ABSTRACT
The crab-eating frog Fejervarya cancrivora inhabits mangrove swamps and marshes in Southeast Asia. In the present study, circulating angiotensin II (Ang II), aldosterone (Aldo), arginine vasotocin (AVT), and corticosterone (Cort) concentrations as well as various blood parameters were studied under osmotically stressful conditions. Following acclimation to hyperosmotic seawater and dry condition for 5days, body weight was significantly decreased. Under both conditions, plasma Na(+), Cl(-), and urea concentrations, hematocrit values (Ht; blood volume indicator), and osmolality were significantly increased. Dehydration associated with hypovolemic and hyperosmotic states of body fluids was induced during acclimation to hyperosmotic seawater and dry condition in the crab-eating frogs. Ang II, Aldo, AVT, and Cort were maintained within relatively narrow concentration ranges in the control frogs; however, in frogs under dry and hyperosmotic seawater conditions, large variations were observed among individuals in each group. Mean plasma Ang II and Aldo concentrations significantly increased in hyperosmotic seawater-acclimated and desiccated frogs. Although mean plasma AVT concentrations in dehydrated frogs of both the groups were approximately 2.0-3.5 times higher than those in the control frogs, the differences were not significant because of the variation. There was a significant correlation between plasma osmolality and AVT as well as Ang II but not Aldo. A significant correlation was also observed between Ht and AVT as well as Ang II. Plasma Ang II was significantly correlated with plasma Aldo. These results indicate that the crab-eating frogs may exhibit similar physiological responses to both seawater-acclimated and dry conditions. It appears that under dehydrated conditions, osmoregulatory mechanisms participate in stabilization of the situation. The renin-angiotensin system may have pivotal roles in body fluid regulation under volemic and osmotic stress in the Fejervarya species with unique osmoregulation.
