Preliminary observations using endocrine markers of pituitary venous dilution during bilateral simultaneous inferior petrosal sinus catheterization in Cushing's syndrome: Is combined CRF and TRH stimulation of value?

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Abstract
We determined whether the measurement of hormones in pituitary blood permits correction for dilution by non-pituitary blood during bilateral simultaneous inferior petrosal sinus blood sampling in Cushing's syndrome. Bilateral simultaneous inferior petrosal sinus blood sampling was performed after combined hCRF and TRH stimulation. Peak ACTH concentrations were corrected for the TSH and PRL inter-sinus ratio, assuming uniform secretion of both hormones into each inferior petrosal sinus. Eight patients with clinical and biochemical features of Cushing's syndrome. Basal and stimulated ACTH, TSH and PRL concentrations were measured after bilateral simultaneous inferior petrosal sinus blood sampling and simultaneously from a peripheral forearm vein. Basal central:peripheral ACTH ratio misdiagnosed four of eight patients as having non-pituitary disease. Peak uncorrected ACTH central:peripheral ratio erroneously suggested two of eight patients had non-pituitary disease. ACTH central:peripheral ratio corrected by TSH and PRL correctly predicted pituitary-dependent disease in all eight cases and provided correct lateralization data in four of five patients with a unilateral pituitary microadenoma. This study suggests that measuring other hormones in pituitary blood after TRH stimulation can offer a simple and reliable method for correcting for dilution by non-pituitary blood during bilateral simultaneous inferior petrosal sinus blood sampling in Cushing's syndrome.