During a long-term study in the rat some enzyme activities were determined in plasma, lung, spleen and skeletal muscle. Twelve rats of each sex were investigated every 49 days from 35 until 1115 days of life. Lactate dehydrogenase in lung and spleen decreases; in muscle and plasma, however, the activity varies considerably. Malate dehydrogenase in the tissues remains nearly unchanged apart from distinct peaks in the first year of life; in plasma the activity takes an M-shaped course. In contrast to the changes of glutamate dehydrogenase in the tissues with a tendency to diminish, this enzyme increases in plasma during the lifetime. Aspartate aminotransferase activity in the tissues, except muscle, varies with a rhythmical behaviour, and in plasma shows a gradual increase. Alanine aminotransferase in lung and spleen has two activity peaks. In muscle this enzyme varies only slightly after a steep initial decrease. In plasma the activity has a tendency to rise. Creatine kinase in the tissues reveals several activity peaks. In plasma the activity course is U-shaped. Adenylate kinase in spleen and lung rises, whereas in muscle the activity varies considerably. The nearly identical decrease of alkaline phosphatase activity in the tissues during ageing is also reflected by a concomitant behaviour in plasma. Leucine arylamidase in lung and muscle both have a U-shaped characteristic, whereas in spleen the activity changes in a shorter period. In plasma, a rhythmical behaviour is apparent. Aldolase in plasma tripled during the observation period. Except for lactate dehydrogenase and aldolase, distinct sex-differences are observed in plasma. With progressive age the animals suffer increasingly from characteristic diseases, which beside experimental components have influenced the enzyme pattern. Enzyme activities in plasma and tissues show a complex pattern and are only of limited importance in understanding the ageing process.

Adenylate Kinase↗

PubMedDate not supplied

Release of enzymes from cells: transport and distribution within the extracellular space.

The distribution in the extracellular space of enzymes released from organ cells was investigated using three models: (1) comparison of enzyme activities in blood plasma and lymph of the ductus thoracicus (dog) and plasma and intestinal lymph (rat); (2) i.v. injection of heterologous, homologous and autologous enzymes in order to increase acutely the activities and to measure the rate constants for the distribution and elimination of the enzymes (rat); or (3) plasmapheresis in order to create an enzyme activity gradient from the interstitial space and to determine the rate constants for the reestablishment of the equilibrium between the extra and intravascular compartments (rat). The results suggest that the enzymes are mainly released into the interstitial fluid and transported via the lymph into the intravascular compartment. From there the enzymes diffuse back into the interstitial compartment and are eliminated by a yet unknown mechanism. Transport of enzymes across the capillary membranes in both directions depends on (1) the permeability of the capillary membranes, which varies from region to region and (2) the molecular seizes of the enzymes.

Animals↗