Factors influencing nonspecific binding of glucocorticoids in myocardial tissue.

Myocardial slices from the left ventricle of cat hearts were incubated in Krebs-Henseleit buffer containing 10 mM glucose which were gassed with 95% O2 and 5% CO2. Tritiated dexamethasone (DEXA 0.171 MM) or methylprednisolone (MP 0.805 mM) was added under varying conditions of temperature, pH, and in the presence of various metabolic inhibitors. Glucocorticoid uptake by myocardial tissue was found to be temperature-dependent, plateauting after 60 min of incubation at 0.21 mumole of DEXA/g of tissue and 0.95 mumole of MP/g of tissue at 37 degrees. Steroid uptake was retarded about 50% at 0 degrees. Increasing the concentration of either steroid resulted in a linear increase in the uptake of that steroid. Incubation in the presence of metabolic or SH-inhibitors produced no significant changes in glucocorticoid uptake. Optimal glucocorticoid uptake occurred between pH 7.3-7.4. Thus, myocardial cells appear to be able to take up large quantities of glucocorticoids, but the uptake process does not appear to be energy-dependent.

Glucose and palmitate uptake in the myocardium of isolated hearts from adrenalectomized cats.

Hearts from chronically adrenalectomized (ADX) cats deprived of any steroid support for 9-12 days were isolated and perfused in a Langendorff apparatus at a constant pressure of 95 mm Hg. The perfusion medium was Krebs-Henseleit buffer with either 10 mM glucose or 0.4 mM palmitate complexed to 3 percent albumin. Labeled 14C substrate was used and the transient rate of glucose and palmitate uptake was measured. Oxygen consumption and [14C] palmitate incorporation into CO2, and heart lipids were also measured. ADX hearts showed an enhanced glucose uptake rate compared with controls, 65 +/- 11.3 mumoles/gm to 16.2 +/- 6. However, the qO2 was not significantly different from control hearts. Palmitate uptake, O2 consumption, and 14CO2 were significantly lower in ADX hearts perfused with fatty acid as the energy substrate. Fatty acid uptake decreased from 9.7 +/- 1.0 to 3.6 +/- 1.1 and lipid fractions in the heart showed significant decreases in [14C] palmitate incorporated into triglycerides (p less than 0.001) and monoglycerides (p less than 0.01). The ADX heart does not appear to have any impairment to glucose uptake but does show an impairment to fatty acid uptake. Because the heart uses lipid as the primary energy source, the impairment probably is not the primary factor responsible for cardiac failure in adrenal insufficiency because of its capability of using other available substrates for energy.

Myocardial substrate utilization in perfused hearts isolated from adrenalectomizedcats.

Isolated hearts form chronically adrenalectomized cats were perfused with Krebs-Henseleit buffer plus either glucose (10mM) or palmitate (0.4 mM) under various conditions of constant pressure and constant flow. Glucose uptake in adrenalectomizedhearts was not diminished from control values under conditions of constant pressure, constant flow, anoxia, or insulin stimulation. Palmatic acid uptake and oxygen consumption were significantly reduced (P less than 0.02) in adrenalectomized hearts. This diminished fatty acid utilization was also reflected in a significantly lower CO'2 production and incorporation of the palmitate into myocardial triglycerides. The decreased fatty acid uptake by adrenalectomized cat hearts may represent aserious defect in myocardial metabolism since lipids are the major energy substrate forthe heart. Whether the defect occurs in fatty acid transport or activation cannot beelucidated by this study. However, it is unlikely that this defect has a major contributory effect on the dysfunction of adrenalectomized hearts since the myocardium iscabable of using other energy substrates readily.