PTH-receptors regulate norepinephrine release in human heart and kidney.

Recent data suggests that chronic renal failure and hyperparathyroidism are associated with sympathetic overactivity. Since peptide hormones are known to modulate norepinephrine (NE) release by activating prejunctional receptors, this study investigates whether parathyroid hormone fragment (1-34) (hPTH(1-34)) increases neuronal NE release in human heart and kidney. Using specific PTH-receptor agonists and antagonists, this study furthermore highlights functional differences between PTH1 and PTH2 receptors. Human atrial and renal tissues were incubated with [(3)H]-NE and superfused. Three electrical stimulations (5Hz, 1min) induced a stable [(3)H]-NE release which was taken as an index of endogenous NE release. RT-PCR with specific primers for PTH1- and PTH2-receptor was performed in heart and kidney. hPTH(1-34) (0.01-0.1µmol/L) and a stable analog of its second messenger cAMP (8-bromo-cAMP) increased [(3)H]-NE release in human atria. This facilitatory effect of PTH was also observed in human renal cortex. The PTH1-receptor antagonist (D-Trp(12), Tyr(34))-pTH-(7-34) (0.5µmol/L) abolished the effect of hPTH(1-34). This data was verified using isolated perfused mouse kidneys. Tuberoinfundibular peptide of 39 residues (TIP-39) (0.1nmol/L-0.1µmol/L) decreased [(3)H]-NE release in atria. PTH1- and PTH2-receptor expressions were demonstrated in human heart and kidney. Moreover, a splice variant of the PTH2-receptor was detected in human kidney. In conclusion, PTH is able to facilitate NE release in human atria and renal cortex by activation of PTH1-receptors. The highly increased PTH levels that can be observed in chronic renal failure might be one contributor for the elevated sympathetic nerve activity and the associated cardiovascular mortality in patients with end stage renal disease.

Nephrogenic systemic fibrosis following exposure to gadolinium-containing contrast agent.

Nephrogenic systemic fibrosis (NSF) is a disease recently described in patients with kidney failure. It is characterized by scleroderma-like thickening of the skin, subcutaneous edema and ensuing joint contractures leading to profound disability. Furthermore, involvement of internal organs has been described. Whereas the pathogenesis is not known to date, recent reports have linked NSF to high doses of gadolinium-containing contrast agents given at magnetic resonance angiography (MRA). We describe a patient with severe NSF. The patient had received erythropoietin and had undergone vascular interventions which are suspected risk factors for this disease. Notably, the disease developed shortly after the application of gadolinium at an MRA, giving support to the recently published hypothesis that gadolinium-containing contrast agents are among the causative factors. We provide a short overview and hope to raise overall awareness towards this entity and the use of MRA contrast agents in renal patients.

Acetylcholine release in human heart atrium: influence of muscarinic autoreceptors, diabetes, and age.

BACKGROUND: An imbalance of sympathetic and parasympathetic drive to the heart is an important risk factor for cardiac death in patients with coronary heart disease, diabetes, and renal insufficiency. The amount of neurotransmitter released from peripheral autonomic nerves is modulated by presynaptic receptor systems. In analogy to alpha-autoreceptors on sympathetic nerves, muscarinic autoreceptors activated by endogenous acetylcholine may exist on parasympathetic nerves in the human heart. METHODS AND RESULTS: We developed a technique to study acetylcholine release from human atria and investigated muscarinic autoreceptor function. A pharmacological and molecular approach was used to characterize the subtype involved. Of the 5 muscarinic receptor subtypes cloned, only mRNA encoding for M(2)- and M(3)-receptors were detected. Potencies of several muscarinic antagonists against the release-inhibiting effect of the nonselective muscarinic agonist carbachol at the cardiac autoreceptor were correlated with published data for human cloned M(1)- through M(5)-receptors. CONCLUSIONS: This analysis clearly indicates that acetylcholine release in human atria is controlled by muscarinic M(2)-receptors. Blockade of these receptors by atropine doubles the amount of acetylcholine released at a stimulation frequency of 5 Hz. In atria of patients >70 years of age and patients with late diabetic complications, acetylcholine release is reduced. Locally impaired cardiac acetylcholine release may therefore represent a pathophysiological link to sudden cardiac death in elderly and diabetic patients.

Contractile effects of tacrolimus in human and rat isolated renal arteries.

1. We tested the vasoactive properties of the immunosuppressive drug FK 506 (tacrolimus) in preconstricted rat and human isolated renal arteries in vitro. 2. In rat renal arteries, tacrolimus (3, 10 microM) showed a direct and dose-dependent contractile effect by maximally 23 microm (10% of the noradrenaline effect), which was only observed in the presence of intact endothelium. Moreover, a lower concentration of tacrolimus (1 microM) potentiated pressor responses to the sympathetic neurotransmitter noradrenaline but not to ATP in this species. ATP- (0.01-10 microM) induced vasodilation was not affected by tacrolimus (1 microM). 3. In contrast, in human interlobar arteries, tacrolimus failed to induce direct vasoconstriction and did not significantly potentiate constrictor responses to noradrenaline. Acetylcholine-(1 microM) induced vasodilation was much smaller in human than in rat renal arteries suggesting the lack of functional endothelium in the human preparation. 4. The findings suggest that tacrolimus releases an endothelium-derived constricting factor in rat renal arteries to increase vascular tone and to potentiate pressor responses to noradrenaline. In human interlobar arteries, this effect of tacrolimus is not observed probably because of the absence of functional endothelium or the necessary mediator mechanism.

Dihydropyridine calcium antagonists and renal function in hypertensive kidney transplant recipients.

OBJECTIVE: To investigate whether calcium antagonists are nephroprotective in hypertensive cyclosporine-treated renal allograft recipients. METHODS: We studied 50 hypertensive and 17 normotensive renal transplants (eight females, nine males; 14-54 years, mean age 38.8 +/- 3.5 years). Hypertensive patients were randomized to be treated with (+Ca; 11 females, 13 males; 20-65 years, mean age 43.1 +/- 3 years) or without (-Ca; 15 females, 11 males; 25-60 years, mean age 41.3 +/- 2.5 years) a calcium antagonist (nitrendipine or nifedipine). Additional antihypertensives were given stepwise according to a standardized protocol: beta1-adrenoceptor blocker, diuretic alpha1-adrenoceptor blocker or vasodilator. Data were analysed at 0, 1, 2 and 3 years on an intention-to-treat basis. RESULTS: Hypertensive patients had a higher body mass index at 0/3 years (23.7 +/- 0.6/25.1 +/- 0.6 kg/m2) than normotensive patients (22.2 +/- 0.6/22.1 +/- 0.7 kg/m2). During the study, blood pressure in normotensive transplants was always slightly, but not significantly, lower than that of transplants with treated hypertension. There was no difference between the groups (+Ca) and (-Ca). Cr51-ethylenediaminetetracetic acid (EDTA) clearance (0/2 years) was 58 +/- 4/57 +/- 6 ml/min in normotensives, 52 +/- 4/47 +/- 4 ml/min in hypertensives (+Ca) and 47 +/- 4/49 +/- 6 ml/min in hypertensives (-Ca). Proteinuria (0/3 years) was 0.16 +/- 0.04/0.15 +/- 0.02 g/24 h in normotensive, 0.26 +/- 0.08/0.23 +/- 0.05 g/24 h in hypertensives (+Ca) and 0.26 +/- 0.07/0.22 +/- 0.05 g/24 h in hypertensives (-Ca). CONCLUSIONS: Post-transplant hypertension is associated with higher body mass index and poor renal function. No difference in the course of Cr51-EDTA clearance, serum creatinine, proteinuria or blood pressure was observed between groups treated with or without calcium antagonists. Calcium antagonists and conventional antihypertensive treatment have the same nephroprotective effect in hypertensive renal transplants, when treatment is started 3 months after transplantation.

Angiotensin converting enzyme inhibition unmasks the sympathofacilitatory effect of bradykinin in human right atrium.

OBJECTIVE: To investigate the role of angiotensin converting enzyme (ACE) inhibition in bradykinin-mediated modulation of noradrenaline release in human and rat atrium. METHODS: Human and rat atrial slices were incubated with [3H]-noradrenaline, superfused with Krebs-Henseleit solution and stimulated electrically at 5 Hz. The stimulation-induced outflow of radioactivity was taken as an index of endogenous noradrenaline release. RESULTS: In the absence of ACE inhibition 0.01-1 micromol/l bradykinin failed to alter the release of noradrenaline in human atrium. In contrast, 0.001-0.1 micromol/l bradykinin enhanced the release of noradrenaline in rat atrium. In the presence of 3 micromol/l of the ACE inhibitor captopril, however, bradykinin significantly enhanced the release of noradrenaline in human atrium. The bradykinin B1-receptor agonist (Des-Arg9)-bradykinin (0.01-1 micromol/l) had no effect on the release of noradrenaline in human atrium both in the absence and in the presence of 3 micromol/l captopril. Captopril (3 micromol/l) potentiated the facilitatory effect of bradykinin in rat atrium. The selective bradykinin B2-receptor antagonist D-Arg[Hyp3,Thi5, D-Tic7,Oic8]-bradykinin (Hoe 140, 0.3 micromol/l) and the cyclo-oxygenase inhibitor indomethacin (10 micromol/l) reduced the facilitatory effect of bradykinin significantly in the presence of captopril in rat and human atrium. Prostaglandin F2alpha (0.1 micromol/l), prostaglandin E2 (0.3 micromol/l) and the thromboxane A2 receptor agonist U-46 619 (0.1 micromol/l) enhanced the release of noradrenaline in human atria, whereas 0.1 micromol/l prostaglandin I2 had no effect. CONCLUSION: These data suggest that bradykinin facilitates the release of noradrenaline in human and rat atrium by activation of bradykinin receptors of the B2-subtype and subsequent release of facilitatory prostaglandins. The facilitatory effect of bradykinin in human atrium can only be demonstrated when its enzymatic degradation is prevented by ACE inhibition.

Prejunctional neuropeptide Y receptors in human kidney and atrium.

The aim of our study was to characterize functionally prejunctional neuropeptide Y (NPY) receptors in human and rabbit renal cortex, as well as in human right atrium. Segments of human atrial appendages and of human and rabbit renal cortex were preincubated with [3H]noradrenaline, superfused with Krebs-Henseleit solution and stimulated electrically in superfusion chambers. The stimulation-induced outflow of radioactivity was taken as an index of endogenous noradrenaline release. The effects of subtype-selective NPY analogs on the stimulation-induced noradrenaline release were studied. NPY, its endogenous analog, peptide YY, and its C-terminal fragment, NPY13-36, but not its analog, [Leu31,Pro34]NPY, concentration dependently (1-100 nM) inhibited [3H]noradrenaline release in all tissues studied. NPY-induced inhibition of [3H]noradrenaline release in human and rabbit kidney was abolished by pretreatment with pertussis toxin. We conclude that prejunctional inhibition of noradrenaline release in human heart and human and rabbit kidney occurs through NPY receptors of the Y2 subtype, which appear to couple to a pertussis toxin-sensitive G protein.

Extracellular ATP in the human kidney: mode of release and vascular effects.

1. We have previously shown that ATP is a co-transmitter of noradrenaline in the rat kidney. In the present study the release of ATP and noradrenaline from human kidney cortex was investigated. Vascular effects of ATP and stable analogues were tested in human and rabbit isolated renal blood vessels. 2. Sympathetic nerve stimulation (20 Hz for 1 min) in human kidney slices released 89 +/- 16 fmol noradrenaline per mg wet weight and 99 +/- 20 fmol ATP per mg wet weight in controls (n = 12). The Na+ channel blocker tetrodotoxin (1 microM) abolished ATP and noradrenaline release. 3. In human isolated extrarenal arteries the P2X-purinoceptor agonist beta, gamma-methylene-L-ATP caused almost no constrictor responses, beta, gamma-methylene-L-ATP induced moderate constrictor responses in intrarenal arteries. In preconstricted human intrarenal arteries ATP induced vasodilation. 4. ATP and the P2Y-receptor agonist 2-methyl-thio-ATP (2-MeSATP) dilated preconstricted rabbit renal arteries. The P2Y-receptor antagonist Reactive Blue 2 (3 microM) shifted the concentration response curves of ATP and 2-MeSATP to the right. 5. In conclusion, sympathetic nerve stimulation induces the release of ATP and noradrenaline in human renal cortex. ATP activates vasoconstrictory P2X- and vasodilatory P2Y-receptors in human renal blood vessels. The net vascular response to ATP in vivo will depend on the tissue distribution of these purinoceptors.

Diagnosis of renovascular disease by intra- and extrarenal Doppler scanning.

The purpose of this prospective, angiographically controlled study was to determine the diagnostic value of color Doppler sonography with two differing approaches of scanning in patients with clinical clues for renal artery stenosis (RAS). In 135 hypertensive patients peak systolic velocity in the main renal arteries and the resistive index (RI) of the intrarenal arteries were measured. The RI side-to-side-difference (delta RI) greater than 0.05 or peak systolic velocity greater than 2 m/s were used to discriminate normal from stenotic renal arteries, defined as angiographically confirmed RAS > 50%. In 88 of 135 patients 107 RAS were demonstrated by selective arteriography. Five renal artery occlusions occurred, which were all diagnosed by color Doppler sonography. Seventy-six RAS were detected by increased peak systolic velocity, and an additional 19 stenoses were identified by delta RI. The combined analysis of peak systolic velocity and delta RI resulted in a sensitivity of 89% and specificity of 92%. The positive predictive value was 92% and the negative predictive value was 88%. Our data suggest that only the combination of intra- and extrarenal scanning with color Doppler sonography represents an effective screening method for significant renal artery stenosis in hypertensive patients.

Pharmacokinetic profile of cyclosporine A after conversion to Sandimmun Optoral: influence on ambulatory blood pressure in renal transplant patients.

The aim of the present study was to investigate whether the pharmacokinetic profile of cyclosporin A under Sandimmun Optoral compared to Sandimmun has an effect on blood pressure in patients with stable renal allograft function. Twenty-eight patients were randomized into two groups. Two pharmacokinetic profiles (I, II; time interval 7 days) were obtained in each group. One group (n = 18) was switched from Sandimmun to an equal dose (1:1) of Sandimmun Optoral after the first kinetic and the other (n = 10) received Sandimmun for both kinetics. Eight blood samples were taken during each kinetic and cyclosporine values were measured. Ambulatory blood pressure measurement was performed during each kinetic. There were no differences in the pharmacokinetic parameters between kinetics I and II in the control group but significant differences in the switched group with increased Cmax (+64%), AUC (+44%), C0 (+17%) and decreased Tmax (-39%) in kinetic II compared to kinetic I. Correlation of C0 with AUC was stronger for Sandimmun Optoral (r = 0.792) than for Sandimmun (r = 0.718). Correlation of C0 with Cmax was similar for Sandimmun Optoral (r = 0.53) and Sandimmun (r = 0.56). Mean 12 h blood pressure of kinetic II tended to be lower than that of kinetic I in the control group, but the opposite was true for the switched group. When blood pressure levels around Tmax +/- 1 h were analyzed only, RR (syst/diast) in mmHg was 135 +/- 3.7/89 +/- 2.2 (kinetic I) and 130 +/- 2.8/85 +/- 2.8 (kinetic II) for control as compared to 134 +/- 2.4/85 +/- 2.9 and 137 +/- 3.1/86 +/- 2.8 for the switched group, respectively. Sandimmun Optoral shows an improved pharmacokinetic profile. However, higher blood concentrations of cyclosporine under Sandimmun Optoral tend to increase slightly systemic blood pressure as compared to that under Sandimmun.

Dopaminergic and alpha-adrenergic control of neurotransmission in human right atrium.

The aim of the present study was to investigate dopamine receptor- and alpha-adrenergic receptor-mediated modulation of norepinephrine release in human atria. Right atrial appendages were incubated with 3H-norepinephrine, placed in superfusion chambers, and field-stimulated by platinum electrodes at a frequency of 5 Hz. The stimulation-induced (S-I) outflow of radioactivity was taken as an index of norepinephrine release. The dopamine D2-receptor agonist quinpirole (0.03-3 microM) concentration dependently inhibited the S-I outflow of radioactivity with an EC50 of 0.03 microM. The concentration-response curve of quinpirole was potently shifted to the right by the D2-receptor antagonists domperidone (0.003 microM, pKB approximately 9.2) and S(-)-sulpiride (0.1 microM, pKB approximately 8.6). The D1-receptor antagonist SCH 23390 (1 microM) slightly (pKB approximately 6.9) shifted the concentration-response curve of quinpirole, whereas the alpha 2-adrenergic antagonist rauwolscine (0.01 microM) and the alpha 1-adrenergic antagonist prazosin (1 microM) had no effect. The D1-receptor agonist did not affect fenoldopam (0.03 and 0.3 microM), but fenoldopam (3 microM) enhanced the S-I outflow of radioactivity. The facilitatory effect of fenoldopam (3 microM) was unaltered by SCH 23390 (0.1 microM) but prevented by rauwolscine (0.01 microM). The alpha 2-adrenergic agonist UK 14304 (0.01-1 microM) (EC50: 0.06 microM), but not the alpha 1-adrenergic agonist methoxamine (0.3-30 microM), inhibited S-I outflow of radioactivity. The concentration-response curve of UK 14304 was shifted to the right by rauwolscine (0.01 microM, pKB approximately 8.6).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta 2-adrenergic receptor and angiotensin II receptor modulation of sympathetic neurotransmission in human atria.

The aim of the present study was to investigate beta-adrenergic receptor and angiotensin II (Ang II) receptor modulation of norepinephrine release in human atria. Slices of human atrial appendages were incubated with [3H]norepinephrine, superfused with Krebs-Henseleit solution, and electrically stimulated in superfusion chambers. Pretreatment of the tissue with 6-hydroxydopamine (1.2 mmol/L) before the [3H]norepinephrine incubation to destroy sympathetic nerves reduced the uptake of radioactivity and abolished the stimulation-induced (S-I) outflow of radioactivity. Furthermore, S-I outflow of radioactivity was prevented by the addition of tetrodotoxin (1 mumol/L) to and omission of extracellular Ca2+ from the superfusion solution. Separation of [3H]norepinephrine from its metabolites revealed that the S-I outflow of radioactivity was mainly composed of intact [3H]norepinephrine. Thus, the S-I outflow of radioactivity was taken as an index of norepinephrine release. Isoproterenol (0.001 to 0.1 mumol/L) dose-dependently enhanced the S-I outflow of radioactivity. The concentration-response curve of isoproterenol was shifted to the right by the selective beta 2-adrenergic receptor antagonist ICI 118551 (0.01 and 0.1 mumol/L) but not by the beta 1-adrenergic receptor-selective antagonist atenolol (0.3 and 30 mumol/L). Ang II (0.001 to 1.0 mumol/L) also dose-dependently enhanced S-I outflow of radioactivity. The facilitatory effect of Ang II was blocked by either the peptide Ang II receptor antagonist saralasin (1.0 mumol/L) or EXP 3174 (0.1 mumol/L), the in vitro active form of the nonpeptide Ang II receptor antagonist losartan. The cell-permeable cAMP analogue 8-bromo-cAMP (30 to 300 mumol/L) dose-dependently enhanced S-I outflow of radioactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine receptor modulation of noradrenaline release by carmoxirole in human cortical kidney slices.

The effect of the dopamine D2-receptor agonist carmoxirole on noradrenaline release was investigated in human and rat cortical kidney slices. After preincubation with 3H-noradrenaline, the slices were electrically stimulated at 5 Hz in superfusion chambers, and the stimulation-induced (S-I) outflow of radioactivity was taken as the index of noradrenaline release. In human but not in rat cortical kidney slices, carmoxirole (0.03 microM) inhibited the S-I outflow of radioactivity. Carmoxirole (0.3 microM) also failed to inhibit the S-I outflow of radioactivity from human kidney slices. When alpha-adrenoceptors were blocked by the non-selective alpha-adrenoceptor antagonist phentolamine (1 microM), carmoxirole (0.03 microM, 0.3 microM) inhibited S-I outflow to a similar extent. The inhibitory effect of carmoxirole (0.03 microM) was prevented by the D2-receptor antagonist (-)-sulpiride (10 microM) but not by the D1-receptor antagonist SCH 23390 (1 microM) in human kidney slices. Phentolamine (1 microM) by itself induced a five-fold greater enhancement of the S-I outflow of radioactivity in rat than in human cortical kidney slices. The data suggest that activation of prejunctional D2-receptors by carmoxirole inhibits noradrenaline release from human renal sympathetic nerves. Carmoxirole in higher concentrations (0.3 microM) blocks inhibitory prejunctional alpha-autoreceptors, which seems to mask the inhibitory D2-receptor mediated effect. The different effects of phentolamine and carmoxirole in human and rat kidney may indicate a difference of the prejunctional alpha-autoreceptor mechanism in the two species.

Dopamine DA2-receptor activation inhibits noradrenaline release in human kidney slices.

Dopamine receptor modulation of noradrenaline release from renal sympathetic nerves was investigated. Human kidney slices were incubated with 3H-noradrenaline, placed into superfusion chambers between two platinum electrodes and field-stimulated at 5 Hz. The slices accumulated radioactivity. Pretreatment of the kidney slices with 6-hydroxy-dopamine (1.2 mM) prior to the 3H-noradrenaline incubation reduced the accumulation of radioactivity. The stimulation induced (S-I) outflow of radioactivity was mainly composed of intact 3H-noradrenaline. The sodium channel blocker tetrodotoxin (1 microM), 6-hydroxy-dopamine pretreatment and omission of calcium from the superfusion solution abolished S-I outflow of radioactivity. The DA1-receptor agonist fenoldopam (SKF 82526; 0.01 and 0.1 microM) did not alter but fenoldopam (1 microM) increased S-I outflow of radioactivity. However, in the presence of either the non-selective alpha-adrenoceptor antagonist phentolamine (1 microM) or the selective alpha 2-adrenoceptor antagonist idazoxan (1 microM) fenoldopam (1 microM) had no effect. The DA2-receptor agonist quinpirole (LY 171555; 1 microM) inhibited S-I outflow of radioactivity, an effect blocked by the selective DA2-receptor antagonists S(-)-sulpiride (10 microM) and domperidone (0.3 microM) but unaltered either by the DA1-receptor antagonist SCH 23390 (1 microM) or by phentolamine (1 microM). The alpha 2-adrenoceptor agonist UK 14304 (0.1 microM) inhibited S-I outflow of radioactivity, and this effect was blocked by phentolamine (1 microM) and idazoxan (1 microM) but unaltered by S(-)-sulpiride (10 microM). Phentolamine and idazoxan, in contrast to S(-)-sulpiride, domperidone and SCH 23390, enhanced S-I outflow of radioactivity by themselves.(ABSTRACT TRUNCATED AT 250 WORDS)