Thermogenic drinking: mediation by osmoreceptor and angiotensin II pathways

Exposure of rats to air at 5 C for 1-12 days is accompanied by a relative dehydration in spite of the continued presence of water. Dehydration during exposure to cold was manifested by: 1) a reduction in the ratio of water/food ingested; 2) an increase in the ratio of urine excreted/water ingested; 3) an increased evaporative water loss; 4) an increased serum osmolality and chloride concentration; and 5) a striking thirst and ingestion of water after transfer from cold to air at 26 C. Drinking began within 15 min and lasted approximately 1 h. Thermogenic drinking persisted for at least 120 days of exposure to cold. It was not thwarted by preventing access to water for either 1 or 2 h after transfer to warm air, but either intragastric or intraperitoneal administration of a water load equal to 3% of body weight inhibited water intake after transfer. These characteristics of thermogenic drinking are similar to those observed after 24 h of dehydration at 26 C; they also suggest that the cold-exposed rat is dehydrated relative to controls. These results suggest that osmoreceptors may play a role in the induction of thermogenic drinking. However, angiotensin II receptors may also play a role. Thermogenic drinking was inhibited by a beta 2-adrenergic, but not a beta 1-adrenergic, antagonist as well as by captopril, an inhibitor of the conversion of angiotensin I to angiotensin II. Further, plasma renin activity increased fourfold within 15 min after removal from cold. This suggests that an additional component involved in thermogenic drinking is the angiotensin II receptor. The extent to which thermogenic drinking is mediated by each pathway is unknown and will require additional studies.