In vitro effects of estradiol, testosterone, and progesterone on 5-methoxyindole content, cyclic adenosine 3',5'-monophosphate synthesis, and norepinephrine release in different parts of the female guinea pig pineal complex.

To examine the effects of estradiol, testosterone, or progesterone on cyclic adenosine 3',5'-monophosphate (AMP) accumulation, 5-methoxyindole levels, and norepinephrine (NE) release by the female guinea pig pineal complex, samples of the deep, intermediate, or superficial portions of the complex were incubated in vitro with varied concentrations of either hormone. Exposure for 10 minutes to physiological amounts of estradiol (10 nM) or to 100 microM NE increased significantly cyclic AMP levels to the same extent in the three pineal regions. A maximal effect on cyclic AMP accumulation was observed at 100-nM concentrations of estradiol, with a tendency to return to basal levels at 1-10 microM of estradiol. Only high concentrations of testosterone or progesterone (i.e., 1-10 microM) increased cyclic AMP accumulation in incubated guinea pig pineal fragments. At a 100-nM concentration estradiol did not affect NE-stimulated cyclic AMP accumulation in guinea pig pineal fragments. In samples of either pineal region incubated for 6 hours in TC 199 medium with 10(-7) M or greater concentrations of estradiol and analyzed for melatonin, 5-methoxyindoleacetic acid, and 5-methoxytryptophol by high-pressure liquid chromatography with electrochemical detection, a significant increase of melatonin levels was found. Neither testosterone nor progesterone modified 5-methoxyindole levels of incubated explants. K+-stimulated transmitter release from guinea pig pineal fragments previously incubated with 3H-NE was not affected by hormone exposure. These results suggest that physiological concentrations of estradiol may exert a postsynaptic stimulation of cyclic AMP and melatonin synthesis to the same extent in all three regions of the female guinea pig pineal complex.