OBJECTIVE: To compare the responses of plasmatic ACTH to CRH or combined CRH/desmopressin stimulation in patients with ACTH-dependent Cushing's syndrome submitted to simultaneous, bilateral inferior petrosal sinuses sampling. MATERIALS AND METHODS: The procedure was performed in 21 patients - 14 women and 7 men - diagnosed with ACTH-dependent Cushing's syndrome in the period between January 1998 and December 2003. Upon catheterization of both inferior petrosal sinuses, blood samples for ACTH test were simultaneously collected from the petrosal sinuses and peripheral vein, both in the basal state and three to five minutes after injection of human CRH (100 mg) (six patients), or combined CRH/desmopressin (100 mg + 10 mg) (15 patients). RESULTS: After three minutes, both groups presented increased ACTH levels: CRH (257.77 ± 240.36 in the right petrosal sinus, and 718.78 ± 1358.82 in the left petrosal sinus [mean ± standard error]); combined CRH/desmopressin (1263.35 ± 1842.91 in the right petrosal sinus [p = 0.06], and 583.93 ± 1020.03 in the left petrosal sinus [p = 0.83]). After five minutes, the ACTH levels decreased in the group with CRH (181.07 ± 217.39 in the right petrosal sinus, and 188.25 ± 270.15 in the left petrosal sinus), and presented a progressive increase in the group with combined CRH/desmopressin (1365.29 ± 1832.31 in the right petrosal sinus [p = 0.03], and 866.43 ± 1431.72 in the left petrosal sinus [p = 0.11]). Gradient was absent in the three patients with ectopic secretion. CONCLUSION: Combined CRH/desmopressin stimulation induced a higher production of ACTH in cases of corticotroph adenomas as compared with CRH stimulation, which can improve the diagnostic sensibility of this procedure.

Keywords: Cushing's syndrome, CRH, Desmopressin, Petrosal sinus sampling