INTERACTION OF OSMOTIC AND VOLEMIC COMPONENTS IN INITIATING SALT-GLAND SECRETION IN PEKIN DUCKS

Pekin Ducks (Anas platyrhynchos) were infused with 1,000 mM NaCl. Chan ges in plasma osmolality (Osm(pl)); relative plasma volume (RPV); and plasma concentrations of electrolytes, arginine vasotocin, and angiote nsin II were determined at initiation of salt-gland secretion and at 5 and 11 h post-infusion. Changes in these parameters and in volume and concentration of secretion produced were not different between the se xes. Although Osm(pl) and RPV were not related prior to infusion, they were linearly related at the onset of secretion (r(2) = 0.51, P = 0.0 13). Osm(pl) and RPV were equally effective stimuli for secretion. Ini tial RPV was a strong determinant of secretion volume (P < 0.01) and t otal sodium (P < 0.001) and potassium (P < 0.001) secreted, but initia l Osm(pl) was not. Plasma arginine vasotocin concentration was increas ed by NaCl infusion but not by subsequent dehydration. Plasma angioten sin II concentration was not significantly affected by NaCl infusion o r by dehydration. These experiments are the first to directly relate t he secretory response of the salt glands to the physiological state of ducks prior to salt loading and to describe the interactive simultane ous changes in Osm(pl) and RPV associated with initiation of secretion .