Add time:08/04/2019         Source:sciencedirect.com

We used in vitro autoradiography to identify the endothelin-1 receptor subtype(s) in the superficial gray layer of the superior colliculus of rats. These studies showed dense binding of (3-[125I]iodotyrosyl13)-[Ala11,15]Ac-endothelin-1-(6-21) (BQ3020) (for endothelin ETB receptors), while tissues incubated with [125I](N-(hexahydro-1-azepinyl)carbonyl)l-Leu(1-Me)d-Trp-d-Tyr (PD151242) (for endothelin ETA receptors) had low binding. In addition, we examined the effects of the endothelin receptor antagonists, (R)-2-[(R)-2-[(S)-2-[[1-hexahydro-1H-azepinyl)]carbonyl]amino-4-methylpentanoyl]-amino-3-(2-pyridyl)propionic acid (FR139317) (endothelin ETA receptor-selective), (+)-(1S,2R,3S)-3-(2-carboxymethoxy-4-methoxyphenyl)-1-(3,4-methylenedioxyphenyl)-5-(prop-1-yloxy)indane-2-carboxylic acid (SB209670) (endothelin ETA/ETB receptor non-selective) and N-cis-2,6-dimethylpiperidinocarbonyl-l-γ-metLeu-d-1-methoxy-carbonylTrp-d-Nle (BQ-788) (endothelin ETB receptor-selective antagonist) on the responses following administration of endothelin-1 into the superficial layer of the superior colliculus. Endothelin-1 microinjected into this nucleus causes decreases in blood pressure (control, 109±6 mmHg, n=6; endothelin-1, 72±5 mmHg, n=6). These effects were greatly reduced by pre-administration into the superior colliculus of BQ-788 (5 nmol/rat) or SB209670 (3 nmol/rat) (94±5 and 98±6%, respectively) but were not affected by FR139317 (5 nmol/rat) (6±3%). Therefore, together with autoradiography, our functional data showed that endothelin ETB receptors are the predominant mediators of depressor responses induced by endothelin-1 injected into the superior colliculus of the rat.

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