Reduced stretch-reflex sensitivity after exhausting stretch-shortening cycle exercise

The stretch-shortening cycle (SSC) is an effective and natural form of muscle function but, when repeated with sufficient intensity or duration, it may lead to muscle damage and functional defects. A reduced tolerance to impact has been reported, which may be partly attributed to a reduced stretch-reflex potentiation. The aim of the present study was to examine the influence of SSC-induced metabolic fatigue and muscle damage on the efficacy of stretch reflexes, as judged by the electromyograph (EMG) response of two shank muscles (lateral gastrocnemius LG, soleus SOL) to controlled ramp stretches. These EMG responses were recorded before and immediately after exhausting SSC-type leg exercise and 2 h, 2 days and 4 days later. Serum concentrations of creatine kinase ([CK]), myoglobin and lactate were measured repetitively along the protocol. Two maximal vertical drop jumps and counter-movement jumps were performed after each reflex test. The exhausting SSC-type exercise induced an immediate reduction (P < 0.05) with a delayed short-term recovery of the LG peak-to-peak reflex amplitude. This was not accompanied by significant changes in the reflex latency. The drop jump performance remained slightly but significantly reduced (P < 0.05) until the 2nd day postexercise. Peak [CK] appeared for all the subjects on the 2nd day, suggesting the presence of muscle damage. The increase in [CK] between the 2nd h and the 2nd day postexercise was found to be negatively related (P < 0.001) to the relative changes in the drop jump height. Furthermore, a significant relationship (P < 0.05) was found between recovery of the stretch reflex in LG and the decrease of [CK] between the 2nd and the 4th day. These findings support the hypothesis of a reduced stretch-reflex sensitivity. While the exact mechanisms of the reflex inhibition remain unclear, it is emphasized that the delayed recovery of the reflex sensitivity could have resulted from the progressive inflammation that develops in cases of muscle damage.     

Diurnal variation in plasma ethanol levels of TO and CBA mice on chronic ethanol drinking or ethanol liquid diet schedules

Data accumulated from epidemiological observations, intervention trials and studies on experimental animals provide a growing body of evidence of the influence of various dietary components on blood pressure. Dietary sodium, usually taken in the form of sodium chloride (common salt), is positively associated with blood pressure, and in many hypertensive patients reduction in sodium intake lowers blood pressure. On the other hand, in certain patients potassium, calcium and magnesium may be protective electrolytes against hypertension. Dietary fats, especially n-3 polyunsaturated fatty acids, may also influence blood pressure, whereas the possible role of other macronutrients, such as proteins and carbohydrates, or vitamins in the regulation of blood pressure is less well understood. Occasional ingestion of coffee transiently increases blood pressure, but the effects of habitual coffee consumption are controversial. Excessive use of alcohol on a regular basis has been associated with elevated blood pressure. It has also been shown in case reports that large amounts of liquorice lead to the development of hypertension. Thus, with appropriate dietary modifications, it is possible to prevent the development of high blood pressure and to treat hypertensive patients with fewer drugs and with lower doses. In some patients antihypertensive medication may not be at all necessary.     

A study of objective functions for organs with parallel and serial architecture

A hemodynamics model of cerebral Willis circulation is proposed. The model consists of the compensation of blood flow as well as the compliance, resistance and inductance of arteries. The impedances of carotid and vertebral arteries are obtained by solving the govern equations. The theoretical impedances correspond well with the experimental results. The simulating results demonstrate that the alteration of the arterial dynamic parameters influences not only the ipsilateral impedance but also the contralateral arterial system. These conclusions suggest that the carotid or vertebral impedance is not suitable for describing the behaviour of its own arterial system, because the impedance is also influenced by the other arterial system and blood pressure.     

Integral kinetics of multisubstrate enzyme reactions. Criteria of kinetic behavior and characteristic coordinates for solution of direct and reverse problems

General schemes of unbranched multisubstrate enzyme reactions associated with enzyme inactivation during catalysis are analyzed. Equations of integral kinetics at constant substrate concentrations and at depletion in one of the substrate are presented. Experimental dose-response curve characterized by additivity of some enzyme intermediates (absorption spectra, fluorescence, EPR, etc.) are theoretically analyzed. Also rapid equilibrium at certain stages of enzyme reaction is considered. The interrelationship of enzyme intermediates is a criterion of the kinetic behavior of enzyme reaction mechanism. New coordinates are suggested for the analysis of the integral kinetics of self-inactivating enzymes. Results of the analysis are used for interpretation of the data on arachidonic cascade enzymes.