The Spectrum of Pituitary Growth Hormone Responses to Pharmacological Stimuli in Acromegaly*

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Abstract
To examine the responsiveness of GH secretion in patients with acromegaly, TRH (500 µg), arginine (0.5 g/kg BW), and LRH (100 µg) were administered to 15 patients with acromegaly. Ten of these patients responded to at least, one of the three agents and showed increases in their plasma GH levels 50% above basal values (categorized as group I). The remaining five patients, however, showed no response to any of these agents (categorized as group II). After the administration of somatostatin (500 ±g, iv, for 75 min), group I patients showed significantly greater decreases in plasma GH (−68.0 ± 4.3%) from the basal value than did group II (−34.2 ±1.8% P <0.001). CB-154 treatment was carried out n eight patients and was effective in group I(four of five patients) but not in group II (none of three patients). In addition, physiological fluctuations of plasma GH within 3 h were much greater in group I than in group II subjects. There were no differences, however, in blood glucose or plasma insulin responses to the administration of somatostatin between these two groups. Moreover, there were no differences in mean basal GH levels, pituitary histology, age, sellar volume, or the presence of bitemporal hemianopsia between the two groups of patients. It is concluded that there are two patterns of GH secretory responses to pharmacological stimuli in patients with acromegaly. The differences between the two patterns might be characterized by the properties of the somatotroph cells themselves rather than by the relation of these cells to the central nervous system and hypothalamus or the histological characteristics of the pituitary adenoma. These responses, to some extent, can be used to predict which patients might respond to CB-154.