Effects of dopaminergic drugs on the sympathoadrenal system

Spectrophotometric Methods for Determination of Dopamine Hydrochloride in Bulk and in Injectable Forms

Two highly simple, economical, accurate and sensitive spectrophotometric methods for determination of dopamine hydrochloride (DAH) in either pure form and pharmaceutical formulations are described. The first method is based on determination of (DAH) spectrophotometrically at maximum absorbance 280 nm (method A). The second one is based on reduction of alkaline KMnO₄ by (DAH) leading to the formation of green manganate species which are measured at 610 nm (method B). Under optimized conditions, the calibration graphs were linear in the range of 3.793 - 45.513, 0.190 - 4.362 μg.mL^-1 of (DAH) for methods A and B respectively. The developed methods were successfully applied for the determination of dopamine hydrochloride in pharmaceutical samples.

Renalase: a novel regulator of cardiometabolic and renal diseases

Renalase is a ~38 kDa flavin-adenine dinucleotide (FAD) domain-containing protein that can function as a cytokine and an anomerase. It is emerging as a novel regulator of cardiometabolic diseases. Expressed mainly in the kidneys, renalase has been reported to have a hypotensive effect and may control blood pressure through regulation of sympathetic tone. Furthermore, genetic variations in the renalase gene, such as a functional missense polymorphism (Glu37Asp), have implications in the cardiovascular and renal systems and can potentially increase the risk of cardiometabolic disorders. Research on the physiological functions and biochemical actions of renalase over the years has indicated a role for renalase as one of the key proteins involved in various disease states, such as diabetes, impaired lipid metabolism, and cancer. Recent studies have identified three transcription factors (viz., Sp1, STAT3, and ZBP89) as key positive regulators in modulating the expression of the human renalase gene. Moreover, renalase is under the post-transcriptional regulation of two microRNAs (viz., miR-29b, and miR-146a), which downregulate renalase expression. While renalase supplementation may be useful for treating hypertension, inhibition of renalase signaling may be beneficial to patients with cancerous tumors. However, more incisive investigations are required to unravel the potential therapeutic applications of renalase. Based on the literature pertaining to the function and physiology of renalase, this review attempts to consolidate and comprehend the role of renalase in regulating cardiometabolic and renal disorders.

Regulation of renalase expression by D5 dopamine receptors in rat renal proximal tubule cells

The dopaminergic and sympathetic systems interact to regulate blood pressure. Our previous studies showed regulation of α1-adrenergic receptor function by D1-like dopamine receptors in vascular smooth muscle cells. Because renalase could regulate circulating epinephrine levels and dopamine production in renal proximal tubules (RPTs), we tested the hypothesis that D1-like receptors regulate renalase expression in kidney. The effect of D1-like receptor stimulation on renalase expression and function was measured in immortalized RPT cells from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). We found that the D1-like receptor agonist fenoldopam (10(-7)-10(-5) mol/l) increased renalase protein expression and function in WKY RPT cells but decreased them in SHR cells. Fenoldopam also increased renalase mRNA levels in WKY but not in SHR cells. In contrast, fenoldopam increased the degradation of renalase protein in SHR cells but not in WKY cells. The regulation of renalase by the D1-like receptor was mainly via the D5 receptor because silencing of the D5 but not D1 receptor by antisense oligonucleotides blocked the stimulatory effect of the D1-like receptor on renalase expression in WKY cells. Moreover, inhibition of PKC, by the PKC inhibitor 19-31, blocked the stimulatory effect of fenoldopam on renalase expression while stimulation of PKC, by a PKC agonist (PMA), increased renalase expression, indicating that PKC is involved in the process. Our studies suggest that the D5 receptor positively regulates renalase expression in WKY but not SHR RPT cells; aberrant regulation of renalase by the D5 receptor may be involved in the pathogenesis of hypertension.

Preliminary pharmacokinetics and cardiovascular effects of fenoldopam continuous rate infusion in six healthy dogs

Fenoldopam is a selective dopamine-1 receptor agonist that causes peripheral arterial vasodilation, increased renal blood flow, and diuresis. Enthusiasm exists for the use of fenoldopam in nonpolyuric kidney injury in dogs, although pharmacokinetic data are lacking. The purpose of this study was to collect basic pharmacokinetic and hemodynamic effect data for fenoldopam when administered to healthy awake dogs. Six healthy, awake beagles were given a 180-min fenoldopam constant rate infusion at 0.8 μg/kg per minute followed by a 120-min washout period. Citrated blood was collected during and after infusion for the measurement of plasma fenoldopam concentration by HPLC with mass spectrometry. Heart rate and indirect systolic blood pressure were concurrently measured. Mean ± SD, steady-state plasma fenoldopam concentrations of 20 ± 17 ng/mL were achieved within 10 min of starting the infusion. Area under the plasma concentration-time curve was 3678 ± 3030 ng/mL · min, and plasma clearance was 66 ± 43 mL/min per kg. Elimination was rapidly achieved in all dogs. Heart rate and systolic blood pressure were unaffected by the fenoldopam infusion. Based on the results of this study, further evaluation of the effects of fenoldopam in dogs at differing doses and in dogs with clinical conditions such as acute nonpolyuric kidney injury is warranted.

Roles of dopaminergic d(1) and d(2) receptors in catecholamine release from the rat adrenal medulla

The aim of the present study was designed to establish comparatively the inhibitory effects of D(1)-like and D(2)-like dopaminergic receptor agonists, SKF81297 and R(-)-TNPA on the release of catecholamines (CA) evoked by cholinergic stimulation and membrane depolarization from the isolated perfused model of the rat adrenal medulla. SKF81297 (30microM) and R-(-)-TNPA (30microM) perfused into an adrenal vein for 60 min, produced great inhibition in the CA secretory responses evoked by ACh (5.32x10(- 3) M), DMPP (10(-4) M), McN-A-343 (10(-4) M), high K(+) (5.6x10(-2) M), Bay-K-8644 (10microM), and cyclopiazonic acid (10microM), respectively. For the release of CA evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid, the following rank order of inhibitory potency was obtained: SKF81297>R-(-)-TNPA. However, R(+)-SCH23390, a selectve D(1)-like dopaminergic receptor antagonist, and S(-)-raclopride, a selectve D(2)-like dopaminergic receptor antagonist, enhanced the CA secretory responses evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid only for 0~4 min. The rank order for the enhancement of CA release evoked by high K(+), McN-A-343 and cyclopiazonic acid was R(+)-SCH23390>S(-)-raclopride. Also, the rank order for ACh, DMPP and Bay-K-8644 was S(-)-raclopride > R(+)-SCH23390. Taken together, these results demonstrate that both SKF81297 and R-(-)-TNPA inhibit the CA release evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors and the membrane depolarization from the isolated perfused rat adrenal gland without affecting the basal release, respectively, but both R(+)-SCH23390 and S(-)-raclopride facilitate the CA release evoked by them. It seems likely that the inhibitory effects of SKF81297 and R-(-)-TNPA are mediated by the activation of D(1)-like and D(2)-like dopaminergic receptors located on the rat adrenomedullary chromaffin cells, respectively, whereas the facilitatory effects of R(+)-SCH23390 and S(-)-raclopride are mediated by the blockade of D(1)-like and D(2)-like dopaminergic receptors, respectively: this action is possibly associated with extra- and intracellular calcium mobilization. Based on these results, it is thought that the presence of dopaminergic D(1) receptors may play an important role in regulation of the rat adrenomedullary CA secretion, in addition to well-known dopaminergic D(2) receptors.

In vivo effects of fenoldopam on autonomic nervous system after inhibition or activation of ganglionic transmission

The study investigated the effects of dopamine D1-like receptor stimulation on the autonomic nervous system. Fenoldopam (20 microg/kg) was injected i.v. in conscious sinoaortic denervated dogs, that is, surgically deprived of baroreflex pathways. In barodenervated dogs, fenoldopam (20 microg/kg) induced arterial hypotension as well as bradycardia and reduced noradrenaline plasma levels. Pentolinium (0.1 mg/kg i.v.), used to induce partial blockade of nicotinic ganglionic receptors, suppressed the fenoldopam-induced decrease in sympathetic tone, suggesting a ganglionic location for the dopamine D1-like receptor. Moreover, the inability of fenoldopam to reduce the nicotine-induced increase in sympathetic tone suggests that a postsynaptic ganglionic location can be excluded for the dopamine D1-like receptor. The results of these "in vivo" experiments strongly suggest a presynaptic location for the ganglionic dopamine D1-like receptor, stimulation of which results in a reduction of sympathetic tone.

Suckling-induced increase in cyclic AMP exclusively in the central region of the rat adenohypophysis

Investigating the cellular events in the pituitary gland, the intracellular cyclic AMP (cAMP) of the neural lobe (NL), intermediate lobe (IL), the inner (IZ-AL) and outer zone (OZ-AL) of the anterior lobe (AL) have been measured during the suckling stimulus. Ten-minutes suckling, parallel to the elevation of plasma PRL, induced a significant increase of cAMP concentration in the IZ-AL. In contrast, 10- and 30-min suckling resulted in a decrease of cAMP level in the NL. Changes in cAMP of the OZ-AL and the IL as well as in the plasma level of alpha-MSH could not be detected. These region-specific changes of cAMP in the pituitary gland during suckling stimulus seems to be related to interacting neuroendocrine signals delivered concomitantly from the hypothalamus and from the NIL to the IZ-AL.