Participation of the serotonergic system in the regulation of water and electrolyte balance

To determine the possible participation of the serotonergic (5-HT) system in the regulation of water and electrolyte balance, rats were submitted to two sessions of water overloading and the 5-HT agonist MK 212 was administered intracerebroventricularly (icv) in 1.0 microliters 20 min after the second session. Urine volume and sodium and potassium excretion were then measured over a period of 120 min. Microinjection of MK-212 (1 micrograms/animal) caused a significant reduction (24 to 57%; mean, 43%) in natriuresis throughout the experimental period, and the administration of 10 micrograms/animal caused a 26-41% reduction (mean, 33%) in kaliuresis. At 20 micrograms/animal, MK-212 did not change any of the parameters investigated. No significant change in urine volume was detected after any of the treatments used.