Cerebral Venous Thrombosis in Patients with COVID-19 Infection: a Case Series and Systematic Review

BACKGROUND

There has been increasing reports associating the coronavirus disease 2019 (COVID-19) with thromboembolic phenomenon including ischemic strokes and venous thromboembolism. Cerebral venous thrombosis (CVT) is a rare neurovascular emergency that has been observed in some COVID-19 patients, yet much remains to be learnt of its underlying pathophysiology.

OBJECTIVE

We present a case series of local patients with concomitant COVID-19 infection and CVT; and aim to perform a systematic review of known cases in the current literature.

METHODS

We describe two patients with concomitant COVID-19 infection and CVT from a nationwide registry in Singapore. We then conducted a literature search in PubMed and Embase using a suitable keyword search strategy from 1st December 2019 to 11th June 2020. All studies reporting CVT in COVID-19 patients were included.

RESULTS

Nine studies and 14 COVID-19 patients with CVT were studied. The median age was 43 years (IQR=36-58) and majority had no significant past medical conditions (60.0%). The time taken from onset of COVID-19 symptoms to CVT diagnosis was a median of 7 days (IQR=6-14). CVT was commonly seen in the transverse (75.0%) and sigmoid sinus (50.0%); 33.3% had involvement of the deep venous sinus system. A significant proportion of patients had raised D-dimer (75.0%) and CRP levels (50.0%). Two patients reported presence of antiphospholipid antibodies. Most patients received anticoagulation (91.7%) while overall mortality rate was 45.5%.

CONCLUSIONS

The high mortality rate of CVT in COVID-19 infection warrants a high index of suspicion from physicians, and early treatment with anticoagulation should be initiated.

Neurology of COVID-19 in Singapore

PURPOSE

To describe the spectrum of COVID-19 neurology in Singapore.

METHOD

We prospectively studied all microbiologically-confirmed COVID-19 patients in Singapore, who were referred for any neurological complaint within three months of COVID-19 onset. Neurological diagnoses and relationship to COVID-19 was made by consensus guided by contemporaneous literature, refined using recent case definitions.

RESULTS

47,572 patients (median age 34 years, 98% males) were diagnosed with COVID-19 in Singapore between 19 March to 19 July 2020. We identified 90 patients (median age 38, 98.9% males) with neurological disorders; 39 with varying certainty of relationship to COVID-19 categorised as: i) Central nervous system syndromes-4 acute disseminated encephalomyelitis (ADEM) and encephalitis, ii) Cerebrovascular disorders-19 acute ischaemic stroke and transient ischaemic attack (AIS/TIA), 4 cerebral venous thrombosis (CVT), 2 intracerebral haemorrhage, iii) Peripheral nervous system-7 mono/polyneuropathies, and a novel group, iv) Autonomic nervous system-4 limited dysautonomic syndromes. Fifty-one other patients had pre/co-existent neurological conditions unrelated to COVID-19. Encephalitis/ADEM is delayed, occurring in critical COVID-19, while CVT and dysautonomia occurred relatively early, and largely in mild infections. AIS/TIA was variable in onset, occurring in patients with differing COVID-19 severity; remarkably 63.2% were asymptomatic. CVT was more frequent than expected and occurred in mild/asymptomatic patients. There were no neurological complications in all 81 paediatric COVID-19 cases.

CONCLUSION

COVID-19 neurology has a wide spectrum of dysimmune-thrombotic disorders. We encountered relatively few neurological complications, probably because our outbreak involved largely young men with mild/asymptomatic COVID-19. It is also widely perceived that the pandemic did not unduly affect the Singapore healthcare system.

Idiopathic eruptive macular pigmentation with papillomatosis (IEMPP): A controversial entity

A 19-year-old man with a 6-month history of progressive development of hyperpigmented, velvety plaques on the face and body. A diagnosis of idiopathic eruptive macular pigmentation with papillomatosis (IEMPP) was determined. This entity is discussed.

Expression of MMP-1, -2, and -8 in longissimus dorsi muscle and their relationship with meat quality traits in cattle

The extracellular matrix (ECM) is the major macromolecule in skeletal muscle, which affects meat quality greatly. The remodeling of the ECM is mainly regulated by matrix metalloproteinases (MMPs). The expression patterns of MMP-1, -2, and -8 in longissimus dorsi muscle were explored using quantitative real-time polymerase chain reaction. The results show that the expression of MMP-1, -2, and -8 decreased significantly from 135 days of pregnancy to postnatal 30 months. While the expression of MMP-1, -2, and -8 showed no significant relationships with intramuscular fat contents, MMP-1 and -2 showed significant negative correlations with the shearing force of the longissimus dorsi muscle in cattle. The expression of MMP-1 also showed a significant negative correlation with cooking loss and a positive correlation with water holding capacity. The expression levels of MMP-1 and -2 were usually higher in fat than in skeletal muscle tissue. The expression of MMP-8 was significantly higher in the mammary fat pad and the longissimus dorsi muscle than in all other tissues. This study indicates that the remodeling of the ECM has important effects both on the development of postnatal skeletal muscle and on meat quality.

The relationship of plumage colours with MC1R (Melanocortin 1 Receptor) and ASIP (Agouti Signaling Protein) in Japanese quail (Coturnix coturnix japonica)

1. The relationship of polymorphisms in the Melanocortin 1 Receptor (MC1R) and Agouti Signalling Protein (ASIP) genes with plumage colour in Japanese quail was investigated by cloning and sequencing the entire coding regions from black, white and maroon Japanese quail embryos at 12 d of incubation. 2. Three SNPs were identified in the MC1R coding region by multiple alignment of sequences from individuals with different plumage colours. A missense C/T mutation located at 169 bp within the Open Reading Frame caused a Ile57Val mutation in the amino acid sequence, and had a significant relationship with the black colour. 3. The expression of MC1R was higher in black plumage quails than that in maroon plumage quails, whereas the expression of ASIP was higher in maroon plumage quails than that in black plumage quails. 4. It is concluded that the black plumage colour in Japanese quails may be caused by either increased production of MC1R or decreased production of ASIP.

Desensitization of adrenomedullin and calcitonin gene-related peptide receptors in vascular smooth muscle cells--effects of receptor activity-modifying protein

Recent researches suggest that adrenomedullin (ADM) and calcitonin gene-related peptide (CGRP) bind to the same calcitonin receptor-like receptors (CRLR), with receptor specificity being determined by a receptor activity-modifying protein (RAMP). Our objective was to explore the significance of CRLR/RAMP hypothesis in cardiovascular tissues through experiments on the phenomenon of desensitization of both ADM and CGRP receptors using cultured rat aortic vascular smooth muscle cells (VSMCs). VSMCs were incubated for 20 min either in serum-free medium (SFM) alone or in the SFM containing vasoactive agonist [10(-8) mol/L ADM, CGRP and proadrenomedullin (PAMP)]. Cells were washed twice and incubated for another 20 min in SFM containing a repetitive agonist ADM or CGRP and 0.5 mmol/L isobutyryl methylxant (an inhibitor of phosphodiesterase). VSMCs were harvested and assayed for cAMP. Exposure of VSMCs to ADM, CGRP, or PAMP alone increased intracellular cAMP generation by 191% (P < 0.01), 385% (P < 0.01) and 67% (P < 0.05), respectively, compared with SFM group. Pre-treatment of VSMCs to ADM or CGRP decreased cAMP generation in response to subsequent stimulation with CGRP by 44% (P < 0.05) and 48% (P < 0.01), respectively. Pre-treatment of VSMCs with 100 nmol/L H-89, a protein kinase A (PKA) inhibitor, abolished the desensitization of CGRP-acting receptor, implying that this desensitization was mediated through PKA. In contrast, there was no attenuation in cAMP response to stimulation with ADM by pre-exposure to ADM or CGRP. Identical results were seen with or without PKA inhibition by H-89. Pre-exposure of VSMCs to PAMP resulted in no change in cAMP generation in response to subsequent stimulation with ADM or CGRP. These results indicate that ADM receptors do not desensitize in VSMCs in contrast to CGRP-receptors, which are desensitized by pre-exposure to ADM or CGRP. These data also suggest that the desensitization phenomenon of ADM is different from that of CGRP.

[Influence of myocardial ischemia/reperfusion in vitro on nuclear envelope NTPase activity and mRNA export in the cardiomyocyte of rabbits]

AIM

To study the alteration of nuclear envelope associated NTPase activity and mRNA nucleocytoplasmic transport in rabbit cardiomyocyte following in vitro ischemia and reperfusion.

METHODS

The model of myocardial perfusion in rabbit was used to produce myocardial I/R injury and cardiomyocyte nuclear envelope vesicles were prepared by density gradient centrifugation for the assay of mRNA transport rate and NTPase activity.

RESULTS

NTPase activity was reduced and mRNA transport rate was significantly decreased in I/R (P < 0.01) but not in ischemia group( P > 0.05).

CONCLUSION

The nuclear envelope vesicles had been injured following ischemia and reperfusion and resulted in NTPase activity reduced and egress of mRNA interrupted, and therefore may lead to decreasing of protein synthesis.

[Role of calcineurin in cardiac fibroblast proliferation stimulated by angiotensin II]

The present study was undertaken to observe the role of calcineurin (CaN) in the angiotensin II (Ang II) stimulated cardiac fibroblast proliferation. In cultured cardiac fibroblasts of neonatal rats, Ang II was used to stimulate proliferation while CaN was inhibited by CaN CsA inhibitor cyclosporin A (CsA). (3)H-TdR incorporation, activity of CaN and intracellular calcium concentration were measured. (3)H-TdR incorporation of Ang II stimulated fibroblasts was 72% higher than control (P<0.01), which was inhibited by CsA (0.1 10 micromol/L) in a dose dependent manner. Intracellular Ca(2+) level and CaN activity of Ang II stimulated fibroblasts were respectively 112% (P<0.01) and 17%(P<0.05) higher than control. It is concluded that CaN may play an important role in signal transduction of the Ang II induced cardiac fibroblast proliferation.

Basic fibroblast growth factor increases nitric oxide and endothelin production in rat aorta

The study was undertaken to investigate the effect of basic fibroblast growth factor (bFGF) on aortic production of nitric oxide (NO) and endothelin of aorta in spontaneously hypertensive rats (SHR) and WKY rats. Rat aortas were cut into vessel slices and incubated with 10 or 100 ng/ml bFGF for 6 hours. Nitric oxide synthase (NOS) activity in aortic slices and contents of NO(-)(2) and endothelin in the medium were determined. The results showed that NOS activity in aortic slices of SHR was 17.6% lower than that of WKY (P<0.01). NO(-)(2) and endothelin contents in the medium of SHR aortic slices were 59.7% lower and 37.4% higher than those of WKY aortic slices. Upon the exposure of low and high doses of bFGF, NOS activity in the aorta of SHR was increased by 29.7% and 59.6% (both P<0.01),respectively, while the NO(-)(2) contents in the medium were increased respectively by 28.2% (P<0.05) and 70.5% (P<0.01). Aortic endothelin production was increased by 24.1% and 44.5% (both P<0.01) respectively while the NOS activity in the aorta of WKY was increased by 24.4% and 53.7% (both P<0.01). NO(-)(2) contents in the medium were augmented by 18.8% (P<0.05)and 25.9% (P<0.01), respectively. Aortic endothelin production was increased by 84.1% and 93.1% (both P<0.01). It is concluded that bFGF may modulate the production of NO and endothelin in both SHR and WKY rats.

Effect of batroxobin against dog heart ischemia/reperfusion injury

AIM

To study the effect of batroxobin(Bat) on dog heart ischemia/reperfusion (I/R) injury.

METHODS

Dog heart I/R injury was induced by occluding the left anterior descending coronary artery for 30 min and restoring blood perfusion for 90 min. Bat was intravenously injected before heart ischemia and 15 min before reperfusion. Plasma creatine kinase (CK), lactate dehydrogenase (LDH), and myocardial malondiaedehyde (MDA) concentrations were measured. The pathologic changes of I/R myocardium were observed.

RESULTS

Bat reduced the mortality rate of I/R dog (I/R group 65.0% vs Bat-I group 30.0% and Bat-II group 28.6%, P < 0.05). Myocytes of I/R heart showed intracellular edema, damaged mitochondria, and concentrated nucleus. Bat decreased these changes. In Bat-I and Bat-II group, plasma CK and LDH level were reduced, the +dp/dtmax and -dp/dtmax at 30 min after ischemia and 90 min after reperfusion were elevated, and left ventricular end dilation pressure (LVEDP) was lowered. The myocardial MDA contents were decreased by 42.3% and 38.1% (P < 0.01) in Bat-I and Bat-II group, respectively.

CONCLUSION

Bat may exert an apparent role against dog heart ischemia/reperfusion injury and improve myocardial function.

[Involvement of calcineurin-dependent signal pathway in the angiotensin II-induced cardiac myocyte hypertrophy]

The present study was undertaken to observe the role of calcineurin (CaN)-dependent signaling pathway in the angiotensin II (Ang II)-induced cardiac myocyte hypertrophy. In cultured myocardial cells of neonatal rats, Ang II was used to stimulate hypertrophy and CaN-pathway blocked by CsA(an inhibitor of CaN). 3H-leucine incorporation, and activities of CaN, mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) were investigated. The results showed that 3H-leucine incorporation of Ang II-stimulated myocardial cells was 46% higher than control (P < 0.01), which could be inhibited by CsA (0.5-5 micrograms/ml) and PD098059(an inhibitor of MAPK). CaN and PKC activities of Ang II-stimulated myocardial cells were 39% and 280% higher than control (P < 0.001) respectively, while no significant increase in MAPK activities was observed. CsA could reverse the increase of CaN activity, but had no effect on PKC. It is concluded that the CaN-dependent signaling pathway may play an important role in the development of the Ang II-induced cardiac myocyte hypertrophy.

[The role of endogenous CO in the regulation of endothelin-induced VSMC proliferation and MAPK activity]

Heme oxygenase (HO) is a rate-limiting enzyme of heme degradation, which converts the cellular heme to bilirubin and carbon monoxide (CO). Recently it is suggested that endogenous CO plays an important role in regulating vascular tone under both physiological and pathological conditions, but it is not clear whether endogenous HO/CO system regulates vascular smooth muscle cell (VSMC) proliferation. In the present study, VMSC 3H-TdR incorporation, mitogen-activated protein kinase (MAPK) activity, HO activity and CO release were determined to study the role of endogenous HO/CO system in regulating the VSMC proliferation induced by endothelin-1 (ET-1) in a cultured system. The results showed that ET-1 increased VSMC 3H-TdR incorporation, MAPK activity, HO activity, and CO release were up-regulated. Pretreatment of HO inhibitor, zinc protoporphyrin-9 (ZnPP-9), increased the ET-1-induced VSMC 3H-TdR incorporation and MAPK activity by 31.8% and 36.6% (P < 0.01, respectively), whereas pretreatment of heme-L-lysinate (HLL), a HO substrate, inhibited these activities. This study demonstrated that up-regulation of VSMC endogenous HO represents a cellular protective response to stress or injury. Inhibition of HO may enhance VSMC proliferation induced by ET-1 in vitro, suggesting that endogenous HO/CO system may be directly involved in the regulation of VSMC proliferation through MAPK signaling pathway.

Role of endogenous carbon monoxide in the pathogenesis of hypotension during septic shock

A sepsis model induced by cecal ligation and puncture was used to study the role of endogenous carbon monoxide in hypotension pathogenesis of rats during septic shock. After administration of zinc deuteroporphyrin 2,4-bisglycol (ZnDPBG),an inhibitor of heme oxygenase (HO),blood pressure (BP),HO activity and carbon monoxide (CO) release from vascular muscle tissue were measured. The results showed that BP of sepsis rats, including systolic and diastolic arterial BP, decreased significantly while HO activity and CO content were significantly increased. In contrast, after administration of ZnDPBG, BP of sepsis rats was significantly increased while the HO activity and CO production were significantly decreased. These findings suggest that HO activity and CO release within vascular musculature are increased during septic shock; inhibition of HO may elevate BP of rats during septic shock through a decrease of endogenous CO production. It is concluded that endogenous CO derived from vascular muscle cells plays an important role in regulating vascular tone, and the up-regulation of HO activity followed by subsequent CO production contributes to hypotension pathogenesis during septic shock.

Role of endogenous carbon monoxide in hypertension pathogenesis of rats

The present study investigated the contribution of endogenous heme oxygenase (HO)/carbon monoxide (CO) system to hypertension pathogenesis of rats. Zinc deuteroporphyrin 2,4-bisglycol (ZnDPBG), an inhibitor of heme oxygenase (HO), was used to inhibit HO activity in vivo. It was found that the blood pressure of rats with HO inhibition was significantly elevated, and plasma levels of adrenaline, noradrenaline, endothelin, nitrate and nitrite were significantly increased. HO activity and HbCO formation within vascular smooth muscle tissues were significantly inhibited after administration of ZnDPBG. Furthermore, administration of exogenous CO into HO inhibiting rats led to MABP decrease, but injection of HO substrate, heme-L-lysinate, had no effect on HO inhibition-induced hypertension. In spontaneously hypertensive rats, injection of exogenous CO resulted in a significant decrease of MABP, and heme-L-lysinate had a similar effect with exogenous CO. These data show that HO/CO system has an anti-hypertension biological action, suggesting that endogenous CO plays an important role in hypertension pathogenesis.

[Changes of mitogen-activated protein kinase activity in cardiac tissues, Ang II and cardiac hypertrophy in spontaneously hypertensive rats]

Mitogen-activated protein kinases (MAPKs) are thought to be critical components in signal transduction pathways in regulation of cell growth and differentiation. The purpose of the present investigation is to study possible involvement of MAPKs in the progress of cardiac hypertrophy in spontaneously hypertensive rats (SHRs) and effects of age on Angiotensin II (Ang II), MAPK activity and cardiac hypertrophy. The animals were divided into three groups: 4 months old WKY rats (n = 8), 4 month old SHRs (n = 8) and 15 month old SHRs (n = 6). Ratio of heart to body weight was measured. Ang II was determined by RIA. MAPK activity in cardiac tissue was assayed by the "in-gel" myelin basic protein phosphorylation. The results show that in comparison with 4 month old WKY rats, Ang II in plasma and cardiac tissues were elevated (216.4%, P < 0.01; 101.2%, P < 0.01) in 4 months old SHRs, while the MAPK activity was increased 107.0% (P < 0.01) with a parallel cardiac hypertrophy (P < 0.01). In comparison with 4 month old SHRs, Ang II and MAPK activity in cardiac tissue of the 15 months old SHRs were decreased (31.3%, P < 0.01; 29.7%, P < 0.05) but the cardiac hypertrophy increased by 38.5% (P < 0.01). MAPK may be involved in the progress of cardiac hypetrophy in SHR and the increased MAPK activity may be partly induced by Ang II.

[Effect of Arg-Gly-Asp-Ser (RGDS) peptide on ADP-induced signal transduction of activated rat platelet]

The purpose of this work was to investigate the effect of Arg-Gly-Asp-Ser (RGDS) peptide on platelet aggregation, protein phosphorylation, protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activity during platelet activation. Experiments were performed on ADP activated rat platelets in vivo. Results showed that 50 mumol/L ADP, in addition to inducing platelet aggregation, obviously enhanced not only PKC and MAPK activities but also 95 and 66 kD protein phosphorylation. When platelets and ADP were incubated together with 50, 100, 200 mumol/L RGDS peptide it was found that the latter markedly inhibited ADP activated platelet aggregation and activation of PKC and MAPK, both in a concentration-dependently manner. RGDS peptide also inhibited 95 and 66 kD protein phosphorylation concentration-dependently and went positively with its activation of PKC and MAPK. The above result suggested that the antithrombotic effect of RGDS peptide was probably mediated through its effect on intracellular signal transduction in the ADP activation of platelets.

[Effect of anoxic preconditioning on protein kinase C activity in neonatal rat cardiomyocytes]

In a model of anoxia/reoxygenation (A/R) of cultured rat cardiomyocytes, protection of cellular damage, activation of protein kinase C (PKC) and PKC-mediated protein phosphorylation by anoxic preconditioning (APC) can be demonstrated as shown by the increase of cell viability, attenuation of formation of lipid peroxides (MDA) and lowering of the leakage of lactate dehydrogenase (LDH) and protein from cells. The results also show that transient anoxia mimicked the outcomes of activation of PKC as shown by increased incorporation of 32P, especially in the 66 kD and 31 kD protein fractions. Preincubation of cardiomyocytes with H7 (an inhibitor of PKC) completely abolished these protective effects of transient anoxia. Protein phosphatase inhibitor OA mimicked the protective effects of A/R, while protein phosphatase activator BDM induced a complete abolishment. In short, we conclude that the protective effect of APC is medicated by activation of PKC.

[Effects of basic fibroblast growth factor on anoxia/reoxygenation injury of rat neonatal cardiomyocytes]

The effects of basic fibroblast growth factor (bFGF) on anoxia/reoxygenation (A/R) injury and protein kinase C (PKC) activity were studied on a model of A/R injury of neonatal rat cardiomyocytes to investigate the possibility of its using as a substrate for pharmacological preconditioning. The data indicated that bFGF improved the viability of cardiomyocytes, lowered the deplection of ATP and leakage of intracellular lactate dehydrogenase (LDH) in a concentration-dependent manner. PKC inhibitor, H7, completely abolished the protective effects. It was also found that bFGF directely activated PKC in cardiomyocytes in a time course similar to that in hypoxic preconditioning. The data suggested that the protective effect of bFGF on cardiomyocyte A/R injury might be mediated by PKC.

[Changes of calcium transport in rat liver nuclei during sepsis]

Calcium transport changes in rat liver nuclei were observed on the model of early sepsis (9 h after operation of cecal ligation and puncture). Calcium content in hepatocytes and nuclei were significantly increased by 20% and 36% respectively (P < 0.05) during sepsis. The activity of Ca(2+)-ATPase in hepatocytic nuclei was increased by 94% (P < 0.01) and 45Ca2+ transport accelerated by 32% (P < 0.01). There was a positive correlation between nuclear 45Ca2+ transport and nuclear Ca(2+)-ATPase activity (r = 0.914, P < 0.01). Calmodulin stimulated the activity of nuclear Ca(2+)-ATPase and 45Ca2+ transport; while calmodulin inhibitor trifluoperazine exerted an opposite effect. The above results suggest that liver nuclear calcium transport is strengthened during early sepsis as a result of changes of Ca(2+)-ATPase activity.

[L-arginine transport in cultured vascular smooth muscle cells of spontaneously hypertensive rats and effect of liposome on the transport]

The characteristics of L-arginine (L-Arg) transport in cultured aortic smooth muscle cells (SMC) of spontaneously hypertensive rat (SHR) and control WKY rats were studied and the effect of liposome as L-Arg carrier on the transport was investigated. The results showed that the L-Arg transport of SMC in SHR was obviously lower than that in WKY rats. Maximum transport velocity (Vmax) of high and low affinity in SHR were respectively 48% (P < 0.01) and 49% (P < 0.01) of WKY rat, while the michaelis constant (K(m)) showed no significant difference (P > 0.05). Increase of L-Arg transport induced by tumor necrosis factor-alpha (TNF alpha) in SMC of SHR was obviously lower than that in WKY rats (P < 0.01). The uptake of L-Arg increased 10 to 20 times in SMC when incubated with liposome encapsulated L-Arg (Liposome-L-Arg) than with free L-Arg. The transport velocity in SMC incubated with liposome-L-Arg showed no significant difference in SHR and WKY rats (P > 0.05). The transport of liposome-L-Arg in SMC was not affected by TNF alpha in both the types of rats. The above results indicate that there exists a functional disturbance in L-Arg transport in the SMC of SHR, but the L-Arg transport in SMC can be obviously enhanced when liposome is used as L-Arg carrier. Thus, it appears that liposome-L-Arg may have clinical perspective in the treatment of hypertension.

[Endothelin-stimulated proliferation of thoracic artery smooth muscle cells involves activation of mitogen-activated protein kinase]

Endothelin (ET) is a potent vasoconstrictor whose responses are mediated through a common G-protein coupled receptor. So far little is known concerning its potential mitogenic capacity. In the present study, experiments were conducted to determine the role of mitogen-activated protein kinase (MAPK) activation in the rabbit thoracic artery smooth muscle cells (VSMC) in response to stimulation by ET-1. It was found that ET-1 produced concentration- and time-dependent increases in 3H-TdR incorporation and in MAPK activity of these cells. All the increases were inhibited by protein kinase C (PKC) inhibitors, such as Staurosporine (STP) and H-7 and by ETA receptor antagonist BQ123, but not by specific tyrosine kinase inhibitor Herbimycin A (Herb). Pre-treatment with PKC activator PMA (phorbol myristate acetate) for 24 h (PKC downregulation) significantly attenuated ET-1-induced MAPK activation. These results indicate that: (1) ET-1-stimulated proliferation of VSMC involves the activation of MAPK and (2) ET-1-induced MAPK activation is mediated through ETA receptor and PKC.