Changes in circulating somatomedin-C levels in bromocriptine-treated acromegaly

To determine whether the improvement in clinical status of patients with active acromegaly correlates with a reduction of circulating somatomedin-C, serum immunoreactive somatomedin-C was measured in twenty-seven patients before and during bromocriptine therapy. The patients were assessed using a clinical and metabolic score which included both subjective criteria of improved sweating and facial features, and objective criteria of a reduction in ring circumference and the area under the glucose tolerance curve. Using this, together with the change in GH levels before and during bromocriptine therapy, the patients could be divided into three groups. In one group, there was no clinical improvement, a less than 30% decline in somatomedin-C, and in four of six patients no significant decline in GH. In both the other groups there was clinical improvement and a greater than 30% decrease in somatomedin-C. In one of these two groups, however GH did not decline, while in the other it was reduced significantly. The results suggest that during bromocriptine treatment of acromegaly, serum somatomedin-C concentrations correlate better with clinical status that does serum GH. Since some patients have no significant fall in GH but show both clinical improvement and a reduction in somatomedin-C, it seems likely that in some patients bromocriptine may improve acromegaly by a mechanism other than a simple decrease in total immunoreactive GH secretion.