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Bromocriptine Does Not Alter Growth Hormone (GH) Responsiveness to GH-Rreleasing Hormone in Accromegaly^*

Divisione di Endocrinologia Ospedale Niguarda Milano, Italy

Address correspondence and requests for reprints to: Dr. Renato Cozzi, Divisione di Endocrinologia, Ospedale Niguarda, Piazza Ospe dale Maggiore, 3,20162 Milano, Italy.

GHRH (100 µg) and TRH (200 µg) were administered to 24 active acromegalic patients before and during chronic bromocriptine (Br) treatment (Br, 10–15 mg/day for 3–5 months) to evaluate the possible effects of the dopamine agonist on GH release induced by these releasing hormones. Mean daily plasma GH levels were reduced by Br treatment from 34 ± 40 (SD) to 16 ± 19 ng/ml (P < 0.01). No significant changes were found when comparing the GH response to GHRH as mean area under the response curve (nanograms per min/ml above the basal) (pretreatment, 5453 ± 7843; during Br, 7017 ± 12763 ng/ml min), and as mean individual peak GH values (pretreatment, 130 ± 148; during Br, 126 ± 187 ng/ml) before and during treatment. The percentage GH increase (pretreat-ment, 340 ± 354; during Br, 617 ± 539%) was however significantly higher during Br.

Br treatment significantly reduced the GH response to TRH in terms of mean of individual peak levels (from 136 ± 134 to 60 ± 52 ng/ml; P < 0.01) and area under the response curve (from 3142 ± 3998 to 1331 ± 1646 ng/min-ml; P < 0.01). However, the percentage GH increase was not significantly different (pretreatment, 486 ± 729; during Br, 1059 ± 1862%).

When the patients were divided into Br responders, i.e. mean daily GH reduction during Br of at least 50% below baseline, and nonresponders, the initial response to GHRH was significantly higher in the latter group, but was unaffected by Br treatment in either group. On the contrary, the response to TRH, statistically significant initially only in the Br responder group, was reduced by Br treatment.

We suggest that cells sensitive to Br and TRH but not to GHRH (lactotroph-like) and cellssensitive to GHRH but not t o Br (pure somatotrophs) may coexist in GH-secreting adenomas.

^* This research was supported by Grant 840064344 of the Italian National Research Council, Special Project "Oncology".

Received June 19, 1985.