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1. In addition to evidence that dopamine (DA) inhibits prolactin (PRL) via the tuberinfundibular system, there is also evidence for excitatory effects of DA via that system as well as evidence for regulation by DA sites lying behind the blood brain barrier. 2. Apomorphine (APO) was given to rats pretreated with either a peripheral (domperidone, DOM) or a central (haloperidol, HAL) DA blocker and prolactin responses examined. 3. Both DOM and HAL caused prolactin elevation. 4. Further elevation of prolactin was produced by APO in HAL treated animals, indicating an excitatory dopamine effect on prolactin.

TRH and LHRH were simultaneously infused into a group of five male patients with primary unipolar depression and four male secondary depressed patients. Blood samples were measured for LH and TSH just before and two hours following infusion. Six healthy male subjects matched for age were similarly studied. Our results showed: 1) that basal levels of TSH and LH were not different in any of the three groups of subjects, 2) TSH responses in the three groups were not significantly different, and 3) the LH response was significantly greater in the secondary depressed patients than the primary unipolar depression and normal controls at all time intervals after infusion. Our results add to the existing evidence for an abnormality in the hypothalamo-pituitary regulation of pituitary hormones-in particular LH. Such an abnormalit has not been reported in the literature to our knowledge. Our results tend to suggest a biological difference in the two subtypes of depression studied. Neuroendocrine studies would appear to be a useful diagnostic procedure in the differentiation of these subtypes of depression.

Corticosterone, prolactin, and growth hormone responses to 5 s of handling or 3 min of novel environment were compared in rats at crest and trough of the diurnal adrenal rhythm 0, 5, 15, 30, and 60 min after stimulation. All hormones responded to stimulation, corticosterone and prolactin with a dramatic rise, and growth hormone with a precipitous fall. Resting corticosterone levels evidenced the expected diurnal variation, and prolactin but not growth hormone also showed a baseline diurnal variation of small magnitude at the times studied. Growth hormone response characteristics were unaffected by time of day or type of stimulation. Both corticosterone and prolactin response profiles differed at both times of day and following both types of stimulation. Corticosterone and prolactin levels were highly correlated and each was negatively correlated with growth hormone levels. This study confirms that hormone responses to stress are complex and depend not only on the stimulus but the context of stimulation.