Parathormone levels during treatment of acromegaly with octreotide : one-year follow-up

Abstract Serum growth hormone (GH), insulin-like growth factor I (IGF-I), calcium, phosphate, osteocalcin, and intact parathormone (PTH) were measured in 10 patients with active acromegaly before and after 1, 6, and 12 months of treatment with octreotide (50 to 100 μg subcutaneously TID). Serum GH and IGF-I decreased after 1 month, and this effect was maintained at 6 and 12 months. A transient decrease in calcium and a persistent decrease in osteocalcin were also seen. Before treatment, calcium, phosphate, and osteocalcin levels were higher in the patients with acromegaly than in the 25 healthy controls; at 12 months, only the phosphate levels remained higher than baseline in the acromegalic patients. The levels of PTH were comparable in both groups before treatment, but were elevated in the patients with acromegaly after treatment. The lower calcium and osteocalcin levels recorded during octreotide treatment are similar to those seen after pituitary adenomectomy, but the phosphate and PTH values suggest that octreotide exerts further actions on calcium homeostasis. In addition to the reduced 1,25-dihydroxyvitamin D synthesis caused by the lowered GH levels, octreotide might cause intestinal malabsorption of calcium, which consequently stimulates PTH secretion.