Meeting Abstract

P3.160  Friday, Jan. 6  Limited sensitivity to aldosterone in salt glands of two lizard species with minimal variation in cation secretion HAZARD, L.C.*; SIERRA, J.; TERODEMOS, H.; CARO, L.; Montclair State University, NJ hazardl@mail.montclair.edu

Many lizards use nasal salt glands to supplement renal excretion of excess dietary sodium and/or potassium (coupled with chloride). In some species, cation secretion is flexible, and varies depending on the dietary input; the sodium:potassium ratio is modified by aldosterone, a sodium-conserving hormone. However, other species have more limited ability to vary the cations secreted. Uromastyx dispar (an herbivore) secretes nearly 100% potassium, and Eumeces schneideri (an insectivore) secretes ~40-60% potassium, regardless of cation load incurred. We hypothesized that the salt glands of these two species would therefore be relatively insensitive to aldosterone. Individuals of both species were given either sodium chloride or potassium chloride loads daily for four days, in conjunction with aldosterone, spironolactone (an aldosterone blocker) or ethanol (vehicle control). Salt gland, urinary, and fecal sodium and potassium output were measured. In U. dispar, aldosterone had no effect on rates of sodium and potassium secretion or on the sodium:potassium ratio; however, spironolactone resulted in a slight increase in sodium secretion consistent with the expected effects of blocking aldosterone. Results were more complex for E. schneideri; in NaCl-treated animals spironolactone increased sodium secretion, but in KCl-treated animals aldosterone appeared to both increase sodium secretion and decrease potassium secretion. These contradictory responses suggest that the roles of aldosterone and other osmoregulatory hormones in regulating lizard salt glands may be more complex than previously thought, and that other regulatory pathways and interactions with other excretory routes may be involved.