Voluntary Consumption of NaCl, KCl, CaCl2, and NH4Cl Solutions by 28 Mouse Strains

INTRODUCTION

The consumption of inappropriately high or low amounts of several minerals can exacerbate many chronic diseases, including hypertension and osteoporosis (e.g., reviewed in [Beauchamp and Engelman, 1991; Tordoff, 2001]). However, despite impressive progress toward characterization of the genetic bases of some of these diseases, there has been little concerted effort to understand the genetic controls of mineral intake. The comparison of animals from inbred strains is an initial step towards identification of genetic factors controlling mineral intake. In previous studies, strain differences in spontaneous intake of NaCl solutions have been noted. For example, rat strains can be characterized by high NaCl intakes (SHR), moderate NaCl intakes (e.g., Dahl-R, Sprague-Dawley, Dark Agouti, WKY, GHR, NT), or low NaCl intakes (e.g., Fisher-344, Dahl-S, Brattleboro) (Wolf et al., 1965; Catalanotto et al., 1972; Fregly, 1975; DiNicolantonio et al., 1983; Midkiff and Bernstein, 1983; Ferrell and Gray, 1985; Midkiff et al., 1985; Ely et al., 1987; Bachmanov, 1989, 1993; Yongue and Myers, 1989; Rowland and Fregly, 1990; Bernstein et al., 1991). NaCl preferences have also been characterized in 12 mouse strains: 129, A2G, BALB/c, BPH/2, BPL/1, BPN/3, C3H/He, C57BL/6, CBA, DBA/2, NZB/B1NJ, and TO (Ninomiya et al., 1989; Lush, 1991; Beauchamp and Fisher, 1993; Gannon and Contreras, 1993; Bachmanov et al., 1998a, 1998b). However, each of these previous studies included five or fewer strains and involved different methods, so it is impossible to compare all the strains directly. Nevertheless, there was a considerable range of responses among the strains tested, including strong preferences for hypotonic and isotonic NaCl (BPN/3, BPL/1 and TO [Lush, 1991; Bachmanov et al., 1998a]), high intakes of hypertonic NaCl (NZB/B1NJ [Bachmanov et al., 1998b]), and strong avoidance of all concentrations of NaCl (CBA [Bachmanov et al., 1998b]).

In contrast to this work on strain differences in ingestion of NaCl solutions, there is little parallel work with other minerals. Rats of the SHR strain ingest more calcium and potassium solutions or calcium-containing diet than do rats of the WKY strain (Ferrell and Dreith, 1986; Bachmanov, 1989, 1993; Tordoff, 1992a). Mice of the BPL/1 strain drink less CaCl2 and more of some concentrations of KCl than do mice of the BPN/3 or BPH/2 strains (Bachmanov et al., 1998a). We are unaware of any published work on strain differences in intake of other minerals.

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To provide a more comprehensive examination of strain differences in mineral intake, we used 48-h two-bottle choice tests to assess the voluntary intake of and preference for, various mineral chlorides by 28 inbred strains of mice. We concentrated on four mineral chlorides: NaCl, KCl, CaCl2, and NH4Cl for several reasons. Each cation is regulated by independent homeostatic systems, and at least for sodium, potassium, and calcium, is the target of a specific appetite (e.g., Eckert, 1938; Scott et al., 1950; Milner and Zucker, 1965; Adam and Dawborn, 1972; Lobaugh et al., 1981; Denton, 1984; Rowland and Fregly, 1988; Tordoff et al., 1998; Tordoff, 2001). At the same time, there is much interplay among the control mechanisms for consumption of each mineral. Physiological examples of this include the regulation of aldosterone by both potassium excess and sodium deficiency, the linked excretion of sodium and calcium, and co-transport involving Na+/Ca2+, Na+/K+, and Na+/H+-ATPases. Behavioral examples include the increase in NaCl intake observed during calcium or potassium deficiency (e.g., Zucker, 1965; Adam and Dawborn, 1972; Tordoff, 1992b, 1996). There are also similarities among NaCl, KCl, CaCl2, and NH4Cl in taste. For example, high concentrations of all four mineral salts have a salty taste component, and all except NaCl are rated as bitter [at least by humans (McBurney and Shick, 1971; Schiffman and Erickson, 1971)]. By comparing the voluntary intake of different minerals by many strains of mice, we hoped to gain insight into the relationships among the factors controlling consumption of these salts.

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