Inhibition of adenosine 3',5'-monophosphate accumulation and parathyroid hormone release by sodium nitroprusside

Sodium nitroprusside effected a significant reduction in intracellular cAMP accumulation and parathyroid hormone release in dispersed bovine parathyroid cells. The inhibition was apparent at 3 x 10-4 M and maximal at 10-2 M nitroprusside. The effect was rapid and reversible and could be demonstrated in both the presence and absence of stimulating agonists [i.e. (-)isoproterenol, dopamine, and cholera toxin]. The inhibition was additive with that previously described for alpha-adrenergic agonists and prostaglandin F2 alpha and was not affected by phentolamine, suggesting that nitroprusside does not act through the inhibitory receptors previously described in this system. The nitroprusside effect on cAMP accumulation and parathyroid hormone release was present at virtually all concentrations of extracellular calcium tested; 2mM EGTA failed to prevent the inhibition. While extracellular calcium may play some role in this inhibition, it is not required for demonstration of the effect.