Modulation of plasma arginine vasopressin during rehydration in the Bedouin goat.

When severely dehydrated Bedouin goats were allowed to drink to satiation their plasma arginine vasopressin concentration immediately dropped from a value of 19.9 +/- 9.4 pmol.l-1 to 9.4 +/- 3.9 pmol.l-1 (P < 0.05). It continued to drop further until a concentration of 1.8 +/- 2.9 pmol.l-1 was recorded, similar to that reported for goats allowed to drink freely. When the goats were shown the water but drinking was denied, plasma arginine vasopressin immediately dropped to 11.7 +/- 4.0 pmol.l-1 (P < 0.05) and further decreased to 10.0 +/- 4.8 pmol.l-1 5 min following their sighting the water. This level, however, was not sustained and 2 h after the initial drop the high pre-trial concentration of plasma arginine vasopressin was regained. Presumably, sighting of water by dehydrated goats induces an abrupt drop in their plasma arginine vasopressin level even before drinking commences. When rehydrated, by introducing water directly to the rumen, circumventing both the sensing of the water and the drinking proper, no immediate drop in the plasma arginine vasopressin concentration of the newly rehydrated goats was observed. A delayed drop in the plasma arginine vasopressin levels took place slowly, concurrently with the drop in osmolality and concentration of Na+ in the plasma. It is suggested that sighting of water by dehydrated goats is involved in the modulation of plasma arginine vasopressin.