Detection of estrogen receptor mRNA in trout pineal and retina: estradiol-17 beta modulates melatonin production by cultured pineal photoreceptor cells.

Pineal photoreceptor cells produce the neurohormone melatonin, a major "Zeitgeber" of the organism. This compound is involved in the control of development, growth, sexual maturation, and seasonal reproductive cycles. The present study reports that the photosensitive pineal organ and the retina of the trout express a 3.5-kb mRNA corresponding to the estradiol-17 beta receptor. The effects of estradiol-17 beta on melatonin production by cultured pineal photoreceptor cells were also studied. Under a light/dark (LD:12/12) cycle, these cells maintained a rhythmic secretion of melatonin, with higher amounts being released during the dark phase. The amplitude of the rhythm tended to increase with time in culture. Application of estradiol-17 beta during the dark phase of an LD cycle (i.e., for 12 hr) affected melatonin release in a dose-dependent manner; low concentrations (10(-10) to 10(-8) mol/liter) were inhibitory, whereas high concentrations (over 10(-7) mol/liter) were stimulatory (when compared to the values obtained at 10(-9) mol/liter). When estradiol-17 beta was given continuously for several 24-hr LD cycles, the inhibitory effect observed during the first dark phase disappeared in subsequent dark periods. In the presence of estradiol-17 beta, at concentrations ranging from 10(-10) to 10(-5) mol/liter, a high amplitude rhythm in melatonin secretion returned more rapidly than in controls. The present results suggest that estradiol-17 beta receptors are expressed in the fish pineal and retina and that estradiol-17 beta modulates melatonin secretion by cultured pineal photoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)