Neuroendocrine effects of light deprivation and pinealectomy in vivo on the time course of changes in prolactin cell activity in vitro.

The purpose of this investigation was to elucidate the differences in the nature and time course of changes in in vitro prolactin (PRL) cell activity between blinded and blind/pinealectomized female hamsters. Adult female golden hamsters were either left intact, blinded and sham-pinealectomized (Blind/Sham) or blinded and pinealectomized (Blind/Pinx). Twelve weeks after surgeries, animals were killed by decapitation and randomized hemipituitaries were incubated for a total of either 30, 60, 90, 120, 180 or 240 min. PRL release in vivo, as estimated by monitoring serum titers of immunoreactive PRL (IR-PRL), was markedly reduced in Blind/Sham animals; pinealectomy completely prevented this depression. PRL storage was assessed by measuring total levels (i.e., medium + pituitaries) of IR-PRL in vitro. Total, pituitary and media values of IR-PRL were all significantly depressed in Blind/Sham females. Pinealectomy of blinded animals almost completely prevented these reductions. PRL synthesis, as evaluated by measuring the amount of 3H-leucine incorporated into PRL in vitro, was profoundly reduced in Blind/Sham females. Surprisingly, pinealectomy failed to prevent the blinding-induced decrease in PRL production. From these data, we conclude that in the light-deprived female hamster the pineal gland inhibits PRL storage and release, while the depression in PRL synthesis may be independent of a pineal influence.