Role of the medial septal area on the cardiovascular, fluid and electrolytic responses to angiotensin II and cholinergic activation into the subfornical organ in rats.

In the present study we investigated the effect of electrolytic lesion of the medial septal area (MSA) on the pressor and dipsogenic response to cholinergic activation and angiotensin II (ANGII) injection into the subfornical organ (SFO) in rats. In addition the effect of MSA lesion on the natriuresis, kaliuresis and diuresis after cholinergic activation of the SFO was also investigated. Sham- and MSA-lesioned rats with a stainless steel cannula implanted into the SFO was used. The injection of ANGII (12 ng) into the SFO in sham rats produced pressor (24 +/- 2 mmHg) and dipsogenic (9.6 +/- 1.1 ml/h) responses. MSA lesion, both acute (2-6 days) and chronic (15-19 days), reduced the pressor (14 +/- 2 mmHg) and dipsogenic (2.7 +/- 1 ml/h) responses to ANGII into SFO. The injection of the cholinergic agonist carbachol (2 nmol) into the SFO in sham rats produced pressor (48 +/- 4 mmHg), dipsogenic (10 +/- 1.2 ml/h), natriuretic (457 +/- 58 microEq/2 h) and kaliuretic (249 +/- 16 microEq/2 h) responses. Acute, but not chronic MSA lesion reduced the pressor (27 +/- 3 mmHg), natriuretic (198 +/- 55 microEq/2 h) and kaliuretic (128 +/- 16 microEq/2 h) responses to carbachol into SFO. No change in the dipsogenic response to carbachol into the SFO was observed in MSA-lesioned rats. Antidiuresis after carbachol was observed only in MSA-lesioned rats. The present results show that the MSA plays a role on the pressor, natriuretic and kaliuretic responses to cholinergic activation of the SFO in rats and on the pressor and dipsogenic responses to ANGII into the same area.(ABSTRACT TRUNCATED AT 250 WORDS)