The sensitivity of pineal gland beta-receptors appears to be dependent upon calcium ions.

Rat pineals were used in vitro to demonstrate that calcium antagonists induce a hyposensitive response to stimulation of serotonin N-acetyl transferase (NAT) by the beta-agonist isoproterenol or by dibutyryl cyclic AMP. Mn2+, Co2+ and La3+ at 10(-3)M 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 beta-receptor.