Sympathetic neural responses to increased osmolality in humans.
The purpose of this study was to examine the relationship between osmolality and efferent sympathetic outflow in humans. We hypothesized that increased plasma osmolality would be associated with increases in directly measured sympathetic outflow. Muscle sympathetic outflow was successfully recorded in eight healthy subjects during a 60-min intravenous hypertonic saline infusion (HSI; 3% NaCl) on one day and during a 60-min intravenous isotonic saline (ISO) infusion (0.9% NaCl) on a different day. The HSI provides an osmotic and volume stimulus, whereas the ISO infusion provides a volume-only stimulus. Muscle sympathetic nerve activity was quantified using the technique of peroneal microneurography. Plasma osmolality increased during the HSI but not during the ISO infusion (ANOVA, P < 0.05). Sympathetic outflow differed between the trials (ANOVA, P < 0.05); during the HSI burst, frequency initially increased from 14.6 +/- 2.5 to 18.1 +/- 1.9 bursts/min; during the ISO infusion, burst frequency initially declined from 14.7 +/- 2.5 to 12.0 +/- 2.1 bursts/min. Plasma norepinephrine concentration was greater at the end of the HSI compared with the end of the ISO infusion (HSI: 297 +/- 64 vs. ISO: 202 +/- 49 pg/ml; ANOVA, P < 0.05). We conclude that HSI-induced increases in plasma osmolality are associated with increases in sympathetic activity in humans.
Farquhar
William B
WB
Department of Health, Nutrition, and Excercise Science, University of Delaware, USA. wbf@udel.edu
Wenner
Megan M
MM
Delaney
Erin P
EP
Prettyman
Allen V
AV
Stillabower
Michael E
ME
D000328:Adult; D001794:Blood Pressure / Q000187:drug effects; D015992:Body Mass Index; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006982:Hypertonic Solutions / Q000009:adverse effects; D007262:Infusions, Intravenous; D007552:Isotonic Solutions / Q000009:adverse effects; D008297:Male; D008839:Microelectrodes; D009132:Muscles / Q000294:innervation; D009476:Neurons, Efferent / Q000187:drug effects*; D009638:Norepinephrine / Q000097:blood; D009994:Osmolar Concentration; D010543:Peroneal Nerve / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology*; D013564:Sympathetic Nervous System / Q000187:drug effects* / Q000503:physiopathology; D013997:Time Factors
D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D012965:Sodium Chloride; D009638:Norepinephrine