EFFECT OF PYRIDOSTIGMINE ON THE HYDROCORTISONE-MEDIATED DECREASE OF CIRCULATING GROWTH-HORMONE LEVELS IN ACROMEGALY

The aims of our study were to investigate the effect of the acetylchol inesterase inhibitor pyridostigmine (PD) administration on growth horm one (GH) secretion in acromegaly and to investigate the effects of PD on GH levels following an iv infusion of hydrocortisone in acromegaly. We studied five adult patients with active acromegaly, three men and two women with a mean age of 60+/-5 years (range 47-71 years) and a me an BMI of 27+/-0.7 kg/m(2) (range 24-28 kg/m(2)). All the patients und erwent: 1) placebo, 2 tablets po or 2) PD, 120 mg po, at time -60 plus a bolus iv injection of 100 mg hydrocortisone succinate in 2 ml salin e at time 0 followed by an iv infusion of 250 mg hydrocortisone succin ate in 250 ml saline from 0 to 120 min, or 3) PD, po or 3) placebo, po at time -60 plus a bolus iv injection of 2 ml saline followed by an i v infusion of 250 ml saline from 0 to 120 min. Serum GH values did not significantly change after PD administration compared to those during placebo treatment and with respect to baseline levels. In all of the acromegalic patients during hydrocortisone succinate infusion, GH valu es clearly decreased with respect to basal levels in varying degrees, with a nadir between 90 and 180 minutes after the beginning of hydroco rtisone infusion. After hydrocortisone + PD administration, all five p atients showed GH values not significantly different with respect to b asal levels and significantly higher with respect to placebo + hydroco rtisone from 30 to 180 minutes. Our data show that, in patients with a ctive acromegaly, PD administration does not significantly increase se rum GH levels with respect to placebo and that the glucocorticoid-medi ated decrease in GH levels is counteracted by the administration of PD . It can be hypothesized that glucocorticoids may cause an increase in somatostatin tone via the cholinergic pathways unmasking the choliner gic stimulating action of PD in acromegaly.