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Bovine pinealocytes in monolayer culture: studies on the adrenergic regulation of melatonin secretion.

Most of what is known regarding adrenergic control of mammalian pineal functions has been derived from investigations with rodents. In an effort to provide a new animal model for pineal research, the bovine pineal gland was selected for practical and theoretical reasons. Bovine pinealocytes in monolayer culture were first characterized in terms of optimal culture conditions, i.e. medium requirements, cell density, preincubation duration and stimulation times. In Dulbecco's minimum essential medium/Ham's F12 medium, 2 x 10(5) cells per well preincubated for 6 days and stimulated for 8 h resulted in large increases in melatonin (mel) release (15- to 17-fold) after adrenergic stimulation. Likewise, cAMP accumulation within 10 min of stimulation increased 4- to 8-fold. (Bu)2cAMP (10(-5)-10(-3) M) produced a significant elevation in MEL secretion. Neither adrenergic dose-response studies, adrenergic antagonist studies nor experiments in which alpha- and beta-agonists were added together provided any evidence for a positive alpha/beta synergism on either MEL release or cAMP accumulation by bovine pinealocytes. This culture system should prove useful for identifying species differences in the signal transduction mechanisms underlying the activation of MEL secretion in the mammalian pineal.