Effect of central administration of serotoninergic agonists on electrolyte excretion control

ABSTRACT

The participation of different central serotoninergic (5HT) receptors in the mediation of Na+ excretion (UNaV), K+ excretion (UKV) and urine output (UV) was evaluated. Male wistar rats weighing 220-280 g were used in each group of 9-18 animals. The rats were injected intracerebroventricularly (icv) with the 5 HT agonists MK212 (1.5, 15.0 and 30.0 *g), 8-OH-DPAT (5.0 and 15.0 *g) 5HT (2.5, 12.5 and 25.0 *g) and DOI (10.0 and 25.0 *g). At the lowest MK212 dose, UNaV was significantly reduced (0.18 ñ 0.04 *Eq/min vs 0.35 ñ 0.04 *Eq/min for saline) at 20 min. At the highest dose, MK212 provoked a significant increase in UNaV (0.60 ñ 0.06 *Eq/min vs 0.34 ñ 0.03 *Eq/min for saline) at 40 min UKV values were significantly modified only at the 1.5-*g dose (0.18 ñ 0.04 *Eq/min vs 0.04 *Eq/min for saline) at 20 min. Icv injection of 8-OH-DPAT provoked a significant reduction in UNaV (0.16 ñ 0.05 *Eq/min vs 0.35 ñ 0.03 Eq/min for saline) and UKV (0.15 ñ0.05 *Eq/min vs 0.34 * ñ 0.02 *Eq?min for saline) at 40 min at both doses. Icv injection of 5HT at the highest dose provoked a signficant increase in UNaV (0.92 ñ 0.10 *Eq/min vs 0.33 ñ 0.04 *Eq/min for saline) and in UKV (0.55 ñ 0.08 *Eq/min vs 0.24 ñ 0.07 *Eq/min for saline) at 40 min. Icv administration of DOT caused a natriuretic response (0.69 ñ 0.12 *Eq/min vs 0.31 ñ 0.04 *Eq/min for saline) at 40 min, with no significant effect on UKV. All the 5HT agonists induced a rapid antidiuretic response (35 to 75% below control levels), which was notably more intense and longer lasting at the highest 8-OH-DPAT dose. The results appear to indicate the involvement of both receptor families (5HT2) in the expression of the antidiuretic response. The present evidence indicates an opposite participation of the different receptor families in elicing the antinatriuretic (5HT1) and natriuretic (5HT2) responses