Meeting Abstract
P1.80 Jan. 4 Response of the salt gland of the lizard Uromastyx dispar to ionic and osmotic challenges HAZARD, L.C.**; HRIB, A.; RICKETTS, J.; DUSSA, H.; Montclair State University, NJ; Montclair State University, NJ; Montclair State University, NJ; Montclair State University, NJ hazardl@mail.montclair.edu
Most vertebrate taxa with cranial salt glands are marine and secrete sodium chloride; secretion is initiated in response to osmotic loads. However, the herbivorous desert iguana (Dipsosaurus dorsalis), which secretes primarily potassium chloride via the gland, secretes only in response to increased plasma potassium and/or chloride, not sodium or other osmotic loads. We examined the control of salt gland secretion in an ecologically similar but distantly related species, Uromastyx dispar. Lizards were injected with salt solutions (5 �mol/g) daily for 4 days, and salt gland secretions, feces, liquid urine and solid urate were collected daily. Salt glands secreted substantial amounts of salt in response to potassium chloride loads. However, when given potassium acetate, histidine chloride, or sodium chloride treatments, secretion was only slightly elevated above control levels. There was little or no secretion in response to sham injection, histidine acetate, and sodium acetate treatments. It appears that Uromastyx requires the presence of both potassium and chloride to achieve high rates of secretion by the salt gland. Potassium acetate-treated animals excreted most potassium as insoluble potassium urate, suggesting that for Uromastyx, losing nitrogen may be less of a physiological liability than losing chloride. Dipsosaurus increases the sodium:potassium ratio (though not secretion rate) following sodium injections. In contrast, sodium-treated Uromastyx did not secrete significant amounts of sodium when given sodium chloride or sodium acetate. The salt gland of Uromastyx appears to be a more specialized potassium chloride secreting tissue, while the salt gland of Dipsosaurus has greater flexibility of cation secretion.
