The TSH response to domperidone reflects the biological activity of prolactin in macroprolactinaemia and hyperprolactinaemia.
OBJECTIVE
To test the hypothesis that patients with hyperprolactinaemia due to biologically inactive macroprolactin will not show the characteristically increased dopaminergic inhibition of TSH release seen in patients with microprolactinomas secreting biologically active monomeric PRL.


METHODS
Comparison of the TSH and PRL responses to dopamine antagonism with domperidone (10 mg i.v.) in patients with hyperprolactinaemia due to macroprolactinaemia or microprolactinomas.


METHODS
Twenty-two patients referred for the investigation of their hyperprolactinaemia were studied: 11 patients with macroprolactinaemia and 11 patients with hyperprolactinaemia due to microprolactinoma.


METHODS
TSH and PRL levels were measured at baseline and 30 min following domperidone in both groups.


RESULTS
Patients with macroprolactinaemia showed normal TSH and PRL responses to dopamine antagonism whereas patients with microprolactinomas showed exaggerated TSH responses and reduced PRL responses. Although there was considerable overlap between the PRL responses in the two groups, there was very clear separation between the PRL/TSH response ratios (normal > 1.0) of 4.0 +/- 1.8 for the macroprolactinaemia group and 0.4 +/- 0.2 for the microprolactinoma group (P < 0.0001).


CONCLUSIONS
These data support the hypothesis that elevated circulating levels of macroprolactin, as opposed to biologically active monomeric PRL, do not exert increased positive feedback on the hypothalamic dopaminergic inhibition of TSH release.
Pinto
L P
LP
Department of Endocrinology, University Hospital of Wales, Heath Park, Cardiff, UK.
Hanna
F W F
FW
Evans
L M
LM
Davies
J S
JS
John
R
R
Scanlon
M F
MF
D000328:Adult; D004294:Domperidone; D018492:Dopamine Antagonists; D005260:Female; D006801:Humans; D006966:Hyperprolactinemia / Q000097:blood*; D008875:Middle Aged; D010911:Pituitary Neoplasms / Q000097:blood*; D011388:Prolactin / Q000097:blood; D015175:Prolactinoma / Q000097:blood*; D018709:Statistics, Nonparametric; D013972:Thyrotropin / Q000097:blood*
D018492:Dopamine Antagonists; C060678:prolactin, polymeric; D004294:Domperidone; D011388:Prolactin; D013972:Thyrotropin