Glycoprotein hormone-producing (GPH)
pituitary adenomas represent approximately 25% of all
pituitary tumors. Elevated serum levels of intact GPHs or their free alpha- and beta-subunits have been demonstrated in patients with such
tumors, and isolated hypersecretion of alpha-subunit has been reported to occur in 7% of patients.
Somatostatin has been shown to decrease GPH subunit levels in cultured
adenoma cells in vitro, and
somatostatin receptors have been identified on the cell membranes of these
tumors. We, therefore, investigated the effect of chronic
somatostatin analog administration on
hormone production and
tumor size in six patients with GPH-producing macroadenomas and elevated serum alpha-subunit levels. Patients initially received native
somatostatin as an iv 250-micrograms bolus at 0800 h, followed by a constant infusion of 2 mg over 4 h, and serum alpha-subunit concentrations were measured at 30-min intervals after baseline sampling for a total of 9 h. Patients then received a
somatostatin analog,
octreotide (100 micrograms, twice daily, sc) for 8 weeks. Serum alpha-subunit levels were determined weekly at 30-min intervals before and for 4 h after the 0800 h
octreotide dose. Pituitary magnetic resonance imaging scans and visual field testing were assessed before and after the study. During the 4-h
somatostatin infusion, four patients had a significant decrease in alpha-subunit levels (P < 0.05). During the 8-week chronic
octreotide administration period, two patients had significant decreases in alpha-subunit levels of 34.6% and 26.7% (P = 0.03 and 0.01, respectively). One of these two patients had a small reduction in
tumor size. Two patients whose serum alpha-subunit level did not significantly change while receiving
octreotide had a reduction in
tumor size or definite improvement in visual field abnormalities. Three patients received a maximum
octreotide dose of 250 micrograms, three times daily. In one patient, there was a significant decrease in alpha-subunit levels by 45% (P = 0.0001) in association with a marked improvement in visual field abnormalities. In another such patient, continued administration of
octreotide to a maximum dose of 250 micrograms, three times daily, was associated with a marked reduction in
tumor size. Of the four patients who demonstrated significant decreases in alpha-subunit concentrations during the initial
somatostatin infusion, three patients had a significant reduction in alpha-subunit levels while receiving
octreotide. One patient who did not have a decrease in alpha-subunit levels during the
somatostatin infusion demonstrated a small decrease in
tumor size during higher dose
octreotide treatment.(ABSTRACT TRUNCATED AT 400 WORDS)