Plasma Corticosterone and Cardiac Glycogen Levels in Rats after Exercise

Abstract

Various physical conditions such as fasting (1-3), hypoxia (I), and exercise (2, 4) produce changes in myocardial glycogen concentrations that are superimposed upon the normal diurnal fluctuation of glycogen levels ( 5 ) . The mechanisms by which these physiological conditions alter cardiac glycogen are not known. Although not all glycogen changes are dependent on the function of the adrenal glands (3, 6 ) , glucocorticoids have been implicated as one regulatory substance of cardiac glycogen (6-8). The purpose of our study was to verify or dispel the proposed cause and effect relationship between glucocorticoid release and myocardial glycogen changes associated with physical exertion.Methods. Male adult Wistar strain rats were used in all the experiments and twothirds of the rats were bilaterally adrenalectomized under Brevital anesthesia. The completeness of the adrenalectomies was verified by comparing plasma glucocorticoid levels in the adrenalectomized rats with those of hypophysectomized rats. All rats were fed ad lib. and the adrenalectomized rats were maintained on 0.9 % NaCl drinking solution. Sham operated animals were used as controls. Half of the adrenalectomized rats were given dexamethasone phosphate, a synthetic glucocorticoid, intraperitoneally 20 pg twice daily.One week postoperation, rats were stressed by 15 min of swimming and then sacrificed at various times following the exercise. The animals were sacrificed with Brevital anesthesia since decapitation produces low glycogen levels (4). The thorax of each anesthetized rat was opened, the heart was removed rapidly (within 5-10 sec), and the resulting pool of blood in the thoracic cavity collected in a syringe. Total glycogen was extracted from whole hearts (9) and quantitatively determined by the anthrone method (10, 11). Plasma glucocorticoids were determined by the fluorescence procedure of Guillemin et al. (12). Data were analyzed by the analysis of variance and Duncan's multiple-range test under consultation with the department of Biometry.Results. Figure 1 shows the myocardial glycogen levels before and at various times following 15 min of swimming in control, adrenalectomized, and dexamethasone treated-adrenalectomized rats. The degree of glycogen depletion was the same in sham operated and adrenalectomized rats; however, the glycogen recovery process was altered by adrenalectomy with glycogen values being significantly lower in the adrenalectomized rats 4 hr following the exercise. Dexamethasone treatment significantly elevated initial myocardial glycogen in adrenalectomized rats and enhanced the recovery of glycogen to levels above that observed in the controls. The magnitude of glycogen depletion during exercise in these rats was greater than in controls or adrenalectomized rats perhaps due to the availability of more endogenous glycogen. Figure 2 shows plasma glucocorticoid levels for the same animals used in determining the glycogen data. Pre-exercise glucocorticoid levels were higher than reported for nonstressed levels in male rats (...

Preliminary Data Regarding Decreased Catalase Specific Activity in the Tears as a Result of Environmental Stress

“…Moreover, physical stress is another element that induces oxidative damage, while swimming [33] along with running [34,35] represent stress factors in rats, as proved by the presence of elevated specific stress indicators, such as plasma glucocorticoids and catecholamines. In this way, Brant and his colleagues also demonstrated in their study that running decreases the plasma rates of vitamin A, a known antioxidant factor [36], which might indicate the presence of oxidative stress.…”

Plasma corticosterone concentrations and in vitro adrenal secretion rates in aging rats: effect of physical training and acute swimming

“…In nontrained, adult male rats, acute bouts of running or swimming resulted in a doubling of plasma corticosterone concentrations (Dieter et 1972;Poland et ^., 1975). Light exercise did not change the basal Cortisol secretion rate in untrained dogs, as measured in adrenal venous effluent blood (Suzuki et , 1967).…”