Received February 15, 2007
Revised March 21, 2007
Accepted after revision June 19, 2007

¹ Federal Rural University of Rio de Janeiro

^* To whom correspondence should be addressed. E-mail: lcreis{at}ufrrj.br.

	Abstract

The present study was carried out to assess the influence of noradrenergic stimulation of the midbrain dorsal (DRN) and median raphe (MRN) nuclei on urinary volume and electrolyte excretion in hydrated rats. Wistar rats were implanted with guide cannula into the MRN or DRN and then submitted to two intra-gastric applications of water in order to attain an increased diuresis. The following treatments were performed: (i) Intra-DRN microinjections of saline (0.2 µl), 1-adrenergic agonist, phenylephrine (PHE, 0.49 and 4.9 nmol 0.2 µl-1), 2-adrenergic antagonist, idazoxan (IDZ, 0.42 and 4.2 nmol 0.2 µl-1) or the 1-adrenergic antagonist (PRZ, 0.24 and 2.4 nmol 0.2 µl-1). (ii) Intra-MRN microinjections of saline, IDZ (4.2 nmol 0.2 µl-1), PHE (4.9 nmol 0.2 µl-1) or PRZ (2.4 nmol 0.2 µl-1). Urine samples were subsequently collected during 120 min at 20-min interval for photometric measurement of sodium and potassium. Intra-DRN administration of PHE and IDZ significantly increased the urinary volume, natriuresis and kaliuresis. Intra-DRN microinjection of higher dose of PRZ reduced the urinary volume and, sodium and potassium excretion. Intra-MRN microinjections of PHE, IDZ or PRZ did not induce any significant effect on urinary volume or electrolyte excretion. These current data suggest that the increase of tonic excitatory noradrenergic input conveyed to DRN influences the hydroelectrolyte homeostasis, possibly through 5-HTergic circuitry.

Key Words: Adrenergic, Osmoregulation, Raphe nucleus