γ3-Melanocyte-Stimulating Hormone Immunoreactivity Is a Component of the Neuroendocrine Response to Maximal Stress (Cardiac Arrest)*

The levels of gamma 3-MSH immunoreactivity (gamma 3MSH-IR), beta-endorphin immunoreactivity (beta-endorphin-IR), ACTH, PRL, and cortisol were determined in 23 patients with cardiac arrest (CA) and in a group of 22 patients consecutively admitted to the Intensive Care Unit (ICU controls). Blood was obtained immediately after CA and at frequent intervals for the next 2 h. In ICU patients, blood was obtained the morning after admission. gamma 3MSH-IR was consistently elevated after CA; it was present in all 23 patients and was detectable in 113 of 114 samples. The mean peak gamma 3MSH-IR level was 162 +/- 20 (+/- SE) pg/ml in CA patients and the mean gamma 3MSH-IR level was 35 +/- 6 pg/ml in ICU controls (P less than 0.01). gamma 3MSH-IR was undetectable (less than 20 pg/ml) in normal subjects. CA also was associated with increases in ACTH, beta-endorphin-IR, cortisol, and PRL. The group of ICU controls had stress hormone levels that were generally within the normal range. Distribution of plasma beta-endorphin-IR by gel chromatography showed two peaks of immunoreactivity corresponding to the beta-endorphin and beta-lipotropin standards in both the CA and ICU control groups. Distribution of gamma 3MSH-IR in CA plasma showed a major peak of immunoreactivity with a mol wt of approximately 6,000 daltons and two minor components of approximately 4,000 and 11,000 dalton. No immunoreactivity coeluted with a gamma 3MSH standard. We conclude that gamma 3MSH-immunoreactive peptides are a consistent component of the massive release of pituitary and adrenal glandular products after CA.