Seasonal effects of central leptin infusion on secretion of melatonin and prolactin and on SOCS-3 gene expression in ewes

Recent studies have demonstrated photoperiodic changes in leptinsensitivityofseasonalmammals.Herein,weexaminedthe interactionofseason(longdays(LD)versusshortdays(SD))and recombinant ovine leptin (roleptin) on secretion of melatonin andprolactin (PRL) andonmRNAexpression of suppressorof cytokine signaling-3 (SOCS-3) in the medial basal hypothalamus(MBH)insheep.Twenty-fourPolishLongwoolewes, surgically fitted with third ventricle (IIIV) cannulas, were utilized in a replicated switchback design involving 12 ewes per season. Within-season and replicate ewes were assigned randomly to one of three treatments (four ewes/treatment) and infused centrally three times at 0, 1 and 2 h beginning at sunset.Treatmentswere1)control,Ringer‐Lockebuffer;2)L1, roleptin, 0 . 5 mg/kg BW; and 3) L2, roleptin, 1 . 0 mg/kg BW. Jugular blood samples were collected at 15-min intervals beginning immediately before the start of infusions and continued for 6 h. At the end of blood sampling, a washout periodofatleast3dayselapsedbeforeeweswerere-randomized and treated with one of the treatments described above (four