DNA synthesis by pituitary tumours, with reference to plasma hormone levels and to effects of bromocriptine

Abstract

In parathyroid adenomas and experimentally in the normal rat pituitary gland, cell replication and secretory activity were previously shown to be correlated. A similar relationship has now been investigated in human pituitary tumours, since this could have relevance to their growth and aetiology. The effect of bromocriptine on the two variables was examined. Data were derived from 50 patients undergoing operation for pituitary tumour, including 15 with acromegaly and 11 with prolactinoma. Preoperative plasma levels of GH, PRL and gonadotrophins were measured by radioimmunoassay. DNA synthesis, an index of cell replication, was measured in vitro in freshly removed tumour tissue. Nuclear diameter of tumour cells was measured in histological sections and immunostaining for relevant hormones was carried out on tumour tissue. DNA synthesis was correlated (P < 0.05) with plasma hormone levels in cases of prolactinoma, both treated and not treated with bromocriptine, and in a group of putative FSH secreting tumours from male patients. The correlation was not significant in cases of acromegaly. Comparisons of mean values between groups treated and not treated with bromocriptine showed significantly lower DNA synthesis and mean nuclear diameter in prolactinomas under treatment but not in GH secreting tumours. The findings in prolactinomas suggest a close relationship between secretion and tumour cell replication dependent on still undefined agents, but including dopamine, affecting both variables, and isoforms of PRL, which may stimulate or inhibit replication of PRL secreting cells. The basis of the relationship in FSH secreting tumours is unknown. The relationship was absent in the non-homogeneous group of GH secreting tumours. When secretion and growth are correlated, the secretory process may be the site of the primary abnormality in the tumour cell. Evidence that bromocriptine inhibits tumour cell replication was obtained for prolactinomas but not for GH secreting tumours.