Deuterium induced extinction of ADH-release in response to intracerebroventricular infusions of hypertonic NaCl and angiotensin

Effect of intracerebroventricular deuterium oxide on water intake and AVP release induced by intravenous infusion of angiotensin II in sheep

The effect of intracerebroventricular (i.c.v.) infusion (0.02 ml min-1) of deuterium oxide (D2O), with NaCl added to isotonicity, on the water intake and arginine vasopressin (AVP) release caused by intravenous (i.v.) infusion of angiotensin II (AII) (4.8 nmol min-1) was studied in euhydrated sheep. The i.c.v. infusion of D2O, which started 80 min before commencement of the AII infusion, induced a water diuresis in four out of six animals and a measurable decrease in plasma AVP concentration. The i.v. infusion of AII effectively stimulated the AVP release and the response was unaffected by prior and simultaneous i.c.v. administration of D2O. However, the water intake measured 2 min after cessation of the AII administration was reduced by 50% when D2O was infused i.c.v. compared to that seen after simply the AII infusion. The inhibitory effect of D2O on AII-induced drinking disappeared rapidly after discontinuation of D2O administration. Compensatory increased drinking was seen during the first post-infusion hour, resulting in an equivalent cumulative intake of water at 60 min post-infusion in the two types of experiments. The present results support the idea that at least some of the cerebral effects of circulating AII on fluid balance are medicated via targets which are simultaneously accessible to influences from the blood and the cerebrospinal fluid.

Delayed drinking in response to electrical and thermal stimulation of the medial forebrain

Water intake in response to electrical and thermal stimulation of the medial forebrain was studied in the goat. When the frontal wall of the third cerebral ventricle was included in a field of bipolar electrical stimulation a dipsogenic response was obtained after discontinuation of the stimulation. Release of antidiuretic hormone (ADH) was apparently also elicited. The water intake was roughtly proportional to the amount of current which had been applied during the stimulation period. Water consumption in response to stimulation attenuated the dipsogenic effect of subsequent stimulation, as did also pre-stimulatory hydration by stomach tube. A 2 degrees C elevation of the temperature of parts of the preoptic/anterior hypothalamic region for 40 min periods incuded cumulative drinking starting after 2.5 to 18 min. There were great interindividual differences in the amount of water consumed in response to the thermal stimulation, possibly due to variations in thermo-couple electrode placement. The dipsogenic effect of forebrain warming was inhibited by pre-hydration, and by lowering of the environmental temperature. The delayed thirst responses are discussed in relation to stimulus-bound drinking previously observed in the same and other species. It appears possible that the delayed drinking was a manifestation of artificially induced excitation of juxtaventricular "thirst" receptors.