Effects of Pirenzepine, Bromocriptine and Their Association on Basal and GHRH- and TRH-Induced GH Secretion in Acromegaly

Abstract

In order to ascertain if pirenzepine (Pz), an antimuscarinic drug, could inhibit GH secretion in acromegaly, 8 patients were submitted to 3 successive treatment courses of 9 days each: Pz, bromocriptine (BRC) and Pz plus BRC. No change in basal levels of GH after Pz administration was seen, but its reduction (p < 0.05) by BRC was observed. Pz plus BRC did not improve this response. None of these drugs abolished the paradoxical GH response to TRH. In 7 normal controls, Pz suppressed the GH responsiveness to GHRH (p < 0.001), but not in acromegalic patients. BRC, instead, blunted this response. In conclusion, cholinergic control of GH secretion is altered in acromegaly. Pz, either when administered alone or associated with BRC, is not useful for the treatment of this disease.

Cholinergic modulation of GH secretion in acromegalic patients before and after pituitary surgery

“…As expected, on the basis of our previous reports (20,21) and others ( 11,18,19 ), we found that the antimuscarinic drug Pz was unable to block GH response to GHRH stimulus in untreated acromegalic patients. Although impaired cholinergic control of GH secre¬ tion is common in acromegaly, the pathophysiological mechanisms have not been sufficiently elucidated.…”

“…Conversely, cholinergic muscarinic receptor antago¬ nists, such as methoscopolamine, atropine and pirenzepine (Pz), virtually abolished the GH responses elicited by a series of physiological, hormonal and pharmacological stimuli, through an enhancement of hypothalamic SRIH secretion (7,16). These findings are in clear contrast to previous reports on acromegalic patients, in whom acute (11,(17)(18)(19) or chronic (20,21 ) administration of antimuscarinic drugs was unable to suppress basal, TRH-, GHRHand guanfacine-stimulated GH release. The neuroendocrine mech¬ anisms involved in this disturbance in acromegaly remain controversial.…”

“…This contrasts with what occurred in normal subjects, where acute or long-term pretreatment with hGH diminished GH responses to a series of specific stimuli (24,25,35,36). These observations concur with the assumption that GH feedback regulation of its own secretion in acromegaly is altered (20,21,28,37,38). These observations concur with the assumption that GH feedback regulation of its own secretion in acromegaly is altered (20,21,28,37,38).…”