Cold-induced thermogenesis in hypothyroid rats.

Hypothyroidism was induced in adult rats by oral administration of methimazole. Euthyroid and hypothyroid rats were maintained at 23 degrees C or exposed at 6 degrees C for 3 weeks. Both euthyroid and hypothyroid rats maintained at 23 degrees C had similar interscapular brown adipose tissue (BAT) composition and thermogenic activity. Cold-exposed hypothyroid rats showed the same interscapular BAT mass and gross tissue composition as cold-exposed euthyroid animals, but the interscapular BAT of cold-exposed hypothyroid rats did not show the characteristic increase in GDP binding, and the increase in mitochondrial mass was lower than in euthyroid rats. From these results we conclude that thyroid hormones do not influence BAT significantly when thermogenic requirements are moderate, but they participate in the trophic response of the tissue when thermogenic requirements are intense. This thyroid hormone participation in the BAT trophic response occurs at the mitochondrial level, both in quantitative (mitochondrial mass) and qualitative (GDP-binding) aspects.

Inhibition of diet-induced thermogenesis during pregnancy in the rat.

Both virgin and pregnant rats were maintained at two different ambient temperatures (28 degrees C and 10 degrees C) for 19 days. Virgin rats maintained their daily food intake and body weight at both temperatures. At 28 degrees C pregnant rats showed a greater daily food intake and body weight than virgin ones and their brown adipose tissue suffered regressive changes in composition when compared with brown fat of virgin rats. At 10 degrees C the increases in daily food intake and body weight of pregnant rats took place from day 15-16 of pregnancy onward and foetuses taken from these pregnant rats were smaller than those taken from pregnant rats at 28 degrees C. It is concluded that pregnant rats at thermoneutrality, although hyperphagic, do not show diet-induced thermogenesis. However, it is proposed that pregnant rats in the cold may show BAT cold-induced thermogenesis.

Brown adipose tissue thermogenesis in T3-treated rats.

T4 treatment results in an inactivation of brown adipose tissue (BAT) which has been attributed to a reduced need of thermoregulatory heat production. Since T3 formation in brown adipocytes is governed by a type II T4 5'-deiodinase which is inhibited by T4, we analyzed the possibility that results obtained by T4 treatment were due to a lack of T3 in the tissue. Hyperthyroidism was induced in adult rats by administration of T3 (50 micrograms/kg body weight daily s.c.). Euthyroid and hyperthyroid rats were maintained at 23 degrees C or exposed at 6 degrees C for 3 weeks. Hyperthyroid rats at 23 degrees C showed an increase in BAT mass and in DNA and total lipids contents; however, BAT thermogenic activity was depressed. BAT from cold-exposed hyperthyroid rats showed the same mass and DNA content than at 23 degrees C, but it showed an increase in thermogenic activity, this increase being lower than in cold-exposed euthyroid rats. We conclude that high levels of T3 in BAT do not stimulate the thermogenic activity of the tissue. On the contrary, they inhibit it in response to lower requirements of facultative thermogenesis, both at 23 degrees C and at 6 degrees C.

Cold acclimation in food-restricted rats.

Food intake, body weight and brown adipose tissue (BAT) mass and composition of rats exposed at 6 degrees C either with food ad libitum or food-restricted were compared with those of rats in the thermoneutral zone, with food ad libitum. Cold acclimation with food ad libitum increases food intake and prevents body weight gains. IBAT (interscapular BAT) increases its mass and changes its composition after 3 weeks of cold exposure. Cold acclimation with food restriction produces a progressive decrease in body weight. IBAT mass increases after 3 weeks but changes in composition occur sooner. It is concluded that the overfeeding that accompanies cold acclimation is not necessary for non-shivering thermogenesis in BAT.

Biliar elimination of histamine and its metabolites in guinea-pigs.

1. Bile of guinea-pigs who have received [14C]-histamine contains 14C. 2. Both sexes eliminate in bile about 3.5% of the 14C administered. 3. Histamine metabolites in bile are mainly methylimidazolacetic acid and imidazolacetic acid and its riboside. 4. Acetylhistamine is present in bile. 5. Male bile contains more free histamine and methylhistamine than that of females.

Cold-induced and diet-induced thermogenesis in progesterone-treated rats.

Both cold-acclimated rats and rats at thermoneutrality received 1.5 mg/day of progesterone over a period of 15 days by means of two subcutaneously implanted Silastic capsules. Progesterone treatment increased total food intake and body mass gain in both groups of treated animals when compared with their controls at the same ambient temperature. However, the interscapular brown adipose tissue (BAT) of the treated rats showed the same thermogenic activity (assessed by GDP-binding), mass and gross composition as that of their respective controls. If it is assumed that enhanced food intake is the physiological drive for diet-induced thermogenesis, it could be concluded that progesterone inhibits diet-induced thermogenesis at thermoneutrality, but has no effect in cold-induced thermogenesis. However, if the physiological drive for diet-induced thermogenesis is not enhanced food intake, but an imbalance in the diet, then given that the same diet was offered to all animals throughout the experimental period, it could be that progesterone does not affect BAT, either at thermoneutrality or in the cold.

Effects of thyroxine and 3,5,3'-triiodothyronine in brown adipose tissue of rats.

Rats of both sexes were either cold acclimated (6 +/- 1 degree C) or treated with thyroxine (T4) or 3,5,3'-triiodothyronine (T3) (500 micrograms/kg body wt daily s.c. for 3 weeks). Wet weight, total proteins, lipids and nucleic acids in the interscapular brown adipose tissue (IBAT) were measured. Values obtained with T4 treatment were similar to those obtained with T3 treatment. T3 is the main thyroidal hormone in the rat and it is formed from T4 deiodination in liver and kidney. As T4-treated rats have not received T3 directly and its IBAT has a similar composition to that of T3-treated rats, it is concluded that peripheral T4 deiodination is governed by the plasma T4 levels. Total proteins and DNA content were similar in cold-acclimated and T3- or T4-treated rats, which is interpreted as thyroidal hormones having an action at these levels.

Inactivation of brown adipose tissue thermogenesis by oestradiol treatment in cold-acclimated rats.

Both cold-acclimated female rats and rats at thermoneutrality received 0.15-0.20 mg daily of 17 beta-oestradiol over 15 days via a Silastic capsule implanted subcutaneously. Controls received empty implants. Comparison between the oestradiol-treated animals and the untreated controls revealed that at thermoneutrality, oestradiol treatment decreased food intake and body weight gain, but did not affect brown adipose tissue (BAT) thermogenesis and composition. By contrast, in cold-acclimated rats, oestradiol treatment did not modify food intake or body weight gain, but it decreased BAT thermogenesis. It is concluded that the effects of oestradiol treatment on BAT depend on the activity of the tissue, i.e. it has no effect on BAT when the tissue is thermogenically inactive, but it decreases cold-induced BAT thermogenesis. It is suggested that oestradiol could be the hormonal factor responsible for the previously observed inactivation of BAT thermogenesis during pregnancy in cold-acclimated rats.

Hematology and blood chemistry of macaws, Ara rubrogenys.

1. The hematology and blood chemistry of 10 captive adult Ara rubrogenys is described. 2. They showed 3,650,000 erythrocytes/mm3, a hematocrit of 49.9% and a blood hemoglobin content of 15.2 g/100 ml. 3. Leukocyte number was 10,000 cells/mm3, the differential counts being 42.2% heterophils, 0.8% eosinophils, 2.4% basophils, 49.9% lymphocytes and 4.5% monocytes. 4. The number of thrombocytes was 21,800 cells/mm3. 5. Plasma composition was (mg/100 ml): glucose 295; triglycerides 102; cholesterol 166; urea 5.8; uric acid 5; creatinine 0.3; bilirubin was not detected and total protein concentration was 3.2 g/100 ml. Enzymatic activities were (units/1): GOT 188; GPT 10 and alkaline phosphatase 315.

Brown adipose tissue thermogenesis in testosterone-treated rats.

The participation of sexual hormones in body weight regulation is partly accomplished by altering food intake. Nonetheless, female sexual hormones also alter brown adipose tissue thermogenesis in females. This study was aimed to find out if male hormones could alter brown adipose tissue thermogenesis in male rats. Testosterone was administered by means of Silastic capsules in adult male rats acclimated either at 28 degrees C (thermoneutrality) or at 6 degrees C (cold), treatment lasting 15 days. Food intake and body weight gain were reduced by hormonal treatment. However, brown adipose tissue mass, protein content, mitochondrial mass and GDP-binding were unchanged at both environmental temperatures. Accordingly, testosterone participation in body weight regulation is thought to be carried out without altering brown adipose tissue thermogenesis. A reduction in the weight of the sex accessory glands was also observed after cold acclimation.

Hematology and blood chemistry of chicks of white and black storks (Ciconia ciconia and Ciconia nigra).

1. The hematology and blood chemistry of 15-68-day-old chicks have been studied. 2. Red cell numbers (1,900,000/mm3), hemoglobin content (11.5 g/dl) and hematocrit (37.5) were similar in both species of storks. 3. Total numbers of leucocytes (63,000/mm3) were similar in both species, whilst differential leucocyte counts were not. 4. Higher levels of plasma protein, GOT and cholesterol in HDL were found in white storks when compared with black storks but not differences were detected in plasma levels of triglycerides, total cholesterol, urea, uric acid, GPT and alkaline phosphatase.

Effect of cold acclimation on GSH, antioxidant enzymes and lipid peroxidation in brown adipose tissue.

Cold acclimation increased the activities of superoxide dismutase, catalase, total and selenium (Se)-dependent glutathione peroxidases (GPx) and glutathione reductase by 2-4-fold in the brown adipose tissue (BAT) of cold-acclimated rats. Nevertheless, when expressed per unit protein, the antioxidant enzyme activities were unaltered. Sensitivity to lipid peroxidation and GSH levels both increased by one order of magnitude in the cold on a per weight basis and were still 3-5 times greater in the cold when expressed per mg of protein. We suggest that activation of BAT leads to a large increase in the potential for lipid peroxidation and that the tissue responds to this challenge by increasing practically all of its antioxidant defences. Nevertheless, GSH, and possibly GPx activity, seem to be the principal defences involved in adaptation of the tissue to a higher sensitivity to peroxidative damage after activation.