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The lack of inhibition of Growth Hormone (GH) levels after glucose load is considered a marker of inappropriate GH secretion in acromegaly. In order to investigate the physiopathology of this phenomenon, we have studied the GH variations after an oral glucose load (0.75 g/kg BW per os, OGTT) or intravenous glucose bolus (25 g i.v., IVGTT), in a group of 12 acromegalic patients, aged 20 +/- 69 yr (mean 48), 5 males and 7 females, with basal GH levels ranging from 11 to 76.2 ng/ml. The results indicate that only a group of acromegalic patients (group 1) had a partial GH inhibition after OGTT (mean decrease: 56.4 +/- 4.2%), but in no patients GH levels were influenced by intravenous administration of glucose. It is possible that in group 1 patients, the gastroenteric response could partially influence the GH secretion by the pituitary tumor, probably due to an increased peripheral somatostatin release. The dissociation of the GH response to OGTT and IVTT could indicate a supersensitivity to peripheral somatostatin, related to a deficiency in central somatostatinergic tone and therefore represent a more unfavourable prognostic sign.

Thyrotropin releasing hormone (TRH) administration is known to induce a greater TSH response in normal subjects than in obese subjects. In obesity even GH and PRL response to various stimuli are blunted, presumably because of an augmented somatostatinergic tone in obese subjects. Further studies have shown that pyridostigmine (Pyr), an acetylcholinesterase inhibitor, is capable of augmenting GH in obesity by means of somatostatin inhibition. In order to evaluate the possible interference of an increased somatostatinergic tone on TSH secretion, we studied the TSH response to a TRH bolus in 5 obese children with or without a pyr pretreatment. Similarly, we tested a group of 10 obese adult subjects, with TRH alone or TRH plus pyr administration, 30 min or 60 min before TRH. All subjects had a body weight of 30-50% greater than I.B.W. Our data show that a pretreatment with pyr, 60 min before TRH administration, significantly augments the TSH response in adult obese subjects but not in children; the modality of pyr administration seems to be crucial to evidenciate such an alteration since the pyr pretreatment is not effective when administered 30 min before TRH. The absence of this pyr effect in obese children induces to hypothesize that somatostatinergic tone is differentially modulated in children vs adult obese subjects.

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