This study was carried out to evaluate the role of the calcium-calmodulin system in cellular mediation of somatocrinin action by cells producing growth hormone. We compared GH release to intra- and extracellular cAMP levels, after incubation of pituitary cells in monolayer culture with somatocrinin alone or somatocrinin associated with exogenous calmodulin, or specific calmodulin inhibitor (W13). Calmodulin (10(-6) M) decreases somatocrinin - induced cAMP levels, maintaining elevated GH levels. W13 (10(-5) M) increases somatocrinin - induced cAMP and GH levels. Thus GH release induced by somatocrinin is modulated by two interrelated systems, adenylcyclase - cAMP system and Ca++-calmodulin system.