Effects of N-terminal peptide of salmon proopiocortin on interrenal function of the rainbow trout.

Effects of N-terminal peptide of salmon proopiocortin (salmon NPP-I) on cortisol secretion was examined in vitro using diced interrenal tissue from the rainbow trout, Salmo gairdneri. ACTH(1-24) at concentrations of 1 to 50 nM stimulated cortisol secretion in dose-dependent manner, whereas salmon NPP-I had no effect over a range of 50 pM to 500 nM. Cortisol secretion in response to various doses of ACTH(1-24) was modified slightly when 1 to 100 nM of salmon NPP-I was added to the incubation medium together with ACTH. An augmentation of in vitro secretion of cortisol in response to ACTH(1-24) was observed when the interrenal was removed from the trout pretreated with one IU of porcine ACTH but not with 10 micrograms of salmon NPP-I. A slight but significant potentiating effect of salmon NPP-I (10 or 100 nM) on the ACTH-induced cortisol secretion was observed when the trout was sensitized to ACTH by porcine ACTH pretreatment. Furthermore, six daily injections of salmon NPP-I into the trout induced hyperplasia of interrenal tissue. These findings suggest that NPP-I, together with ACTH, may be involved in controlling interrenal function in the trout. Such activities could be due to conservative region in the N-terminal portion of NPP.