THE DYNAMICS OF GROWTH HORMONE AND PROLACTIN SECRETION IN ACROMEGALIC PATIENTS WITH "MIXED" PITUITARY TUMOURS

Abstract

The dynamics of growth hormone (GH) and prolactin (PRL) secretion in response to thyrotropin-releasing hormone (TRH) and bromocriptine were evaluated in 15 untreated and 1 previously unsuccessfully treated patients with acromegaly. In 7 of these patients elevated basal PRL levels were found. In 4 of the 7 hyperprolactinemic patients plasma PRL concentrations closely followed the pattern of GH secretion in response to TRH (400 .mu.g). The maximal paradoxical increment of GH in response to TRH was paralleled by a delayed PRL response, while a close relationship was observed between the suppression of the elevated GH and PRL levels in these patients after 1 single dose of 2.5 mg bromocriptine. In 1 of these patients parallel escapes of plasma GH and PRL during bromocriptine treatment were seen. A significant higher sensitivity to the GH-lowering effect of 2.5 mg bromocriptine was noted from 2-8 h in these 4 patients with presumably mixed GH/PRL secreting pituitary adenomas, compared with the response in 9 untreated acromegalic patients with normal basal PRL levels. In the 3 acromegalic patients with slightly elevated PRL levels, no or a normal increase of PRL levels in response to TRH was observed, while the suppressive effect of bromocriptine on plasma GH concentrations was not different from that seen in the acromegalic patients with normal PRL levels. However, as a group the 7 patients with hyperprolactinaemia showed a significantly higher GH-lowering effect to 2.5 mg bromocriptine than the 9 normoprolactinemic acromegalic patients. A close relationship between the magnitude of the increment of GH in response to TRH nad the decrease of plasma GH after 2.5 mg bromocriptine was present in the whole group of 16 acromegalics (P < 0.01). No such correlation was shown in the type of response of plasma GH to an oral glucose load or the coefficient of variation of basal plasma GH levels on 5 different days. In the population of acromegalic patients with elevated plasma PRL levels a sub-population of patients is present with mixed pituitary adenomas which secrete GH and PRL in a parallel manner. The characteristics of the secretion of both hormones, in these patients can be recognized as a parallel, delayed response of both hormones to TRH and an increased sensitivity to the suppressive effect of bromocriptine.