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A A Kassenaar

Publications and source records attributed to A A Kassenaar.

At least 19 recordsLinked to original sources
PubMed1985

Coupled diminished energy turnover and phosphorylase a formation in contracting hypothyroid rat muscle.

Hypothyroidism leads to a diminished phosphorylase a formation and a reduction in both glycogen breakdown and lactate production during tetanic stimulation of fast-twitch skeletal muscle (mixed type). Phosphorylase kinase activity is almost 50% lower in the hypothyroid (Tx) group, and the possibility that this might explain the reduction in phosphorylase a formation is discussed. In both the Tx group and the euthyroid (C) group the reconversion of phosphorylase a to b correlates well with a decrease in the energy cost for contraction.

Animals↗
PubMed1984

The influence of hypothyroidism on the adrenergic stimulation of glycogenolysis in perfused rat liver.

The ability of noradrenaline (1 microM), phenylephrine (10 microM), and isoproterenol (1 microM) to stimulate glycogenolysis in euthyroid and hypothyroid perfused rat livers was investigated. It was found that hypothyroidism severely impaired alpha-receptor-mediated (noradrenaline, phenylephrine) glucose release. The initial Ca2+ efflux and K+ influx induced by these agonists in the euthyroid control group were almost totally absent in the hypothyroid group, while glycogen phosphorylase a activity in the hypothyroid rat livers was markedly lower than in the controls after infusing noradrenaline for 1 min. Diminished CA2+ efflux (and possibly diminished K+ influx) is likely to play a role in the large impairment in the action of noradrenaline or phenylephrine on glycogenolysis in the perfused hypothyroid rat liver. After prolonged stimulation (15 min) with noradrenaline, however, the phosphorylase a activity in the hypothyroid and euthyroid groups did not differ significantly. This was accompanied by Ca2+ influx in the hypothyroid livers, probably facilitated by a beta-adrenergic effect of noradrenaline in this group. Hypothyroidism potentiated the effect of isoproterenol on glycogenolysis. The glucose 6-phosphate content in the hypothyroid rat livers was markedly higher than in the euthyroid group after stimulation by noradrenaline or isoproterenol.

Animals↗
PubMed1983

The influence of the thyroid state on energy turnover during tetanic stimulation in the fast-twitch (mixed type) muscle of rats.

The effects of thyroid hormones on energy metabolism and force development during tetanic stimulation of fast-twitch skeletal muscle (mixed type) were studied. Hypothyroid, euthyroid, and hyperthyroid (ten days of daily administration of 15 micrograms T3/100 gm body weight) rats showed the same tension-time integral (force x time) under tetanic stimulation. The ATP turnover rate was significantly lower in the hypothyroid group than in the euthyroid and hyperthyroid animals. The ratio difference in the energy/force ratio in the Tx group cannot be ascribed to differences in internal work. Lactate production was diminished in the hypothyroid group; this was probably not the result of a block in glycogenolysis but rather was a reflection of more economic energy expenditure during contraction. After tetanic stimulation, the phosphorylation potential ([ATP]/[ADP]f[Pi]) was decreased most strongly in the hyperthyroid group, mainly because of the higher accumulation of Pi compared with the other groups, which suggests that during the recovery phase the stimulation of oxidative phosphorylation is greater in this group.

Adenosine Diphosphate↗
PubMed1983

Force development and metabolism in perfused skeletal muscle of euthyroid and hyperthyroid rats.

The effect of experimental hyperthyroidism on skeletal muscle metabolism during force development and subsequent recovery was studied in a perfused preparation of the gastrocnemius and plantaris muscle of rats. After equilibration, the muscles were stimulated for 15 minutes at 1 Hz, and were allowed to recover during the following 15 minutes. The basal oxygen consumption of the skeletal muscle preparation was increased by 40% in the hyperthyroid rats as compared with euthyroid rats. The results show that: 1. Active force at 1 Hz was significantly reduced in the hyperthyroid rats compared with euthyroid rats, but the decay of force was similar in the two groups. 2. The increase in oxygen and glucose consumption and in lactate production during stimulation of the muscles was equal in hyperthyroid and euthyroid rats, but during recovery, oxygen consumption was significantly higher in the hyperthyroid than in euthyroid rats. 3. The increase in ATP turnover during force development and recovery (calculated from changes in O2 uptake, lactate production, and the breakdown of creatine-phosphate) in relation to the sum of force was significantly increased in the hyperthyroid state.

Adenosine Triphosphate↗
PubMed1981

Thyroid hormone-catecholamine interrelationships during exposure to cold.

Basal plasma levels for adrenalin (A), noradrenalin (NA), L-triiodothyronine (T3), and L-thyroxine (T4) were determined in rats with a chronically inserted catheter. The experiments described in this report were started 3 days after the surgical procedure when T3 and T4 levels had returned to normal. Basal levels for the catecholamines were reached already 4 h after the operation. The T3/T4 ratio in plasma was significantly increased after 3, 7, and 14 days in rats kept at 4 degrees C and the same holds for the iodide in the 24-h urine after 7 and 14 days at 4 degrees C. The venous NA plasma concentration was increased 6- to 12-fold during the same period of exposure to cold, whereas the A concentration remained at the basal level. During infusion of NA at 23 degrees C the T3/T4 ratio in plasma was significantly increased after 7 days compared to pair-fed controls, and the same holds for the iodide excretion in the 24-h urine. This paper presents further evidence for a role of the sympathetic nervous system on T4 metabolism in rats at resting conditions.

Animals↗
PubMed1981

Force development and metabolism in skeletal muscle of euthyroid and hypothyroid rats.

The effects of thyroid hormone depletion on skeletal muscle metabolism in relation to force development were studied. For this purpose, the triceps surae muscles were perfused and stimulated at 5 Hz. The basal oxygen consumption of the skeletal muscle preparation was 50% lower in hypothyroid rats as compared with euthyroid rats. The results show that: 1. Active force development was the same in euthyroid and hypothyroid rats during 30 min of stimulation. 2. The increase in oxygen consumption during contraction was twice as high in the euthyroid group compared with the hypothyroid group. 3. Lactate release and glucose consumption were considerably high in the euthyroid group than in the hypothyroid group during the last 15 min of stimulation. The data show that force development is not impaired in hypothyroid rats but, on the contrary, indicate that the contraction process proceeds more economically in hypothyroid rats than in euthyroid rats.

Animals↗
PubMed1981

The disappearance of L-thyroxine and triiodothyronine from plasma and red and white skeletal muscle after administration of one sc dose of L-thyroxine to hyperthyroid and euthyroid rats.

Rats were made hyperthyroid by repeated sc injections of L-thyroxine (T4) in a two-week period. At several time-points after the last injection, the triiodothyronine (T3) and T4 concentrations in plasma and red and white skeletal muscle were determined by a radioimmunoassay. This was done to investigate the relationship between the change in thyroid-hormone concentration in plasma and muscle and to see whether this change was similar in both muscle types. The results show that: 1. Information about the T3 and T4 concentrations in the muscles of the hyperthyroid rats can only be obtained by direct measurement in the muscles and cannot be gathered from the plasma-T3 concentration at any time-point or from below-normal plasma-T4 concentrations. 2. In hyperthyroid rats T4 and T3 are cleared more rapidly from the plasma than from the skeletal muscle. 3. A proportionally higher T3 concentrations is present in the red compared with the white skeletal muscle of hyperthyroid rats.

Animals↗
PubMed1980

Involvement of adrenergic receptors in skeletal muscle metabolism of the cold-adapted rat.

Hind-limb perfusion was used to investigate alterations of alpha and beta receptor-mediated metabolic effects in cold-adapted (CA) rats. The response to beta receptor stimulation by isoproterenol in the isolated hind-limbs of CA rats was slightly diminished. Oxygen consumption and lactate production were reduced in CA rats after beta receptor stimulation. Noradrenalin infusion caused less vasoconstriction in CA rats than in the controls (CO). Desensitization of alpha and beta receptors due to chronic sympathetic overstimulation may be the underlying cause of these observations. Compared with the controls, metabolism was enhanced in perfused hind-limbs of CA rats with an active nervous system. Decreased vascular resistance due to the lower perfusion pressure in CA rats might contribute to this increased metabolism.

Adaptation, Physiological↗
PubMed1979

A methodological study in measuring T3 and T4 concentration in red and white skeletal muscle and plasma of euthyroid rats.

T3 and T4 concentrations were determined in plasma and red and white skeletal muscle of the rat. Because of the small tissue samples (+/- 300 mg), the ultra-sensitive Wick radioimmunoassay (RIA) for serum was adapted for determination in ethanol extracts. The dilution curves of the plasma and tissue extracts showed excellent parallelism with the standard curves for both T3 and T4. The mean T4 level found in female rats (n = 6) was 22.6 +/- 5.2 ng/ml in plasma and did not differ significantly between red (1.85 +/- 0.28 ng/g) and white (1.90 +/- 0.25 ng/g) skeletal muscle. The mean T3 level in 11 normal female rats was 0.629 +/- 0.0098 ng/ml in the plasma and was significantly higher in the red muscle (2.07 +/- 0.26 ng/g) than in the white muscle (1.65 +/- 0.20 ng/g). The higher T3 levels found in the red muscle as compared with the white muscle may help to elucidate the different responsiveness of these muscle types observed in altered thyroid states.

Animals↗
PubMed1979

Studies on the origin of altered thyroid hormone levels in the blood of rats during cold exposure. II. Effect of propranolol and chemical sympathectomy.

The effect of sympathetic activity on T4 and T3 levels in cold-exposed rats was investigated. Administration of the highest dose of propranolol (2 mg/100 g b.w.) twice daily during 4 days decreased T4 and T3 concentrations in plasma of rats living at 23 degrees C (T4 from 46.4 +/- 2.6 to 25.8 +/- 5.3 nmol/l and T3 from 1.08 +/- 0.6 to 0.82 +/- 0.12 nmol/l). No significant effect on T4 and T3 levels (49.0 +/- 11.6 and 1.48 +/- 0.16 n/mol, respectively) after the administration of the same dose regimen of propranolol was observed in rats exposed to cold for 4 weeks. T4 and T3 levels in rats exposed to cold for 4 weeks were not significantly altered 1 week after sympathectomy, while remaining in the cold. However, chemical sympathectomy before cold exposure delayed the cold induced T3 elevation occurring during the first week of cold exposure (controls: from 1.16 +/- 0.19 to 1.44 +/- 0.29 nmol/l; sympathectomized rats: from 1.07 +/- 0.12 to 1.17 +/- 0.22 nmol/l). After 2 weeks of cold exposure the T3 levels of controls and sympathectomized rats were not significantly different (controls: 1.45 +/- 0.12 nmol/l, sympathectomized rats: 1.38 +/- 0.15 nmol/l). No effect of sympathectomy was observed on T4 levels. These experiments show that the role of sympathetic activity in increasing T3 is not clear during cold exposure. They provide some evidence that sympathetic activity may play a role in the initiation of the process leading to increased T3 plasma levels during cold exposure.

Adaptation, Physiological↗
PubMed1979

Effect of iodine intake and food consumption.

Rats were exposed to cold (4 degrees C) for 1 and 4 weeks. The T4 plasma concentrations initially declined (24.5 +/- 7.7 nmol/l) after 1 week but returned to normal levels after 4 weeks (52.9 +/- 14.2 nmol/l). The T3 concentrations were elevated after both 1 and 4 weeks at 4 degrees C (1.31 +/- 0.21 and 1.38 +/- 0.12 nmol/l, respectively). Control values (23 degrees C) for T4 were 42.6 +/- 10.3 and for T3 1.11 +/- 0.13 nmol/l. Addition of 0.015 g KI/l to the drinking water prevented the T4 decrease in plasma after 1 week of cold exposure. No effect of iodide was observed at 23 degrees C. The suppletion of KI did not change pattern of T3 increase after cold exposure. After 4 weeks of cold exposure the T4 levels of the iodide-supplemented animals did not differ from the non-sulemented group. No evidence was found that increased food intake is a contributory factor in the development leading to increased T3 plasma levels during cold exposure.

Adaptation, Physiological↗
PubMed1978

Effects of experimental hypothyroidism on skeletal muscle metabolism in the rat.

Hind-limb perfusion was used to study the effect of thyroidectomy on some metabolic parameters in the skeletal muscle of the rat. A week after thyroidectomy obtained by one dose of 3/4 mCi 131I, neither T4 nor T3 was detected in the blood. Lactate production and glycerol production were already decreased a week after the treatment and reached a base level at two weeks. At that time, the oxygen consumption was significantly lower (70% of initial level) than in the control animals and decreased further in the third week to nearly 50% of the control level. Glucose consumption and alanine release were decreased three weeks after thyroidectomy. One dose of T3 (10 microgram/100 g b. w.), administered to animals two weeks after the injection of 131I, restored the oxygen consumption, lactate production, and glycerol production to normal levels in 24 h. After 48 h, the glucose consumption was normal. Glycerol production was already significantly increased 6 h after T3 injection in animals one week after thyroidectomy, and in another group of animals two weeks after thyroidectomy. Apparently the diminished oxygen consumption in the latter group does not retard the lipolytic response to T3. No direct relationship could be found between the activity of lipolytic process and the thyroid hormone controlled oxygen consumption.

Alanine↗
PubMed1977

Influence of experimental hyperthyroidism on skeletal muscle metabolism in the rat.

In this study hind-limb perfusion was used to investigate the influence of thyroid hormones on some metabolic parameters in the skeletal muscle of the rat. Daily injection of 20 microng L-thyroxine (T4) per 100 g b. w. for a week caused a 25% increase in oxygen consumption. Further enlargement of the T4 dose had little additive effect. In the dose range 20--80 microng T4/100g b.w., no important changes occurred in lactate production or glucose consumption. Only at the highest T4 dose did the glucose consumption increase significantly. The most profound effect of T4 was on lipolysis. A daily dose of 20 microng T4/100 g b. w. gave a doubling of glycerol production rate, the maximum occuring at a dose of 40 microng T4/100 g b. w. Inactivation of the nervous system was without influence on the T4-induced increase in oxygen consumption. However, the T4-induced elevation of lipolysis disappeared after abolition of the nervous activity. This raises the possibility that the T4 effect on lipolysis in skeletal muscle is a potentiation of catecholamine effects. The T4-induced oxygen consumption increase might be dependent not on the lipolytic process but rather on other energy-consuming cell processes.

Animals↗