title: Inhibitory dopamine receptors on sympathetic neurons innervating the cardiovascular system of the pithed rat. Characterization and role in relation to presynaptic alpha 2-adrenoceptors.
abstract: Additional experimental evidence was obtained for an inhibitory function of prejunctional alpha 2-adrenoceptors and/or dopamine receptors located on noradrenergic neurons innervating the heart and resistance vessels of the pithed normotensive rat. Mixed alpha 2-adrenoceptor/dopamine receptor agonists, differing in selectivity towards either receptor type, i.e. N,N-di-n-propyldopamine (DPDA), 2-N, N-di-n-propylamino-6, 7-dihydroxy-1,2,3,4-tetrahydro-naphthalene (DP-6,7-ADTN), B-HT 920 and B-HT 933 (azepexole) were used. In pithed normotensive rats, DPDA (30 and 100 micrograms/kg/min) dose-dependently inhibited the electrical stimulation-induced increase in diastolic pressure, but did not significantly affect the stimulation-evoked increase in heart rate. The inhibition exerted by DPDA was blocked by haloperidol and sulpiride (0.3 mg/kg of each), but not by yohimbine (1 mg/kg), indicating the involvement of dopamine receptors. In this respect, sulpiride and haloperidol were found approximately equipotent. DP-6,7-ADTN (10 and 30 micrograms/kg/min) impaired both tachycardic and vasoconstrictor responses in a dose-dependent manner. Sulpiride (0.3 mg/kg) only partially restored the DP-6,7-ADTN-depressed stimulation-evoked increase in diastolic pressure, whereas yohimbine (1 mg/kg) alone was without effect. The combination of both antagonists completely prevented the inhibition caused by DP-6,7-ADTN. On the other hand, yohimbine (1 mg/kg), but not sulpiride (0.3 mg/kg), selectively antagonized the DP-6,7-ADTN-induced inhibition of stimulation-evoked tachycardia. B-HT 920 (1, 3 and 10 micrograms/kg/min) very effectively reduced the increase in diastolic pressure and heart rate caused by electrical stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000315:Adrenalectomy; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D002319:Cardiovascular System / Q000294:innervation*; D004558:Electric Stimulation; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D013564:Sympathetic Nervous System / Q000166:cytology / Q000502:physiology*; D013569:Synapses
chemical_list: D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D011954:Receptors, Dopamine; C024763:talipexole