title: Pharmacological properties of presynaptic beta-adrenoceptors in guinea-pig pulmonary arteries.
abstract: Pharmacological properties of the facilitatory presynaptic beta-adrenoceptor mechanism were studied in superfused spiral preparations of guinea-pig pulmonary arteries preloaded with 3H-norepinephrine. (-)-Isoproterenol (0.3 microM)-induced increases in total 3H efflux per pulse evoked by transmural field stimulation (1, 5, 10 and 20 Hz, 10 V, 2 msec pulse width, 100 pulses and 30 min intervals) were neither dependent on impulse-frequencies nor selective at lower frequencies. Isoproterenol increased 3H efflux at 5 Hz in a concentration-dependent manner (1 nM to 1 microM): pD2 was 7.7. Salbutamol increased 3H efflux in a similar manner to isoproterenol: pD2 was 7.4. Prenalterol at 3 microM only slightly increased 3H efflux. Tazolol (10 nM to 3 microM) produced no increases. Atenolol (3 microM) and practolol (3 microM) did not antagonize isoproterenol (0.3 microM)-induced increases in 3H efflux. Butoxamine (3 microM) and H 35/25 (3 microM) did antagonize this parameter. (-)-Epinephrine (1 nM to 0.1 microM) decreased 3H efflux at 5 Hz and concentration-dependently increased this parameter in the presence of 10 microM phentolamine. (-)-Norepinephrine (10 nM to 1 microM) concentration-dependently inhibited evoked 3H efflux and did not increase the parameter in the presence of 10 microM phentolamine, 10 microM cocaine and 10 microM normetanephrine. Thus, there exist presynaptic beta 2-subtype receptors on noradrenergic nerve endings innervating guinea-pig pulmonary arteries.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects / Q000294:innervation*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*; D017981:Receptors, Neurotransmitter / Q000187:drug effects*
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D017981:Receptors, Neurotransmitter; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine