The effects of angiotensin II (A-II) and corticotropin (ACTH) on insulin-like growth factor-I (IGF-I) receptors of bovine adrenocortical cells were investigated. Pretreatment of cells for 48 h with ACTH or A-II induced in a dose-dependent manner an increase in [125I]IGF-I binding (ED50 congruent to 10(-11)M, Vmax = 10(-10) M with ACTH; ED50 congruent to 3.10(-9) M, Vmax = 10(-7) M with A-II). This resulted from an increase in the number of binding sites without modification of the binding affinity. Pretreatment with 8-Bromo-cAMP (10(-3) M), a phorbol ester (PMA 10(-7) M) + ionophore A23187 (10(-7) M) produced a positive regulation of IGF-I receptors. Glucocorticoids did not mediate the effect of A-II and ACTH on IGF-I receptors. Since previous studies have shown that IGF-I increased ACTH and A-II receptors the present data indicate the existence of a reciprocal positive trophic effect between IGF-I and the two hormones on the regulation of their specific membrane-bound receptors.