Effect of melatonin on steroid production by rat adrenals under in vitro superfusion conditions

In vitro superfusion of adrenals from male and female Wistar rats resulted in a gradual decline of the corticosterone content in the samples collected for a period of 80 minutes. ACTH administration either in the beginning or in the end of the perfusion period led to a marked increase in the level of this steroid. Contrary to this, progesterone content in the collected perfusates was constant throughout the experiments and was not influenced by ACTH. The quantities of testosterone secreted under these conditions were below the sensitivity of the assay. Perfusion with melatonin (200 pg/ml) did not affect corticosterone secretion, but resulted in a significant increase of the progesterone content in the recovered fractions. This effect was immediate and was followed by a decline in the progesterone concentration, observed during melatonin perfusion.