Effects of repetitive administration of thyrotropin-releasing hormone at short intervals in acromegaly

Abstract

Abstract. We investigated the pattern of GH secretion in response to repetitive TRH administration in patients with active acromegaly and in normal subjects. Nine acromegalic patients and 10 normal subjects received three doses of 200 μg of TRH iv at 90-min intervals. There was a marked serum GH rise in acromegalic patients after each TRH dose (net incremental area under the curve [nAUC]: first dose = 4448 ± 1635 μg · min · 1−1; second dose = 3647 ± 1645 μg · min · 1−1; third dose = 4497 ± 2416 μg · min · 1−1; NS), though individual GH responses were very variable. In normal subjects TRH did not elicit GH secretion even after repeated stimulation. Each TRH administration stimulated PRL release in acromegalic patients, though the nAUC of PRL was significantly higher after the first (1260 ± 249 μg · min · 1−1) than after the second and the third TRH administration (478 ± 195 and 615 ± 117 μg · min · 1−1, respectively; P < 0.01). In normal subjects too, PRL secretion was lower after repeated stimulation (first dose = 1712 ± 438 μg · min · 1−1; second dose = 797 ± 177 μg · min · 1−1; third dose = 903 ± 229 μg · min · 1−1 P < 0.01), though different kinetics of PRL secretion were evident, when compared with acromegalic patients. TSH secretion, assessed in only 4 patients, was stimulated after each TRH dose, though a minimal but significant reduction of nAUC of TSH after repeated TRH challenge occurred. Both T3 and T4 increased steadily in the 4 patients. The same pattern of TSH, T3, and T4 secretion occurred in normal subjects. Our study demonstrates that repetitive TRH administration in acromegalic patients leads to similar, but individually heterogeneous GH responses. A qualitative difference in PRL responsiveness occurred in acromegalic patients compared with normal subjects, whereas TSH, T3, and T4 secretion was qualitatively and quantitatively similar in both groups.