Hyperthyroidism with elevated plasma TSH levels and pituitary tumor: study with somatostatin.

In a 51-year-old man with hyperthyroidism, elevated plasma TSH levels, and evidence of pituitary tumor, plasma TSH levels decreased from a mean basal value of 11 muU/ml to 6 mu/u/ml during the infusion of 200 mug of somatostatin in 60 min. Thyrotropin releasing factor failed to increase plasma TSH levels. T3 administration failed to supress significantly the elevated thyroid 131I uptake. During T3 administration plasma TSH levels showed a downtrend but were not clearly suppressed. These findings are discussed in light of the pertinent literature.