Calcium deprivation increases NaCl intake of Fischer-344 rats

Calcium: taste, intake, and appetite

This review summarizes research on sensory and behavioral aspects of calcium homeostasis. These are fragmented fields, with essentially independent lines of research involving gustatory electrophysiology in amphibians, ethological studies in wild birds, nutritional studies in poultry, and experimental behavioral studies focused primarily on characterizing the specificity of the appetite in rats. Recently, investigators have begun to examine potential physiological mechanisms underlying calcium intake and appetite. These include changes in the taste perception of calcium, signals related to blood calcium concentrations, and actions of the primary hormones of calcium homeostasis: parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D. Other influences on calcium intake include reproductive and adrenal hormones and learning. The possibility that a calcium appetite exists in humans is discussed. The broad range of observations documenting the existence of a behavioral limb of calcium homeostasis provides a strong foundation for future genetic and physiological analyses of this behavior.

The importance of calcium in the control of salt intake

There is no doubt that the renin-angiotensin-aldosterone system (RAAS) can have a major influence on salt intake but the conditions used to demonstrate this are rare outside the laboratory. Changes in RAAS activity do not explain the voluntary intake of NaCl solution shown by non-deprived rats or the preference for salty foods shown by humans. As a first attempt to investigate an alternative mechanism, my colleagues and I are studying the effects of dietary calcium on salt appetite. Even though calcium-deprived rats have normal RAAS activity, they show a striking increase in NaCl intake, which can surpass the effects of the most severe manipulations of the RAAS. The physiological mechanism underlying this behavior is unknown but it probably involves an adrenal factor, perhaps corticosterone. Whatever the mechanism, the calcium-deprived rat and other low-renin models of salt intake provide a promising approach to help understand the physiological basis of excess salt consumption by humans.