The effect of adrenocorticotrophic hormone on water intake in mice

The systemic administration of adrenocorticotrophic hormone (ACTH) stimulates the intake of sodium chloride and water in many species. In mice the daily intake of water may reach half of the total body water content. To establish whether this very high water intake was primary or secondary to the sodium chloride intake, Synacthen was infused s.c. at 2.8 micrograms/day by Alzet miniosmotic pump to mice that did not have access to sodium chloride solution. On low-sodium food, the daily water intake increased from 2.99 +/- 0.08 ml (mean +/- SEM) to 9.85 +/- 0.74 ml (p < 0.05, n = 6) by day 7 of infusion and remained significantly higher than the control value until the fourth postinfusion day. On high-sodium food, the daily water intake also increased 350% from a higher baseline, 4.55 +/- 0.14 ml, and returned to the control value by the second postinfusion day. The same ACTH treatment for 4 days increased plasma [Na] and appeared to expand plasma volume. The results show that a high water intake caused by ACTH administration in mice is not secondary to a concurrent increase in sodium chloride intake. The water intake may be induced by stimulation of the secretion of adrenal steroid hormones which increase plasma [Na].