Elektrolytver�nderungen in tiefer Hypothermie

Effect of acetazolamide on early ischemic cerebral edema in gerbils

Acetazolamide was given in the early stage of ischemic cerebral edema produced by unilateral permanent carotid occlusion in gerbils. The animals were studied 1, 4, and 6 hours after ischemia. The tissues were examined for water and electrolyte concentrations and ischemic areas were visualized by 2,3,5-triphenyltetrazolium chloride (TTC) and H-E staining. Acetazolamide injected just after occlusion showed a positive effect in reducing edematous changes. Later administration of the drug had neither positive nor harmful effect on the ischemic brains. Thus, acetazolamide seems to be useful for cerebrovascular response studies in the early stage of a brain lesion.

Influence of glycogen content, temperature, and Euro Collins solution on membrane potential and sodium activity of superfused porcine liver slices

The influence of glycogen content, temperature, and Euro Collins (EC) solution on membrane potential (Vm) and intracellular sodium activity (aNai) were measured in cells of superfused porcine liver slices by means of double-barrelled ion-sensitive microelectrodes. Vm was -26.1mV in fasted pigs and -20.6mV after glucose feeding, when measured in HEPES-buffered solution (P less than 0.0001). aNai was not measurably affected by glucose feeding. During superfusion with Tyrode solution, lowering the temperature from 35.5 degrees C to 15.5 degrees C led to a fast Vm decrease of roughly 2mV followed by an increase of 1-3mV. At the same time, aNai increased from 12.8 to 18.2mM within 10 min. Superfusion with EC solution for 10 min caused comparable changes in fed and fasted pigs. Vm depolarized at either temperature by about 16mV. At 35.5 degrees C the initial aNai of 17.5mM was roughly halved, whereas at 15.5 degrees C it decreased from 21.0 to 14.3mM. The results suggest that the nutritional state markedly affects the electric properties of liver. However, the effect on membrane potential of high-potassium organ-protective solutions seems to be distinctly more pronounced. Moreover, cellular Na+ activity decreases in consequence of an extracellular Na+ reduction with protective solutions, which might be balanced to some extent by a simultaneous temperature decrease.

Hypothermia-induced reduction in the permeation of radiolabelled tracer substances across the blood-brain barrier

The permeability of the rat blood-brain barrier during different levels of hypothermia was examined using a new and more sensitive quantitative radiotracer technique. In contrast to the findings of previous studies, tracer permeation as measured here by the calculated cerebrovascular permeability-area product (PA), did not increase during hypothermia. Rather, rats maintained at specific temperatures between 30-16 degrees C (1 h) by contact surface cooling, displayed lowered permeation (PA) of i.v. injected 14C-sucrose, 125I-bovine serum albumin and 3H-alpha-amino-isobutyric acid in all brain regions examined. This effect was temperature-dependent and reversible on rewarming to normothermic temperature. Elevated plasma tracer concentration vs. time was characteristic of hypothermic rats except those cooled to 30 degrees C. That no elevation in plasma tracer accompanied alterations in tracer permeation at 30 degrees C, indicates hypothermic induced reductions in PA are independent of altered plasma tracer levels. Furthermore, the nature of alpha-amino-isobutyric acid to rapidly distribute to intracellular vs. extracellular sites suggests the effects of hypothermia seen here are due primarily to the condition of cerebrovascular membranes.

Brain edema during ischemia and after restoration of blood flow. Measurement of water, sodium, potassium content and plasma protein permeability

The left cerebral hemisphere of Mongolian gerbils was used to elucidate the mechanisms of brain edema which develop during cerebral ischemia and after restoration of cerebral blood flow following temporary ischemia. Water content was measured by the tissue-drying method. Sodium and potssium ion concentration was measured by flame photometry. Passage of 131I-albumin (RISA) from blood to the cerebral parenchyma was measured on a gamma scintillation counter. Our findings indicate that pure cytotoxic edema develops during ischemia and during a short period after restoration of cerebral blood flow. Vasogenic edema, which is accelerated by the leakage of plasma constitutents from blood due to blood-brain barrier damage, developed after restoration of the cerebral blood flow. After less than 1 hr of ischemia, restoration of the cerebral blood flow drastically reduced the degree of brain edema. However, restoration of the cerebral blood flow greatly worsened the brain edema following more than 3 hr of ischemia.