Efflux of cyclic nucleotides from rat pineal: release of guanosine 3',5'-monophosphate from sympathetic nerve endings.

Potassium and norepinephrine stimulate the efflux of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) from intact pineal glands. The postsynaptic beta-adrenergic receptor mediates the efflux of cyclic AMP. In contrast, the efflux of cyclic GMP requires calcium and intact nerve endings. It appears that sympathetic nerve endings may release cyclic GMP into the synaptic space.