Effect of diet and triiodothyronine on the activity of sn-glycerol-3-phosphate dehydrogenase and on the metabolism of glucose and pyruvate by adipose tissue of obese patients

Lipogenesis and the metabolism of sn-glycerol-3-phosphate were studied in 23 fat biopsies from eight grossly obese patients. The first biopsy was obtained after a minimum of 12 days on a 3500 cal diet, the second biopsy after 2 wk on a 900 cal diet, and the third biopsy after an additional 2 wk on 900 cal supplemented with thiiodothyronine, 250 mug/day.Oxygen consumption and respiratory quotient declined during caloric restriction. Oxygen consumption was restored to the initial level during treatment with triiodothyronine, and the respiratory quotient rose somewhat.Lipogenesis from glucose and pyruvate was demonstrated in fat obtained from the first biopsy but could not be detected in the other biopsies. The incorporation of radioactivity from pyruvate into fatty acids was stimulated by the addition of glucose. Insulin stimulated lipogenesis in pieces of fat from the first biopsy, but isolated fat cells were unaffected by insulin. After caloric restriction no effects of insulin could be detected. The activity of both the cytoplasmic and mitochondrial sn-glycerol-3-phosphate dehydrogenase in homogenates of adipose tissue declined with caloric restriction. Treatment with triiodothyronine enhanced the activity of the mitochondrial sn-glycerol-3-phosphate dehydrogenase but did not affect the cytoplasmic enzyme.

Effects of epinephrine on glucose transport and metabolism in adipose tissue of normal and hypothyroid rats

Epinephrine increases the oxidation of glucose in adipose tissue even when its lipolytic effects are markedly reduced or abolished by propranolol, nicotinic acid, ouabain, or thyroidectomy. In order to locate the site(s) at which epinephrine stimulates glucose utilization, we studied the effects of epinephrine on the oxidation of various metabolites of glucose. Epinephrine neither increased the production of (14)CO(2) from 1- or 3-(14)C-pyruvate nor affected pyruvate conversion to glyceride-glycerol. To assess the possibility that epinephrine might accelerate the entry of glucose into adipocytes, we studied the accumulation of the nonmetabolized sugar l-arabinose in the intracellular water of adipose tissue. Epinephrine increased arabinose penetration into adipocytes to a degree comparable with that caused by 0.1 mU/ml of insulin. Virtually identical results were obtained in tissues from thyroidectomized rats in which the lipolytic effects of epinephrine were significantly reduced. It is concluded that epinephrine increases glucose oxidation by promoting its entry into adipose tissue and that the effect is independent of lipolysis.

Lipogenesis from glucose and pyruvate in fat cells from genetically obese rats

Subcutaneous fat cells were isolated from genetically obese rats and from rats with obesity produced by hypothalamic lesions. Insulin did not augment the oxidation of fatty acids or their synthesis from glucose-1-(14)C or glucose-1-(3)H by fat cells from either group. Radioactivity from pyruvate-3-(14)C was incorporated into fatty acids to the same degree by fat cells from these two groups. The presence of 5 mm glucose in the incubation medium containing fat cells and pyruvate-3-(14)C or aspartate-3-(14)C stimulated the synthesis of fatty acids to a greater extent in cells of genetically obese rats. Fasting, in contrast, reduced the incorporation of radioactivity from pyruvate and glucose into fatty acids by fat cells from the genetically obese animals. In all experiments the fat cells from genetically obese rats converted more radioactivity into glyceride-glycerol relative to CO(2) than did fat cells from hypothalamic obese rats. Parabiosis between one thin and one genetically obese litter mate was performed in three pairs of rats without influencing growth of either rat. Thus in the present studies fat cells from genetically obese rats showed two differences from normal fat cells: they channeled more radioactivity from pyruvate into fatty acids in the presence of glucose, and they uniformly converted more radioactivity into glyceride-glycerol.

Increased sensitivity of the thyroid in iodine-depleted rats to the goitrogenic effects of thyrotropin

The present studies demonstrate that iodine depletion increases the sensitivity of the thyroid to the goitrogenic effects of thyrotropin. Iodine depletion was induced by feeding rats a low iodine diet containing propylthiouracil for 10-14 days before hypophysectomy. Accumulation of iodine in the thyroid after hypophysectomy was prevented by continuing the antithyroid drugs in the diet. Doses of thyrotropin as low as 3 mU/100 g of body weight per day produced significant thyroid enlargement in 3-7 days in iodine-depleted rats. Adding propylthiouracil or perchlorate to the diet during treatment with thyrotropin did not reduce or augment the goitrogenic response to thyrotropin in iodine-depleted rats. Increasing the level of circulating iodide also did not reduce the goitrogenic response to thyrotropin. The increased sensitivity of the iodine-depleted thyroid gland may provide an explanation for the development of thyroid enlargement without requiring an increased level of circulating thyrotropin.

Effects of epinephrine, corticotropin, and thyrotropin on lipolysis and glucose oxidation in rat adipose tissue

(Log dose)-response curves have been determined for lipolysis and for the conversion of glucose-(14)C to (14)CO(2) by adipose tissue from rats in the presence of epinephrine, corticotropin, and thyrotropin. The stimulatory effect of epinephrine on lipolysis was greater than that of corticotropin or thyrotropin. Lipolysis induced by epinephrine was inhibited by propranolol but only slightly by phenoxybenzamine, whereas lipolysis induced by corticotropin was inhibited by phenoxybenzamine to a much greater extent than by propranolol. Neither blocking drug had a pronounced effect on the response to thyrotropin. Epinephrine stimulated the oxidation of glucose-(14)C to CO(2) more than did either thyrotropin or corticotropin. Moreover, epinephrine stimulated the conversion of glucose-(14)C to CO(2) and fatty acids even when lipolysis was not increased. These studies indicate that epinephrine can affect glucose utilization independently of its effect on lipolysis.

Studies on lipolysis in human adipose cells

Epinephrine stimulated lipolysis and the uptake of oxygen by subcutaneous adipose cells of man. When glucose-(14)C was present in the medium, its utilization was not increased by epinephrine, although lipolysis was accelerated. Insulin did not reduce the production of fatty acids that had been stimulated by epinephrine. The combination of human growth hormone and cortisol stimulated the production of fatty acids by isolated human adipose cells to a lesser extent than epinephrine. When human growth hormone or cortisol was used singly, or when bovine growth hormone was added in combination with cortisol, no effect on fatty acid production was observed. Furthermore, an acetone-dried preparation of human pituitary glands, which was shown to stimulate lipolysis in rat adipose cells, had no effect on fatty acid formation in human adipose cells. This suggested that the human pituitary gland contained no more potent lipolytic agents than growth hormone and was supported by the lack of response of human adipose cells to purified corticotropin.

Rhythmic changes in renal function in the rat

Cold exposure causes rats to increase their urine output. This increase in urine output was found to occur in 5- to 8-day cycles with peak urine volumes three or more times the volumes prior to exposure to the cold. Cycles in urine volume occurred on a constant electrolyte intake and in animals receiving exogenous Pitressin. The peaks in urine volume were accompanied by a threefold increase in the variability of sodium excretion but not potassium excretion. The increase in urine volume which occurred at the same time in all rats in a group began at night and continued through the following day. These data have been discussed in the light of a possible mechanism controlling sodium intake with water intake and electrolyte excretion.

Distribution of urea, thiourea-C14 and sucrose-C14 in dog kidney during antidiuresis

The distribution of urea, thiourea-C14 and sucrose-C14 in the kidney and urine during antidiuresis has been investigated. An inverse relationship between the urine to papilla ratio and the papilla to cortex ratio for these three compounds has been demonstrated. For urea, the urine to papilla ratio is only 1.5, while the urea concentration in the papilla is 14 or more times that in the cortex. Studies with sucrose-C14 showed a urine to papilla ratio of 20 or more while the papilla sucrose-C14 concentration was only three to four times as high as the cortex. Thiourea-C14 behaved in a manner similar to urea, with high concentrations of isotope in the papilla and a urine to papilla ratio of 9. These results have been discussed in terms of the permeability of the collecting duct and the countercurrent exchanger function of medullary blood flow.

Freezing point depression of rat kidney slices during water diuresis and antidiuresis

The freezing point depression of slices of rat kidney removed during water diuresis or antidiuresis has been investigated with a microcryoscopic method. The osmotic pressure gradient in the inner medulla first demonstrated by Wirz has been confirmed. The inner medulla was found to be hypertonic to plasma during water diuresis. Hypotonic tubules were present throughout the cortex and outer stripe of the outer medulla.