The sensitivity of pineal glandβ-receptors appears to be dependent upon calcium ions

Summary Rat pineals were usedin vitro to demonstrate that calcium antagonists induce a hyposensitive response to stimulation of serotonin N-acetyl transferase (NAT) by the -agonist isoproterenol or by dibutyryl cyclic AMP. Mn²⁺, Co²⁺ and La³⁺ at 10^–3M all significantly reduce the effects of isoproterenol stimulation. In addition, the two enantiomers of D600 also inhibit NAT induction, the D-form slightly more effectively than the L-form. Interestingly, La³⁺ is also able to inhibit NAT after DBcAMP, indicating that Ca²⁺ can also control enzyme induction at an intracellular site beyond the -receptor.