Several studies suggests that ghrelin (GHRL) has neurobiological effects that extend beyond control of food intake. Our previous results confirmed that GHRL modulates the secretory activity of the pineal gland (PG) through nocturnal melatonin (MEL) secretion in sheep, the seasonally reproductive animals. Here we investigated the effects of GHRL (10 ng/ml) on the expression of enzymes limiting synthesis of MEL, including tryptophan 5-hydroxylase 1 (TPH1), serotonin N-acetyltransferase (AA-NAT) and its phosphorylated form p31T-AA-NAT in sheep PG explants (n = 72) during the 4-hour incubation in a gas-liquid interface, at a short (SD) and long (LD) photoperiods. After each hour of incubation selected explants were frozen in liquid nitrogen and stored at -80°C for subsequent analysis (real-time PCR, western-blotting, ELISA). Results show that GHRL regulates nightly MEL secretion in a TPH1-independent manner. The factor modulating GHRL activity was photoperiod. During SD photoperiod GHRL significantly reduced the expression of p31T-AA-NAT, AA-NAT and inhibited MEL secretion from PG explants. Whereas, during LD photoperiod no effect of GHRL on MEL secretion and expression of examined enzymes was noted. Studies indicate that GHRL directly affects PG under in vitro conditions and causes MEL secretion in animals which exhibit seasonality in reproductive and metabolic processes.