03 December 2008
In some acromegalics, GH release can be induced by TRH and/or LHRH administration. The pathogenesis of these GH paradoxical responses was supposed to be a somatotroph-reduced sensitivity to somatostatin, somatotrophin release-inhibiting factor (SRIF), or an hypothalamic derangement of the SRIF release. In this study, this hypothesis was investigated by means of GH suppression during chronic therapy with octreotide [Somatostatin analogue (SMS)] in order to evaluate the possible correlation between GH and insulinlike growth factor 1 (IGF-1) normalization and the disappearance of these paradoxical responses in 15 acromegalic patients: 15/15 with a paradoxical GH rise after TRH and 7/15 with a paradoxical GH rise after LHRH. SMS therapy was administered subcutaneously at the dose of 150-450 µg/day. During the treatment, GH and IGF-1 levels normalized in 12 patients and were reduced in the remaining 3 others. The GH response to TRH disappeared in 7 patients, while the GH response to LHRH disappeared in 4 patients, χ<sup>2</sup> analysis failed to show any significant correlation between GH and IGF-1 normalization and the disappearance of GH response to TRH and LHRH (χ<sup>2</sup> = 0.00686). No linear correlation existed between GH/IGF-1 decrease and GH peak or area under the curve at any time (‘r’ values: TRH test, GH -0.47, IGF-1 -0.48; LHRH test, GH -0.50, IGF-1 -0.49). The absence of any significant correlation between GH/IGF-1 normalization and the disappearance of GH paradoxical responses during chronic octreotide administration suggests that other factors apart from SRIF sensitivity are involved in the genesis of these responses.