Lysophosphatidic acid-induced platelet shape change revealed through LPA(1-5) receptor-selective probes and albumin.

Lysophosphatidic acid (LPA), a component of mildly-oxidized LDL and the lipid rich core of atherosclerotic plaques, elicits platelet activation. LPA is the ligand of G protein-coupled receptors (GPCR) of the EDG family (LPA(1-3)) and the newly identified LPA(4-7) subcluster. LPA(4), LPA(5) and LPA(7) increase cellular cAMP levels that would induce platelet inhibition rather than activation. In the present study we quantified the mRNA levels of the LPA(1-7) GPCR in human platelets and found a rank order LPA(4) = LPA(5) > LPA(7) > LPA(6) = LPA(2) >> LPA(1) > LPA(3). We examined platelet shape change using a panel of LPA receptor subtype-selective agonists and antagonists and compared them with their pharmacological profiles obtained in heterologous LPA(1-5) receptor expression systems. Responses to different natural acyl and alkyl species of LPA, and octyl phosphatidic acid analogs, alpha-substituted phosphonate analogs, N-palmitoyl-tyrosine phosphoric acid, N-palmitoyl-serine phosphoric acid were tested. All of these compounds elicited platelet activation and also inhibited LPA-induced platelet shape change after pre-incubation, suggesting that receptor desensitization is likely responsible for the inhibition of this response. Fatty acid free albumin (10 microM) lacking platelet activity completely inhibited platelet shape change induced by LPA with an IC(50) of 1.1 microM but had no effect on the activation of LPA(1,2,3,&5) expressed in endogenously non-LPA-responsive RH7777 cells. However, albumin reduced LPA(4) activation and shifted the dose-response curve to the right. LPA(5) transiently expressed in RH7777 cells showed preference to alkyl-LPA over acyl-LPA that is similar to that in platelets. LPA did not increase cAMP levels in platelets. In conclusion, our results with the pharmacological compounds and albumin demonstrate that LPA does not induce platelet shape change simply through activation of LPA(1-5), and the receptor(s) mediating LPA-induced platelet activation remains elusive.

[Surgical treatment of left ventricular-right atrial communication complicated with aortic and mitral valves regurgitation: report of a case].

A 50-year-old man with a heart murmur from early childhood and a one year history of general fatigue was admitted. Cardiac examination showed a left ventricular-right atrial (LV-RA) communication, and aortic and mitral valve regurgitation (III/IV). At surgery, the LV-RA communication was located in the atrioventricular membranous portion 3 mm above the septal leaflet of the tricuspid valve. The etiology of the LV-RA communication was congenital and valvular diseases were acquired changes caused by sclerosis due to infected endocarditis or hypertension. The diameter of the LV-RA communication defect was 6 mm, and the fibrous tissue around the defect was closed directly. Next, double-valve replacement was performed safely. However, the day after surgery, the patient developed complete atrioventricular block and implantation of a DDD pacemaker was required. He was discharged without other complication. We recommend the careful closure of the LV-RA communication defect, if the defect is small and rich in fibrous tissue.

[Surgical repair of extracardiac unruptured aneurysm of the sinus of Valsalva; report of a case].

A 65-year-old man presented with a 6 year history of dyspnea. An unruptured aneurysm of sinus of Valsalva and aortic regurgitation had been detected at another hospital a year previously, and he was referred to our hospital for surgery. At operation, an extracardiac saccular aneurysm was widely localized to the noncoronary sinus of Valsalva and protruded into the left atrium. The aneurysm of the sinus of Valsalva (ASV) was repaired with patch closure using a dacron sheet, and aortic valve replacement was performed with a 21 mm Carpentier-Edward valve. However, there was uncontrollable bleeding from the patch suture line, so ascending aorta replacement and repair of the Valsalva sinus were additionally needed. He was discharged without any postoperative complication 7 weeks after operation. Cases of an ASV protruding into the left atrium are very rare. We recommend remodeling of the aortic root with wide replacement of 1 sinus for extracardiac succular ASV, because the tissue around the ASV is so fragile.

Property of metallothionein as a Zn pool differs depending on the induced condition of metallothionein.

Metallothionein (MT) is a low-molecular-weight, cysteine-rich, heavy metal-binding protein with several putative physiological functions as a radical scavenger and a regulator of metabolism of Zn. Although the induction of hepatic MT by a wide range of stressors is a well-known phenomenon, little is known about the role of MT in stressful situations. Since MT regulates Zn metabolism, we investigated the differences between affinities of MT for Zn in various stressful conditions in this study. Divalent cadmium ions are capable of displacement of Zn from MT in vitro. Therefore, we assayed the binding of Zn to MT induced by various stimuli using in vivo administration of Cd. MT was induced by paraquat (PQ), a reactive oxygen generator, fasting stress and restraint stress. Apo-MT induced by them bound to Zn in vivo. Zn, which bound to MT induced by PQ, was displaced by the administration of Cd. However, Zn that had bound to MT induced by fasting stress and restraint stress was not displaced by Cd. Moreover, we assessed the in vivo affinity of Zn to MT induced by fasting stress under the condition of subchronic Cd exposure. Cd was administered to mice by subcutaneously implanted Alzet osmotic minipumps, which released constant amounts of Cd over a 14-day period. After 4 days, mice were fasted for 24 h and hepatic MT was examined. Interestingly, it was found that Zn had displaced Cd bound to MT. These findings indicate that the affinity of MT for Zn differs depending on the stimulus by which MT was induced. This is the first report on differences in the properties of MT depending on the stimulus used to induce MT.

Differentiation of Th1 and Th2 cells in lymph nodes and spleens of mice during experimental autoimmune uveoretinitis.

PURPOSE: Experimental autoimmune uveoretinitis (EAU) is a T-cell-mediated autoimmune disease that can be elicited in susceptible rodent strains by immunization with a retinal autoantigen, such as interphotoreceptor retinoid-binding protein (IRBP). In this study, we investigated whether there is a correlation between inflammation in the eye and T-helper (Th)1- and Th2-type responses in the lymph nodes and the spleen after immunization of B10.A mice with IRBP. METHODS: B10.A mice were immunized with IRBP emulsified with complete Freund's adjuvant (CFA), and eyes were then enucleated for histological examination of EAU at 1, 2, 4, 6, or 8 weeks after immunization. In addition, lymph node cells and spleen cells were collected, and cultured with IRBP to measure T-cell proliferation responses and Th1-type (interleukin [IL]-2, interferon [IFN]-gamma), Th2-type (IL-4, IL-10) cytokine production. RESULTS: Pathologically, severe ocular inflammation occurred 2 weeks after IRBP immunization, persisted for 2 weeks, and then gradually resolved. Interleukin-2 and IFN-gamma production were observed in draining lymph node cells at 1 and 2 weeks after IRBP immunization. Those responses then diminished, whereas IFN-gamma production by spleen cells was observed from week 1, peaked at week 4, and gradually decreased. Alternatively, significant production of IL-4 or IL-10 by draining lymph node cells was not detected at any time point. Both IL-4 and IL-10 production by spleen cells was observed at week 6. CONCLUSIONS: Th1-type responses were observed early in draining lymph nodes, then in the spleen after IRBP immunization. The levels of IFN-gamma production by spleen cells reflected the severity of EAU, confirming their pathogenic role in this disease. Th2-type responses were generated in the spleen only as the disease receded, suggesting a role for Th2 cells in the spontaneous termination of EAU.

Clinical outcome of stent implantation in small coronary arteries using different types of coronary stents.

PURPOSE: We evaluated the results of stent placement in small coronary arteries. SUBJECTS: The subjects were divided into 2 groups: the first contained 911 lesions treated with stenting in the coronary arteries (stent group), and the second contained 1,203 background- and patient-matched lesions treated with balloon angioplasty (POBA group). There was no significant difference in the background of patients or lesions between the groups. A "small coronary artery" was defined as a coronary artery with a reference vessel diameter < 3.0 mm. RESULTS: There was no significant difference in incidence of acute myocardial infarction (AMI), coronary artery bypass grafting, or death between the groups. In the stent group, acute occlusion (0.8%) and subacute thrombosis (2.1%) occurred. The restenosis rate of 29.8% in the stent group was significantly lower than in the POBA group (38.2%; p < 0.01). The restenosis rate of 19.4% in stented vessels 3.0 mm diameter was significantly lower than in vessels < 3.0 mm diameter (29.8%; p < 0.01). The rate of restenosis was 22.9% for the Multi-Link stent, 24.4% for the NIR stent, 34.1% for the GFX stent, and 35.3% for the PS stent. The restenosis rate of 23.8% in stented vessels > 2.5 mm diameter and < or = 20 mm length was significantly lower than in vessels , < or = 2.5 mm diameter and > 20 mm length (32.7%; p < 0.01). Factors associated with restenosis, analyzed using a stepwise multivariate logistic regression model, included ostial lesions and post-procedural minimum lumen diameter. CONCLUSIONS: Stent implantation in vessels < 3.0 mm diameter using a newly designed coronary stent yielded favorable clinical results, while there was a high prevalence of restenosis, leading to diffused stenotic lesions, in vessels < 2.5 mm diameter.

Efficacy of cutting balloon angioplasty for in-stent restenosis: an intravascular ultrasound evaluation.

BACKGROUND: The increase in the use of stents has seen the increasing emergence of in-stent restenosis (ISR). Reports suggest that the Cutting Balloon (Interventional Technologies, San Diego, California) may be a useful treatment modality for this new clinical entity. METHODS: In this study, we compared the efficacy of Cutting Balloon angioplasty (CBA) with conventional balloon angioplasty (PTCA) for ISR in 47 patients (47 lesions). Results were evaluated with intravascular ultrasound (IVUS). The CBA group included 25 patients (mean age, 65 +/- 78 years; 7 females) and the PTCA group included 22 patients (mean age, 69 +/- 51 years; 6 females). RESULTS: The procedural success rate was 100% in both groups. IVUS showed that luminal area acute gain was larger in the CBA group (2.5 +/- 0.8 mm2) compared to the PTCA group (1.8 +/- 1.0 mm2), while late loss was smaller in the CBA group (0.5 +/- 0.4 mm2) compared to the PTCA group (1.3 +/- 0.5 mm2). The change in total area was similar in both groups. The increase in area at the stented portion was 0.4 +/- 0.8 mm2 in the CBA group and 1.2 +/- 0.5 mm2 in the PTCA group. The restenosis rate at follow-up (mean follow-up, 5.4 months) was higher in PTCA patients (59%) than in the CBA patients (24%). CONCLUSION: CBA may result in no increase in total vessel area, a constant stent area, a decrease in plaque area, and an increase in lumen area (induced by the decrease in plaque area). Our IVUS findings suggest that compared to PTCA, the dilatation mechanism of CBA may be associated with reduced dilatation of both the total vessel area and the stent area for ISR. The mechanism of this modality may minimize injury to the intimal membrane and may potentially be a primary device for in-stent restenosis in the future.

Intravascular ultrasound findings in patients with abnormal coronary flow reserve after stenting.

A coronary flow reserve (CFR) of 2.0 has been advocated as the endpoint for coronary intervention therapy. Experience shows, however, that CFR does indeed exceed 2.0 in many cases poststenting, while remaining below 2.0 in others. In this study, we assessed the clinical characteristics and IVUS findings of patients whose CFR remained below 2.0 after stent implantation, specifically 16 patients with CFR below 2.0 (22 lesions, 64 +/- 9 years, 4 female), and 102 patients with CFR above 2.0 (112 lesions, mean age 66 +/- 11 years, 22 female). Patient population comprised patients selected for retrospective study, but participants were selected on the basis of matching patient and lesion characteristics. The IVUS findings showed that incidence of calcified lesions and post-PTCA dissection of hard plaque were higher among patients with CFR < 2.0. Further, IVUS-obtained vascular measurements showed post-PTCA area stenosis to be 58.7 +/- 15.2% in the CFR < 2.0 group, and 45.3 +/- 12.5% among CFR > or = 2.0 patients (P < 0.05). These findings indicate that patients with diffuse calcified lesions or high post-PTCA % area stenosis, as determined by IVUS, are more likely to have lower CFR after stenting.

Efficacy of directional coronary atherectomy before stent implantation for coronary ostial lesions.

We evaluated stent implantation following directional coronary atherectomy (DCA) for coronary ostial lesions. The subjects were 27 patients (27 lesions) who underwent stent deployment after DCA, and 47 patients (47 lesions) who underwent stent deployment alone as the control group. There were no differences in numbers of lesions with multi-vessel disease, left anterior descending artery lesions, de novo lesions or reference vessel diameters in the two groups. The percent diameter stenosis after stent implantation was lower in the DCA-stent group than in the stent-alone group (9 +/- 10% versus 17 +/- 14%, respectively; p < 0.01). The initial procedural success rate was 92.6% in the DCA-stent group and 91.4% in the stent-alone group. The initial clinical success rate was 100% in the DCA-stent group and 95.7% in the stent-alone group. The restenosis rate was lower in the DCA-stent group (20% versus 43% in the stent-alone group). This study showed that debulking by DCA before stenting is more effective compared to stenting alone.

Efficacy of cutting balloon angioplasty for lesions at the ostium of the coronary arteries.

We evaluated 37 patients (39 lesions, 11 women/26 men, median age of 66 years old) with coronary ostial lesions who underwent cutting balloon angioplasty (CB). Seventy-four patients (78 lesions, 18 women/56 men, median age of 65 years old) who had undergone plain old balloon angioplasty (POBA) for coronary ostial lesions were also enrolled as the control group. At clinical diagnosis, unstable angina was seen in 8.1% of the CB group and in 9.5% of the POBA group. Post myocardial infarction silent ischemia was seen in 28.3% of the POBA group and 32.4% of the CB group. The success rate was 94.8% in the CB group and 84.6% in the POBA group. The frequency of intimal dissection was not significantly different between the two groups. However, all cases of intimal dissection in the CB group were mild (either type A or B), whereas the POBA group included many cases of severe intimal dissection (types B through F). No cardiac event was observed in the CB group. However, in the POBA group, cardiac death occurred in 1.4% and emergency bypass surgery occurred in 0.7% of the patients. Calculating the restenosis rate based on the cumulative percent diameter stenosis curve resulted in 43% for the CB group and 53% of the POBA group. We concluded that the cutting balloon was useful for ostial lesions as compared to plain old balloon angioplasty.

The recruitment pattern of single vasoconstrictor neurons in human.

The aim of this study is to determine the recruitment pattern among individual vasoconstrictor neurons under the baroreceptor-mediated influence in man. Spikes of single vasoconstrictor units were detected from microneurograms with a template-matching method. A total of 39 single vasoconstrictor units were detected. Single vasoconstrictor units were different from each other in their susceptibility to be activated in response to changes in the R-R interval or blood pressure. The units with higher firing probability had a shorter threshold R-R interval and a higher threshold diastolic blood pressure than units with lower firing probability. In sympathetic responses consisting of only one spike (single-spike responses), units with a lower threshold frequently appeared and units with a higher threshold joined mull-spike responses. The units with a short threshold R-R interval tended to have a long inhibitory latency from R wave, suggesting low conduction velocity. The correlation between firing probability and firing threshold and that between appearance in single-spike response and multi-spike response suggest a hierarchical manner of recruitment of vasoconstrictor units. For beat-to-beat responses, however, some deviation from the hierarchical recruitment was also observed.

Effects of premotion silent period on single motor unit firing at initiation of a rapid contraction.

We compared the single motor unit (SMU) activity between movements with a premotion silent period (PMSP) and without PMSP in EMG. Fourteen SMUs in the gastrocnemius muscle and 6 SMUs in the soleus muscle were recorded from 5 volunteers during isometric plantar flexion. Tonically firing SMUs failed to fire just before the onset of a rapid contraction with PMSP more frequently than without PMSP. SMUs tended to fire within 10 msec (the gastrocnemius SMUs) or 20 msec (the soleus SMUs) from the onset of the phasic EMG discharge when PMSP occurred. In a rapid contraction without PMSP, the initial firing of SMUs occurred with longer latency than that in a rapid contraction with PMSP. The latency of the initial SMU firing in a rapid contraction related to the preceding time of the last SMU firing during a sustained contraction to the onset of the phasic EMG discharge. When the preceding firing was long enough, the latency distributed around 10 msec. On the other hand, for shorter preceding times, the latency lengthened with shortening of the preceding time. It is suggested that the PMSP makes the preceding time long and increases the susceptibility of motor units to the descending command at the initiation of a rapid contraction.

Percutaneous transluminal coronary angioplasty for culprit lesions in patients with post myocardial infarction angina based on dextrocardia and anomalous coronary arteries. Case reports and methods.

Four cases of successful coronary angioplasty for anomalous coronary arteries, including dextrocardia associated with three-vessel disease, single left coronary artery with proximal left anterior descending lesion, anomalous right coronary artery (RCA) from adjacent left coronary sinus of Valsalva associated with proximal RCA lesion, and anomalous left circumflex angulated lesion bifurcated from the RCA, were encountered. Four cases with 8 target lesions who had a mean age of 63.5 +/- 11.5 years old are presented. All the targets lesions were completely dilated through balloon angioplasty, including use of a newly developed support device for cases with large jeopardized myocardium. The factors for complete revascularization were appropriate selection of catheters and originality and ingenuity of procedural technique based on the anatomic characteristics.

Lack of association between cholesterol and coronary heart disease mortality and morbidity and all-cause mortality in persons older than 70 years.

OBJECTIVES: To determine whether elevated serum cholesterol level is associated with all-cause mortality, mortality from coronary heart disease, or hospitalization for acute myocardial infarction and unstable angina in persons older than 70 years. Also, to evaluate the association between low levels of high-density lipoprotein cholesterol (HDL-C) and elevated ratio of serum cholesterol to HDL-C with these outcomes. DESIGN: Prospective, community-based cohort study with yearly interviews. PARTICIPANTS: A total of 997 subjects who were interviewed in 1988 as part of the New Haven, Conn, cohort of the Established Population for the Epidemiologic Study of the Elderly (EPESE) and consented to have blood drawn. MAIN OUTCOME MEASURES: The risk factor-adjusted odds ratios of the 4-year incidence of all-cause mortality, mortality from coronary heart disease, and hospitalization for myocardial infarction or unstable angina were calculated for the following: subjects with total serum cholesterol levels greater than or equal to 6.20 mmol/L (> or = 240 mg/dL) compared with subjects with cholesterol levels less than 5.20 mmol/L (< 200 mg/dL); subjects in the lowest tertile of HDL-C level compared with those in the highest tertile; and subjects in the highest tertile of the ratio of total serum cholesterol to HDL-C level compared with those in the lowest tertile. RESULTS: Elevated total serum cholesterol level, low HDL-C, and high total serum cholesterol to HDL-C ratio were not associated with a significantly higher rate of all-cause mortality, coronary heart disease mortality, or hospitalization for myocardial infarction or unstable angina after adjustment for cardiovascular risk factors. The risk factor-adjusted odds ratio for all-cause mortality was 0.99 (95% confidence interval [CI], 0.56 to 2.69) for the group who had cholesterol levels greater than or equal to 6.20 mmol/L (> or = 240 mg/dL) compared with the group that had levels less than 5.20 mmol/L (< 200 mg/dL); 1.00 (95% CI, 0.59 to 1.70) for the group in the lowest tertile of HDL-C compared with those in the highest tertile; and 1.03 (95% CK, 0.62 to 1.71) for subjects in the highest tertile of the ratio of total serum cholesterol to HDL-C compared with those in the lowest tertile. CONCLUSIONS: Our findings do not support the hypothesis that hypercholesterolemia or low HDL-C are important risk factors for all-cause mortality, coronary heart disease mortality, or hospitalization for myocardial infarction or unstable angina in this cohort of persons older than 70 years.

[Two cases of acute leukemia with t(6;9) (p23;q34)].

Two cases of acute leukemia with a t (6;9) (p23;34) chromosome abnormality are reported. The first case was a 34-year-old female who was hospitalized in October 1989. A diagnosis of FAB-M1 was made. Chromosomal analysis of the bone marrow cells showed a 46, XX, t (6;9) (p23;q34). Complete remission was achieved after two courses of BHAC-DMP therapy. In September 1991, at the time of relapse, chromosomal analysis revealed two abnormal clones consisting of a 46, XX, t (6;9) (p23;q34), -12, -17, +der (12) t (12;17) (p11.2;q11.2) with a residual normal clone. She died in February 1992. The second case was a 42-year-old male who was hospitalized in January 1990. He was diagnosed as having RAEB. Chromosomal analysis of the bone marrow cells showed 46, XY, t (6;9) (p23;q34). Three months later, the disease progressed to acute leukemia accompanied by leg ulceration with leukemic cell infiltration. Small-dose ara-C therapy was given, but with no effect. After two subsequent courses of therapy with low-dose etoposide, complete remission was achieved. Four months later, relapse occurred, and the patient died of sepsis in February 1991. In the literature, 31 cases of myeloproliferative disorders with t (6;9) have been reported.

[A case of nonbacterial thrombotic endocarditis presenting positive findings by two-dimensional echocardiography].

A 55-year-old woman was admitted to our hospital because of left hemiparesis. Brain CT and cerebral angiography demonstrated cerebral embolism due to occlusion of the sphenoidal part of the right middle cerebral artery. Two-dimensional echocardiography revealed mitral valve vegetation measuring 10 x 7 mm and slight mitral-valve regurgitation. Blood cultures were negative. She developed disseminated intravascular coagulation. Chest roentgenography and abdominal ultrasonography showed multiple liver and lung tumors, but she died before the primary lesion was detected. At autopsy, adenocarcinoma of the gall bladder was found. Friable vegetation was attached to the auricular surface of the mitral valve. Microscopic examination confirmed the diagnosis of nonbacterial thrombotic endocarditis. Although echocardiography is an important tool for diagnosing nonbacterial thrombotic endocarditis, few reports have described echocardiographic detection of nonbacterial thrombotic endocarditis. Because vegetation of nonbacterial thrombotic endocarditis is smaller than that of infective endocarditis (less than 3 mm), it is difficult for echocardiography to detect nonbacterial thrombotic endocarditis. Thus, a negative examination does not exclude the possibility of nonbacterial thrombotic endocarditis. To make an antemortem diagnosis of nonbacterial thrombotic endocarditis, we must perform echocardiography carefully in cases of cerebral infarction with carcinoma and/or DIC.

[Myocardial viability in old myocardial infarction as evaluated by T1-201 SPECT and two-dimensional echocardiography].

Myocardial viability of the infarcted area was evaluated in 49 patients with old myocardial infarction by thallium-201 myocardial single photon emission computed tomography (SPECT), two-dimensional echocardiography (2 DE) and electrocardiography (ECG). The following results were obtained: 1. T1 uptake (%TU) correlated significantly with the % systolic thickening ratio (% delta Th) and the interventricular septal excursion (IVSE) (r = 0.66, r = 0.75), suggesting that both parameters are useful in predicting myocardial viability of the infarcted areas. 2. In 18 patients, the % delta Th was 0, IVSE ranged from -3 mm to +3 mm, and a positive correlation between %TU and IVSE was present, suggesting an advantage of IVSE over % delta Th as a parameter. 3. Forty-nine patients were categorized into 4 groups based on their ECG findings; 3 with QS and complete RBBB (Group A); 19 with QS and ST elevation (Group B); 10 with QS without ST elevation (Group C); and 17 with non-QS (Group D). All of %TU, % delta TH and IVSE increased in the order of Groups A < B < C < D. 4. The bull's eye method showed redistribution in 5 of 19 patients (26%) in Group B, 5 of 19 (26%) with % delta Th < or = 0 and 2 of 9 (22%) with IVSE < or = 0. These results suggested that transmural myocardial infarction, which has been considered irreversible, may be viable and PTCA or coronary bypass surgery is recommended if ECG or 2DE gives indications of myocardial viability.

Effects of pre-motion electromyographic silent period on dynamic force exertion during a rapid ballistic movement in man.

The effects of pre-motion silent period (PSP) on dynamic force exertion were studied in ten healthy subjects performing ballistic elbow extensions. The experiments were designed to evaluate the significance of mean differences between the averaged dynamic force curves of two groups: PSP-presence groups and PSP-absence groups. The presence of PSP was judged quantitatively and automatically by means of a newly developed method using statistical analysis. The results indicated that there were two effects of PSP on dynamic force exertion: one was a reducing effect, observed prior to the movement; the other was a reinforcing effect, observed in the first part of the ballistic movement. The duration of the reinforcement was significantly correlated with the duration of the reducing effect of PSP. The findings suggested that the reinforcement of dynamic force may be produced by the pre-stretch of agonistic muscles caused by prior force reduction due to PSP occurrence. The fact that PSP plays an important role in dynamic force exertion suggests that PSP may be incorporated in the central motor control system designed to interrupt the background activity, to stretch the agonist and to reinforce the dynamic force.

Postural adjustments for jumping reaction movement in mentally retarded children: findings from EMG patterns.

EMG patterns during a jumping reaction task were studied in 53 mentally retarded children. EMGs were recorded from the knee extensors (VM and RF) and the knee flexors (hamstrings). Lack of synchronization between onset of phasic discharge in the VM and the RF and between onset in the hamstrings and the knee extensors was characteristic of retarded children. Deviation from the EMG pattern of normal adults decreased with increasing MA. The premotor time tended to be prolonged with increasing time differences between the VM and the RF responses. Shorter RT between the VM and the RF was consistent across EMG patterns. These were more apparent in subjects with MAs above 7 than in those with MAs below 6. It is suggested that the asynchronized EMG pattern reflects postural requirements due to poor formation of preparatory set.