Growth hormone responses to the releasing hormones GHRH and GnRH and the inhibitors somatostatin and bromocriptine in TRH-responsive and non-responsive acromegalics.

In acromegalics, the percent peak GH responses to TRH (pTRH) and bromocriptine (pBr) are inversely related with those to GHRH, favouring the hypothesis that in the adenomas of some patients there is a preponderance of GH-producing cells with lactotrope-like characteristics, whereas in others pure somatotropes predominate. The aim of the present study was to investigate whether patients responsive to TRH with allegedly lactotrope-like tumours differ from those patients not responding to TRH with more somatotrope-like adenomas in their answer to the GH inhibitors Br and SRIH and the releasing hormones GHRH and GnRH. The present study demonstrates that the observed reciprocal relations between the GH responses to GHRH, TRH and Br are only present in acromegalics paradoxically responding to TRH (pGHRH vs pTRH -0.73, pGHRH vs pBr -0.60, pTRH vs pBr +0.54, P less than 0.0002-P less than 0.02, N = 20), not in TRH-non-responders (N = 10). In contrast, in these latter patients, not in the former, close relations were found between the percent peak GH responses to GnRH (pGnRH) and pGHRH (r = +0.81, P less than 0.005) and between pGnRH and the percent maximum GH decrements in response to SRIH (pSRIH) (r = +0.64, P less than 0.05). Expectedly, the GH response to Br in the TRH-responders was significantly higher than in the non-responders (75 +/- 4% vs 54 +/- 3%, P less than 0.02), although it was also substantial in the latter. The GH response to SRIH was remarkedly similar in both groups (64 +/- 5 vs 57 +/- 9%, P greater than 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)