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Clearance from cerebrospinal fluid of intrathecally administered beta-endorphin in monkeys
Abstract:
Five adult male monkeys (Macaca mulatta) weighing 7.1-9.9 kg were given synthetic human beta-endorphin (800 micrograms) and [14C]methoxy-inulin (50 microCi) in 400 microliters of normal saline intrathecally. Serial samples of cerebrospinal fluid were drawn through a previously positioned indwelling spinal catheter and were assayed for concentrations of beta-endorphin (determined by radioimmunoassay) and inulin (determined by liquid scintillation counter). Spinal fluid concentrations of beta-endorphin and inulin peaked and declined in a parallel manner. The clearance ratio (calculated from the reciprocal of the ratio of the areas under the respective curves of elimination of the two species) remained remarkably similar from animal to animal, giving a mean value of 1.060 +/- 0.090 (SEM). This ratio, being near unity, suggests that beta-endorphin is eliminated from spinal fluid in a fashion similar to that of inulin, which is removed exclusively by bulk absorption.
Insights
This study found that beta-endorphin, a natural painkiller, is cleared from cerebrospinal fluid similarly to inulin. This suggests beta-endorphin elimination occurs via bulk absorption in the spinal fluid.
Area of Science:
- Neuroscience
- Pharmacology
- Physiology
Background:
- Beta-endorphin is a key endogenous opioid peptide involved in pain modulation.
- Understanding the elimination kinetics of beta-endorphin from cerebrospinal fluid (CSF) is crucial for its therapeutic applications.
Purpose of the Study:
- To investigate the elimination rate and mechanism of synthetic human beta-endorphin from the CSF in non-human primates.
- To compare the clearance of beta-endorphin with that of inulin, a substance cleared solely by bulk absorption.
Main Methods:
- Intrathecal administration of synthetic human beta-endorphin and [14C]methoxy-inulin into adult male rhesus monkeys.
- Serial sampling of CSF via an indwelling spinal catheter.
- Assay of beta-endorphin concentrations using radioimmunoassay and inulin using liquid scintillation counting.
Main Results:
- CSF concentrations of both beta-endorphin and inulin exhibited parallel peak and decline patterns.
- The clearance ratio between beta-endorphin and inulin was consistently near unity across all subjects (mean value of 1.060 +/- 0.090).
Conclusions:
- Beta-endorphin appears to be eliminated from the CSF through a process similar to bulk absorption, analogous to inulin clearance.
- These findings support the understanding of opioid peptide pharmacokinetics within the central nervous system.