The role of @entity2493 in animals which do not show marked seasonal changes in reproduction is disputed, in part because of the wide variation in reported concentrations. One reason for this may be the difficulties associated with the measurements of low molar concentrations of @entity2493 and the presence of a wide variety of potentially cross-reacting substances. The availability of a high affinity antiserum has allowed an assay, with low cross-reactivity and good sensitivity, to be established for the direct measurement of @entity2493 in a wide range of biological fluids, in particular serum, plasma and follicular fluid from @entity1 and @entity35 . The high affinity of the antiserum enabled a @entity4463 label of high specific activity to be used, removing the problems associated with the iodination of a small molecular weight compound. @entity2493 concentrations in the assay were evaluated by four different methods: UV absorbance, gas chromatography, comparison of the immunoreactive concentrations of the label with the expected concentration by dilution and by comparison with a previously established assay which uses the same antiserum. @entity2493 was measured in serum from twelve healthy @entity1 over two 24-h periods; eight @entity1 with normal menstrual cycles and four taking the contraceptive pill. Concentrations were found to range from 19.8 to 215 pmol/l during the day in both groups. In @entity1 with normal menstrual cycles peak concentrations of 513.2 +/- 54.1 (S.E.M.) pmol/l were recorded at 04.00 h, whereas higher concentrations were found in @entity1 taking the pill, reaching a peak of 849.12 +/- 21.8 (S.E.M.) pmol/l at 04.00 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Validation of a sensitive direct assay for XXXX for investigation of circadian rhythms in different species.

@entity2493 :: ('MESH:D008550', 'Chemical') :: ['melatonin', 'Melatonin'] @entity1 :: ('9606', 'Species') :: ['women', 'man'] @entity4463 :: ('CHEBI:29304', 'Chemical') :: ['tritium'] @entity35 :: ('10116', 'Species') :: ['rat']
@entity2493 :: (MESH:D008550,Chemical) :: ['melatonin']
