Summary
Additional experimental evidence was obtained for an inhibitory function of prejunctional α2-adrenoceptors and/or dopamine receptors located on noradrenergic neurons innervating the heart and resistance vessels of the pithed normotensive rat. Mixed α2-adrenoceptor 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-tetrahydronaphthalene (DP-6,7-ADTN), B-HT 920 and B-HT 933 (azepexole) were used.
In pithed normotensive rats, DPDA (30 and 100 μg/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 μg/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 μg/kg/min) very effectively reduced the increase in diastolic pressure and heart rate caused by electrical stimulation. Inhibitory dopamine as well as α2-adrenoceptors participated in the vascular effects of B-HT 920, whereas α2-adrenoceptors were only involved in the cardioinhibitory response to this agonist.
B-HT 933 (0.6 and 1 mg/kg/min) dose-dependently reduced the stimulation-evoked increase in arterial pressure through selective stimulation of inhibitory α2-adrenoceptors, dopamine receptors not taking a part.
The results confirm and extend the observations that in addition to α2-adrenoceptors inhibitory dopamine receptors are located on the sympathetic neurons connected with the arterial vasculature of the pithed normotensive rat. The sympathetic nerves innervating the rat heart do not contain inhibitory dopamine receptors; their activity only can be modulated by α2-adrenoceptor stimulation. In the pithed normotensive rat, activation of prejunctionally located α2-adrenoceptors more effectively inhibits the sympathetic activity directed to the heart than that to the resistance vessels.
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References
Andén NE, Golembiowska-Nikitin K, Thornström U (1982) Selective stimulation of dopamine and noradrenaline autoreceptors by B-HT 920 and B-HT 933, respectively. Naunyn-Schmiedeberg's Arch Pharmacol 321:100–104
Andén NE, Nilsson H, Ros E, Thornström U (1983) Effects of B-HT 920 and B-HT 933 on dopamine and noradrenaline autoreceptors in the rat brain. Acta Pharmacol Toxicol 52:51–56
Badia A, Bermejo P, Jané F (1982) Pre- and postsynaptic effects of sulpiride in the rat isolated vas deferens. J Pharm Pharmacol 34:266–268
Barret RJ, Ginos JZ, Lokhandwala MF (1982) Evaluation of peripheral dopamine receptor and α-adrenoceptor blocking activity of sulpiride. Eur J Pharmacol 79:273–281
Buylaert WA, Willems JL, Bogaert MG (1978) The receptor mediating the apomorphine vasodilatation in the hindleg of the dog. J Pharm Pharmacol 30:113–115
Buylaert WA, Willems JL, Bogaert MG (1981) Peripheral prejunctional dopamine receptors. In: Vanhoutte PM, Lensen I (eds) Vasodilatation. Raven Press, New York, pp 125–130
Cavero I, Lefèvre-Borg F, Gomeni R (1981a) Blood pressure lowering effects of N,N-di-n-propyl-dopamine in rats: evidence for stimulation of peripheral dopamine receptors leading to inhibition of sympathetic vascular tone. J Pharmacol Exp Ther 218:515–524
Cavero I, Lefèvre-Borg F, Gomeni R (1981b) Heart rate lowering effects of N,N-di-n-propyl-dopamine in rats: evidence for stimulation of central dopamine receptors leading to inhibition of sympathetic tone and enhancement of parasympathetic outflow. J Pharmacol Exp Ther 219:510–519
Cavero I, Massingham R, Lefèvre-Borg F (1982a) Peripheral dopamine receptors, potential targets for a new class of antihypertensive agents. I. Subclassification and functional description. Life Sci 31:939–948
Cavero I, Massingham R, Lefèvre-Borg F (1982b) Peripheral dopamine receptors, potential targets for a new class of antihypertensive agents. II. Sites and mechanisms of action of dopamine receptor agonists. Life Sci 31:1059–1069
Clapham JC, Hamilton TC (1982) Presynaptic dopamine receptors mediate the inhibitory action of the dopamine agonists on stimulation-evoked pressor responses in the rat. J Auton Pharmacol 3:181–188
Costall B, Naylor RJ (1981) The hypotheses of different dopamine receptor mechanisms. Life Sci 28:215–229
Drew GM (1980) Postsynaptic α2-adrenoceptors mediate pressor responses to 2-N,N-dimethylamino-5,6-dihydroxy-1,2,3,4-tetrahydronaphthalene (M-7). Eur J Pharmacol 65:85–87
Dubocovich ML, Langer SZ (1980) Dopamine and α-adrenoceptor agonists inhibit neurotransmission in the cat spleen through different presynaptic receptors. J Pharmacol Exp Ther 212:144–152
Enero MA, Langer SZ (1975) Inhibition by dopamine of 3H-noradrenaline release elicited by nerve stimulation in the isolated cat's nictitating membrane. Naunyn-Schmiedeberg's Arch Pharmacol 289:179–203
Gillespie JS, Maclaren A, Pollock D (1970) A method of stimulating different segments of the autonomic ouflow from the spinal column to various organs in the pithed cat and rat. Br J Pharmacol 40:257–267
Goldberg LI, Kohli JD (1979) Peripheral pre-and postsynaptic dopamine receptors: are they different from dopamine receptors in the central nervous system? Comm Psychopharmacol 3:447–456
Hicks PE, Cannon JG (1979) NN-Dialkyl derivatives of 2-amino-5,6-dihydroxy-1,2,3,4-tetrahydro-naphthalene as selective agonists at presynaptic α-adrenoceptors in the rat. J Pharm Pharmacol 31:494–496
Hicks PE, Cannon JG (1980) Cardiovascular effects of 2-(N,N-dimethyl)-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene in pithed rats: differential antagonism by yohimbine and prazosin. J Pharm Pharmacol 32:786–787
Horn PT, Kohli JD, Goldberg LI (1980) Effects of (R) and (S) sulpiride on guinea pig blood pressure. Fed Proc 39:1861 (Abstr)
Kobinger W, Pichler L (1977) Pharmacological characterization of B-HT 933 (2-amino-6-ethyl-4,5,7,8-tetrahydro-6H-oxazolo-[5,4-d]-azepin-dihydrochloride) as a hypotensive agent of the “clonidine-type”. Naunyn-Schmiedeberg's Arch Pharmacol 300:39–46
Kobinger W, Pichler L (1980) Investigation into different types of post- and presynaptic α-adrenoceptors at cardiovascular sites in rats. Eur J Pharmacol 65:393–402
Kobinger W, Pichler L (1981) 98-1 subtypes: selectivity of various agonists and relative distribution of receptors as determined in rats. Eur J Pharmacol 73:313–321
Kohli JD, Cripe LD (1979) Sulpiride: a weak antagonist of norepinephrine and 5-hydroxytryptamine. Eur J Pharmacol 56:283–286
Kohli JD, Goldberg LI, Volkman PH, Cannon JG (1978) N,N-di-n-propyldopamine: a qualitatively different dopamine vascular agonist. J Pharmacol Exp Ther 207:16–22
Langer SZ (1973) The regulation of transmitter release elicited by nerve stimulation through a presynaptic feed-back mechanism. In: Usdin E, Snyder S (eds) Frontiers in catecholamine research. Pergamon Press, New York, pp 543–549
Langer SZ (1977) Presynaptic receptors and their role in the regulation of transmitter release. Br J Pharmacol 60:481–497
Langer SZ (1980) Presynaptic regulation of the release of catecholamines. Pharmacol Rev 32:337–362
Llenas J, Massingham R, Roberts DJ (1982) Substituted benzamides: selective antagonists of peripheral presynaptic dopamine receptors in the dog. Br J Pharmacol 76:208P
Lokhandwala MF, Barrett RJ (1982) Cardiovascular dopamine receptors: physiological, pharmacological and therapeutic implications. J Auton Pharmacol 3:189–215
Massingham R, Dubocovich ML, Langer SZ (1980) The role of presynaptic receptors in the cardiovascular actions of N,N-di-n-propyldopamine in the cat and dog. Naunyn-Schmiedeberg's Arch Pharmacol 314:17–28
Meel JCA van, Jonge A de, Timmermans PBMWM, Zwieten PA van (1981) Selectivity of some alpha-adrenoceptor agonists for peripheral alpha-1 and alpha-2 adrenoceptors in the normotensive rat. J Pharmacol Exp Ther 219:760–767
Pichler L, Kobinger W (1981) Centrally mediated cardiovascular effects of B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine dihydrochloride a hypotensive agent of the “clonidine-type”. J Cardiovasc Pharmacol 3:269–277
Pichler L, Placheta P, Kobinger W (1980) Effect of azepexole (B-HT-933) on pre- and postsynaptic α-adrenoceptors at peripheral and central nervous sites. Eur J Pharmacol 65:233–241
Scatton B, Zivkovic B, Dedek J (1980) Antidopaminergic properties of yohimbine. J Pharmacol Exp Ther 215:494–499
Shepperson NB, Langer SZ (1981) The effects of the 2-amino-tetrahydronaphthalene derivative M-7, a selective Postsynaptic α2-adrenoceptors mediate pressor responses to 2-N,N-dimethylamino-5,6-dihydroxy-1,2,3,4-tetrahydronaphthalene (M-7) agonist in vitro. Naunyn-Schmiedeberg's Arch Pharmacol 318:10–13
Shepperson NB, Duval N, Massingham R, Langer SZ (1982) Differential blocking effects of several dopamine receptor antagonists for peripheral pre- and postsynaptic dopamine receptors in the anesthetized dog. J Pharmacol Exp Ther 211:753–761
Spedding M (1980) Effects of metoclopramide and isoprenaline in the rat vas deferens; interactions with α-adrenoceptors. Br J Pharmacol 71:113–120
Starke K (1977) Regulation of noradrenaline release by presynaptic receptor systems. Rev Physiol Biochem Pharmacol 77:1–124
Starke K (1981) Presynaptic receptors. Ann Rev Pharmacol Toxicol 21:7–30
Timmermans PBMWM, Zwieten PA van (1980a) Postsynaptic α1- and α2-adrenoceptors in the circulatory system of the pithed rat. Selective stimulation of the α2-type by B-HT 933. Eur J Pharmacol 63:199–202
Timmermans PBMWM, Zwieten PA van (1980b) Vasoconstriction mediated via postsynaptic α2-adrenoceptor stimulation. Naunyn-Schmiedeberg's Arch Pharmacol 313:17–20
Timmermans PBMWM, Wilffert B, Mathy MJ, Dijkstra D, Horn AS, Zwieten PA van (1983) 98-6 agonist selectivities of mono- and dihydroxy-2-N,N-di-n-propylaminotetralins. Eur J Pharmacol 97:55–65
Wallenstein S, Zucker SL, Fleiss JL (1980) Some statistical methods useful in circulation research. Circ Res 47:1–9
Westfall TC (1977) Local regulation of adrenergic neurotransmission. Physiol Rev 57:659–728
Westfall TC (1980) Neuroeffector mechanisms. Ann Rev Physiol 42:383–434
Zwieten PA van, Timmermans PBMWM (1980) Centrally mediated hypotensive activity of B-HT 933 upon infusion via the cat's vertebral artery. Pharmacology 21:327–332
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Wilffert, B., Smit, G., de Jonge, A. et al. Inhibitory dopamine receptors on sympathetic neurons innervating the cardiovascular system of the pithed rat. Naunyn-Schmiedeberg's Arch. Pharmacol. 326, 91–98 (1984). https://doi.org/10.1007/BF00517303
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DOI: https://doi.org/10.1007/BF00517303