Effect of in vivo pretreatment of rats with a new protein purified from Bordetella pertussis on in vitro secretion of insulin: role of calcium.

Rats were injected once iv with an islet-activating protein (IAP), a new protein purified from the culture medium of Bordetella pertussis. Three days later, their pancreases were studied in vitro for insulin secretory responses. As with pertussis vaccine, pretreatment of rats with IAP was effective in enhancing insulin release from pancreas during perfusion or from islets during incubation in response to secretagogues such as glucose and glibenclamide. The alpha-adrenergic inhibition of insulin secretion induced by epinephrine was also reversed by the pretreatment with IAP. 3-Isobutyl-1-methylxanthine caused insulin release due to accumulation of cAMP. This 3-isobutyl-1-methylxanthine-induced insulin release during perfusion was enhanced in a Ca-containing perfusate, but was conversely reduced in a Ca-free perfusate by the IAP pretreatment. Upon the addition of Ca to the Ca-free perfusate, more insulin was released from pancreases of IAP-treated rats than from those of nontreated rats.