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Drug‐Induced Changes in Blood Pressure Lead to Changes in Extracellular Concentrations of Epinephrine, Dihydroxyphenylacetic Acid, and 5‐Hydroxyindoleacetic Acid in the Rostral Ventrolateral Medulla of the Rat
Author(s) -
Dev Bhaskar R.,
Mason Patrick A.,
Freed Curt R.
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb11354.x
Subject(s) - ascorbic acid , phenylephrine , microdialysis , uric acid , chemistry , neurochemical , epinephrine , endocrinology , 5 hydroxyindoleacetic acid , extracellular fluid , medicine , rostral ventrolateral medulla , blood pressure , catecholamine , extracellular , heart rate , biochemistry , serotonin , receptor , food science
Neurochemical changes in the extracellular fluid of the rostral ventrolateral medulla (RVLM) were produced by changes in arterial blood pressure. Blood pressure was raised or lowered with systemic infusions of phenylephrine or nitroprusside and neurochemicals were recovered from RVLM by in vivo microdialysis. A dialysis probe 300 μm in diameter and 500 μm in length was stereotaxically implanted in the RVLM of the urethane‐anesthetized rat. Sterile physiological Ringer's solution was perfused at a rate of 1.5 μl/min. The perfusate was collected under ice‐cold conditions every 15 min for the assay of epinephrine, dihydroxyphenylacetic acid (DOPAC), 5‐hydroxyindoleacetic acid (5‐HIAA), ascorbic acid, and uric acid. After stable baseline neurochemical concentrations were achieved, animals were infused with phenylephrine or nitroprusside intravenously to raise or lower the blood pressure. Increasing blood pressure 50 mm Hg above the baseline value by phenylephrine led to a significant reduction in heart rate and a reduction in extracellular epinephrine and DOPAC concentrations. The 5‐HIAA concentration was increased during the hypertensive drug infusion. There were no changes in the concentrations of ascorbic acid or uric acid. Hypotension produced by nitroprusside (—20 mm Hg) led to neurochemical changes which were the reciprocal of those seen during hypertension. During hypotension, heart rate increased as did the extracellular fluid epinephrine concentration. The 5‐HIAA concentration fell with hypotension and remained depressed following the nitroprusside infusion. Ascorbic acid and uric acid concentrations did not change during hypotension but ascorbic acid did increase after the nitroprusside infusion stopped. These data provide direct evidence that epinephrine release in RVLM is linked to changes in systemic blood pressure. Furthermore, because changes in epinephrine concentration parallel changes in sympathetic activity as measured by heart rate, epinephrine in the extracellular fluid space of the RVLM may be a marker for sympathetic nerve activity.