Effect of pyridostigmine and pirenzepine on GH responses to GHRH in hyperthyroid patients.
OBJECTIVE
We wished to investigate whether thyrotoxicosis can influence the cholinergic modulation of GH secretion.


METHODS
Pyridostigmine was given orally, then GHRH injected i.v., and levels were measured. In a separate study, pirenzepine was injected i.v., then GHRH, and growth hormone levels were measured.


METHODS
Thyrotoxic patients were compared with normal subjects.


METHODS
GH was measured from -30 to +120 minutes at intervals of 15 minutes.


RESULTS
Pyridostigmine markedly increased GH responses to GHRH in normal subjects, but not in thyrotoxic patients. Pirenzepine abolished the GH response to GHRH in thyrotoxic patients.


CONCLUSIONS
GH responses to GHRH in hyperthyroid patients were suppressed by cholinergic muscarinic receptor blockade with pirenzepine. Activation of cholinergic pathways with pyridostigmine did not increase GH responses to GHRH in these patients. This may be a consequence of increased hypothalamic cholinergic function or reduced hypothalamic GHRH activity in hyperthyroidism. Our findings demonstrate a further mechanism by means of which thyroid status may affect the secretory activity of the somatotroph.
Valcavi
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Sezione Endocrino Metabolica, Arcispedale S. Maria Nuova, Reggio Emilia, Italy.
Dieguez
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Zini
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Dotti
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D000293:Adolescent; D000328:Adult; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000097:blood; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000503:physiopathology*; D007031:Hypothalamus / Q000503:physiopathology; D008297:Male; D010890:Pirenzepine; D010902:Pituitary Gland / Q000187:drug effects / Q000503:physiopathology; D011729:Pyridostigmine Bromide; D012636:Secretory Rate / Q000187:drug effects
D010890:Pirenzepine; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D011729:Pyridostigmine Bromide