Differences in autonomy of the growth hormone secretion in patients with acromegaly

Abstract

In order to examine the autonomy of the growth hormone (GH) secretion in patients with acromegaly, TRH (500 μg), arginine (0.5 g/kg BW), and LH-RH (100 μg) were administered to 15 patients with acromegaly, and plasma GH was then determined. Ten of these cases showed an increase in GH 50% above the basal value in response to at least one of the 3 stimulants. The remaining 5 cases, however, showed no response to any of them. The former 10 cases were regarded as a less autonomous type, while the latter 5 were regarded as a more autonomous type with regard to GH secretion. When physiological fluctuations of plasma GH within 3 hr were studied, maximum GH increase from the value of 0 time was significantly greater in the less autonomous type (+33.2±3.9%) than in the more autonomous type (+14.6±4.0%) (p<0.02). Following the administration of somatostatin (500 μg i.v. for 75 min), the less autonomous type showed a significantly greater decrease in GH (-68.0±4.3%) from the basal value than did the more autonomous type (-34.2±1.8%) (p<0.001), although both types showed gradual and significant GH decrease compared with the physiological fluctuations. There were no differences, however, in plasma glucose and insulin response to the administration of somatostatin between these two types. Again, there were no differences in mean basal GH levels, histological picture of the pituitary, age, sellar volume, and the presence of bitemporal hemianopia between the two. When further examination was done of both types with CB-154, 4 out of 5 of the less autonomous type showed an adequate fall in GH to the normal range and clinical improvement. On the other hand, 3 of the more autonomous type showed no adequate fall in GH or clinical improvement. It is concluded that there are two types of acromegaly: one is less autonomous and the other is more autonomous in GH secretion. The difference between the two types might be characterized by the property of the receptors and the subsequent secretory process of the somatotroph itself, rather than that of the GH regulation system such as the CNS and hypothalamus, or that of the histological construction of the pituitary adenoma. As for practical treatment, the less autonomous type could be treated with CB-154, and the more autonomous type might require some other extensive therapy such as surgical hypophysectomy and/or X-ray irradiation.