The Effect of Stress on Serum Prolactin in the Female Rat 1 2

Summary

Changes in serum prolactin in response to ether vapor, ether vapor plus serial bleeding, acute restraint and chronic restraint stresses were measured in cycling, castrate, pregnant, and lactating female Long-Evans rats. Serum prolactin was measured by radioimmunoassays in serial blood samples taken before and after administration of each stressor. Pretreatment prolactin levels were elevated in rats in the afternoon of proestrus and estrus, on Day 1 of pregnancy, and during lactation. Low initial prolactin concentrations were observed during diestrus, on the morning of estrus, and in castrate females. Low intensity stress, such as ether vapor alone, did not affect serum prolactin concentrations in any group tested. The effect of higher intensity stress was related to the pretreatment concentration of serum prolactin. If the initial prolactin levels were high, such as on the afternoon of proestrus and estrus, on Day 1 of pregnancy, and during lactation, high intensity stress was associated with a reduction in serum prolactin in all cases except for the group of rats on the afternoon of estrus which received the restraint stress treatment. On the other hand, if the pretreatment prolactin levels were low, such as in diestrous and castrate rats, high intensity stress was found to increase serum prolactin concentrations. Rats subjected to chronic restraint stess had increased pretreatment serum prolactin during the treatment regime. Although their initial prolactin concentrations were increased, these rats had lowered levels of prolactin at the end of their restraint periods. These data reaffirm the importance of understanding the effects of stress on hormone control mechanisms, and emphasize the importance of avoiding irregular or undue stress in animals used for studies of prolactin secretion.