PRELIMINARY-OBSERVATIONS USING ENDOCRINE MARKERS OF PITUITARY VENOUS DILUTION DURING BILATERAL SIMULTANEOUS INFERIOR PETROSAL SINUS CATHETERIZATION IN CUSHINGS-SYNDROME - IS COMBINED CRF AND TRH STIMULATION OFVALUE

OBJECTIVE We determined whether the measurement of hormones in pituita ry blood permits correction for dilution by non-pituitary blood during bilateral simultaneous inferior petrosal sinus blood sampling in Cush ing's syndrome. DESIGN 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-sinu s ratio, assuming uniform secretion of both hormones into each inferio r petrosal sinus. PATIENTS Eight patients with clinical and biochemica l features of Cushing's syndrome. MEASUREMENTS Basal and stimulated AC TH, TSH and PRL concentrations were measured after bilateral simultane ous inferior petrosal sinus blood sampling and simultaneously from a p eripheral forearm vein. RESULTS Basal central:peripheral ACTH ratio mi sdiagnosed four of eight patients as having non-pituitary disease. Pea k uncorrected ACTH central:peripheral ratio erroneously suggested two of eight patients had non-pituitary disease. ACTH central:peripheral r atio 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. CONCL USION This study suggests that measuring other hormones in pituitary b lood after TRH stimulation can offer a simple and reliable method for correcting for dilution by non-pituitary blood during bilateral simult aneous inferior petrosal sinus blood sampling in Cushing's syndrome.