title: Time-dependent effects of melatonin on immune measurements in male Syrian hamsters.
abstract: Adult, male Syrian hamsters received daily subcutaneous melatonin (25 microg) injections or vehicle injections at 08:00 or 17:00 hr for 11 weeks. Body weights were measured weekly throughout the experiment and testes weights, spleen weights, and serum was collected at the end of the experiment. The spleens were sectioned and immunocytochemically analyzed for immunoglobulin G and serum levels of interferon-gamma, interleukin-2, and interleukin-4 were determined in heterologous mouse assays. Melatonin injections at 17:00 hr, but not at 08:00 hr, increased body weights, decreased testes weights and serum testosterone levels, and had no effect on immunoglobulin G content in the spleen. Likewise, melatonin injections at 17:00 hr, but not at 08:00 hr, increased serum interferon-gamma levels, had no effect on interleukin-2 levels, and appeared to increase interleukin-4 levels. Since melatonin injections at 08:00 hr were ineffective in altering immune measurements and correlations between reproductive measures and immune measures were high, the most parsimonious explanation for these results is that melatonin injections at 17:00 hr depressed reproductive hormone levels and these depressed levels altered immune measures.
authors.affiliation: Department of Human Anatomy and Medical Neurobiology, College of Medicine, Texas A&M University Health Science Center, College Station 77843-1114, USA. thchamp@tamu.edu
authors.forename: T H
authors.initials: TH
authors.lastname: Champney
authors.forename: G C
authors.initials: GC
authors.lastname: Allen
authors.forename: M
authors.initials: M
authors.lastname: Zannelli
authors.forename: L A
authors.initials: LA
authors.lastname: Beausang
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D006224:Cricetinae; D016207:Cytokines / Q000097:blood; D007107:Immune System / Q000187:drug effects*; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000032:analysis; D007279:Injections, Subcutaneous; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D008647:Mesocricetus; D009929:Organ Size / Q000187:drug effects; D013154:Spleen / Q000187:drug effects / Q000276:immunology; D013737:Testis / Q000187:drug effects; D013997:Time Factors
chemical_list: D016207:Cytokines; D007074:Immunoglobulin G; D008550:Melatonin