MELATONIN SYNTHESIS IN THE BOVINE PINEAL-GLAND IS REGULATED BY TYPE-II CYCLIC-AMP-DEPENDENT PROTEIN-KINASE

We investigated the expression of regulatory (R) and catalytic (C) sub units of cyclic AMP-dependent protein kinase (cAK; ATP:protein phospho transferase; EC 2.7.1.37) in the bovine pineal gland. In total RNA ext racts of bovine pineal glands moderate levels of RI alpha/RII beta and high levels of C alpha and C beta mRNA were found. We were able to de tect a strong signal for RII and C subunit at the protein level, where as RI was apparently absent, Probing sections of the intact bovine pin eal gland with RI and RII antibodies stained only RII in pinealocytes. Pairs of cyclic AMP analogues complementing each other in activation of type II cAK, but not cAKI-directed analogue pairs, showed synergist ic stimulation of melatonin synthesis. Moreover, melatonin synthesis s timulated by the physiological activator norepinephrine in pineal cell cultures was inhibited by cAK antagonists. Taken together these resul ts show the presence of RII regulatory and both C alpha and C beta cat alytic subunits and thus cAKII holoenzyme in the bovine pineal gland, The almost complete inhibition of norepinephrine-mediated melatonin sy nthesis by the cAK antagonists emphasizes the dominant role of cyclic AMP as the second messenger and cAK as the transducer in bovine pineal signal transduction.