Pineal Gland Inhibition of Prolactin Cell Activity Is Independent of Gonadal Regression

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Abstract
In order to determine whether the inhibitory effect of the pineal gland on the PRL cells of blind-anosmic female rats is a result of the attendant gonadal regression observed in these animals, mammotroph activity was compared between intact and ovariectomized rats eight weeks after prepubertal blinding and olfactory bulbectomy. PRL synthesis was evaluated by measuring the amount of 3H-leucine incorporated into PRL by interior pituitaries in vitro. PRL synthesis was reduced by 47% in blind-anosmic rats, an effect which was reversed by pinealectomy. Although ovariectomy itself led to a 64% decrease in PRL synthesis, dual-sensory deprivation in these animals resulted in a further 59% suppression of PRL production. PRL storage, as estimated by measuring total immunoreactive PRL in vitro also appeared to be significantly depressed in blind-anosmic female rats. Once again, ovariectomy had no effect on this reduction. PRL release, as assessed by monitoring serum levels of the hormone, was decreased in blind-anosmic rats. Ovariectomy also caused a reduction in serum PRL levels; however, the combination of blinding and olfactory bulbectomy had no further depressive effect on circulating PRL titers in these animals. Correlated with the decrease in PRL cell activity in both intact and ovariectomized blind-anosmic rats was a pineal-induced decrease in anterior pituitary weight and DNA content in both sets of animals. From these data we conclude that the pineal’s inhibition of the PRL cell in blind-anosmic female rats is largely independent of the gonads and, therefore, could not be secondary to gonadal involution.