Summary
The effect of clonidine on the number ofα 2-adrenoceptors in human platelet membranes, determined by3H-yohimbine binding, was investigatedin vitro andin vivo. Incubation of platelet membranes with clonidine (1–100 µM) for 16 h at 25 °C led to a concentration-dependent decrease in the number of3H-yohimbine binding sites of 10–25%; the affinity of3H-yohimbine to the sites was not changed (KD approximately 3–4 nM). In such “desensitized” membranes, inhibition of3H-yohimbine binding by clonidine resulted in steep, monophasic displacement curves, which in comparison to the curves from control membranes (IC50 for clonidine 90 nM), were shifted to the right (IC50: 321 nM) and were not affected by 10−4M guanosine-5′-triphosphate (GTP).
Treatment of 3 hypertensive patients with clonidine (3×150 µg/d for 7 days) reduced blood pressure and heart rate. Simultaneously, both3H-yohimbine binding sites on platelet membranes and plasma catecholamine levels decreased within three days and remained at a reduced level during treatment. After abrupt cessation of clonidine treatment, blood pressure, heart rate and plasma catecholamines rapidly increased, reaching values after two days similar to or higher than those before treatment.3H-yohimbine binding sites, however, initially decreased further before returning to control values. In platelet membranes derived from hypertensive patients treated with clonidine for at least three weeks, GTP (10−4M) had no influence on inhibition of3H-yohimbine binding by (—)-adrenaline and clonidine. It is concluded that clonidine desensitizesα 2-adrenoceptors in human platelet membranesin vitro andin vivo. An important step in the desensitization process is the uncoupling of receptor occupancy by agonists and adenylate cyclase activity, as indicated by loss of the regulatory activity of GTP on desensitized membranes. The clonidine withdrawal syndrome may be caused by enhanced release of endogenous catecholamines not adequately regulated by presynapticα 2-adrenoceptors, which have become subsensitive after chronic clonidine treatment.
Similar content being viewed by others
References
Bock KD, Heimsoth V, Merguet P, Schönermark J (1966) Klinische und klinisch-experimentelle Untersuchungen mit einer neuen blutdrucksenkenden Substanz: Dichlorphenylaminoimidazolin. Dtsch Med Wschr 91: 1761–1768
Brodde O-E, Anlauf M, Graben N, Bock KD (1982a) Age-dependent decrease ofα 2-adrenergic receptor number in human platelets. Europ J Pharmacol 81: 345–347
Brodde O-E, Engel G, Hoyer D, Bock KD, Weber F (1981) The β-adrenergic receptor in human lymphocytes: subclassification by the use of a new radioligand: (±)-125iodocyanopindolol. Life Sci 29: 2189–2198
Brodde O-E, Hardung A, Ebel H, Bock KD (1982b) GTP regulates binding of agonists toα 2-adrenergic receptors in human platelets. Arch Int Pharmacodyn Ther: 258: 193–207
Cooper B, Handin RI, Young LH, Alexander RW (1978) Agonist regulation of the human plateletα-adrenergic receptor. Nature 274: 703–706
Davies B, Sudera D, Mathias C, Bannister R, Sever P (1981) Beta-Receptors in orthostatic hypotension. N Engl J Med 305: 1017–1018
Engberg G, Elam M, Svensson TH (1982) Clonidine Withdrawal: Activation of brain noradrenergic neurons with specifically reducedα 2-receptor sensitivity. Life Sci 30: 235–243
Glusa E, Markwardt F (1981) Influence of clonidine-like hypotensive drugs on adrenergic platelet reactions. Biochem Pharmacol 30: 1359–1360
Grant JA, Scrutton MC (1979) Novelα 2-adrenoceptors primarily responsible for inducing human platelet aggregation. Nature 277: 659–661
Hansson L, Hunyor SN, Julius S, Hoobler SW (1973) Blood pressure crisis following withdrawal of clonidine (Catapres, Catapresan) with special reference to arterial and urinary catecholamine levels and suggestions for acute management. Am Heart J 85: 605–610
Hökfelt B, Hedeland H, Dymling J (1970) Studies on catecholamines, renin, and aldosteron following catapresan® (2-(2,6-dichlorophenylamine)-2-imidazoline hydrochloride) in hypertensive patients. Eur J Pharmacol 10: 389–397
Hoffman BB, DeLean A, Wood CL, Schocken DD, Lefkowitz RJ (1979) Alpha-adrenergic receptor subtypes: quantitative assessment by ligand binding. Life Sci 24: 1739–1746
Hoffman BB, Lefkowitz RJ (1980) Radio-Ligand Binding Studies of Adrenergic Receptors: New Insights into Molecular and Physiological Regulation. Ann Rev Pharmacol Toxicol 20: 581–608
Hoffman BB, Mullikin-Kilpatrick D, Lefkowitz RJ (1980) Heterogeneity of radio-ligand binding toα-adrenergic receptors. J Biol Chem 255: 4645–4652
Hsu CY, Knapp DR, Halushka PV (1979) The effects of alpha adrenergic agents on human platelet aggregation. J Pharmacol exp Ther 208: 366–370
Karliner JS, Motulsky HJ, Insel PA (1982) Apparent “Down-Regulation” of Human Platelet Alpha2-Adrenergic Receptors is Due to Retained Agonist. Molec Pharmacol 21: 36–43
Kent RS, DeLean A, Lefkowitz RJ (1980) A quantitative analysis of beta-adrenergic receptor interactions: resolution of high and low affinity states of the receptor by computer modeling of ligand binding data. Molec. Pharmacol 17: 14–23
Kobinger W (1978) Centralα-adrenergic systems as target for hypotensive drugs. Rev Physiol Biochem Pharmacol 81: 40–100
Langer SZ (1981) Presynaptic regulation of the release of cate-cholamines. Pharmacol Rev 32: 337–362
Lefkowitz RJ (1980) Recent Developments in Adrenergic Receptor Research. Ann Rep Med Chem 15: 217–223
Lefkowitz RJ (1978) Identification and regulation of alpha- and beta-adrenergic receptors. Fed Proc 37: 123–129
Levitzki A (1981) The β-adrenergic receptor and its mode of coupling to adenylate cyclase. CRC Crit Rev Biochem 11: 81–112
Majewski H, Story DF (1979) Effects of withdrawal of clonidine treatment on pre-junctionalα-adrenoceptor sensitivity in rat atria. Clin Exp Pharmacol Physiol 6: 205–206
Michel T, Hoffman BB, Lefkowitz RJ (1980) Differential regulation of theα 2-adrenergic receptor by Na+ and guanine nucleotides. Nature 288: 709–711
Mickey JV, Tate R, Mullikin D, Lefkowitz RJ (1976) Regulation of adenylate cyclase-coupled beta adrenergic receptor binding sites by beta-adrenergic catecholaminesin vitro. Molec Pharmacol 12: 409–419
Minneman KP, Pittman RN, Molinoff PB (1981) β-Adrenergic receptor subtypes: properties, distribution and regulation. Ann Rev Neurosci 4: 419–461
Mukherjee C, Lefkowitz RJ (1977) Regulation of beta adrenergic receptors in isolated frog erythrocyte plasma membranes. Molec Pharmacol 13: 291–303
Nagel M, Schümann HJ (1980) A sensitive method for determination of conjugated catecholamines in blood plasma. J Clin Chem Clin Biochem 18: 431–432
Oates JA, Conolly ME, Prichard BNC, Shand DG, Schapel G (1977) The Clinical Pharmacology of Antihypertensive Drugs In: Handbook Exp Pharmacol Vol 39 “Antihypertensive Agents” (Ed F. Gross, Springer, Berlin) pp 571–632
Perkins JP (1981) Catecholamine-induced modification of the functional state of β-adrenergic receptors. Trends Pharmacol Sci 2: 326–328
Ross EM, Gilman AG (1980) Biochemical Properties of Hormonesensitive Adenylate Cyclase. Ann Rev Biochem 49: 533–564
Scatchard G (1949) The attraction of proteins for small molecules and ions. Ann NY Acad Sci 51: 660–672
Schmitt H (1977) The pharmacology of clonidine and related products. In: Antihypertensive Drugs (Ed F. Gross) Handbook of Experimental Pharmacology, Springer, Berlin, Vol 39: 299–396
Smith SK, Limbird LE (1981) Solubilization of human plateletα-adrenergic receptors: Evidence that agonist occupancy of the receptor stabilizes receptor-effector interactions. Proc Natl Acad Sci USA 78: 4026–4030
Starke K (1981a)α-Adrenoceptor subclassification. Rev Physiol Biochem Pharmacol 88: 199–236
Starke K (1981b) Presynaptic Receptors. Ann Rev Pharmacol Toxicol 21: 7–30
Starke K (1977) Regulation of noradrenaline release by presynaptic receptor systems. Rev Physiol Biochem Pharmacol 77: 1–124
Su Y-F, Harden TK, Perkins JP (1980) Catecholamine-specific desensitization of adenylate cyclase. J Biol Chem 255: 7410–7419
U'Prichard DC, Kahn DJ, Daiguji M, Mitrius JC (1981) Neural and non-neuralα 2-adrenergic receptors: changes in multiple affinity states following desensitization. Proc 8th International Congress of Pharmacology Tokyo/Japan; Abstract 0–34
Weber MA (1980) Discontinuation syndrome following cessation of treatment with clonidine and other antihypertensive agents. J Cardiovasc Pharmacol 2, Suppl I: S73-S89
Wessels MR, Mullikin D, Lefkowitz RJ (1979) Selective Alteration in high affinity agonist binding: A mechanism of beta-adrenergic receptor desensitization Molec Pharmacol 16: 10–20
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Brodde, O.E., Anlauf, M., Graben, N. et al. In vitro and in vivo down-regulation of human plateletα 2-adrenoceptors by clonidine. Eur J Clin Pharmacol 23, 403–409 (1982). https://doi.org/10.1007/BF00605989
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00605989