Differences in hormone release patterns from the anterior pituitary and the pineal gland

Patterns of hormone release from peptide- and monoamine-hormone secreting cells were compared. LH, GH and PRL secretion from rat anterior pituitary cells and melatonin secretion from the rat pineal gland fragments were studied in a dynamic, in vitro system. The following fundamental differences were found: 1. Adenohypophysial cells respond to a specific stimulus (releasing hormones) with hormone secretion within seconds. There is a 90-minute lag, however, between the beginning of specific stimulation (norepinephrine, 1 microM for 30 min) and the onset of melatonin (MT) release from the pineal cells. 2. Hormone secretion from the pituitary cells returns to the basal value five to 10 minutes after the stimulus has been stopped. Once initiated, MT release from the pineal lasts for five to seven hours even if the NE stimulus was stopped one hour before the beginning of the MT response. 3. A transitory increase in potassium concentration (by 50-100 mM) induces a sharp, distinct rise of hormone secretion from pituitary cells, similar in shape and size experienced as response to releasing hormone stimulation. Pineal cells do not respond to elevation of potassium concentration at all. 4. High concentration of tropic hormones can be extracted from pituitary cells at the end of the superfusion experiment. Their hormone content is equivalent to the amount released from non-stimulated cells in a 50 to 80 hours period (LH and GH cells). No significant quantity of MT can be extracted from non-stimulated, disintegrated pineal cells. This diversity in the control of hormone secretion from anterior pituitary and the pineal gland can be considered as a model for peptide and monoamine-hormone producing glands.