Brain angiotensinergic mediation of enhanced water consumption in lactating rats

The mechanism by which lactating rats increase fluid consumption to meet the demands of milk production is unknown. Because ANG II is the most potent dipsogenic stimulus known, this study examined whether angiotensinergic signaling plays a role in enhanced drinking in lactating rats. ANG II administered intracerebroventricularly caused a significantly greater dipsogenic response in lactating rats than in control rats, suggesting that dipsogenic responsivity to ANG II is enhanced in the brains of lactating rats. The angiotensin type 1 (AT1) ANG II receptor subtype antagonist SKF-108566, also given intracerebroventricularly, caused a significant reduction in water consumption in lactating rats, whereas it did not significantly affect water intake in control rats. In contrast, stimulation of drinking by the muscarinic agonist carbachol, also administered intracerebroventricularly, did not differ between lactating and control rats. Inhibition of drinking by the muscarinic antagonist atropine also did not differ significantly between lactating and control rats. These results suggest that the increased drinking in lactating rats involves an increased responsivity to ANG II in neurons that mediate dipsogenesis, as well as an enhancement in the amount of angiotensinergic input to these ANG II-responsive neurons.