J. L. Weller coauthored, with D. C. Klein, a 1970 investigation of circadian rhythms in the rat pineal gland. The experiment measured serotonin N-acetyltransferase activity over time rather than inferring all biochemical events from the final amount of melatonin.[ref]
Night-time activity exceeded daytime activity by more than fifteenfold. Persistence in darkness and in blinded animals, together with suppression by constant light, supplied controls on how the rhythm related to environmental illumination.[ref]
An enzyme-activity measurement asks what a preparation can do under the assay conditions. It is different from measuring how much enzyme is present or how much product has accumulated in an intact animal. That distinction makes the work an example of connecting a daily biological pattern to a defined biochemical readout.
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