Coexistence of presynaptic beta 1- and beta 2-adrenoceptors in splenic strips from young rats and betaxolol-induced beta 1-stereoselective antagonism.
The pharmacological properties of facilitatory presynaptic beta-adrenoceptors were characterized using three kinds of beta-agonists and antagonists in superfused strips from young Sprague-Dawley rats, loaded with [3H]noradrenaline. Isoproterenol (10(-9) M to 10(-7) M) concentration-dependently facilitated [3H] release evoked by transmural field stimulation at 5 Hz. Salbutamol (10(-8) M and 10(-7) M) and prenalterol (10(-8) M to 10(-6) M) also facilitated the stimulation-evoked [3H] release. Pretreatment with ICI 118,551 (10(-6) M) completely antagonized the concentration-facilitation curve for isoproterenol (10(-9) M to 10(-7) M). Atenolol (10(-6) M) antagonized only the isoproterenol (10(-9) M)-induced facilitation. dl-Betaxolol (10(-6) M) antagonized the isoproterenol (10(-9) M and 10(-8) M)-induced facilitation and the antagonistic action for isoproterenol (10(-8) M) was more marked than that of atenolol, whereas the same concentration of d-betaxolol produced no antagonism. Thus, presynaptic beta 1- and beta 2-adrenoceptors coexist on noradrenergic neurons innervating splenic strips of young rats. Betaxolol is a useful tool to characterize presynaptic beta 1-adrenoceptors.
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
K
K
Sato
M
M
Kuwahara
Y
Y
Goshima
Y
Y
Misu
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D015784:Betaxolol / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013154:Spleen / Q000187:drug effects / Q000378:metabolism*; D013237:Stereoisomerism
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D015784:Betaxolol; D009638:Norepinephrine