PINEAL PHOTORECEPTOR CELLS IN CULTURE - E STRADIOL-17-BETA EFFECTS ONMELATONIN PRODUCTION

Pineal photoreceptor cells produce the neurohormone, melatonin, a majo r << Zeitgeber >> of the organism. This compound has been involved in the control of development, growth, sexual maturation, and seasonal re productive cycles. We investigated, here, the effects of estradiol-17b eta on melatonin production by cultured pineal photoreceptor cells. Un der a light/dark (LD : 12/12) cycle, cultured trout pineal cells maint ained a rhythmic secretion of melatonin with higher amounts being rele ased during the dark phase. The amplitude of the rhythm tended to incr ease with time spent in culture. Application of estradiol-17beta durin g the dark phase of a LD cycle (i. e., for 12 h) affected melatonin re lease in a dose-dependent manner: low concentrations (10(-10) to 10(-8 ) mol/l) were inhibitory whereas high concentrations (over 10(-7) mol/ l) were stimulatory. When estradiol-175 was applied continuously for s everal 24 h LD cycles, the inhibitory effect observed during the first dark phase disappeared later on. Rather, in the presence of estradiol -17beta, at the concentrations of 10(-9) and 10(-6) mol/l, a high ampl itude rhythm in melatonin secretion was recovered faster, when compare d to controls. Replacement of 10 % fetal calf serum by 0.1 % bovine se rum albumin did not affect the responses of the photoreceptor cells to 10(-6) mol/l of estradiol-17beta. The present results bring the first evidence that estradiol-17beta modulates melatonin secretion by cultu red pineal photoreceptors. They further support the idea according to which sexual hormones exert a feedback regulation on the pineal. Pinea l photoreceptors appear as multieffector cells which transduce informa tion from, both, physical (photoperiod) and internal (chemical) factor s.