Effect of ergovaline, loline, and dopamine antagonists on rat pituitary cell prolactin release in vitro.
Cultured rat pituitary cells were studied to: determine the effects of ergovaline and loline on in vitro prolactin release; delineate the agonistic activity of these alkaloids at the D2 dopamine receptor, using 2 selective D2 dopamine receptor antagonists; and compare the efficacy of 2 dopamine receptor antagonists in reversing effects of the treatments on in vitro prolactin secretion. Ergovaline reduced in vitro prolactin release by at least 40% (P < 0.05) at concentrations of 10(-4), 10(-6), and 10(-8) M. However, loline reduced (P < 0.05) prolactin release only at the highest concentration, 10(-4) M. Two standard dopamine agonists, dopamine and alpha-ergocryptine, were used to verify that the inhibitory control mechanisms of in vitro prolactin release were intact. Both compounds reduced prolactin release by at least 40% for concentrations of 10(-4), 10(-6), or 10(-8) M. Selective D2 dopamine receptor antagonists (10(-6) M), domperidone and sulpiride, reversed (P < 0.05) the effect of loline on in vitro prolactin release. However, only domperidone (10(-6) M) was able to reverse (P < 0.05) the effect of ergovaline and only at the lowest ergovaline concentration (10(-8) M). Domperidone was more effective (P < 0.05) in reversing the prolactin-suppressing effect of alpha-ergocryptine than was sulpiride. The dose-response curve for domperidone (cubic fit, P < 0.0001) indicated a threshold concentration (10(-7) M) for reversal of alpha-ergocryptine's (10(-8) M) effect on prolactin release. However, at similar concentration of sulpiride (quadratic fit, P < 0.007), a threshold level was not obtained.(ABSTRACT TRUNCATED AT 250 WORDS)
Strickland
J R
JR
Animal Science Department, College of Veterinary Medicine, University of Tennessee, Knoxville 37901-1071.
Cross
D L
DL
Birrenkott
G P
GP
Grimes
L W
LW
D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004294:Domperidone / Q000494:pharmacology*; D004298:Dopamine / Q000494:pharmacology*; D018492:Dopamine Antagonists; D004305:Dose-Response Relationship, Drug; D004873:Ergolines / Q000494:pharmacology; D004879:Ergotamines / Q000494:pharmacology*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013469:Sulpiride / Q000494:pharmacology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000470:Alkaloids; D018492:Dopamine Antagonists; D004873:Ergolines; D004879:Ergotamines; D014662:Vasoconstrictor Agents; C076760:ergovaline; C100269:ergocryptine; D004294:Domperidone; D013469:Sulpiride; D011388:Prolactin; C059478:loline; D004298:Dopamine