INCREASED MELATONIN LEVELS AFTER HEMORRHAGIC-SHOCK IN MALE AND FEMALEC3H HEN MICE/

Although hemorrhagic shock leads to significant alterations of several hormones, e.g. ACTH, corticosterone and beta-endorphin, it is not kno wn whether plasma melatonin levels are affected under this condition a nd if so, whether the effects are comparable in males and females. Usi ng a radioimmunoassay, it was found that plasma melatonin levels were significantly increased in male and proestrus female C3H/HeN mice imme diately after hemorrhagic shock. However, in male mice, by two hours a fter hemorrhage and resuscitation, plasma melatonin returned to levels comparable to those seen in control and sham-operated animals. Proest rus female mice, on the other hand, showed significantly increased pla sma melatonin levels at two hours after surgery when compared to unope rated control animals. Although the significance and biological role o f the transient increased plasma melatonin levels after hemorrhagic sh ock remain to be determined, it appears that the pineal gland and/or a n extrapineal source of melatonin, of both male and proestrus female m ice responds to severe hypotension by increased release of melatonin.