DYNAMICS OF GROWTH-HORMONE AND PROLACTIN SECRETION IN ACROMEGALIC PATIENTS WITH MIXED PITUITARY TUMORS

The dynamics of growth hormone (GH) and prolactin (PRL) secretion in response to thyrotrophin-releasing hormone (TRH) and bromocriptine were evaluated in 15 untreated and 16 previously unsuccessfully treated patients with acromegaly. In 7 of these patients elevated basal PRL levels were found. In 4 of the 7 hyperprolactinaemic patients plasma PRL concentrations followed closely the pattern of GH secretion in response to TRH (400 μg). 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 one single dose of 2.5 mg bromocriptine. In one of these patients parallel escapes of plasma GH and PRL during bromocriptine tratment were seen. In addition, a significant higher sensitivity to the GH-lowering effect of 2.5 mg bromocriptine was noted from 2 up to 8 h in these 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 normoprolactinaemic acromegalic patients. A close relationship between the magnitude of the increment of GH in response to TRH and 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. It is concluded that 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 the two 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.