Adult guinea pigs were carefully standardized for at least seven days prior to each experiment; this included an artificial light-dark cycle with light extending from 0600 to 1800. On three experimental days, eight animals were injected subcutaneously with 300 μg of histamine at six-hour intervals over a 24-hour period; each animal received four injections during one day. The size of the erythema produced each time was measured. In all three experiments a prominent group rhythm was demonstrated with maximum response occurring during the dark phase; minimum response always occurred during the latter part of the light phase. Such results indicate a strong synchronization among the animals of the group. Two additional, similar studies were performed on animals standardized in one case for 21 days and in the second for 35 days under continuous illumination. The group rhythms of histamine response under these conditions, when compared to the light-dark adapted group rhythm, were greatly modified in phasing and profile. The circadian rhythm in response to histamine persisted in each individual animal. The change in the phasing and profile of the group rhythm was due to a partial desynchronization among the individual animals subjected to continuous illumination.

ARTICLESCircadian variation in rat serum 5-hydroxytryptamine and effects of stimuli on the rhythmLE Scheving, JD Dunn, JE Pauly, and WH HarrisonLE Scheving, JD Dunn, JE Pauly, and WH HarrisonPublished Online:01 Feb 1972https://doi.org/10.1152/ajplegacy.1972.222.2.252MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation More from this issue > Volume 222Issue 2February 1972Pages 252-255 Copyright & PermissionsCopyright © 1972 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1972.222.2.252PubMed5058363History Published online 1 February 1972 Published in print 1 February 1972 Metrics