Abstract. The effect of an iv injection of growth hormone releasing factor (GRF) on Prl secretion in healthy volunteers and patients with active acromegaly was investigated. Thirteen normal subjects received 100 μg GRF 1-44, and 19 acromegalics received 100 μg GRF 1-44. Nine normals and 9 patients were given the diluent only and served as placebo control. In healthy volunteers GRF did not affect Prl secretion significantly when compared to placebo, whereas in acromegalics Prl levels after GRF were higher than after placebo.
We have divided acromegalics in Prl-responders to GRF (n = 11) and Prl-non-responders (n = 8) using the criterion of strict parallelism between GH and Prl secretion after GRF. In cases with no GH response to GRF a clear increase of Prl levels with the maximum 15–30 min after GRF was also regarded as a Prl response. Acromegalic Prl-responders and Prl-non-responders did not significantly differ in age, sex, previous therapy, and basal GH and Prl levels. However, Prl-non-responders had a significantly reduced response of both GH and Prl to TRH (GH: 147.3 ± 16.0 vs 590.1 ± 127.8%; mean ± se; Prl: 159.4 ± 32.6 vs 504.9 ± 109.3%). It is concluded that 50 or 100 μg GRF does not affect Prl secretion in normal subjects. In contrast, in acromegaly GRF leads to Prl secretion in more than half of all patients.