Prolactin response to morphine in depression

The mean maximum prolactin response following administration of morphine sulfate, 5 mg, i.v., was significantly lower in 15 unmedicated inpatients with major depressive disorder than in 8 normal controls and 11 unmedicated inpatients with other psychiatric diagnoses. The maximum prolactin response of 8/15 depressed patients was less than the lowest response of any of the normal controls. Six of 15 depressed patients had blunted prolactin responses (less than 2 ng/ml) in the 60-minute sample. The diminished increase in serum prolactin after morphine in depressed patients may reflect anterior pituitary dysfunction or abnormalities in central endogenous opioid, dopamine, serotonin, or other neuroregulatory systems.