Corticosteroids and control of nasal salt gland function in the lizard Tiliqua rugosa

The scincid lizard Tiliqua rugosa possesses a well-developed nasal gland composed of both mucoserous and salt-secreting cells. Confusion over its secretory capacities (see H. Saint- Girons , M. Lemire , and S. D. Bradshaw, 1977, Zoomorphologie 88, 277-288) has been resolved and NaCl- and KCl-injected animals can secrete a hyperosmotic fluid with an F/P ratio of about 3.6. The concentration of Na+ in the secretion varied from a mean of 434 mmol/liter when sodium loaded to 167 mmol/liter when potassium loaded. Potassium concentrations varied from 226 to 433 mmol/liter, respectively. Na:K ratios thus vary from 1.98 with NaCl loading to 0.42 with KCl loading, demonstrating the gland's capacity to vary the nature of the secretion. Rates of fluid production did not differ significantly between NaCl- and KCl-loaded individuals and varied from 13.3 to 19.6 microliter (100 x g hr)-1. Adjacent studies on the north African agamid lizard Uromastix acanthinurus suggested that aldosterone may influence the rate and composition of the nasal gland secretions and this possibility was investigated in Tiliqua by hormone binding studies. High affinity binding for both corticosterone and aldosterone was demonstrated during the breeding season, with a Kd of 5.2 x 10(-9) and 12.9 x 10(-9) M, respectively. Binding of aldosterone to nasal gland receptors was not evident in nonbreeding animals and the binding of corticosterone was primarily nonspecific in these individuals. These data suggest that hormone receptor concentrations and affinity vary on a seasonal basis and in concert with reproductive activity.