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W X Liu

Publications and source records attributed to W X Liu.

13 recordsLinked to original sources
PubMed1996

Autoregulation of myocardial glycogen concentration during intermittent hypoxia.

During hypoxia, the heart consumes glycogen to generate ATP. Tolerance of repetitive hypoxia logically requires prompt replenishment of glycogen, a process whose regulation is not fully understood. To examine this, we imposed a defined hypoxic stimulus on the rat heart while varying its workload. In intact rats, hypoxia reduced myocardial glycogen approximately 30% and increased both the fraction of glycogen synthase in its physiologically active (GS I) form (from 0.24 +/- 0.06 to 0.82 +/- 0.07; P < 0.005) and glycogen synthesis (from 0.087 +/- 0.011 to 0.375 +/- 0.046 mumol.g-1.min-1; P < 0.005). Reducing cardiac work (with propranolol or heterotopic transplantation) reduced glycogen breakdown, glycogen synthase activation, and glycogen synthesis in parallel, stepwise fashion in intact rats. Correspondingly, hypoxia increased GS I activity in the perfused heart in vitro, but only under conditions where glycogen was consumed. This suggests myocardial glycogen synthase is activated by systemic hypoxia and catalyzes rapid posthypoxic glycogen synthesis. Hypoxic glycogen synthase activation appears to be a proportionate, wholly intrinsic response to local glycogenolysis, operating to preserve myocardial glycogen stores independent of any extracardiac mediator of carbohydrate metabolism.

Animals↗
PubMed1995

Effect of nonworking heterotopic transplantation on rat heart glycogen metabolism.

To determine whether the contractile work history of cardiac muscle influences its responsiveness to insulin, we examined the effect of insulin infusion on glycogen metabolism in the rat heart 1 wk after transplantation into a nonworking heterotopic infrarenal position. Nonworking heterografts had higher basal glycogen concentrations than did in situ working hearts of the same animals (29.9 +/- 2.7 vs. 23.3 +/- 0.8 mumol/g; P < 0.05), and a smaller fraction of their glycogen synthase enzyme activity was in the physiologically active glycogen synthase I form (8 +/- 2 vs. 22 +/- 3%; P < 0.02). During a 25-min infusion of insulin (1 U/min) and glucose (30 mg.kg-1.min-1), the fractional glycogen synthase I activity of heterografts remained lower than that of in situ hearts (29 +/- 5 vs. 56 +/- 7%; P < 0.02) and heterografts synthesized glycogen more slowly (0.126 +/- 0.07 vs. 0.352 +/- 0.06 mumol.g-1.min-1; P < 0.02). These effects could be duplicated by a 24-h fast, which similarly increased myocardial glycogen concentration (to 32.9 +/- 5.6 mumol/g). These observations suggest that the performance of repetitive contractile work is necessary to maintain the myocardium maximally responsive to insulin. Mechanical unloading increases myocardial glycogen concentration, thereby reducing the magnitude of insulin's stimulation of glycogen synthase and consequently the rate of incorporation of circulating glucose into glycogen.

Animals↗
PubMed1992

An experimental study of pituitary transplantations in rabbits.

Experimental pituitary transplantations were carried out between the New Zealand white and American chinchilla rabbits. These two kinds of experimental rabbits were of different genotypes. The grafts were transplanted underneath the median eminences of the recipients after hypophysectomy. The rabbits with the transplants were treated with cyclosporine (CsA) and prednisone for the first month. Blood samples were taken at regular intervals for the determinations of serum thyroxine, prolactin and luteinizing hormone. The results suggested that neonatal grafts could survive and function almost normally with the aid of CsA and prednisone, but not without them. The results also disclosed that the interrelationship between the pituitary graft and the host's hypothalamus could be established. Pituitary transplantation from adult rabbit donors failed even though the recipients had been treated with CsA and prednisone in our experiment.

Animals↗
PubMed1990

Superior cardiac hemodynamics of atrioventricular synchrony over rate responsive pacing at submaximal exercise: observations in activity sensing DDDR pacemakers.

The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist II). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage I at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 +/- 4 vs 81 +/- 3 beats/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 +/- 14 vs -2 +/- 7%; Stage I: 36 +/- 6 vs 16 +/- 7%; Stage II: 25 +/- 15 vs 10 +/- 8%; recovery: 26 +/- 12 vs 4 +/- 9%; P less than 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 +/- 6 vs 23 +/- 6% at an AV interval of 150 msec, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

[Effects of anisodamine on blood coagulation, fibrin and thrombosis in rabbits].

Anisodamine at dose of iv 10 and 20 mg/kg prolonged plasma prothrombin time, bleeding time and coagulation time, and showed positive reaction of plasma protamine paracoagulation test in conscious rabbits. The drug prolonged the thrombin time and reduced the contend of plasma fibrin. Anisodamine markedly inhibited blood platelet aggregation both in vitro and in vivo, dose-dependently. The extracorporeal thrombosis time was prolonged, the length and weight of thrombus was decreased after iv anisodamine 20 mg/kg. These results suggest that anisodamine has inhibitory action thrombosis and blood coagulation.

Animals↗
PubMed1989

[Experimental study of behavior and cerebral morphology of rat pups generated by fluorotic female rat].

In order to study the effects of fluoride on the central nervous system, 33-42-day old rat pups generated by three groups of female Wistar rats, which were given distilled water containing 0, 30 and 60 ppm NaF respectively beforehand as drinking water for 85 days, were used for behavior test and cerebral morphological examination. The results of behavior test showed that the latent period of pain reaction and that of conditioned reflex in the 30 ppm F and 60 ppm F groups were longer than that in the control group (P less than 0.05 or P less than 0.01). morphological examination of the pup brains showed that the nerve cell density of the 60 ppm F group was higher than that of the control group (P less than 0.05). Electronmicroscopically, mild degeneration of organelles of the nerve cells was observed in those brains of the 60 ppm F group.

Animals↗