Perifusion studies of bromocriptine-treated and untreated macroprolactinomas: effects of dopamine, bromocriptine and TRH.
There have been no detailed in-vitro studies of PRL secretion by human macroprolactinoma cells exposed to bromocriptine (BC) to within a few days of surgical removal. We have studied cells from four such tumours (serum PRL 7.05-247 U/l) and six untreated tumours (serum PRL 4-80.35 U/l) using a perifusion technique. The BC-treated tumours had shown tumour shrinkage and were treated until 40-96 h before surgery, but in one patient serum PRL had not suppressed below 15 U/l despite chronic treatment. Pretreatment serum PRL responses to TRH were blunted in all 10 patients. During perifusion with dopamine (DA, 5 mumol/l) untreated prolactinomas had a higher PRL secretion rate (19.3 +/- 2.7 microU/mg tissue/min, mean +/- SEM) than BC-treated (3.9 +/- 0.7, P = 0.005). When DA was removed, PRL secretion from untreated tumours increased to 129.7 +/- 18.7 microU/mg/min, but in three of the BC-treated, little increase occurred. In the fourth (from the patient whose serum PRL had not fully suppressed) PRL secretion increased from 4.4 to 25.6 microU/mg/min after DA withdrawal, and DA and BC dose-related inhibition of PRL was similar to that observed in untreated tumours. TRH (10 ng/ml), without DA, provoked increased PRL release from both untreated (266% basal secretion, n = 3) and BC-treated (298%, n = 3) tumours; this effect was completely inhibited by DA (5 mumol/l). The absence of hormones other than PRL following potassium (55 mmol/l) excluded contaminating normal pituitary. We conclude: (1) The effects of BC on prolactinoma PRL secretion may persist for at least 4 days; (2) partial in-vivo BC resistance can be due to factors other than DA receptor malfunction; (3) the apparent discrepancy between in-vivo and in-vitro TRH responses was consistent with the presence of increased hypothalamic DA tone in vivo; and (4) BC may have differential effects on TRH and DA-controlled PRL pools in the tumourous lactotroph.
Bevan
J S
JS
Department of Endocrinology, Radcliffe Infirmary, Oxford, UK.
Burke
C W
CW
D001971:Bromocriptine / Q000627:therapeutic use*; D002470:Cell Survival; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006801:Humans; D010477:Perfusion / Q000379:methods*; D010911:Pituitary Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D011388:Prolactin / Q000378:metabolism; D015175:Prolactinoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D001971:Bromocriptine; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D004298:Dopamine