Corticosterone and prolactin responses to predictable and unpredictable novelty stress in rats.

Prolactin along with corticosterone is a stress responsive hormone. The present study examined the effect of predictable and unpredictable psychological stress on corticosterone and prolactin secretion. Repeated unpredictable exposure to the novelty cage produced a more substantial increase in the level of corticosterone than predictable exposure to the same novelty apparatus. In contrast, predictable novelty stress induced a more substantial elevation in prolactin levels than unpredictable stress. Furthermore, it was observed that both corticosterone and prolactin returned to control levels 30 minutes after the fifth exposure to the novelty cage. It was concluded that the pattern of exposure to novelty is an important paradigm which effects the magnitude of hormonal responding. An important relationship between corticosterone release and prolactin secretion is also indicated.