Photoperiod-induced changes in hypothalamic de novo DNA methyltransferase expression are independent of triiodothyronine in female Siberian hamsters (Phodopus sungorus)

•Short days induce uterine involution and body mass loss in female hamsters.•Daily triiodothyronine injections did not stimulate uterine growth.•Triiodothyronine reduced pituitary thyrotropin-stimulating hormone mRNA.•Triiodothyronine did not affect hypothalamic Gnrh or Gnih mRNA.•Short days stimulated hypothalamic de novo DNA methyltransferase mRNA.