5-HT7 receptor efficacy distribution throughout the canine stomach.
This study aimed to determine, quantify and explain regional differences in the relaxant response to the selective 5-HT(1) and 5-HT(7) receptor agonist 5-carboxamidotryptamine (5-CT) throughout the canine stomach. Longitudinal muscle strips from eight gastric corpus regions and six antrum regions were mounted for isotonic measurement. The 5-CT-induced relaxation was examined on a prostaglandin F(2alpha)-induced submaximal response, expressed as percentage of this response and fitted to the operational model of agonism (OMOA). 5-HT(7) receptor messenger RNA (mRNA) expression was compared by means of quantitative PCR. 5-CT inhibited PGF(2alpha)-induced tonic contraction (corpus) and increase of phasic contraction amplitude (antrum). The consistent antagonism produced by the selective 5-HT(7) receptor antagonist SB-269970 (10 nm, pA(2) estimates 8.2-8.9) confirmed that in every region, the inhibition by 5-CT was 5-HT(7) receptor mediated. However, variation in the maximum effect (61-108%) and pEC(50) (6.4-8.6) was observed throughout the different regions. The OMOA explained these differences as differences in the efficacy parameter tau (ratio of receptor density and coupling efficiency; log tau estimates ranging from 0.1 to 2.1). The log tau gradient decreases going from the lesser to the greater curvature. A proportional difference (68%) in the relative expression of 5-HT(7) receptor mRNA between the lesser and the greater curvature indicates that differences in receptor density contribute to the observed functional differences. This study illustrates that 5-HT(7) receptors are present throughout the ventral wall of the canine stomach, but the efficacy (expressed as log tau) is clearly greater close to the lesser curvature. Differences in 5-HT(7) receptor expression at least partially explain the functional differences.
Janssen
Pieter
P
Heymans Institute of Pharmacology, Ghent University, Ghent, Belgium. pieter.janssen@astrazeneca.com
Prins
Nicolaas H
NH
Peeters
Pieter J
PJ
Zuideveld
Klaas P
KP
Lefebvre
Romain A
RA
D017398:Alternative Splicing; D000818:Animals; D015237:Dinoprost / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism; D015870:Gene Expression; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009599:Nitroprusside / Q000494:pharmacology; D010636:Phenols / Q000494:pharmacology; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011985:Receptors, Serotonin / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D010636:Phenols; D020033:Protein Isoforms; D012333:RNA, Messenger; D011985:Receptors, Serotonin; C404922:SB 269970; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides; C104425:serotonin 7 receptor; D009599:Nitroprusside; D012701:Serotonin; D013779:Tetrodotoxin; C047087:5-carboxamidotryptamine; D015237:Dinoprost