[Study of control of the production of melatonin by perifusion of pineal bodies in rats].

We have documented the kinetic characteristics of melatonin production in perifused pineals removed from rats sacrified at 6 circadian stages (L:D = 12:12) i.e. 3, 7, 11, 15, 19, 23 hours after light onset (HALO). The initial melatonin production levels were as expected higher in glands removed during the dark than in those removed during the light. The higher the initial level was, the more rapide it decreased. Whatever the circadian stage the melatonin production decreased during the first 3-4 hours, then remained fairly constant up to 8 hours of perifusion. The perifusion of rat pineal glands removed at different times of the light-dark cycle showed a greater, beta-adrenergic-stimulated production of melatonin in glands obtained at the beginning of either the light or the dark stage. The effect of isoproterenol was found dependent upon its enantiomeric forms (-, +/-, +). The relative order of potency was (-) > (+/-) > (+) enantiomer. These results show that the response of pineal beta-adrenergic receptors to isoproterenol is stereospecific this response is also circadian stage dependent.