BEHAVIORAL BIOLOGY 17, 519-527 (1976), Abstract No. 6110

Ingestion of Potassium Chloride and Sodium Chloride Solutions by Albino and Hooded Rats

PAUL E. VAN HEMEL 1

Department of Psychology, Franklin and Marshall College, Lancaster, Pennsylvania 17604

The intake of KC1 by albino rats tested with an ascending series of 10 concentrations between 0.1 and 5.0% declined as concentration increased in two-bottle tests, whereas intake of NaC1 increased as concentration increased to 0.88% but declined thereafter. These patterns were basically unchanged when the tests were repeated 15 days later. In single-bottle tests with order of presentation varied, albino and hooded rats were presented water and nine KC1 solutions ranging in concentration from 0.08 to 2.62%. No clear intake difference between water and dilute KC1 appeared, but the highest concentration of KC1 did produce a reduced intake. These baseline data show that normal diet-replete rats were indifferent to dilute KCI solutions in two standard preference testing situations where a preference for dilute NaC1 readily appeared, and that they avoided high concentrations of KC1.

Since Richter's early studies of NaC1 solution intake in rats (Richter, 1936, 1939; Richter and Eckert, 1938), the classic function relating NaCI concentration and intake in rats has been described many times. The increasing intake as concentration increases in the hypotonic range, the peak at isotonic concentration, and the decline in intake with further concentration increases are familiar findings in the two-bottle preference test (Mook, 1969; Pfaffmann, 1963). The same pattern may also be obtained using a singlestimulus method, either b y giving rats NaC1 solutions to drink without the alternative of water (Rabe and Corbit, 1973; Weiner and Stellar, 1951) or by using NaC1 solutions for continuous reinforcement of bar pressing by waterdeprived rats (Myer and Van Hemel, 1969). Although the phrase "preferenceaversion function" has been applied to this pattern o f intake, it is probably incorrect to apply it in the case o f behavior that occurs in response to single substances (Mook, 1969). Whatever it is termed, this pattern of intake has provided a baseline for many studies o f the effects of sodium deficiency on 1The author is grateful to the Franklin and Marshall College Committee on Grants for financial support, and to Susan B. Van Hemel for a critical reading of the manuscript. 519 Copyright © 1976 by Academic Press, Inc. All rights of reproduction in any form reserved.

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diet preferences (for reviews, see Denton, 1967; Stricker, 1973; Wolf, 1969), for studies of taste psychophysics (e.g., Morrison and Norrison, 1966), and for studies of the effects on hunger of various prior treatments with NaC1 solutions (Hsiao and Trankina, 1969; Kakolewski and Deaux, 1970; Oatley and Toates, 1973; Schwartzbaum and Ward, 1958; Smith, Pool, and Weinberg, 1959; Van Hemel and Myer, 1970). This function has also been useful in discovering the determinants of NaC1 solution intake itself (Kissileff, 1969, Mook, 1963; Myer and Van Hemel, 1969; Rabe and Corbit, 1973). Recently, there have appeared reports of increased intake of KC1 solutions as one result of several studies examining the effects of potassium deficiency in rats on diet preferences (e.g., Adam, 1973; Adam and Dawborn, 1972; Cullen and Scarborough, 1972; Milner and Zucker, 1965; Zucker, 1965). Unfortunately, examination of results from normal control groups in these and other studies reveals an inconsistency that makes it difficult to interpret experiments using intake of potassium or KC1 as a dependent variable. Some investigators have reported data that suggest rats may normally avoid KC1. Nachman and Pfaffmann (1963) found that normal rats preferred 0.1M NaC1 to 0.1M KC1. Fregly and Kim (1970) found that intake of 0.1 M KC1 never exceeded that of distilled water. Furthermore, Adam and Dawbom (1972), using KC1 solutions ranging in concentration from 0.0013M to 0.67M, were unable to demonstrate a preference for dilute KC1 over water in normal rats. However, other studies have suggested that normal rats ingest more dilute KC1 than water (Cullen and Scarborough, 1972; Fregly, 1959; Zucker, 1965). Cullen and Scarborough have even characterized the response of normal rats to an ascending series of KC1 concentrations as a classic preference-aversion function, although the preference disappeared .when a group of their subjects was retested with the same series. With increasing interest in potassium appetite, it is essential to determine clearly the relationship between KC1 concentration and intake in normal rats. The present experiments were conducted to explore further the ingestion by normal rats of KC1 solutions. Concentrations covering a fairly wide range were tested to provide reference data on intake of both dilute and more concentrated solutions. In the first experiment, intake of KC1 in an ascending series of concentrations was compared with intake of NaC1 similarly presented, with the two-bottle method used to assess preference. Because the preference observed by Cullen and Scarborough (1972) was unstable, both series were presented a second time to determine the reliability of any obtained preferences. EXPERIMENT I

Method Subjects. The subjects were 20 experimentally nawe female SpragueDawley-derived rats, approximately 100 days old and weighing 221-328 g at the beginning of the experiment.

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Apparatus. Twenty preference testing chambers, each 31 × 39 × 23 cm high, with galvanized metal walls and wire mesh floors and tops, were in a room in which a 12-12 hr light-dark cycle was maintained. Purina Laboratory Chow was continuously available in each chamber, and each chamber had three openings permitting access to drinking tubes from 250 ml glass bottles attached to the outside of the chamber. The openings were in a horizontal row near the floor on the front wall of the chamber. Procedure. Ten rats were assigned to each of two groups, matched by weight, and each rat was placed in a test chamber. For 10 days, distilled water was presented in a single bottle at the center opening of each chamber, and the bottles were weighed daily to determine the amount ingested. Then followed a 20-day two-bottle preference testing period, during which each of 10 solutions of KC1 for one group, and NaC1 for the other group, was available for 2 successive days. On the first of those 2 days the solution was on one side of the center opening, and on the second of those 2 days it was on the other side. Distilled water was available in the other bottle every day. The concentrations of KC1 and NaC1 solutions, mixed percentage by weight as recommended when weight consumed is the dependent measure (Pfaffmann, Young, Dethier, Richter, and Stellar, 1954), were 0.10, 0.15, 0.24, 0.37, 0.57, 0.88, 1.36, 2.10, 3.24, and 5.0%. This range in molar concentration is approximately 0.013M to 0.67M for KC1, and approximately 0.017M to 0.85 M for NaC1. Concentrations were presented in ascending order. Following the first 20-day preference testing period, distilled water only was available at the center opening for 15 days, and then there followed a second 20-day preference testing period identical to the first. Results Figure 1 shows for each testing period the mean 2-day ingestion of NaC1 solutions and water by the NaC1 group and the mean 2-day ingestion of KC1 and water by the KC1 group. The data from one NaC1 group rat that persistently spilled its solutions during the second test period are not included. The clear indication in the figure that the rats ingested more NaC1 than KC1 was borne out by analysis of variance on the solution intake data, which revealed a significant direct effect of type of salt, F(1, 17) -- 6.74, p < 0.05. Apparently, the difference in ingestion of the two types of solution was not accompanied by reliable differences in associated water intake; analysis of variance on the water intake data yielded no direct or interactive effects of type of salt. The intake of the solutions varied with concentration, and analysis of variance on the solution intake data revealed significant concentration effects for the KC1 group, F(9, 81) = 13.31, p .10). However, the Scheffd test indicated that the lowered intake of 2.62% KC1 was significantly different from the average intake of all other test solutions (p < 0.05).

DISCUSSION In two experiments, involving different measurement techniques, albino and hooded rats avoided ingesting large amounts of KC1 solutions with concentrations above 2.0%. Within the range of 0.08 to 5.0% KC1, there appeared no ascending and then descending function relating concentration and intake, such as that easily obtained with a comparable range of concentrations of NaC1. It is clear that the relationship between intake and concentration of KC1 in these experiments was not a classic preferenceaversion function comparable to the function produced by varying concentration of NaC1. The findings of the present study are in accord with previous reports that normal rats do not prefer dilute KC1 over water (Adam and Dawborn, 1972; Fregly and Kim, 1970), and that they avoid KC1 solutions of 2.0 and 3.0% (Richter and Eckert, 1938). It is difficult to reconcile the discrepancy between these results and the preference found by Cullen and Scarborough (1972). Because the most preferred solution in their experiment was not tested in Experiment I, the absence of a sharp peak there is not surprising. But no sharp peak appeared in Experiment II when that concentration was tested. Perhaps the gradual introduction of KC1 beginning with the very low concentrations first tested by Cullen and Scarborough, allowed the preference to appear in their experiment. Such a gradual introduction is not typical of tests for change of preference following dietary restriction of potassium (e.g., Adam and Dawborn, 1972; Milner and Zucker, 1965).

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It is easier to identify differences between the present study and that o f Zucker (1965) that could account for his finding that KC1 was preferred over a considerable range of NaC1 concentrations. He used very young hooded rats, and simply measured amount o f time spent drinking the different solutions during a 5-min test, rather than amount ingested over a longer time. It is quite likely that the patterns of ingestion o f KC1 are controlled b y postingestional consequences that did not appear in such a short test, and that the taste o f KC1 is not aversive. The taste o f quite high concentrations o f NaC1 is not strongly aversive to rats (Myer and Van Hemel, 1969), even though the consequences o f ingesting such concentrations o f NaC1 are aversive (Kissileff, 1969; Myer and Van Hemel, 1969; Rabe & Corbit, 1973). Whether the ingestion of KC1 by normal rats is controlled primarily b y oral or postingestional factors was not analyzed in the present experiments. The functions obtained in the present experiments provide some baseline data for KC1 ingestion over a fairly broad range o f concentrations. In standard preference tests, rats in these experiments did not prefer dilute KC1 solutions tested, as they did dilute NaC1 solutions, and they clearly avoided concentrated KC1 solutions.

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Mook, D. G. (1963). Oral and postingestional determinants of the intake of various solutions in rats with esophageal fistulas. J. Comp. PhysioL Psychol. 56, 645-659. Mook, D. G. (1969). Some determinants of preference and aversion in the rat. Ann. N. Y. Acad. Sci. 157, 1158-1175. Morrison, G. R., and Norrison, W. (1966). Taste detection in the rat. Canad. J. Psychol. 20, 208-217. Myer, J. S., and Van Hemel, P. E. (1969). Saline as a reinforcer of bar pressing by thirsty rats. J. Comp. Physiol. Psychol. 68,455-460. Nachman, M., and Pfaffmann, C. (1963). Gustatory nerve discharge in normal and sodium-deficient rats. J. Comp. Physiol. Psychol. 56, 1007-1011, Oatley, K., and Toates, F. M. (1973). Osmotic inhibition of eating as a subtractive process. Z Comp. Physiol. Psychol. 82, 268-277. Pfaffmann, C. (1963). Taste stimulation and preference behavior. In Y. Zotterman (Ed.), "Olfaction and Taste," pp. 257-273. New York: Macmillan. Pfaffmann, C., Young, P. T., Dethier, V. G., Richter, C. P., and Stellar, E. (1954). The preparation of solutions for research in chemoreception and food acceptance. J. Comp. Physiol. PsychoL 47, 93-96. Rabe, E. F., and Corbit, J. D. (1973). Postingestional control of sodium chloride solution drinking in the rat. J. Comp. Physiol. Psychol. 84, 268-274. Richter, C. P. (1936). Increased salt appetite in adrenalectomized rats. Amer. J. Physiol. 115, 155-161. Richter, C. P. (1939). Salt taste thresholds of normal and adrenalectomized rats. Endocrinology 24, 367-371. Richter, C. P., and Eckert, J. F. (1938). Mineral metabolism of adrenalectomized rats studied by the appetite method. Endocrinology 22, 214-224. Schwartzbaum, J. S., and Ward, H. P. (1958). An osmotic factor in the regulation of food intake in the rat. J. Comp. Physiol. Psychol. 51,555-560. Siegel, S. (1956). "Nonparametdc Statistics." New York: McGraw-Hill. Smith, M., Pool, R., and Weinberg, H. (1959). The effect of peripherally induced shifts in water balance on eating. Jr. Comp. Physiol. Psychol. 52, 289-293. Strieker, E. M. (1973). Thirst, sodium appetite, and complementary physiological contributions to the regulation of intravascular fluid volume. In A. N. Epstein, H. R. Kissfleff, and E. Stellar (Eds.), "The Neuropsychology of Thirst: New Findings and Advances in Concepts," pp. 73-98. Washington, D. C.: V. H. Winston & Sons. Van Hemel, P. E., and Myer, J. S. (1970). Control of food-motivated instrumental behavior in water-deprived rats by prior water and saline drinking. Learning and Motivation 1, 86-94. Weiner, I. H., and Stellar, E, (1951). Salt preference of the rat determined by a single-stimulus method. J. Comp. PhysioL Psychol. 44, 391-401. Wolf, G. (1969). Innate mechanisms for regulation of sodium intake. In C. Pfaffmann (Ed.), "Olfaction and Taste III," pp. 548-553. New York: Rockefeller University Press. Zucker, I. (1965). Short-term salt preference of potassium-deprived rats. Arner. J. Physiol. 208, 1071-1074.

Ingestion of potassium chloride and sodium chloride solutions by albino and hooded rats.

BEHAVIORAL BIOLOGY 17, 519-527 (1976), Abstract No. 6110 Ingestion of Potassium Chloride and Sodium Chloride Solutions by Albino and Hooded Rats PAU...
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