An investigation into some cerebral mechanisms involved in schedule-induced drinking in the pig.

When pigs were fed small amounts at regular short intervals (5-10 min), drinking followed each ingestion. This resulted in a greatly increased total water intake (schedule-induced polydipsia: s.i.p.). Injection of angiotensin II into the lateral cerebral ventricle of water-replete pigs on normal feeding also produced a significant increase in water intake. Prior administration of the angiotensin II antagonist, saralasin, attenuated the dipsogenic effect of angiotensin II, but did not modify s.i.p. The tranquilizing drug, azaperone, had no effect on normal water intake and did not modify the response to angiotensin II. However, azaperone reduced the water intake of animals on scheduled feeding. From this, it was concluded that the increased drinking due to scheduled feeding did not involve the renin-angiotensin system but it is tentatively suggested that it may involve central dopaminergic neuronal systems.