Somatomedin A increments are diminished in acromegaly with concomitant hyperprolactinaemia

The influence of prolactin (Prl) on growth hormone (GH) regulated somatomedin A (SMA) levels was studied in 30 patients with acromegaly before and after transsphenoidal pituitary surgery. Pre-operative GH levels were elevated in all patients and SMA levels in all but one patient. Eleven patients (33%) showed hyperprolactinaemia. There was no correlation between GH and SMA levels. Plasma GH did not differ in patients with GH and Prl producing adenomas compared to those with isolated GH hypersecretion. SMA levels, however, were significantly lower in patients with hyperprolactinaemia than in those with normal serum prolactin (P less than 0.001). After surgery GH decreased in all and SMA levels in all but one patient. Despite similar post-operative GH levels SMA decreased to significantly lower levels in patients with combined hypersecretion of GH and Prl compared to patients with normal prolactin levels (P less than 0.05). Nine of the 11 patients with hyperprolactinaemia showed normal Prl after surgery. The SMA levels in patients with acromegaly seem to be suppressed in patients with pre-operatively concomitant hyperprolactinaemia before as well as after adenomectomy regardless of the normalization of Prl. Our findings offer one explanation of the lack of correlation between SMA and GH levels in acromegaly.