PLASMA OSMOLALITY AND SALT GLAND SECRETION IN THE DUCK

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Abstract
Secretion by the supra‐orbital glands of conscious Aylesbury ducks began when plasma osmolality and [Na+] were increased by 2–8 per cent after oral administration of hyperosmotic NaCl solution. Peak rates of secretion occurred when these parameters were elevated by 8–19 per cent. Oral administration of water in volumes sufficient to decrease plasma osmolality and [Na+] below these values abolished or reduced the flow of secretion.Comparable or larger increases in plasma osmolality produced by hyperosmotic KCl solution administered orally or by intravenous injection of urea or dextrose failed to evoke secretion.Intravenous injection of hyperosmotic sucrose or mannitol increased plasma osmolality and decreased plasma [Na+] but evoked secretory responses which declined although plasma osmolality remained increased.An osmotic component appears to be involved in the secretory mechanism of the salt glands but the relation between secretion and plasma osmolality is not simple and probably depends on the permeability of certain cells to different solutes.

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