/1 NaC1; g r o u p 4: Murac o n S S P - T o x - Z + 0.05 mole/1 NaC1; g r o u p 5: M u r a c o n S S P - T o x - Z + 0.15 mole/1 NaC1. (3) 1, 2, 3, 4, 9, a n d 14 d a y s a f t e r i n s t i t u t i o n o f t h e s e r e g i m e n s p l a s m a b r o m i d e was d e t e r m i n e d in all animals. F r o m t h e results m e a n half-lives p e r group were calculated. Bromide determinations B r o m i d e was d e t e r m i n e d f o l l o w i n g t h e m o d i f i e d m e t h o d o f H u n t e r [ 3 ] , as d e s c r i b e d b y V a n L o g t e n et al. [ 4 ] . RESULTS T h e m e a n p l a s m a b r o m i d e c o n c e n t r a t i o n at t h e b e g i n n i n g o f t h e b r o m i d e a d m i n i s t r a t i o n was 0.55 + 0 . 4 6 mmole/1. A f t e r t h r e e w e e k s o f b r o m i d e a d m i n i s t r a t i o n it was 8.57 + 0.57 mmole/1. T h e resulting biological half-lives, t o g e t h e r w i t h t h e c h l o r i d e i n t a k e , are s h o w n in T a b l e I. T h e c h l o r i d e i n t a k e was e s t i m a t e d o n t h e a s s u m p t i o n t h a t TABLE I INFLUENCE OF CHLORIDE INTAKE ON BROMIDE HALF-LIFE Group
1
2
3
4
5
Diet Drinking water
normal tap water
"salt free . . . . tap water
salt free . . . . 0.02 mole/1 NaC1 12.0 28
salt free . . . . 0.05 mole/1 NaCl 6.9 55
salt free" 0.15 mole/1 NaC1 2.5 144
Half-life (days) 3.5 Chloride intake a 91 (mg/day)
25.1 10
a A daily intake per rat of 11 g food and 25 ml drinking water is assumed.
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I/2 bromide (days)
chloride intake (rag/day)
Fig. 1. Relation between chloride intake and bromide half-life. The dotted lines refer to the normal situation: rats drinking tap water and feeding on normal Muracon SSP-Tox ad libitum.
the animals had an average f o o d intake of 11 g and drank on average 25 ml per day. It can be seen t hat the shortest and the longest half-life differ by a factor o f 10. The relation between bot h variables is shown in Fig. 1. T h e y are a p p r o x i m a t e l y inversely proportional. DISCUSSION When a substance is repeatedly administered to an organism, a m ore or less co n s tan t c o n c e n t r a t i o n of it will build up in the tissue fluids. The mean plasma level at steady state is given by the expression: D . tv, - 1 . 4 4 - -D . t w C~-ln 2"V'T V-7 in which D is the absorbed dose, tl/2 the biological half-life, V the apparent distribution volume and T the interval between administrations [ 5 ] . If D, V and T remain constant, C~ is directly p r o p o r t i o n a l to tl/,. Administration of a substance by adm i xt ur e to f ood complicates the situation, w i t h o u t changing, however, the relation of Ca to tl/2, provided D and T do n o t fluctuate unduly. A difference in half-life by a factor 10 thus means a difference by a factor 10 in stationary plasma c o n c e n t r a t i o n . If exchange bet w een plasma and the target organ is rapid, the same applies to the c o n c e n t r a t i o n in the target organ. A no-effect level is empirically determined~ In principle, however, it is a derived q u ant i t y: derived from the highest non-toxic steady state level of the
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substance under consideration in the target organ. The latter level -- in the case of bromide -- is greatly influenced by the chloride intake. Consequently the no-effect level of bromide will be comparably affected by this intake. S5remark [6] determined the chloride half-life in a group of volunteers under normal circumstances as regards activity and food intake. He found a half-life of 12 -+ 3 days. It is to be expected that diminished salt intake will cause prolongation of this half-life. If acceptable daffy intakes are to be established, the influence of a salt-free diet on bromide half-life in m a n w i l l have to be taken into account. ACKNOWLEDGEMENTS
The help of Dr. H.G. Verschuuren in obtaining the special diets is gratefully acknowledged. Dr. H.A.M.C. Vaessen kindly provided the chloride analyses in the diets. Mr. P.W.M. Zeylmans carefully carried out long series of bromide analyses. REFERENCES 1 2 3 4 5 6
R.L. Wolf and G.S. Eadie, Am. J. Physiol., 163 (1950) 436. A. Langley Czerwinski, J. Pharm. Sci., 47 (1958) 467. G. Hunter, Biochem. J., 60 (1955) 261. M.J. van Logten, M. Wolthuis, A.G. Rauws and R. Kroes, Toxicology, 1 (1973) 321. J.G. Wagner, J. Clin. Pharmacol., 7 (1967) 84. R. SSremark, Acta Physiol. Scand., 50 (1960) 306.
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THE INFLUENCE OF DIETARY CHLORIDE ON BROMIDE EXCRETION IN THE RAT
A.G. RAUWS and M.J. VAN LOGTEN
Laboratories o f Pharmacology and Toxicology, National Institute o f Public Health, P.O. Box 1, Bilthoven (The Netherlands) (Received April 8th, 1974) (Accepted April 22nd, 1974)
SUMMARY
The influence of graded doses of chloride in drinking water on the excretion rate of bromide was investigated in the rat. Bromide half-life varies from 2.5 days during high chloride intake to 25 days during low chloride intake. It is concluded that chloride will have a marked influence on the no-effect level of bromide.
INTRODUCTION
Bromide ions, after absorption into an organism, replace an equivalent a m o u n t of chloride ions in the extracellular fluid. Just like chloride, bromide is excreted predominantly by the kidneys. The greater part of both halogen ions is reabsorbed in the kidney tubules after glomerular filtration. Bromide is reabsorbed to a greater extent than chloride [ 1 ]. As a result bromide has a biological half-life in the order of days. If chloride intake is increased, bromide reabsorption decreases, due to competition by chloride: consequently the excretion rate of bromide increases [2]. In this investigation the relation between bromide half-life and chloride intake is studied because of its implications for the toxicity of bromide when administered daily. MATERIAL AND METHODS
Animals Female Wistar-SPF rats of approx. 120 g were used. They were housed under conventional conditions. After 3 weeks, during which bromide was administered, their mean weight was approximately 160 g; two weeks later -at the end of the experiment -- it was approximately 180 g.
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Diet Muracon SSP-Tox, Muracon SSP-Tox-Br with 2000 ppm sodium bromide a d d e d , a n d M u r a c o n S S P - T o x - Z (salt-free, n o salt m i x t u r e a d d e d ) w e r e obt a i n e d f r o m T r o u w a n d Co., P u t t e n , T h e N e t h e r l a n d s . T h e c h l o r i d e c o n t e n t s o f M u r a c o n S S P - T o x a n d M u r a c o n S S P - T o x - Z w e r e 8.25 m g / g a n d 0.95 m g / g respectively. T h e f o o d was s u p p l i e d ad libitum. T a p w a t e r or s o d i u m c h l o r i d e s o l u t i o n s c o n t a i n i n g 0.02, 0.05 or 0.15 mole/1 w e r e s u p p l i e d ad libitum. Design (1) Five g r o u p s o f 6 rats received M u r a c o n S S P - T o x - B r f o r 3 weeks, until t h e i r p l a s m a b r o m i d e level was a p p r o x i m a t e l y 10 mmole/1. (2) T h e n t h e f o l l o w i n g r e g i m e n s o f f o o d a n d d r i n k i n g w a t e r w e r e instituted: g r o u p 1: M u r a c o n S S P - T o x + t a p w a t e r ; g r o u p 2: M u r a c o n S S P - T o x - Z + t a p w a t e r ; g r o u p 3: M u r a c o n S S P - T o x - Z + 0.02 mole/1 NaC1; g r o u p 4: Murac o n S S P - T o x - Z + 0.05 mole/1 NaC1; g r o u p 5: M u r a c o n S S P - T o x - Z + 0.15 mole/1 NaC1. (3) 1, 2, 3, 4, 9, a n d 14 d a y s a f t e r i n s t i t u t i o n o f t h e s e r e g i m e n s p l a s m a b r o m i d e was d e t e r m i n e d in all animals. F r o m t h e results m e a n half-lives p e r group were calculated. Bromide determinations B r o m i d e was d e t e r m i n e d f o l l o w i n g t h e m o d i f i e d m e t h o d o f H u n t e r [ 3 ] , as d e s c r i b e d b y V a n L o g t e n et al. [ 4 ] . RESULTS T h e m e a n p l a s m a b r o m i d e c o n c e n t r a t i o n at t h e b e g i n n i n g o f t h e b r o m i d e a d m i n i s t r a t i o n was 0.55 + 0 . 4 6 mmole/1. A f t e r t h r e e w e e k s o f b r o m i d e a d m i n i s t r a t i o n it was 8.57 + 0.57 mmole/1. T h e resulting biological half-lives, t o g e t h e r w i t h t h e c h l o r i d e i n t a k e , are s h o w n in T a b l e I. T h e c h l o r i d e i n t a k e was e s t i m a t e d o n t h e a s s u m p t i o n t h a t TABLE I INFLUENCE OF CHLORIDE INTAKE ON BROMIDE HALF-LIFE Group
1
2
3
4
5
Diet Drinking water
normal tap water
"salt free . . . . tap water
salt free . . . . 0.02 mole/1 NaC1 12.0 28
salt free . . . . 0.05 mole/1 NaCl 6.9 55
salt free" 0.15 mole/1 NaC1 2.5 144
Half-life (days) 3.5 Chloride intake a 91 (mg/day)
25.1 10
a A daily intake per rat of 11 g food and 25 ml drinking water is assumed.
30
I/2 bromide (days)
chloride intake (rag/day)
Fig. 1. Relation between chloride intake and bromide half-life. The dotted lines refer to the normal situation: rats drinking tap water and feeding on normal Muracon SSP-Tox ad libitum.
the animals had an average f o o d intake of 11 g and drank on average 25 ml per day. It can be seen t hat the shortest and the longest half-life differ by a factor o f 10. The relation between bot h variables is shown in Fig. 1. T h e y are a p p r o x i m a t e l y inversely proportional. DISCUSSION When a substance is repeatedly administered to an organism, a m ore or less co n s tan t c o n c e n t r a t i o n of it will build up in the tissue fluids. The mean plasma level at steady state is given by the expression: D . tv, - 1 . 4 4 - -D . t w C~-ln 2"V'T V-7 in which D is the absorbed dose, tl/2 the biological half-life, V the apparent distribution volume and T the interval between administrations [ 5 ] . If D, V and T remain constant, C~ is directly p r o p o r t i o n a l to tl/,. Administration of a substance by adm i xt ur e to f ood complicates the situation, w i t h o u t changing, however, the relation of Ca to tl/2, provided D and T do n o t fluctuate unduly. A difference in half-life by a factor 10 thus means a difference by a factor 10 in stationary plasma c o n c e n t r a t i o n . If exchange bet w een plasma and the target organ is rapid, the same applies to the c o n c e n t r a t i o n in the target organ. A no-effect level is empirically determined~ In principle, however, it is a derived q u ant i t y: derived from the highest non-toxic steady state level of the
31
substance under consideration in the target organ. The latter level -- in the case of bromide -- is greatly influenced by the chloride intake. Consequently the no-effect level of bromide will be comparably affected by this intake. S5remark [6] determined the chloride half-life in a group of volunteers under normal circumstances as regards activity and food intake. He found a half-life of 12 -+ 3 days. It is to be expected that diminished salt intake will cause prolongation of this half-life. If acceptable daffy intakes are to be established, the influence of a salt-free diet on bromide half-life in m a n w i l l have to be taken into account. ACKNOWLEDGEMENTS
The help of Dr. H.G. Verschuuren in obtaining the special diets is gratefully acknowledged. Dr. H.A.M.C. Vaessen kindly provided the chloride analyses in the diets. Mr. P.W.M. Zeylmans carefully carried out long series of bromide analyses. REFERENCES 1 2 3 4 5 6
R.L. Wolf and G.S. Eadie, Am. J. Physiol., 163 (1950) 436. A. Langley Czerwinski, J. Pharm. Sci., 47 (1958) 467. G. Hunter, Biochem. J., 60 (1955) 261. M.J. van Logten, M. Wolthuis, A.G. Rauws and R. Kroes, Toxicology, 1 (1973) 321. J.G. Wagner, J. Clin. Pharmacol., 7 (1967) 84. R. SSremark, Acta Physiol. Scand., 50 (1960) 306.
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