Orphan nuclear receptor RZRbeta: cyclic AMP regulates expression in the pineal gland.

The nuclear orphan receptor RZRbeta is highly expressed in the rat pineal gland. Recent studies proposed that melatonin, the pineal hormone which regulates a wide variety of circadian-linked phenomena, may be the natural ligand of this receptor. These provocative reports prompted us to learn more about RZRbeta and how it might function in circadian physiology. Here we confirm high expression of this receptor in the pineal gland, and report that pineal RZRbeta expression exhibits a strong daily rhythm. Expression is under photoneural regulation and involves an adrenergic --> cAMP mechanism.