Stimulatory Effect Of Dopamine Research Articles

Presence of dopamine-dependent adenylate cyclase activity in human renal cortex

The effects of dopamine (DA) and of two selective DA DA1 agonists (SKF 38393 and SKF 82526) on adenylate cyclase activity were studied with human kidney cortex membrane preparations. DA elicited a dose-related stimulation of adenylate cyclase activity with an EC 50 of 60 μM. The selective DA DA1 antagonist SCH 23390 behaved as a competitive antagonist, shifting the dose-response curce to the right. The non-selective β-adrenoceptor antagonist (−)-propranolol did not affect the EC 50 of the dose-response curve to DA but attenuated the maximal stimulatory effect of DA at concentrations higher than 100 μM. (+)-Sulpiride inhibited DA-induced adenlylate cyclase stimulation in a dose-dependent manner with an IC 50 of 4.6 × 10 −8 M but (−)-sulpiride was without effect. Both SKF 38393 and SKF 82526 stimulated the adenylate cyclase activity of human kidney cortex; this effect was completely antagonized by SCH 23390. Our results, demonstrating the presence of DA-sensitive adenylate cyclase activity, strongly suggest the presence of a DA receptor of the DA1 subtype in human kidney cortex.

Dopaminergic stimulation of cAMP accumulation in cultured rat mesangial cells.

Dopamine (DA) alters renal hemodynamics, and DA receptors have been demonstrated in isolated glomeruli. To determine the glomerular cell type bearing DA receptors, we studied the effect of dopaminergic agonists and antagonists on adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in rat glomerular mesangial and epithelial cells in culture. DA caused a marked dose- and time-dependent increase in cAMP accumulation in mesangial but not epithelial cells. The stimulatory effect of DA was abolished by the DA antagonists haloperidol, trifluoperazine, and cis-thiothixene but not by beta- or alpha-adrenergic or histamine antagonists. Similar to the effects of DA, two dopamine type I receptor agonists, fenoldopam and SKF 38393, markedly stimulated cAMP accumulation in the mesangial cells. Moreover, the effects of DA were blocked by Sch 23390, a specific DA1 receptor antagonist, but not domperidone, a specific DA2 antagonist. These results show that DA regulates cAMP accumulation in mesangial cells via DA1-type receptors.

Influence of dopamine on atrial natriuretic peptide level in premature infants.

The role of dopamine (DA) in the activation and/or release of atrial natriuretic peptide (ANP) was investigated in 11 premature infants during the early postnatal period. Mean plasma concentration of ANP and free DA level before DA infusion was 252.6 +/- 210 fmol/ml, and 0.4 +/- 0.2 ng/ml, respectively. DA infusion in a dose of 2 micrograms/kg/min caused a rise in plasma free DA level to 59.7 +/- 21.5 ng/ml and a significant increase in GFR, diuresis, sodium excretion and fractional sodium excretion. The plasma concentration of ANP, however, remained unchanged (252.6 +/- 210.0 vs. 213 +/- 143.0 fmol/ml). Thus, our data failed to demonstrate a stimulatory effect of DA on ANP release in premature infants. The role of the high plasma concentration of ANP in preterm neonates immediately after birth has to be clarified.

D 1-dopamine receptor activation mediates [ 3H]acetylcholine release from rabbit retina

Dopamine and dopamine receptor agonists (0.1 microM-10 mM) evoked in a concentration-dependent manner, calcium-dependent release of [3H]acetylcholine from the rabbit retina labeled in vitro with [3H]choline. This stimulatory effect of dopamine was antagonized by SCH23390 and by alpha-flupenthixol, but not by S-sulpiride or propranolol. Increases in intracellular cyclic AMP by forskolin, 3-isobutyl-1-methylxanthine and 8-bromo-cyclic AMP also evoked calcium-dependent release of [3H]acetylcholine. These results indicate that activation of a receptor with the biochemical and pharmacological characteristics of a D1-dopamine receptor mediates calcium-dependent release of acetylcholine from rabbit retina, possibly through a cyclic AMP-dependent process.

Dopamine, noradrenaline and isoprenaline: secretory and electrophysiological effects in vitro on mouse pancreas.

The amylase release from mouse pancreatic fragments was studied after dopamine (DA), and alpha- or beta-sympathomimetic agonist application. The electrical parameters of the acinar cell membrane were also monitored. Both DA (from 5 X 10(-6) to 10(-4) M) and beta-stimulants (isoprenaline from 5 X 10(-6) to 5 X 10(-5) M; noradrenaline from 3 X 10(-4) to 10(-3) M) evoked an increase in amylase release, while noradrenaline in alpha-receptor stimulating doses failed to have any effect. The stimulatory effect of DA was blocked by ganglion blockers (Arfonad 10(-5) M; pentamethonium 3 X 10(-5) M) in a competitive manner and a dual antagonism was observed with atropine (10(-7) M, 10(-9) M). An alpha-receptor antagonist (phentolamine 10(-5) M) and a beta-receptor antagonist (propranolol 10(-5) M) had no influence on the dopamine response. Moreover, the DA-induced stimulation was dependent on the presence of extracellular calcium. Perfusion with 10(-4) and 10(-3) M-DA or local application (from 77 micrograms to 4.3 mg), resulted in marked membrane depolarization with diminution of the input resistance. This effect was blocked by atropine (10(-5) M) and pentamethonium (10(-4) M), but not by propranolol (10(-5) M) or phentolamine (10(-5) M). The isoprenaline- (IP) and noradrenaline- (NA) induced increase in amylase release was competitively blocked by propranolol (10(-5) M) but not by phentolamine (10(-5) M). Atropine caused a dose-dependent (10(-7) M, 10(-6) M) decrease in the maximal response (non-competitive antagonism), while the ganglion blocker pentamethonium (10(-4) M) was without effect. NA caused membrane depolarization accompanied by a decrease in the input resistance after local application (from 77 micrograms to 1.6 mg). This effect persisted in the presence of 10(-5) M-phentolamine but was abolished by 10(-5) M-propranolol. IP perfusion (10(-4) and 10(-3) M) or local application (0.3 M; from 32 to 130 micrograms) caused the same electrical changes as those induced by NA and DA. The effect of IP persisted in the presence of 10(-5) M-phentolamine, 10(-4) M-pentamethonium and 10(-4) M-domperidone, but was abolished by propranolol (10(-5) M) and tetrodotoxin (5 X 10(-6) M) and markedly diminished by atropine (10(-5) M).(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine stimulates rat cortical somatostatin release

Release of somatostatin from slices of rat frontal cortex was studied. Increasing the potassium ion concentration in the medium from 6mM to 55 mM resulted in a significantly increased release of somatostatin. Dopamine increased the release of somatostatin from cortex and this effect of dopamine was blocked by haloperidol and other dopaminergic antagonists. Other catecholamines as well as serotonin, histamine and acetylcholine failed to stimulate the release of somatostatin. The stimulatory effect of dopamine on release of somatostatin from cortical slices provides an approach for examination of the receptor properties and function of dopamine in this brain region.

Parathyroid Hormone and Calcitonin Secretion in Man: Effect of Dopamine Agonists and Antagonists

This study was undertaken to evaluate the physiological role, if any, of dopamine (DA) in modulating parathyroid hormone (PTH) and calcitonin (CT) secretion in man. Infusion of DA (5 micrograms/kg/min) into 6 normal men, decreased serum immunoreactive prolactin (iPRL) and concomitantly increased serum iPTH to 140 +/- 6.8% of baseline (P less than 0.01) at 30 min, with decline thereafter, despite continuation of the DA infusion. Serum iCT levels did not significantly change. Chlorpromazine (50 mg IM), decreased serum iPTH to 75 +/- 5.4% and 79 +/- 3.7% of baseline (P less than 0.01) at 30 and 60 min, respectively, associated with an increase in iPRL. There was subsequent return of iPTH to baseline even though iPRL remained elevated. iCT levels did not significantly change. These observations would suggest that DA may play a physiological role in iPTH, but not iCT, secretion. However, infusion of more nearly physiological doses of DA (0.02, 0.2, and 2.0 micrograms/kg/min) lowered serum iPRL to levels similar to those after the larger DA dose, but with no concomitant increase in either iPTH or iCT. Also, 1) the DA agonist bromocriptine decreased serum iPRL without modifying iPTH or iCT; 2) the DA precursor, levodopa, and the DA antagonist, metoclopramide, had no effect on serum iPTH or iCT levels. These studies suggest that 1) the transient stimulatory effect of DA on iPTH secretion is pharmacological, and 2) DA does not have a physiological role in secretion of iPTH or iCT in man.

D-l and D-2 dopaminergic receptors regulate protein phosphorylation in the rat neurohypophysis

Dopamine stimulates the phosphorylation of the neuron-specific synaptic vesicle proteins Synapsin I, Protein IIIa and Protein IIIb in the posterior pituitary gland of the rat [ Tsou and Greengard (1982) Proc. natn. Acad. Sci. U.S.A. 79, 6075–6079 . This effect has been characterized in the present investigation. The stimulatory effect of dopamine was mimicked by the selective D-l receptor agonist SKF 38393 and was competitively and potently inhibited by the selective D-l receptor antagonist SKF 83509 as well as by the mixed D-l/D-2 antagonist fluphenazine. Conversely, the effect of dopamine was attenuated by a D-2 receptor agonist (LY 141865) and potentiated by a D-2 receptor antagonist (sulpiride). Norepinephrine also stimulated phosphorylation of the synaptic vesicle proteins, apparently through activation of the D-l receptor. D-l and D-2 dopaminergic receptors may play a role in the regulation of hormone secretion from the neurohypophysis. Evidence exists that in the isolated neurophypophysis activation of D-l receptors facilitates, while activation of D-2 receptors inhibits, release of vasopressin. Further work will be required to determine whether the regulation by D-l and D-2 receptors of the protein phosphorylation in the neurohypophysial peptidergic terminals is related to the regulation by those receptors of the neurohypophysial hormone secretion.

Age-associated decrease of dopamine-sensitive adenylate cyclase in rabbit renal artery

Using renal arteries from young (6 months), mature (18 months) and old (70 months) rabbits, the effect of dopamine on 3′,5′-cyclic adenosine monophosphate (cAMP) generation was studied. No significant differences in basal adenylate cyclase values were found in homogenates of renal artery from young, mature or old rabbits. The protein content of the renal artery was also unchanged during the lifespan. Dopamine stimulated the production of cAMP. The stimulatory effect of dopamine was similar in the renal artery of young and mature rabbits but was lower by about 40% in old rabbits. The present results led us to hypothesize an impairment of the peripheral dopaminergic system in old age similar to that described for the central dopaminergic system.

Dopamine stimulates somatostatin release from perifused hypothalamic cells.

We studied the release of immunoreactive somatostatin (IR-SRIF) from hypothalamic cells that were obtained from rats and dispersed with the aid of collagenase. Twenty-four hours after dispersion, cells were placed in a column supported by a matrix of preswollen Biogel P2 and perifused. Fractions were collected on ice and subsequently assayed for SRIF. SRIF release was stimulated markedly by potassium depolarization (KCl, 56 mM), by the Na+-K+-ATPase inhibitor ouabain (10(-4) M), and by dopamine at concentrations as low as 10(-11) M. The stimulatory effects of membrane depolarization were calcium dependent and were not observed in the absence of exogenous calcium in the perifusion medium or in the presence of EDTA (0.05 M). Metoclopramide, the dopamine antagonist, abolished the stimulatory effect of dopamine. In conclusion, release of IR-SRIF by dispersed rat hypothalamic cells can be studied in a simple perifusion apparatus. Release is stimulated by membrane depolarization in a calcium-dependent manner and by dopamine at physiological concentrations.

The effects of dopamine agonists and antagonists on Na +, K +-ATPase and Mg 2+-atpase activities of synaptosomes

The effects of dopamine agonists and antagonists on the Na +,K +-ATPase and Mg 2+-ATPase activities of rat cerebral cortex synaptosomes have been determined. Dopamine, ADTN, apomorphine and S-584, but not piribedil, stimulated the activities of the enzymes. The stimulatory effect of dopamine was not antagonised by dopamine antagonists and apparently the catechol group is responsible for the enzyme stimulation.

Characterization and localization of catecholamine-susceptible Na-K ATPase activity of rat striatum: Studies using catecholamine receptor (ant)agonists and lesion techniques

Na-K ATPase activity of homogenates of rat striatum is stimulated by dopamine (DA) and noradrenalin (NA) in similar and concentration-dependent ways. The enzyme is also stimulated by apomorphine and 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (ADTN), agonists of DA receptors. Other DA agonists, such as bromocriptine and piribedil, show no effect at all, while another, lergotrile, stimulates only slightly. The stimulatory effect of DA and apomorphine is not counteracted by haloperidol. cis-Flupenthixol, another DA receptor antagonist, does strongly inhibit DA stimulation of striatal Na-K ATPase activity at concentrations which inhibit basal activity to a limited extent only. However, this effect is not related to the DA receptor blocking activity of the drug, as trans-flupenthixol, an isomer which is much less active in DA receptor blocking tests, inhibits the stimulation by DA even more. With drugs blocking α and β noradrenergic receptors (phentolamine and dihydroergotoxine, respectively propranolol), no specific inhibition of the NA stimulation of Na-K ATPase activity of striatum, cerebral cortex and cerebellum is found. In addition, no effect of the α receptor agonist clonidine is observed. From these experiments with catecholamine receptor agonists and antagonists, we conclude that stimulation of brain Na-K ATPase most probably is not related to catecholamine receptor mechanisms. Lesion experiments suggest that the DA susceptible striatal Na-K ATPase activity is not specifically localized in DA neurons or in DA innervated neurons. Neither degeneration of DA-containing terminals (caused by 6-hydroxydopamine) nor degeneration of neurons postsynaptically with regard to DA terminals (caused by kainic acid) affects DA susceptibility of the striatal enzyme. We therefore conclude that catecholamine susceptibility probably is a general characteristic of striatal Na-K ATPase (and probably also of that of other brain regions). Our conclusions are in line with suggestions in the literature that stimulation of brain Na-K ATPase by catecholamines is a nonspecific phenomenon and is indirectly effected by abolition of the inhibitory effect of divalent metal ions on the enzyme. Indeed, the striatal enzyme is stimulated by EDTA too.

Chemical lesion and drug induced supersentivity and subsensitivity of caudate dopamine receptors

In order to elucidate the mechanism of denervation supersensitivity, the effects of 6-hydroxydopamine lesion, placed in the substantia nigra, were examined on rat brain caudate adenylate cyclase and 3H-haloperidol binding to membrane dopamine receptors. In addition, the effects of chronic administration of L-DOPA, bromocriptine and piribedil were also investigated on 3H-haloperidol binding and dopamine, K + isoproterenol (IPNE) and 2-Cl-adenosine stimulated formation of cyclic AMP in caudate slices. 6-Hydroxydopamine lesions resulted in significantly greater stimulation of adenylate cyclase by dopamine at various concentrations tested. The haloperidol binding sites were increased by 28% on lesioned side caudate without changes in dissociation constants (K D). Three weeks after treatment with L-DOPA, bromocriptine or piribedil, the 3H-haloperidol binding sites were decreased by 40% with no change in K D. The stimulatory effect of dopamine on cyclic AMP formation was also abolished, although there was no change in IPNE, K +, or 2-Cl-adenosine stimulated cyclic AMP formation in caudate slices, suggesting a specific effect of dopamine agonists on dopamine receptors. The results of these studies suggest a close relationship between at least some populations of dopamine receptors and adenylate cyclase in the caudate nucleus.

Dopamine-induced dissociation between renal metabolic rate and sodium reabsorption.

The stimulatory effect of dopamine on renal energy metabolism and its relationship to changes in tubular sodium reabsorption and plasma concentration of free fatty acids (FFA) were examined in anesthetized dogs. Dopamine infused intravenously at 25 mug/kg body wt-min for 30-60 min increased renal oxygen consumption (Rvo2) by 28 +/- 3%; glomerular filtration rate rose from 37 +/- 3 to 40 +/- 2 ml/min without significant changes in sodium excretion. Plasma FFA increased about 6 times. Total-body metabolic rate increased to 152 +/- 7% and fell to 119 +/- 5% of control after normalizing plasma FFA by beta-pyridylcarbinol; Rvo2 remained unchanged. Cortical and outer medullary heat accumulation rated increased to 137 +/- 6 and 133 +/- 10% after 1 h and to 163 +/- 18 and 179 +/- 26% of control after 2 h of dopamine infusion without further changes in sodium reabsorption. Furosemide reduced cortical and outer medullary metabolic rates as much as in control experiments (14 +/- 8 and 69 +/- 7%, respectively). Hence, dopamine exerts a renal calorigenic effect which cannot be accounted for by increased sodium reabsorption or attributed to increased supply of FFA.

Biochemical characterization of the dopamine receptor in the mammalian caudate nucleus

I SHALL summarize very briefly some of the work which we ,have been doing in our laboratory relevant to the nature of the dopamine receptor and to the mechanism of action of neuroleptic drugs. Our involvement in the world of dopamine began with the superior cervical ganglion, and I’ll devote a small fraction of my presentation to summarize that work, which was carried out by MCAFEE, J. W. KEBABIAN and myself. We obtained evidencele3 suggesting that cyclic AMP mediates dopaminergic transmission in the ganglion and, thereby, modulates nicotinic cholinergic transmission through the ganglion. Part of the evidence that we had for this conclusion was the observation that dopamine, which was known to hyperpolarize the post ganglionic neurons of the ganglion, also causes an increase in ganglionic cyclic AMP. Moreover, we found that cyclic AMP is able to mimic the hyperpolarizing action of dopamine. The question as to how dopamine causes an increase in cyclic AMP was then studied, and it was found, using cell-free preparations of the ganglion, that dopamine stimulated an adenylate cyclase. This occurred at very low concentrations of dopamine, and the effect was specific for dopamine. These and other of our studies with the ganglion suggested that the “dopamine receptor” in the ganglion was the dopamine-binding portion of a dopamine-sensitive adenylate cyclase, and that this enzyme might be involved in the mediation of dopaminergic synaptic transmission in the ganglion. In view of the work of HORNYKIEWICZ, CARLSSON and their collaborators, as well as of a number of other investigators, we turned our attention to the dopamine receptor of the caudate nucleus, with the idea that possibly this dopamine receptor, which had been well characterized pharmacologically, both in intact experimental animals and clinically, might, like the dopamine receptor in the ganglion, be the dopamine-binding portion of a dopamine-sensitive adenylate cyclase. To test that possibility, KEBABIAN, PETZOLD and I prepared homogenates of caudate nuclei of the rat, and examined the homogenates for the presence of dopamine-sensitive adenylate cyclase activity.4 There was, indeed, such an adenylate cyclase in the caudate nucleus, and interestingly, virtually all of the known properties of the caudate dopamine receptor could be mimicked by the properties of this cell-free enzyme system. For instance, this adenylate cyclase was stimulated by very low concentrations of dopamine (Fig. 1). (Norepinephrine was considerably less effective than dopamine in stimulating enzyme activity, and isoproteronol was virtually ineffective.) The stimulatory effect of dopamine was mimicked by very low concentrations of apomorphine (Fig. 2). The stimulatory effect of either dopamine or apomorphine was prevented

Dopamine-sensitive adenylate cyclase in caudate nucleus of rat brain, and its similarity to the "dopamine receptor".

An adenylate cyclase that is activated specifically by low concentrations of dopamine has been demonstrated in homogenates of caudate nucleus of rat brain. A half-maximal increase in the activity of the enzyme occurred in the presence of 4 muM dopamine. Concentrations of dopamine as low as 0.3 muM stimulated the activity of the enzyme. The adenylate cyclase activity of the homogenates was also stimulated by low concentrations of apomorphine, a substance known to mimic the physiological and pharmacological effects of dopamine. The stimulatory effect of dopamine was blocked by low concentrations of either haloperidol or chlorpromazine, agents known to block the actions of dopamine in mammalian brain. The results suggest that dopamine-sensitive adenylate cyclase may be the receptor for dopamine in mammalian brain. The isolation of this enzyme from caudate nucleus should facilitate the search for new therapeutic agents useful in the treatment of extrapyramidal diseases.