The effects of corticotrophin-releasing hormone, arginine vasopressin and their antagonists on ACTH release from perifused horse anterior pituitary cells.
Antagonists are useful for probing hormone action and receptor characteristics. In this study we have investigated the inhibitory effects of analogues of arginine vasopressin (AVP) and corticotrophin-releasing hormone (CRH) on stimulated release of immunoreactive ACTH from perifused equine anterior pituitary cells in vitro. Our aims were to gain some insight into the characteristics of the CRH and AVP receptors of the horse pituitary and to establish whether the response induced by AVP and CRH together could be blocked by combining antagonists. Experimental design included 5-min pulses of AVP (12.5 nmol/l), CRH (0.3 nmol/l) or CRH plus AVP given every 40 min alternately with pulses of secretagogue(s) plus appropriate antagonist(s). The effect of combined antagonists on the response to lower secretagogue concentrations (CRH, 0.03 nmol/l plus AVP, 2.5 nmol/l) was also tested. Response in the presence of an antagonist was compared with the mean response to secretagogue in the immediately preceding and following pulse and was expressed as per cent expected ACTH. The ACTH response to AVP was inhibited over the dose range 0.4-50 mumol/l by Phaa-D-Tyr(Et)2Lys6Arg3VP (P < 0.002; ANOVA) and by d(CH2)5[Tyr(Me)2]AVP (P < 0.001). Suppression of the expected ACTH response to AVP by these two antagonists was most effectively achieved by antagonist concentrations of 10 mumol/l (to 28 +/- 2.1%) and 25 mumol/l (to 22 +/- 5.1%) respectively. Inhibition was not improved by preinfusion compared with a bolus pulse. Aaa-D-Try(Et)2Val4Abu6Arg8.9VP and the non-peptide antagonist OPC-21268 had no inhibitory effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Ellis
M J
MJ
Department of Endocrinology, Christchurch Hospital, New Zealand.
Mulligan
R S
RS
Evans
M J
MJ
Donald
R A
RA
D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D001127:Arginine Vasopressin / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D001681:Biological Assay; D002478:Cells, Cultured; D003346:Corticotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D006736:Horses / Q000502:physiology*; D008297:Male; D010880:Piperidines / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D015363:Quinolones / Q000494:pharmacology
D010880:Piperidines; D015363:Quinolones; C090569:vasopressin, des-Gly(9)-phenylacetyl(1)-O-Et-Tyr(2)-Lys(6)-Arg(8)-; D001127:Arginine Vasopressin; C068644:OPC 21268; C025043:vasopressin, 1-(1-mercaptocyclohexaneacetic acid)-2-(O- methyl-L-tyrosine)-8-L-arginine-; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone