Sympathetic and respiratory activities during increases in osmolarity in an in situ rat preparation.

Abstract

In the present study, we investigated the changes in the thoracic sympathetic (tSNA) and phrenic nerve activity (PNA) induced by hypertonic saline (HS) infusion in different concentrations in decorticated arterially‐perfused in situ rat preparations. Juvenile male Holtzman rats (P 28‐38, 60‐100 g, n = 6/group) were used. In one group of rats, intra‐arterial infusions of HS (0.175; 0.3; 0.7; 1.5 e 2 M NaCl; 200 µL each in 15 seconds) were made in ascending order and in another group only a single infusion of 2 M NaCl was done. Infusion of 2 M NaCl increased tSNA when combined with previous HS infusions in ascending concentrations (35.1 ± 5.6% vs. Ringer solution: ‐1.1 ± 2.1%, p<0.05), whereas single infusion of 2 M NaCl did not change tSNA (‐0.1 ± 2.1% vs. Ringer solution: 1.4 ± 1.9%). Infusion of 2 M NaCl did not induce significant change in the PNA either alone (3.0 ± 0.5 bpm, Ringer solution: ‐2.5 ± 1.5 bpm) or combined with previous HS infusions in ascending concentrations (4.9 ± 1.7 bpm vs. Ringer solution: 1.5 ± 0.4 bpm). The osmolality of the perfusate increased after HS infusion in ascending concentrations (306.5 ± 1.8 vs. pre infusion: 298.3 ± 1.6 mOsm/kg; p<0.05). These data show that acute 2 M NaCl infusion increases tSNA only when preceded by the administration of ascending concentrations of HS in the in situ rat preparations.Supported by Capes; CNPq; FAPEG and FAPESP