Absence of an opioid stimulatory tone on growth hormone secretion in women with microprolactinoma.
BACKGROUND
Literature data suggest that prolactinoma is a tumor with a complex pathogenesis and that its growth is the result of changes at the pituitary and/or hypothalamic level. Abnormal release of hypothalamic factors (including endogenous opioid peptides) may contribute to prolactinoma development. An increased endogenous opioid tone (EOT) occurs in patients with prolactinoma, and seems to play an important role in pituitary secretion, as suggested by the ability of the opiate receptor antagonist naloxone to stimulate luteinizing hormone pulsatile secretion in these patients.


OBJECTIVE
To investigate the effect of the EOT on growth hormone (GH) secretion in women with prolactinoma.


METHODS
Eleven women aged 30.4+/-6.7 years (range 20-41), with an established diagnosis of microprolactinoma, were studied. GH-releasing hormone (GHRH), 100 microg as an intravenous (i.v.) bolus, was administered with and without preadministration of i.v. naloxone, an opioid receptor antagonist, 2 mg as a bolus followed by a constant infusion of 1.6 mg/h. Blood samples were taken for 120 min after GHRH administration.


RESULTS
Naloxone did not affect the GH response to GHRH, measured as single times, mean peak values, or as integrated concentrations.


CONCLUSIONS
Our data suggest that an opioid stimulatory tone on GH secretion in women with prolactinoma is absent.
Fanciulli
Giuseppe
G
Dipartimento-Struttura Clinica Medica-Patologia Speciale Medica, University of Sassari, Sassari, Italy. gfanciu@uniss.it
Tomasi
Paolo A
PA
Delitala
Giuseppe
G
D000328:Adult; D005260:Female; D013007:Growth Hormone-Releasing Hormone; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D009270:Naloxone; D009292:Narcotic Antagonists; D018847:Opioid Peptides / Q000502:physiology*; D015175:Prolactinoma / Q000503:physiopathology*
D009292:Narcotic Antagonists; D018847:Opioid Peptides; D019382:Human Growth Hormone; D009270:Naloxone; D013007:Growth Hormone-Releasing Hormone