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A multihormonal response to CRH during inferior petrosal sinus sampling in patients with Cushing's disease has recently been described. Whether it reflects multihormonal secretion by the corticotropic adenoma, or secretion by non-tumorous adjacent cells via paracrine mechanisms remains debatable. We have compared the effect of CRH on ACTH, GH, PRL and TSH secretion during inferior petrosal sinus sampling with its effect on the in vitro secretion of the corticotropic adenoma after excision in one case of Cushing's disease. Before CRH injection in vivo results show significant central-peripheral gradients for all hormones but only ACTH lateralized to the side of the tumor. After CRH administration, the petrosal concentrations of all hormones increased preferentially on the side of the adenoma resulting in significant intersinus gradients: 8.1 for ACTH, 2.0 for GH, 1.8 for PRL and 1.5 for TSH. In vitro results: the adenoma cells were immunostainable for ACTH only. In culture, they secreted ACTH only. Addition of CRH to the culture induced a mean increase of 160% in ACTH secretion but GH, PRL and TSH remained undetectable. Our results favor the hypothesis that the multihormonal response to CRH seen during inferior petrosal sinus sampling in Cushing's disease reflects a paracrine stimulation of the adjacent non-tumorous pituitary cells by the corticotropic adenoma.

The diagnostic accuracy of the CRH test was compared with that of the LVP test in 28 consecutive patients with ACTH-dependent Cushing's syndrome. A false negative response to CRH was found in 3 of 21 patients with pituitary-dependent Cushing's disease and to LVP in 4. The 7 patients with ectopic ACTH secretion were unresponsive to CRH, whereas 2 did respond to LVP. CRH and high-dose dexamethasone tests combination led to concordant results in 79% of patients. In all cases the etiological diagnosis suggested was correct. LVP and high-dose dexamethasone tests combination led to concordant results in only 71% of patients and the etiological diagnosis suggested was erroneous in one. Individual tolerance to the CRH test was also clearly better than that to the LVP test. It is concluded that the CRH test, alone or in combination with the high-dose dexamethasone test must be preferentially used to the LVP test in the differential diagnosis of ACTH-dependent Cushing's disease.