SCINTIGRAPHIC IMAGING OF PITUITARY-ADENOMAS - AN IN-VIVO EVALUATION OF SOMATOSTATIN RECEPTORS

We have performed pituitary scintigraphy with the somatostatin (SS) an alog pentetreotidean by (In-111-P) in patients with GH-secreting adeno ma or with ''clinically non functioning'' adenoma (NFA) to evaluate th e presence and the functionality of SS receptors (SS-R). In-111-P pitu itary accumulation was expressed as Activity Ratio (AR): the ratio bet ween the uptake of radioactivity by the adenoma and that of the normal brain tissue. In subjects without pituitary disease, AR ranged from 1 .6 to 2.2 and a value lower than 2.2 was thus arbitrarily considered a s normal. In 15 out of the 17 patients with GH-secreting adenoma, an a ccumulation of the radioligand was shown. Median AR was 3.8 (range 1-6 .9; in 14 AR were greater that 2.2) and ARs were directly correlated ( r=0.54; p<0.05) with the suppressibility of plasma GH levels by octreo tide (OC) acute administration. In two patients who repeated scintigra phy during chronic OC treatment, AR values were reduced. In all the 22 patients with NFA an accumulation of In-111-P at the pituitary level was observed and median AR was 3.0 (range 5.5-20; in 14 greater that 2 .2). in vitro autoradiography of: surgical specimens in 6 NFA patients revealed SSR in 4 cases with high scintigraphic AR and negative resul ts in two cases with low AR. Scintiscan was repeated during chronic OC treatment in 5 patients with high score: AR decreased in one patient, increased in three, and did not change in the other patient. No chang es in tumor size were shown in any of these patients. A total of 8 pat ients (3 GH secreting and 5 NFA) had ''normal'' AR values Conclusions: in acromegaly scintigraphy with In-111-P visualizes functioning pitui tary SS-R coupled to intracellular events that control hormonal hypers ecretion and tumor growth. In contrast, in spite of the positivity of In-111-P imaging in most patients with NFA, their receptors might: hav e a defect in the coupling-transduction process, as they are not inhib ited by OC treatment and no tumor shrinkage is observed. (J. Endocrino l. Invest. 21: 512-519, 1998) (C) 1998, Editrice Kurtis.