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Afternoon injections of melatonin in the Djungarian hamster Phodopus sungorus : Long lasting sex‐specific effects and influence of acute treatment on the endogenous pineal melatonin rhythm
Author(s) -
Niklowitz Petra,
Bockers Tobias M.,
Lerchl Alexander
Publication year - 1996
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1996.tb00291.x
Subject(s) - melatonin , endocrinology , medicine , phodopus , hamster , endogeny , circadian rhythm , biology , hormone , pineal gland
The effects of exogenous melatonin on gonadal function and on the endogenous melatonin profiles of male and female Djungarian hamsters were investigated. Daily afternoon subcutaneous injections of melatonin (50 μ.g) in hamsters kept in long photoperiods (LD 16: 8) led to gonadal inhibition in all the treated females (n=13) but in only 2 of 13 males within the treatment period of 8 weeks (uteri: 244±11 mg in controls vs. 79±4 mg in treated hamsters, P <0.001; ovaries: 13.6±0.6 mg in controls vs. 7.9±0.7 mg in treated hamsters, P <0.001; testes: 1,021±54 mg in controls vs. 732±100 mg in treated hamsters, P <0.05; and accessory glands: 641±38 mg in controls vs. 548±70 mg in treated hamsters, P >0.05). These results indicate that there are some circumstances under which the gonadal responses of the reproductive organs of male and female Djungarian hamsters differ. Interestingly, pineal concentrations of melatonin were found to be significantly higher in males ( P <0.01), possibly indicating a more robust endogenous supply with the hormone, whereas serum melatonin levels were not significantly different between males and females. However, the subcutaneous injection of melatonin (5, 25, and 125 μg) exerted no acute effect on the endogenous, circadian melatonin‐profile, independent of dosage and sex.