Contractions In Renal Arteries Research Articles

Indoxyl sulfate decreases uridine adenosine tetraphosphate-induced contraction in rat renal artery.

The protein-bound uremic toxin indoxyl sulfate has negative effects on a variety of physiological activities including vascular function. Uridine adenosine tetraphosphate (Up4A), a new dinucleotide molecule affects vascular function including induction of vasocontraction, and aberrant responsiveness to Up4A is evident in arteries from disorders such as hypertension and diabetes. The link between indoxyl sulfate and the Up4A-mediated response is, however, unknown. We used Wistar rat's renal arteries to see if indoxyl sulfate will affect Up4A-mediated vascular contraction. In renal arteries of indoxyl sulfate, the contractile response generated by Up4A was dramatically reduced compared to the non-treated control group. Indoxyl sulfate increased endothelin-1-induced contraction but had no effect on phenylephrine, thromboxane analog, or isotonic K+-induced renal arterial contractions. UTP, ATP, UDP, and ADP-produced contractions were reduced by indoxyl sulfate. CH223191, an aryl hydrocarbon receptor (AhR) antagonist, did not reverse Up4A, and UTP contraction decreases caused by indoxyl sulfate. The ectonucleotidase inhibitor ARL67156 prevents indoxyl sulfate from reducing Up4A- and UTP-mediated contractions. In conclusion, we discovered for the first time that indoxyl sulfate inhibits Up4A-mediated contraction in the renal artery, possibly through activating ectonucleotidase but not AhR. Indoxyl sulfate is thought to play a function in the pathophysiology of purinergic signaling.

Inhibition of neurogenic contractions in renal arteries and of cholinergic contractions in coronary arteries by the presumed inhibitor of ADP-ribosylation factor 6, NAV2729

NAV2729 is a presumed inhibitor of the monomeric GTPase ADP ribosylation factor 6 (ARF6) and inhibits smooth muscle contraction outside the cardiovascular system. Its effects on vascular smooth muscle contraction or a possible role of ARF6 in vasocontraction have not yet been examined. Here, we report effects of NAV2729 on neurogenic and agonist-induced contractions in renal interlobar and coronary arteries. Contractions of pig interlobar and coronary arteries were induced in an organ bath by agonists or by electric field stimulation (EFS). Owing to divergent characteristics of both vessel types, EFS-induced contractions were only examined in interlobar arteries, and contractions by agonists acting on muscarinic receptors only in coronary arteries. NAV2729 inhibited frequency-dependent EFS-induced contractions of interlobar arteries. The degree of inhibition was similar using 5 µM and 10 µM NAV2729. Inhibition of EFS-induced contractions was resistant to a nitric oxide synthase inhibitor and to diclofenac. The neurogenic and adrenergic character of EFS-induced contractions was confirmed by inhibition by tetrodotoxin and prazosin. In coronary arteries, NAV2729 (5 µM) inhibited concentration-dependent contractions induced by carbachol and methacholine. Contractions induced by α1-adrenergic agonists, endothelin-1, the thromboxane receptor agonist U46619, or serotonin remained unchanged by NAV2729 in both vessel types. NAV2729 inhibits neurogenic contractions in interlobar arteries and contractions induced by cholinergic agonists in coronary arteries. In both vessel types, NAV2729 does not inhibit contractions induced by receptor agonists other than those acting on muscarinic receptors. Addressing effects in other vessels and in other smooth muscle–rich organs merits further attention.

SMIT (Sodium-Myo-Inositol Transporter) 1 Regulates Arterial Contractility Through the Modulation of Vascular Kv7 Channels.

The SMIT1 (sodium:myo-inositol transporter 1) regulates myo-inositol movement into cells and responses to hypertonic stimuli. Alteration of myo-inositol levels has been associated with several diseases, including hypertension, but there is no evidence of a functional role of SMIT1 in the vasculature. Recent evidence showed that in the nervous system SMIT1 interacted and modulated the function of members of the Kv7 family of voltage-gated potassium channels, which are also expressed in the vasculature where they regulate arterial contractility. Therefore, in this study, we evaluated whether SMIT1 was functionally relevant in arterial smooth muscle. Approach and Results: Immunofluorescence and polymerase chain reaction experiments revealed that SMIT1 was expressed in rat renal and mesenteric vascular smooth muscle cells. Isometric tension recordings showed that incubation of renal arteries with raffinose and myo-inositol (which increases SMIT1 expression) reduced the contractile responses to methoxamine, an effect that was abolished by preincubation with the pan-Kv7 blocker linopirdine and by molecular knockdown of Kv7.4 and Kv7.5. Knockdown of SMIT1 increased the contraction of renal arteries induced by methoxamine, impaired the response to the Kv7.2-Kv7.5 activator ML213 but did not interfere with the relaxant responses induced by openers of other potassium channels. Proximity ligation assay showed that SMIT1 interacted with heteromeric channels formed by Kv7.4 and Kv7.5 proteins in both renal and mesenteric vascular smooth muscle cells. Patch-clamp experiments showed that incubation with raffinose plus myo-inositol increased Kv7 currents in vascular smooth muscle cells. SMIT1 protein is expressed in vascular smooth muscle cells where it modulates arterial contractility through an association with Kv7.4/Kv7.5 heteromers.

Efficacy of therapeutic plasma exchange on angiotensin II type‐1 receptor antibodies on two kidney transplant recipients

Angiotensin II type-1 receptor antibody (AT1RAb) has been reported to cause antibody mediated rejection (AMR) in kidney transplant recipients possibly by contraction of renal arteries. We here report 2 kidney transplant recipients with elevated AT1RAbs and negative HLA donor specific antibodies (DSA) and anti-major histocompatibility complex class I chain-related gene A (MICA) Abs who received therapeutic plasma exchange (TPE) treatment followed by IVIG. CASE 1: Thirty-eight-year-old patient received second kidney transplant for end stage renal disease (ESRD) with chronic rejection. Three years post-transplant, she developed AMR with AT1RAb level >40 U/mL. She received 5 TPE and AT1RAb decreased by 20%, and biopsy showed improvement of AMR. She received another 3 TPE and AT1RAb decreased by 60%. Her creatinine (Cr) was stabilized at around 1.4 mg/dL. CASE 2: Twenty-four-year-old patient received kidney transplant for ESRD with unclear etiology. Two weeks post-transplant, her Cr rose with AT1RAb level at 18 U/mL and biopsy showed possible AMR. She received 6 TPE treatments and AT1RAb decreased by 55% and biopsy showed improvement of AMR. She received weekly TPE for subsequently rising AT1RAb but TPE was discontinued because of unsuccessful decrease of AT1RAb. Her Cr was stabilized at around 1.7 mL/dL. We reported 2 patients who received TPE treatments to decrease AT1RAbs. A course of TPE treatment successfully decreased AT1RAb. Histological improvement was observed quickly and Cr was also stabilized following the TPE treatment. Further study is necessary to determine the optimal use of TPE in renal transplant recipients with AT1RAbs.

Sympathetic denervation facilitates L-type Ca2+ channel activation in renal but not in mesenteric resistance arteries.

Sympathetic denervation enhances agonist-induced vasoconstriction. This effect may involve altered function of signaling mechanisms such as Rho kinase (Rock) and L-type Ca channels downstream from vasoconstrictor receptors. We tested if enhanced Rock and L-type calcium channel activation contribute to exaggerated norepinephrine-induced vasoconstrictions in renal and mesenteric resistance arteries after sympathectomy. Rats underwent neonatal sympathectomy or sham sympathectomy. Resistance arteries were investigated by small vessel myography. Vascular Rock and L-type Ca channel expression as well as Rock activation were investigated by quantitative real-time PCR and Western blot. Vascular smooth muscle cell (VSMC) membrane potential was recorded with microelectrodes. Sympathetic denervation enhanced norepinephrine sensitivity in renal and mesenteric arteries. Both, Rock inhibition or L-type Ca inhibition shifted the norepinephrine concentration-response curve to the right. This effect was more pronounced in renal than in mesenteric arteries from sympathectomized vs. sham-sympathectomized animals. The L-type Ca channel activator S-(-)-BayK8644 elicited strong vasoconstrictions only in renal arteries from sympathectomized rats. Rock activity and L-type Ca channel α-subunit expression were similar in renal arteries from sympathectomized and sham-sympathectomized animals. VSMC membrane potential was -57.5 ± 2.0 and -64.3 ± 0.3 mV (P < 0.01), respectively, in renal arteries from sympathectomized and from sham-sympathectomized rats. Depolarization enhanced and KATP channel activation abolished S-(-)-BayK8644-induced contractions in renal arteries from sympathectomized rats. Sympathetic denervation enhances L-type Ca channel-dependent signaling in renal but not in mesenteric arteries. This effect may be partly explained by the decreased VSMC membrane potential in denervated renal arteries.

Enhanced uridine adenosine tetraphosphate-induced contraction in renal artery from type 2 diabetic Goto-Kakizaki rats due to activated cyclooxygenase/thromboxane receptor axis

The dinucleotide uridine adenosine tetraphosphate (Up4A), which has both purine and pyrimidine moieties, was reported as a novel endothelium-derived contracting factor. Recently, growing evidence has suggested that Up4A plays an important role in regulation of the cardiovascular function. We previously demonstrated that Up4A-induced vasoconstrictions are altered in arteries from DOCA-salt hypertensive rats. We have assessed responses to Up4A shown by renal arteries from type 2 diabetic Goto-Kakizaki (GK) rats (42-46weeks old) and identified the molecular mechanisms involved. Concentration-dependent contractions to Up4A were greater in renal arterial rings from the GK than age-matched control Wistar group. In both groups, the inhibition of nitric oxide synthase (with N (G)-nitro-L-arginine) increased the response to Up4A, whereas the inhibition of cyclooxygenase (COX) (with indomethacin) decreased the response. Specific inhibitors of COX-1 (valeroyl salicylate) and COX-2 (NS398), a thromboxane (TX) receptor (TP) antagonist (SQ29548), and P2 receptor antagonist (suramin) also decreased the response to Up4A. Protein expressions of COXs in renal arteries were greater in the GK than Wistar group. The production of TXB2 (a metabolite of TXA2) by Up4A did not differ between these groups. Concentration-dependent contractions to U46619, an agonist of the TP receptor, were greater in renal arteries from the GK than Wistar group. The expression of P2X1 and P2Y2 receptors did not differ between these groups. These results suggest that enhancement of the Up4A-induced contraction in renal arteries from GK rats may be attributable to the increased activation of COXs/TP receptor signaling.

Renal Ischemia and Transplantation Predispose to Vascular Constriction Mediated by Angiotensin II Type 1 Receptor-Activating Antibodies

We previously described angiotensin II type 1 receptor-activating antibodies (AT1R-Abs) in renal transplant recipients with vascular rejection and malignant hypertension. In this study, we tested the hypothesis that AT1R-Abs can cause renal artery contraction by AT1R activation with renal ischemia representing a key permissive factor and therefore contribute to renal pathologic condition. Isolated renal and mesenteric arteries from Lewis rats were incubated with purified AT1R-Abs from patients with human leukocyte antigen antibody-negative vascular rejection. Vascular contraction was measured using small vessel myography. The measurements were repeated with renal arteries derived from native kidneys subjected to ischemia-reperfusion or after transplantation in a low-responder Fischer 344-to-Lewis rat kidney-transplantation model. AT1R-Abs acted in a vascular bed-specific manner and caused small contractions only in native rat renal arteries but not in mesenteric arteries. AT1R-Abs did not alter the vascular reactivity to phenylephrine, angiotensin II, or acetylcholine in native renal arteries. In contrast, AT1R-Abs caused a pronounced (>10-fold) contraction of renal arteries after ischemia and after allogeneic transplantation. Pretreatment with pharmacologic AT1R blocker only partially inhibited the AT1R-Abs-induced contraction, which was almost completely abolished by neutralizing peptides targeting epitopes of AT1R-Abs on the second loop of AT1R. These data demonstrate that AT1R-Abs can induce renal vascular contraction under predisposing conditions such as in ischemic or transplanted kidneys. Neutralizing antibodies against specific epitopes in the AT1R can ameliorate this contraction.

Calcitriol protects renovascular function in hypertension by down-regulating angiotensin II type 1 receptors and reducing oxidative stress

The present study investigated whether or not calcitriol, an active form of vitamin D, protects against renovascular dysfunction in hypertension and, if so, whether or not such protection alters the expression of key proteins involved in that dysfunction. Changes in isometric tension showed that the impaired endothelium-dependent relaxations in renal arteries of hypertensive patients were enhanced by 12 h in vitro treatment with calcitriol. Dihydroethidium fluorescence revealed an elevated level of reactive oxygen species (ROS) in these arteries which was reduced by calcitriol. Immunofluorescence showed that calcitriol treatment reduced the expression of AT(1)R, NOX-2, NOX-4, and p67(phox) and increased that of superoxide dismutase (SOD)-1. Twelve-hour exposure to calcitriol prevented angiotensin (Ang) II-induced increases in ROS and the over-expression of NOX-2, NOX-4, and p67(phox) in renal arteries from normotensive patients. A specific antagonist of the human vitamin D receptor (VDR), TEI-9647, abolished these effects of calcitriol. Both in vitro exposure to and chronic in vivo administration of calcitriol enhanced relaxations to acetylcholine and abolished exaggerated endothelium-dependent contractions in renal arteries of normotensive rats pre-exposed to Ang II or harvested from spontaneously hypertensive rats (SHR). Reactive oxygen species levels and expressions of AT(1)R, NAD(P)H oxidase subunits, SOD-1, and SOD-2 in SHR arteries were normalized by the chronic treatment with calcitriol. In vivo and in vitro activation of VDR with calcitriol improves endothelial function by normalizing the expressions of AT(1)R and radical generating and scavenging enzymes and thus preventing ROS over-production. The present findings suggest that calcitriol is effective in preserving endothelial function in hypertension.

Renal and cardiovascular role of the neuropeptide Y Y1 receptor in ischaemic heart failure rats.

The cardiovascular role of the neuropeptide Y Y1 receptors in-vivo and in-vitro in ischaemic heart failure was evaluated by using the novel neuropeptide Y Y1 selective antagonist BIBP 3226 (R-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amid e). In pithed rats, incremental doses of BIBP 3226 inhibited the exogenous neuropeptide Y induced pressor response in a dose-related fashion and a bolus injection of BIBP 3226 (0.5 mg kg(-1)) significantly shifted the pressor response curve of exogenous neuropeptide Y to the right. The potentiation effect to exogenous neuropeptide Y on the pressor response to preganglionic sympathetic nerve stimulation in ischaemic heart failure rats as well as on the contractile response to noradrenaline in renal arteries in sham-operated animals were also inhibited by the neuropeptide Y Y1 antagonist. In conscious ischaemic heart failure rats, incremental doses of BIBP 3226 (0.125-1 mg kg(-1)) significantly reduced basal blood pressure and heart rate. Compared with sham-operated rats, neuropeptide Y by itself induced no contraction and no potentiation on noradrenaline elicited contraction in renal artery of the ischaemic heart failure rat. Furthermore, under in-vivo conditions, BIBP 3226 did not influence basal renal function or the response to exogenous neuropeptide Y on urinary volume, urinary sodium and urinary potassium. Our results demonstrate that although there is a downregulation of the Y1 receptors by ischaemic heart failure, Y1 receptors are still mainly involved in cardiovascular actions of exogenous neuropeptide Y and play a role in maintaining basal blood pressure and heart rate in ischaemic heart failure. However, our data do not imply any significant role of Y1 receptors on basal renal function in the ischaemic heart failure rat model.

Hypertension and the absence of EDHF‐mediated responses favour endothelium‐dependent contractions in renal arteries of the rat

Experiments were designed to determine the modulation by nitric oxide (NO) and endothelium-dependent hyperpolarizations (EDHF-mediated responses) of endothelium-dependent contractions in renal arteries of normotensive and hypertensive rats. Rings, with or without endothelium, of renal arteries of 8-month-old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were suspended in myographs for isometric force recording. ACh evoked relaxations in preparations contracted with phenylephrine. L-NAME (inhibitor of NOS) attenuated (WKY) or abolished (SHR) these relaxations. TRAM-34 plus UCL 1684 (inhibitors of EDHF-mediated responses) did not decrease the relaxation, except in rings of WKY when L-NAME was also present. High concentrations of ACh caused a secondary increase in tension, augmented in rings of WKY by L-NAME or TRAM-34 plus UCL 1684. The increase in tension was prevented by indomethacin. Under baseline tension, ACh induced endothelium-dependent contractions, prevented by indomethacin (COX inhibitor) or terutroban (TP receptor antagonist). The calculated endothelium-dependent contractions were larger in rings of SHR compared with those of WKY. In preparations of SHR, the contractions were augmented by L-NAME in the presence of SC19220 (EP-1 receptor antagonist). In arteries of WKY, the endothelium-dependent contractions were augmented by TRAM-34 plus UCL 1684. The responses were reduced by SC19220. In the renal artery of the rat, EDCF-mediated contractions are augmented by hypertension. The endothelium-dependent contractions are facilitated by NOS inhibition (in the presence of an EP-1 receptor antagonist) and by the withdrawal of EDHF-mediated responses.

Characteristics of contractile activity in the renal artery of ovariectomized rats

The incidence of cardiovascular disease is markedly lower in cycling, pre-menopausal women and post-menopausal women receiving estrogen than in men or untreated post-menopausal women. Clinical studies demonstrate a protective role of estrogen in hormone replacement therapy in terms of reducing cardiovascular risk. However, the benefits of hormone replacement therapy in cardiovascular disease remain unclear. We investigated the effects of estrogen on the contractile responses of the renal artery of ovariectomized Wistar rats (OVX) compared to both ovariectomized 17 beta-estradiol-treated rats (OVXE) and sham-operated (control) rats. Isometric contraction of renal artery was recorded with a strain gauge transducer. The maximum contractile response of the renal artery smooth muscle to KCl (80 mM) in the OVXE group was significantly higher than that in both the control and OVX groups. The phenylephrine (PE) concentration-response curves in all three groups indicated a greater sensitivity at lower concentrations of PE following treatment with 100 microM L-arginine methyl ester (L-NAME). The EC50 values for PE in the three groups were 2 times lower in the presence of L-NAME than those lacking exposure to L-NAME. The EC50 value for PE in the OVX group was approximately 3 times lower in the presence of L-NAME than in those lacking exposure to L-NAME and 100 nM BMY 7378, an alpha 1D-adrenoceptor antagonist. The rate of relaxation of the PE-induced contraction (T1/2) was significantly reduced in the OVX group relative to both the control and OVXE groups. T1/2 values after treatment with 100 microM L-NAME were slower than those lacking exposure to L-NAME in all groups. Further, the T1/2 value of the OVX group was 2 times greater than that of the control; this change was reversed in the OVXE group. In conclusion, our results suggest that estrogen regulates contraction and relaxation in the renal artery via NO synthase activity and alteration of the Ca2+ transport systems.

Difference in the Characteristics of ETA-Receptor-Stimulated Response Between Rat Small Pulmonary and Renal Arteries

We investigated the difference in the characteristics of endothelin-1 (ET-1)-induced contraction and the responses of intracellular Ca(2+) concentration ([Ca(2+)](i)) between rat small pulmonary artery and renal artery. ET-1 (30 nM) failed to elicit any contraction in renal arteries pretreated with 3 microM BQ-123, an ETA blocker. However, in the pulmonary artery a combination of BQ-123 and BQ-788, an ETB blocker (5 microM each), only partially inhibited the ET-1-induced contraction (by 25%). To focus on the ETA receptor, in the presence of 5 microM BQ-788, nitric oxide donors (sodium nitroprusside and (+/-)-S-nitroso-N-acetylpenicillamine) and forskolin reduced both the ET-1-induced contraction and increase in [Ca(2+)](i) in both pulmonary and renal arteries. However, the effects were stronger in the renal than in the pulmonary artery. ET-1-induced increase in [Ca(2+)](i) was only partially attenuated by 10 microM verapamil (to 81% of control) in pulmonary arteries but was reduced to 56.1% of control in renal arteries. Our results provide evidence that ET-1 may activate ET receptor(s) insensitive to both BQ-123 and BQ-788 in rat small pulmonary artery, at least under these conditions. Furthermore, the effects of relaxants such as L-type Ca(2+) channel blocker and nitric oxide donors on the ET-1-induced contraction were studied.

Accessory β subunits regulate the expression of L‐type Ca 2+ (Ca v 1.2) channels and Ca 2+ ‐dependent contractions in vascular smooth muscle cells

Long-lasting or “L-type” calcium (CaL) channels mediate voltage-dependent Ca2+ influx and contraction in vascular smooth muscle cells (VSMCs). We have suggested that pressure-induced depolarization of VSMCs induces the expression of the pore-forming α1C subunit of the CaL channel, thereby contributing to the elevated Ca2+ influx and vascular tone observed in arteries of hypertensive rats. This study investigated the hypothesis that CaL channel β subunits, which may increase the cell surface expression of CaL channels, promote CaL channel expression in the VSMCS of small renal arteries. Initial Western blots indicated that cultured rat renal arteries minimally expressed the β2 subunit, which was apparent as an immunoreactive band at ~68 kD in renal VSMC membranes. In similar renal arteries, incorporation of fluorescein-labeled antisense directed against the β subunit resulted in a profound loss of CaL channel α1C subunits. The downregulation of CaL channel α1C subunits in response to βantisense was associated with a loss of Ca2+-dependent contraction in renal arteries. Interestingly, depolarization of renal VSMCs for 48 hours resulted in an upregulation of the β2 subunit that correlated with an increased expression of CaL channel α1C subunit proteins. Thus, the expression of functional CaL channel α1C subunits in small arteries may rely on ancillary β subunits, which may promote the trafficking, insertion or membrane stability of the CaL channel in the VSMC membrane. Supported by NIH R01HL064806-07.

Hydrogen peroxide is an endothelium-dependent contracting factor in rat renal artery.

In addition to endothelium-derived relaxing factor and hyperpolarizing factor, vascular endothelium also modulates smooth muscle tone by releasing endothelium-derived contracting factor(s) (EDCF), but the identity of EDCF remains obscure. We studied here the involvement of hydrogen peroxide (H2O2) in endothelium-dependent contraction (EDC) of rat renal artery to acetylcholine (ACh). ACh (10(-6), 10(-5), and 10(-4) M) induced a transient contraction of rat renal artery with intact endothelium in a concentration-related manner, but not in the artery with endothelium removed. In phenylephrine-precontracted renal arteries, ACh induced an endothelium-dependent relaxation response at lower concentrations (10(-8)-10(-6) M), and a relaxation followed by a contraction at higher concentrations (10(-5) M). Inhibition of nitric oxide synthase by N(omega)-nitro-L-arginine (10(-4) M) enhanced the EDC to ACh. Catalase (1000 U ml(-1)) reduced the EDC to ACh. H2O2 (10(-6), 10(-5), and 10(-4) M) induced a similar transient contraction of the renal arteries as ACh, but in an endothelium-independent manner. Inhibition of NAD(P)H oxidase and cyclooxygenase by diphenylliodonium chloride and diclofenac greatly attenuated ACh-induced EDC, while inhibition of xanthine oxidase (allopurinol) and cytochrome P450 monooxygenase (17-octadecynoic acid) did not affect the contraction. Antagonist of thromboxane A2 and prostaglandin H2 receptors (SQ 29548) and thromboxane A2 synthase inhibitor (furegrelate) attenuated the contraction to ACh and to H2O2. In isolated endothelial cells, ACh (10(-5) M) induced a transient H2O2 production detected with a fluorescence dye sensitive to H2O2 (2',7'-dichlorofluorescein diacetate). The peak concentration of H2O2 was 5.1 x 10(-4) M at 3 min and was prevented by catalase. Taken together, these results show that ACh triggers H2O2 production through NAD(P)H oxidase activation in the endothelial cells, and that ACh and H2O2 share the same signaling pathway in causing smooth muscle contraction. Therefore, H2O2 is most likely the EDCF in rat renal artery in response to ACh stimulation.

Differential type 4 cAMP-specific phosphodiesterase (PDE4) expression and functional sensitivity to PDE4 inhibitors among rats, monkeys and humans

It has been suggested that the rat is relatively more susceptible to toxicity induced by inhibitors for type 4 cAMP-specific phosphodiesterase (PDE4). In this study designed to elucidate possible biochemical basis for the higher susceptibility, we compared PDE4 expression levels and their functional relevance among rats, monkeys and humans. In several toxicologically relevant tissues and blood leukocytes, the mRNA expression levels of PDEs 4A, 4B, 4C and 4D were significantly higher in rats than in humans. We confirmed that higher PDE4 expression levels were correlated with a higher enzyme activity level in rat leukocytes. The PDE4 enzyme activity level of leukocytes in monkeys fell between that of rats and humans. Functionally, the potencies of the PDE4 inhibitors rolipram, SB 207499 and SCH 351591 in inhibiting tumor necrosis factor production from leukocytes were in the following order: rat > monkey > human. In addition, rolipram was about 10-fold more potent in rats than in humans in inhibiting phenylephrine-induced contraction of renal artery. These inhibitors were confirmed to be highly selective for PDE4 in comparison to all other PDE families, and to inhibit rat and human PDE4s with identical potencies. Taken together, these results suggest that the higher susceptibility of rats to PDE4 inhibitor-induced toxicity might be due to their higher expression levels of PDE4, and that PDE4 inhibitors may be safer in humans than in monkeys and, particularly, rats.

Systemic vascular effects during acute rejection of lung allografts.

Circulating leukocytes activated during rejection of organ allografts could potentially have generalized effects on systemic blood vessels of the transplant recipient. Experiments were designed, therefore, to determine the function of the endothelium and smooth muscle of arteries from nontransplanted organs in dogs who received single lung transplants. Dogs underwent single lung allotransplantation and were immunosuppressed for 5 days. Immunosuppression was then withheld for 3 days, allowing rejection to occur. Dogs were studied at this time (rejecting) or following treatment for rejection for an additional 6-8 days (treated). Arteries from unoperated, untreated dogs also were studied to provide baseline responses of healthy tissue. Rings cut from left circumflex coronary, nonoperated native pulmonary, and renal arteries were suspended in organ chambers for measurement of isometric force. Endothelium-dependent relaxations to the calcium ionophore A23187 were not affected by rejection in any of the arteries. Contractions to angiotensin I were reduced significantly only in native pulmonary arteries. Contractions to KCI and endothelin-1 increased in renal arteries with endothelium during rejection. These contractions in renal arteries were reduced following treatment of rejection. None of the responses of the coronary arteries were affected significantly by rejection of the lung allograft. These results demonstrate that contractions of arteries in the transplant recipient's native organs are altered during rejection of lung allografts. The effects are organ specific, may include production of endothelium-derived contractile factors in renal arteries, and can be partially reversed by treatment of rejection.

Effect of pregnancy on contraction and endothelium-mediated relaxation of renal and mesenteric arteries

We have hypothesized that differences in the effect of pregnancy on mechanisms modulating vascular reactivity underlie the redistribution of cardiac output. Because pregnancy increases mesenteric blood flow by 75% and renal blood flow by only 10% in the guinea pig, we investigated the effect of pregnancy on vascular reactivity in these two beds. Relaxation in response to acetylcholine (ACh), an endothelium-dependent relaxing agent, and contraction induced by the thromboxane mimetic U-46619 were measured in ring segments of mesenteric and renal arteries from pregnant and nonpregnant guinea pigs. To determine the role of the endothelium, nitric oxide (NO), and vasodilator prostaglandins in modulating vascular response, rings were denuded, treated with N omega-nitro-L-arginine (L-NNA) to inhibit NO synthase, or treated with indomethacin to inhibit cyclooxygenase. Pregnancy increased ACh-stimulated relaxation of mesenteric arteries but not renal arteries. L-NNA significantly reduced ACh sensitivity (based on the concentration that produced 50% of the maximal response) in arteries from pregnant and nonpregnant animals, and indomethacin slightly decreased maximal relaxation only in the renal artery of nonpregnant animals. ACh sensitivity of mesenteric arteries was still increased after L-NNA or indomethacin. Pregnancy reduced the threshold concentration of U-46619 in mesenteric artery but had no effect on contraction of renal artery. Contraction of both arteries was enhanced by denudation. L-NNA and indomethacin were less effective than denudation in arteries from pregnant and nonpregnant animals, which suggests that pregnancy alters thromboxane contraction by endothelium-dependent mechanisms other than NO and prostaglandins. Thus, pregnancy differentially alters vascular reactivity of mesenteric and renal arteries in the guinea pig.

Sodium pump activity and contraction of renal artery from spontaneously hypertensive rats

We investigated the hypertensive changes in renal arteries isolated from 21-week-old spontaneously hypertensive rats (SHR), and from age-matched normotensive Wistar-Kyoto rats (WKY). The maximam contraction of renal arteries from SHR in response to norepinephrine (NE), serotonin (5-HT) and KCl was greater than that of arteries from WKY. The threshold and EC 50 concentrations of NE, 5-HT and KCl were not significantly different between SHR and WKY. Contraction induced by removal of K + was inhibited by 10 −8 M prazosin. Less than 10 −7 M NE in K +-free solution did not cause contraction. Addition of 5.9 mM KCl to K +-free solution in the presence of 10 −5 M NE induced relaxation, which was followed by contraction to about the same level as that before KCl addition. The duration of the K +-induced relaxation in SHR (22.4 ± 0.9 min) was slightly, but significantly shorter than that in WKY (26.6 ± 0.8 min) arteries. In K +-free solution with reduced Na +, the duration of the relaxation induced by KC1 was shorter than that in the normal solution, for both SHR (13.8 ± 0.3 min) and WKY (14.1 ± 0.5 min). Such differences could be caused by increased influx and decreased efflux of Ca 2+, which depend on the Na + concentration and are related to the Na +-Ca 2+ exchange. The results suggest that enhanced renal vascular reactivity in hypertension may depend on structural changes and increased Na + pump activity.

Different Modulation by Cyclooxygenase Inhibitors of the Response to Angiotensin II in Monkey Arteries and Veins.

In coronary, renal and femoral arteries and mesenteric veins isolated from Japanese monkeys, tachyphylaxis to angiotensin (ANG) II (10(-7) M)-induced contraction rapidly developed. Contractions caused by ANG II in coronary arteries were attenuated by treatment with indomethacin and aspirin and also by endothelium denudation. Indomethacin inhibited the response of the arteries with and without endothelium to a similar extent. OKY 046, a thromboxane A2 synthesis inhibitor, failed to inhibit the response. In contrast, contractions of renal arteries were potentiated and prolonged by the cyclooxygenase inhibitors. ANG II-induced contractions of mesenteric veins were prolonged but those of femoral arteries were not altered by indomethacin. It is concluded that ANG II contracts monkey coronary arteries, possibly due to the release of vasoconstrictor prostanoids but not thromboxane A2 from endothelial and subendothelial tissues and also due to its direct action on smooth muscle, whereas contractions of renal arteries and mesenteric veins are blunted by vasodilator prostanoids, possibly PGI2. Cyclooxygenase products even if released do not appear to regulate femoral artery contractions produced by ANG II.

Different Modulation by Cyclooxygenase Inhibitors of the Response to Angiotensin II in Monkey Arteries and Veins

In coronary, renal and femoral arteries and mesenteric veins isolated from Japanese monkeys, tachyphylaxis to angiotensin (ANG) II (10-7 M)-induced contraction rapidly developed. Contractions caused by ANG II in coronary arteries were attenuated by treatment with indomethacin and aspirin and also by endothelium denudation. Indomethacin inhibited the response of the arteries with and without endothelium to a similar extent. OKY 046, a thromboxane A2 synthesis inhibitor, failed to inhibit the response. In contrast, contractions of renal arteries were potentiated and prolonged by the cyclooxygenase inhibitors. ANG II-induced contractions of mesenteric veins were prolonged but those of femoral arteries were not altered by indomethacin. It is concluded that ANG II contracts monkey coronary arteries, possibly due to the release of vasoconstrictor prostanoids but not thromboxane A2 from endothelial and subendothelial tissues and also due to its direct action on smooth muscle, whereas contractions of renal arteries and mesenteric veins are blunted by vasodilator prostanoids, possibly PGI2. Cylooxygenase products even if released do not appear to regulate femoral artery contractions produced by ANG II.