Beta-endorphin, ACTH, and cortisol response to hemorrhage in conscious pigs

Some of the interrelations of neuroendocrine changes associated with hypovolemia were investigated in a model simulating an arterial hemorrhage. beta-Endorphin, adrenocorticotropin hormone (ACTH), and cortisol levels were measured by radioimmunoassay before, during, and after controlled bleeding of conscious splenectomized pigs. All animals showed significant (P less than 0.05) increases in the three neuroendocrine substances during hemorrhage. beta-Endorphin values initially were 55 +/- 7 pg/ml (+/- SE) and rose to a peak of 386 +/- 44 pg/ml at the nadir of blood pressure (mean arterial pressure = 47.5 mmHg). ACTH showed a similar pattern, increasing from 49 +/- 10 to a peak of 518 +/- 56 pg/ml. Cortisol values reached their peak of 18.2 +/- 2.5 micrograms % during the recovery phase. beta-Endorphin values displayed a close inverse correlation to blood pressure during hemorrhage, but returned to basal levels more rapidly than blood pressure during the recovery period. Plasma ACTH levels rose significantly more slowly than beta-endorphin as the hemorrhage progressed. An equimolar ratio of ACTH and beta-endorphin returned only as levels declined following the hemorrhagic insult. In awake pigs therefore an arterial hemorrhage is accompanied by endorphin release proportional to the decrement in blood pressure, a somewhat retarded buildup of ACTH, and a still later cortisol peak during recovery.