Calculation of lipolysis and esterification from glycerol metabolism in rat adipose tissue

Pieces of epididymal fat pad from fed and 48-hr-fasted rats were incubated for various periods of time in Krebs-Ringer bicarbonate containing [1-(14)C]glycerol. The radioactive substrate taken up by the tissue increased linearly with time in both groups and was mainly converted to glyceride-glycerol and CO(2). The slopes of the regressions of (14)C-labeled glyceride-glycerol with time were not different between the groups, while those of (14)CO(2) were smaller in the fasted than in the fed animals. Because the radioactive glycerol in the medium is being continuously diluted with the glycerol coming out of the tissue, it is necessary to take account of this factor in calculating the actual amount of glycerol utilized by the tissue. The glycerol produced by the tissues is higher in the fasted than in the fed animals, and in both groups it increases hyperbolically with time. As negligible amounts of the (14)C-labeled glycerol taken up by the tissue recirculates to the medium, the rates of glycerol release (lipolysis), esterification, and oxidation to CO(2) were calculated.

Effects of hypo- and hyper-thyroidism on liver composition, blood glucose, ketone bodies and insulin in the male rat

1. Thyroidectomized rats injected daily with 0, 0.1, 2 or 25mug of l-thyroxine/100g body wt. were compared with intact controls. In plasma, the protein-bound iodine was decreased in the rats given the 0 or 0.1mug doses and increased in those given the 25mug dose. 2. Blood glucose decreased in those given 2mug and was augmented in those given 25mug, and ketone bodies were the same in all the groups. 3. Plasma insulin was lowest in the rats given the 0 or 0.1mug doses and was highest in those given the 2 or 25mug doses of thyroxine. 4. After 48h starvation, the decrease in blood glucose and increase in ketone bodies observed in all the groups was greatest in the group not supplemented with thyroxine. 5. Plasma insulin concentrations remained at the value for fed animals in the rats given the 25mug dose of thyroxine but decreased in the other groups. 6. In fed animals, concentrations of hepatic DNA P, citrate, total fatty acids and acetyl-CoA were similar in all the groups, and glycogen was low only in the rats given the 25mug dose of thyroxine. 7. After 48h starvation, liver DNA P, total fatty acids and acetyl-CoA increased in all the groups, except in the rats given the 25mug dose, where both total fatty acids and acetyl-CoA remained at the value for fed animals. Liver citrate did not change in the groups given the 0 or 25mug doses of thyroxine, but decreased in the other groups. 8. The results are discussed in relation to the regulation of intermediary metabolism in hypo- and hyper-thyroidism.

Thyroid function, plasma insulin, glucose and ketones and in vitro hepatic gluconeogenesis in rats under chronic low iodine intake

Weaning female rats were fed for 13–14 months with a low iodine diet (LID) and compared with age matched controls on KIO3 supplemented LID (C). At sacrifice the LID rats had large goitres, low plasma PBI and thyroidal 127I content, a rapid thyroidal-131I (*I) turnover and increased *MIT/*DIT and *T3/*T4 ratios. Body weights were slightly higher in LID and pituitary growth hormone like protein bands were the same in both groups. There were no differences between LID and C, whether fed or fasted for 48 h with regard to plasma insulin, glucose and ketone bodies. In vitro disposition of trace or 10−2 m alanine-U-14C by liver slices were the same as measured by 14C incorporation into CO2, glucose and lactic acid. The response of these parameters to fasting was normal: plasma insulin and glucose decreased and ketone bodies and in vitro gluconeogenesis increased. The lack of alteration in the intermediary metabolism of rats, sufficiently iodine deficient to develop goitre, has been interpreted as indicating either that: 1) thyroid hormones have no direct effect on the parameters of intermediary metabolism studied, or 2) there is enough hormone available to the tissues to keep a normal metabolism but not to suppress TSH secretion, thus suggesting different sensitivities to the hormone.

Carbohydrate metabolism in pregnancy. 8. Metabolism of adipose tissue isolated from fed and fasted pregnant rats during late gestation

The effects of late pregnancy on adipose tissue metabolism have been examined in fed and fasted rats. Lumbar fat was excised from 19-day pregnant and age-matched virgin rats which had been given unrestricted access to food ("fed") or fasted for 48 hr before sacrifice. In the fed state, adipose tissue from pregnant rats displayed an increased content of free fatty acids (FFA). This coincided with augmented cleavage of preformed glycerides during incubation in vitro as evidenced by greater net production of FFA and glycerol, and altered disposition of labeled glucose. The enhanced lipolysis was independent of the availability of glucose and was not accompanied by impaired responsiveness to the antilipolytic or to the lipogenic actions of added insulin. In the presence of glucose and albumin, esterification as well as lipolysis was greater in adipose tissue from pregnant than nongravid animals. All the differences were exaggerated by prior fasting. These properties of adipose tissue during late gestation have been ascribed to a primary activation of lipolysis rather than impaired esterification or resistance to insulin. It has been suggested that the hormones of pregnancy may be responsible. Although increased intake of food and heightened availability of insulin may offset the net lipolytic effects in the fed state, a heightened turnover of adipose stores is always present. Thus, the pregnant animal appears better poised to mobilize preformed fat whenever exogenous nutrients are withheld.

Carbohydrate metabolism in pregnancy. VI. Plasma fuels, insulin, liver composition, gluconeogenesis, and nitrogen metabolism during late gestation in the fed and fasted rat

The effects of late pregnancy on metabolic fuels, liver composition, gluconeogenesis, and nitrogen metabolism have been examined in fed and fasted rats. Plasma free fatty acid (FFA) and immunoreactive insulin (IRI) are greater and glucose and ketones are lower in fed 19-day pregnant than they are in agematched virgin rats. A 48 hr fast elicits greater increases in FFA and ketones and more profound reductions in glucose in the pregnant rats and obliterates the differences in IRI. Fetal weight is not modified by such fasting but maternal weight losses exceed that of the nongravid rats. Livers from rats 19 days pregnant contain more and larger hepatocytes. Per mumole hepatic deoxyribonucleic acid (DNA)-phosphorus, water and protein are more abundant, whereas glycogen is unaffected. Livers from fed pregnant rats contain more lipid phosphorus and less neutral lipid fatty acid. After a 48 hr fast, hepatic steatosis supervenes in gravid animals due to accumulated neutral fat. The contents of hepatic acetyl-coenzyme A (CoA) and citric acid are not different in fed pregnant and virgin rats but are greater in the pregnant rats after fasting. Formation of glucose-(14)C and glycogen-(14)C from administered pyruvate-(14)C are the same in fed pregnant and virgin rats, but greater in the pregnant ones after a 24 or 48 hr fast. Pregnancy does not affect creatinine excretion, and urinary urea is not different in fed pregnant, virgin, and postpartum animals. Contrariwise, more nitrogen, potassium, and phosphorus are excreted by the pregnant animals during a 2 day fast. The increment in urinary nitrogen is due largely to urea on the 1st day, whereas heightened ammonia accounts for half the increase on the 2nd and correlates with the enhanced ketonuria. Muscle catabolism, gluconeogenesis, and diversion to fat are activated more rapidly and to a greater degree when food is withheld during late gestation in the rat. These catabolic propensities are restrained in the fed state. The capacity for "accelerated starvation" may confer survival benefit upon an intermittently eating mother in the presence of a continuously feeding fetus.

Mechanism of goitorogenesis by very low doses of propylthiouracil and the role of iodine intake

The effects of the daily feeding of 6 μg of propylthiouracil1/rat for about two weeks on the thyroid of animals maintained on different levels of iodine intake (from 0.5–3.6 μg/day/100 g BW) have been investigated. We have confirmed previous observations by other authors (Yamada & Schichijo 1962; Greer et al. 1962) showing that very low doses of PTU increase thyroid weight in rats on a low iodine supply without necessarily decreasing their rather low plasma PBI or their high thyroidal 131I uptake, and that the same doses no longer have an effect on thyroid weight if the iodine intake is raised. In the present experiments this occurred when the iodine intake was raised to about 1.2–1.3 μg/day/100 g BW. As shown here, it is unlikely that these low doses of PTU block synthesis of the thyroid hormones. They do, however, slightly inhibit the extrathyroidal deiodination of T4 and they probably trigger thyrotrophin (TSH) release from the pituitary gland. The present findings are compatible with the view that very small doses of PTU can be goitrogenic if the rats are on an iodine intake which is barely adequate for normal peripheral requirements, because these are increased chronically, even if slightly. Because of the low iodine stores the thyroid would then be unable to compensate for these increased hormone requirements. Even a small increase of available iodine may avoid this situation so that the effects of the low PTU doses are no longer detectable either in the plasma TSH activity or in the thyroid weight. The low PTU doses used here appear to hasten and aggravate a situation which would eventually develop from a more prolonged or a more severe degree of iodine deficiency only. The experimental situation induced by these low PTU doses might serve as an interesting model system for the study of simple goitre in areas in which iodine deficiency is not too extreme.