Assessment of relative efficacies of 5-HT1A receptor ligands by means of in vivo animal models.
We have evaluated the effects of ligands with varying efficacies at beta-adrenoceptors and 5-HT1A receptors in three in vivo models reflecting pre- and/or postsynaptic 5-HT1A receptor activation. Forepaw treading in rats is mediated by postsynaptic 5-HT1A receptors, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamin)tetralin)-induced discriminative stimulus is predominantly mediated by postsynaptic, but presynaptic 5-HT1A receptors might also be involved, and footshock-induced ultrasonic vocalization involves predominantly presynaptic 5-HT1A receptors. In vitro receptor binding studies demonstrated high beta-adrenoceptor and 5-HT1A receptor affinity of (-)-penbutolol, high beta-adrenoceptor and 60 times lower 5-HT1A receptor affinity of (+)-penbutolol, high beta-adrenoceptor affinity and about 100 times lower 5-HT1A receptor affinity of pindolol and (-)-tertatolol, only affinity for beta-adrenoceptors of metoprolol and ICI 118,551 (erythro-D,L-1-(7-methylindan-4-yloxy)-3-isopropylamine-b utan-2-ol, and only affinity for 5-HT1A receptors of WAY 100.635 ((N-[2-[4- (2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclo-hexane-carboxamide). (-)-Penbutolol, (-)-tertatolol, pindolol and WAY 100.635 antagonized 5-MeODMT-induced (5-methoxy-N, N-dimethyltryptamine) forepaw treading in rats, and (+)-penbutolol, ICI 118,551 and metoprolol were inactive. (-)-Penbutolol, WAY 100.635 and (-)-tertatolol antagonized 8-OH-DPAT-induced discriminative stimulus in rats, pindolol and metoprolol showed a mixed antagonistic and agonistic profile. Pindolol antagonized footshock-induced ultrasonic vocalization in rats, tertatolol inhibited maximum 36% and WAY 100.635, (-)-penbutolol, (+)-penbutolol, metroprolol and ICI 118,551 were inactive. (-)-Penbutolol and WAY 100.635 reversed 8-OH-DPAT-induced inhibition of ultrasonic vocalization completely, (-)-tertatolol reversed maximum 52% and (+)-penbutolol and pindolol were inactive. It is concluded, that efficacies at 5-HT1A receptors can be estimated by applying a battery of in vivo test models that involve post- and presynaptic receptors to a variable degree. The in vivo ranking order of efficacy at 5-HT1A receptors was: WAY 100.635 = (-)-penbutolol < (-)-tertatolol < pindolol.
Sánchez
C
C
H. Lundbeck A/S, Copenhagen-Valby, Denmark.
Arnt
J
J
Moltzen
E
E
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D008297:Male; D008959:Models, Neurological; D010869:Pindolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects*; D014828:Vocalization, Animal / Q000187:drug effects*
D011985:Receptors, Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D010869:Pindolol