Presynaptic dopamine receptors mediate the inhibitory action of dopamine agonists on stimulation-evoked pressor responses in the rat.

Abstract

The effects of the dopamine agonists TL-99, M-7 (N, N-dimethyl analogues of aminotetralins) and N, N-dinpropyldopamine (NNPD) on stimulation-evoked pressor responses and tachycardia in pithed Sprague-Dawley rats were investigated when pressor responses to the compounds per se had subsided. Various antagonists were used to characterise the effects of the dopamine agonists. 2 M-7 (3 micrograms/kg i.v.), and NNPD (1 mg/kg i.v.), but not TL-99 (1-30 micrograms/kg i.v.), inhibited pressor responses evoked by low frequency electrical stimulation of the spinal cord in the pithed rat. 3 M-7 (3 micrograms/kg i.v.), but neither NNPD (1 mg/kg i.v.) nor TL-99 (1-30 micrograms/kg), inhibited tachycardia evoked by low frequency electrical stimulation of the spinal cord in the pithed rat. 4 The inhibition of stimulation-evoked pressor responses by M-7 and NNPD was prevented by pimozide, metoclopramide and sulpiride but not by yohimibine, atropine, cimetidine or propranolol. 5 The inhibition of stimulation-evoked tachycardia by M-7 was prevented by yohimbine (and to a certain extent by sulpiride) but not pimozide, metoclopramide, atropine or cimetidine. 6 Pressor responses elicited by TL-99, M-7 and NNPD were selective antagonised by yohimbine, but not by prazosin, indicating that these responses were mediated by stimulation of vascular postsynaptic alpha 2-adrenoreceptors. 7 This study demonstrates that, in the rat, presynaptic dopamine receptors exist on sympathetic pre- or postganglionic nerve endings to blood vessels, but not on sympathetic pre- or postganglionic nerve endings to the heart, where inhibition by M-7 of stimulation-evoked tachycardia is mediated by stimulation of presynaptic alpha 2-adrenoreceptors.

• Authors: J C Clapham, T C Hamilton
• Journal: Journal of autonomic pharmacology (J Auton Pharmacol) Vol. 2 Issue 3 Pg. 181-8 (Sep 1982) ISSN: 0144-1795 [Print] England
• PMID: 7142233 (Publication Type: Journal Article)

Chemical References

• Naphthalenes
• Naphthols
• Receptors, Dopamine
• Tetrahydronaphthalenes
• 5,6-dihydroxy-2-dimethylaminotetralin
• N,N-di-n-propyldopamine
• 2-(N,N-dimethylamino)-6,7-dihydroxytetralin
• Dopamine

Topics

• Animals
• Dopamine (analogs & derivatives, pharmacology)
• Electric Stimulation
• Heart Rate (drug effects)
• Male
• Naphthalenes (antagonists & inhibitors)
• Naphthols (antagonists & inhibitors)
• Rats
• Rats, Inbred Strains
• Receptors, Dopamine (physiology)
• Spinal Cord (physiology)
• Synapses (drug effects, physiology)
• Tetrahydronaphthalenes (antagonists & inhibitors)