Effects of salt loading on salt gland function in the euryhaline turtle,Malaclemys terrapin

Summary The estuarine turtle,Malaclemys terrapin is able to ionregulate when acclimated to fresh water, 55% sea water or 100% (full strength) sea water, but when in 100% sea water it does not volume regulate successfully. Orbital gland secretions collected by a new eye cup method are very low in animals from all three salinities without salt load. After salt loading the animals from all three groups produce an orbital gland secretion with a sodium concentration greater than sea water. The concentration of ions and kinetics of the response are similar in all three groups. Orbital gland secretion returns to control preload levels well before the injected load is excreted. There is no correlation between the plasma sodium concentration and any of the parameters of the orbital gland response. There is also no correlation between the concentration of sodium in the tear fluid or the rate of sodium excretion and the level of K⁺-stimulatedp-nitrophenylphosphatase activity in the gland. Some of these unexpected results may relate to the estuarine habitat occupied byMalaclemys.Abbreviations K ⁺–NPPase potasium stimulated p-nitrophenylphosphatase - Na–K-ATPase sodium, potassium stimulated adenosine triphosphatase