Biomedical subjects
Publications and source records attributed to W A Behrens.
The ascorbic acid content of brown adipose tissue increased 62% when rats underwent cold acclimation; however, the increase was 126% when rats living in the cold were fed a basal diet supplemented with 2% ascorbic acid. These findings suggest a role for ascorbic acid in this tissue during nonshivering thermogenesis.
The effect of high dietary ascorbic acid intake on the homeostasis of ascorbic acid and on the metabolism of catecholamine was studied in rats. In order to eliminate changes in serum levels due to stress, blood was obtained without anesthesia through implanted cannulas. Rats with a high intake of ascorbic acid (20 g/kg diet, for 7-9 weeks) had significantly higher levels of ascorbic acid in serum (83%), liver (28%), kidney (47%) and superior cervical ganglia (43%). The values were slightly, but not significantly higher in adrenal gland, brain and interscapular brown adipose tissue. However, no significant differences were observed in the levels of noradrenalin, adrenalin and dopamine in any of the tissues analyzed. Dopamine beta-hydroxylase activity was also unchanged. There was thus no evidence of an effect of high dietary intakes of ascorbic acid on the metabolism of catecholamines in the intact rat.
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Dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating) (EC 1.14.17.1) activity in serum of blood obtained by decapitation of white rats at 19, 20, and 21 days in utero, immediately after birth, and postnatally to 70 days, was measured. Noradrenaline (NA) and DBH in plasma from undisturbed, cannulated, postweaning rats were also assayed. During the last few days in utero and the first 2 postnatal days serum DBH activity tripled and then remained elevated during the suckling period. Upon weaning, serum DBH activity declined at first precipitously and then more slowly, until the adult level was reached around 70 days of age. This postweaning decrease in DBH activity was also observed with the cannulated animals. In contrast, plasma NA levels remained low and constant throughout the postweaning period. In suckling rats treated with 6-hydroxydopamine from 2 to 12 days of age, serum DBH activity decreased to less than half its initial value by day 8. It is suggested that the observed changes in serum DBH activity in fetal and postnatal rats reflect ontogenetic changes in sympathetic nerve terminals and that they are probably not correlated with release of NA.
Oxygen consumption and concentration of noradrenaline (NA) in arterial plasma have been measured in warm-acclimated (WA) and in cold-acclimated (CA) rats during exposure to cold and in barbital-sedated WA or CA rats receiving intravenous infusions of NA at various doses at room temperature. In WA and in CA rats in the cold, NA in plasma increased rapidly from a resting level of 0.1 to 0.2 ng/ml at thermoneutrality to values 5 to 10 times greater at -19 degrees C. The increases were directly related to the degree of cold exposure and were maintained throughout exposure. In barbital-sedated WA or CA rats infused with NA the plasma levels of NA which stimulated calorigenesis were approximately 10 times greater than those resulting from overflow of NA into the blood during intense cold exposure and were in the range found by others to be effective in stimulating O2 consumption in isolated brown adipocytes.
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Dopamine-beta-hydroxylase (DBH) (EC 1.14.17.1) activity is present in the interscapular brown adipose tissue (IBAT) as early as 2 days of age in the white rat. The specific and the total activities of this enzyme, as well as those of cytochrome oxidase (COX) (EC 1.9.3.1) in IBAT increase up to at least 20 days of age. Daily administration of 6-hydroxydopamine (6-OHDA) between the second and the twelfth day after birth does not significantly alter IBAT weight gain relative to untreated controls, but the increase in protein content with age is reduced to about half the normal value at the end of the treatment. The treatment with 6-OHDA also results in a drastic lowering of DBH specific and total activities, and a much smaller rate of increase of COX specific and total activities with age in IBAT compared with controls. These results provide additional evidence for a previously proposed role of sympathetic nervous system activity in the development of the thermogenic potential of IBAT in the newborn rat.
The pH optimum for rat serum dopamine beta-hydroxylase (DBH) (3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating)(EC 1.14.17.1) was 4.0 in acetate buffer; other requirements were as reported by others. DBH activity in serum of 20-day-old fetuses is slightly higher than in that of their mothers. Levels of the enzyme in blood a few hours after birth are almost five times greater than in the adult, remain high during the suckling period, then drop rapidly during the 4th week after birth to about three times the adult level, which is then slowly reached over the next few weeks. These fluctuations in serum DBH activity coincide with the period of intense development and maturation of the sympathetic nervous system. There was not significant effect of cold exposure on blood DBH activity when newborn, suckling, weanling or adult warm- and cold-acclimated rats were exposed to cold. Similarly, exposure to cold that elicited two- to three-fold increases in O2 consumption failed to increase DBH activity in thoracic duct lymph. Therefore serum and lymph DBH activities are not sensitive indices of sympathetic secretory activity in the intact rat.