Clearance of 125I-labeled interleukin-6 from brain into blood following intracerebroventricular injection in rats.
To test the hypothesis that interleukin-6 (IL-6) induced within the brain can be released into peripheral blood, 125I-labeled IL-6 was injected into the lateral cerebral ventricle of rats, and its concentration in peripheral blood followed serially. Acid-precipitable tracer appeared within 5 min of injection and entered the blood following first-order kinetics (fractional rate, 0.0116 +/- 0.0022/min). Comparison of areas under the curve of intracerebroventricular (icv) vs. iv injection showed that 37.1-46.5% of tracer injected into the lateral cerebral ventricle appeared in the blood over a 4-h period. icv IL-6 exits at least in part via venous drainage (superior sagittal sinus/aortic concentration gradient was 1.47 +/- 0.23 and 3.05 +/- 0.87 in two separate groups). Prior icv injection of human IL-1beta (100 ng) did not alter rate of degradation or of exit ofradioiodine-labeled IL-6 from the brain. These studies indicate that a relatively high proportion of IL-6 that arises in the brain enters the peripheral circulation. Direct secretion of IL-6 from brain to blood may be a mechanism by which the brain modifies peripheral metabolic, endocrine, and immune activity.
Chen
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Department of Medicine, University of Arizona College of Medicine, Tucson 85724, USA.
Castro
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Chow
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Reichlin
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D000818:Animals; D001011:Aorta; D001921:Brain / Q000378:metabolism*; D003392:Cranial Sinuses; D007276:Injections, Intraventricular; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000097:blood* / Q000134:cerebrospinal fluid / Q000493:pharmacokinetics*; D007457:Iodine Radioisotopes; D008297:Male; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley
D007375:Interleukin-1; D015850:Interleukin-6; D007457:Iodine Radioisotopes