NONUNIFORM SYMPATHETIC-NERVE RESPONSES TO INTRAVENOUS HYPERTONIC SALINE INFUSION

Peripheral hyperosmolality produced by the intravenous infusion of hyp ertonic saline (HTS) increases mean arterial blood pressure (MAP) in e xperimental animals. The mechanisms mediating the presser response hav e not been fully ascertained, but likely involve vasopressin and/or ac tivation of the sympathetic nervous system. The primary aim of this st udy was to determine if HTS infusion produces regionally uniform or no nuniform changes in sympathetic nerve discharge (SND). For this purpos e we recorded renal, splanchnic and lumbar SND during intravenous HTS infusion (2.5 M NaCl, 10 mu l/100 g BW per min) in chloralose-anesthet ized, Sprague-Dawley rats, In rats with intact arterial baroreceptors, HTS infusion significantly increased MAP (17 +/- 2 mmHg) and lumbar S ND (29 +/- 13%) but reduced splanchnic (-52 +/- 7%) and renal SND (-33 +/- 8%). After sinoaortic denervation (SAD), FITS infusion significan tly increased MAP (28 +/- 6 mmHg) and lumbar SND (27 +/- 9%) and decre ased renal SND (-22 +/- 8%). The increase in lumbar SND occurred signi ficantly sooner in SAD compared with baroreceptor-intact rats. In cont rast, splanchnic SND remained unchanged from control levels during HTS infusion after SAD. These results demonstrate that I-ITS infusion pro duces regionally nonuniform changes in SND, and suggest that the press er and lumbar sympathoexcitatory responses to HTS infusion are opposed by the arterial baroreceptors.