Serum Levels of 20 Kilodalton Human Growth Hormone (20K-hGH) in Patients with Acromegaly before and after Treatment with Octreotide and Transsphenoidal Surgery

Circulating human GH (hGH) consists of several molecular isoforms. It was previously reported that the proportion of 20 kilodalton hGH (20K-hGH) was elevated in the serum of patients with active acromegaly. In this study, we investigated the effects of octreotide and transsphenoidal adenomectomy on the proportion of 20K-hGH in the serum of 7 acromegalic patients. To achieve an acute effect, octreotide (100 μg) was subcutaneously injected as a bolus. To observe the chronic effects of octreotide therapy and surgery, serum samples were obtained by repetitive blood sampling before and 3 to 8 weeks after treatment. Serum levels of 20K-hGH and 22 kilodalton hGH (22K-hGH) were determined by specific enzyme-linked immunosorbent assay. A bolus injection of octreotide elicited a parallel decrease in serum 22K-hGH and 20K-hGH, resulting in an unchanged proportion of 20K-hGH to total circulating hGH. The proportion of 20K-hGH was decreased in 4 of 4 patients 4 to 7 weeks after surgery and in 2 of 4 patients after chronic treatment with octreotide for 3 to 8 weeks. The proportion of serum 20K-hGH was positively related to mean serum 20K-hGH as well as serum total hGH levels, but not with serum IGF-I levels. These findings suggest that high serum levels of 20K-hGH or total hGH per se might elicit a chronic change in the clearance kinetics of 20K-hGH and increase the proportion of 20K-hGH in acromegalic patients.