Effects of repetitive daily acute stress on pituitary LH and prolactin release during exposure to the same stressor or a second novel stress.

The present study was carried out to examine the effect of repetitive acute stress on pituitary secretion of prolactin (PRL) and luteinizing hormone (LH) during subsequent exposure to the same stimulus or to a second, novel stress. Intact adult male rats were subjected to either a single or 10 daily acute episodes of a psychological stress, transfer to a novel environment, or a physical stressor, restraint. A single acute exposure to either stress caused a temporary but significant increase in circulating concentrations of LH and PRL, and repetitive daily exposure to these stressors resulted in the habituation of stress-stimulated release of both hormones by the 10th consecutive day. When rats previously exposed to daily novel environment stress were subjected to a single episode of restraint stress, they showed an attenuation of both the LH and PRL secretory responses to this type of stress, compared to rats exposed to only one episode of restraint. These results indicate that repeated daily exposure to specific acute stress stimuli can result in the eventual habituation of both the LH and PRL hormonal responses to stress. At least with regard to the paired stressors examined in this study, adaptation to one type of acute stress stimulation may result in altered hormonal responsiveness to a second, unfamiliar stressor.