Differences in isoproterenol-stimulated melatonin production by perifused rat pineal glands: time dependent effects and role of enantiomeric forms.

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 and circadian stage dependent.