Role of extracellular calcium on the regulation of melatonin synthesis in the Syrian hamster pineal gland

Abstract

The role of extracellular calcium on the induction of cyclic AMP production, N-acetyltransferase (NAT) activity and melatonin synthesis, induced by forskolin, was investigated in Syrian hamster pineal glands. Pineals were removed from hamsters killed either in the first half of the normal dark period or late in the dark period. Forskolin immediately increased NAT activity and melatonin levels only when the glands were collected late in the dark period, while in the first half of the dark phase, hamster pineals responded to forskolin with an increase of NAT activity and melatonin production only after 6 hr of incubation. The absence of calcium prevented the induction of melatonin synthesis by forskolin only when glands were collected early in the dark phase and incubated for 6 hr. In the second half of the normal dark period removal of calcium markedly decreased NAT activity and melatonin levels in glands incubated with forskolin for either 4 or 6 hr. However, the absence of extracellular calcium had no significant effect on the induction of cyclic AMP production by forskolin in pineals collected either early in the dark period or late in the dark phase. These data indicate that at least part of the action of extracellular calcium is indirect and that it affects steps in the induction of melatonin synthesis beyond the accumulation of cAMP.

Melatonin secretion in a strictly subterranean mammal, the Damaraland mole‐rat (Cryptomys damarensis)

“…Note that other studies have found no significant effect of gender (e.g. Santana et al, 1991;Reiter, Reiter et al, 1994) or reproductive status (Reiter & Richardson, 1992;Zarazaga, Malpaux & Chemoneau, 1996). An explanation for this unusual finding warrants further investigation, particularly in light of the extensive reproductive skew in this eusocial mammal.…”

Cryptochrome deficiency enhances transcription but reduces protein levels of pineal Aanat

“…Pineal glands of the WT (n = 21; male n = 9, female n = 12) and Cry1 −/− /Cry2 −/− (n = 21; male n = 10, female n = 11) mice were sampled from mice kept in LD at ZT3 and individually incubated with 200 μL of DMEM at 37°C and 5% CO 2 for 30 min. After this pre-incubation, 200 μL of forskolin (FSK, final concentration, 50 μM) or vehicle (DMEM) was added to the culture medium at projected ZT3.5 and incubated at 37°C and 5% CO 2 for 1 h. The dose was reported to increase cAMP level and melatonin synthesis in cultured pineal gland (Santana et al 1988(Santana et al , 2001). The cultured pineal glands were rinsed by transferring them three times to new culture wells containing 200 μL of cold 0.1 M Tris-HCl buffer (pH 7.2).…”

Mammalian neurohormones: potential significance in reproductive physiology of St. John's wort (Hypericum perforatum L.)?

“…Viability of microspores in vivo varied with weather conditions and daylength (Tian et al 1998;Zeng et al 1999) and photoperiod-sensitive varieties of rice have been developed in which pollen aborts in the late microspore stage when exposed to long daylengths (Wu and Wang 1990). This loss of microspore viability has also been associated with an alteration in the concentration and distribution of calcium (Tian et al 1998;Poovaiah et al 1999), a key regulator of the rate-limiting enzyme in melatonin biosynthesis, N-acetyltransferase (Meissl et al 1996;Santana et al 2001). Our data show a decrease in serotonin and increase in melatonin corresponding to the transition from the tetrad to uninucleate microspore phases that may reflect an adaptation to changing photoperiod potentially through altered distribution of Ca 2+ .…”