The growth hormone responses to octreotide in acromegaly correlate with adenoma somatostatin receptor status

We studied the correlation between the presence of somatostatin (SRIH) receptors in GH secreting tumors and the in vivo GH responsiveness to the SRIH analog octreotide in 11 acromegalic patients. To test in vivo octreotide (SMS 201-995) responsiveness, the patients were given a single dose (100 micrograms, sc) and their plasma GH levels were measured for several hours. Somatostatin receptor content was measured by receptor autoradiography on frozen tumor tissue sections using either a somatostatin-28 analog or a SRIH octapeptide analog (Tyr3-octreotide) as iodinated radioligands. In eight acromegalic patients, who had complete and long lasting GH inhibition after octreotide administration, SRIH receptors with high affinity for octreotide were distributed homogeneously in the tumor tissue. Two patients had moderate, short duration, and incomplete inhibition of GH secretion after octreotide administration, and their tumors had very low capacity and/or affinity SRIH receptors. A further patient who had a moderate response to octreotide had SRIH receptors that were nonhomogeneously distributed throughout the tumor. These data suggest that the therapeutic efficacy of octreotide may be related to tumor SRIH receptor levels; the best in vivo responses to octreotide occurred in patients whose tumors contained a high density of homogeneously distributed receptors which had a high affinity for octreotide.