Circadian rhythms in serum and CSF cortisol of rhesus monkeys, and their modulation by timed injections of L-5-hydroxytryptophan
Abstract
Levels of in serum and cerebrospinal fluid have been studied in male and female rhesus monkeys. Untreated animals showed circadian rhythms of cortisol in both compartments, highest values occurring at 08.00 h and lowest at 20.00 h, but the decline following the morning peak was slower in cerebrospinal fluid (CSF) than in serum. Both levels and CSF/serum ratios (c. 0.017-0.027) were similar in males and females. The ratio between highest and lowest points on the circadian rhythm was greater for CSF (males: 2.50; females: 2.63) than for serum (1.69 and 1.78). There were significant correlations between CSF and serum levels in individual monkeys at each of the four time points studied. No circadian rhythm in CSF homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5-HIAA) was found, nor any correlation between these monoamine metabolites and cortisol levels. Injecting cortisol once daily in the evening (18.00h) resulted in greater proportional elevation in the CSF than in serum cortisol in samples taken two hours later, and the values in the two compartments were no longer correlated at this time. There was no effect on CSF 5-HIAA levels, Injecting L-5-hydroxytryptophan (L-5-HTP) (2.5 mg/kg) at four different time points produce...Continue Reading
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