Apparent lack of beta 3-adrenoceptors and of insulin regulation of glucose transport in brown adipose tissue of guinea pigs.

Norepinephrine-induced thermogenesis was substantial in adipocytes from brown adipose tissue (BAT) of cold-acclimated guinea pigs but absent in adipocytes from BAT of warm-acclimated guinea pigs. There was no thermogenic response to any beta 3-adrenergic agonist (CL-316,243, ZD-7114, BRL-28410, CGP-12177). The receptor was characterized as a beta 1-adrenoceptor. Adrenergic agonists stimulated adenylate cyclase in membranes from BAT of both warm- and cold-acclimated guinea pigs also via a beta 1-adrenoceptor; beta 3-adrenergic agonists had no effect. Glucose transport by brown adipocytes from warm-acclimated guinea pigs was not stimulated by either norepinephrine or insulin. Cold acclimation induced the appearance of stimulation of glucose transport by norepinephrine in association with the appearance of a large capacity for thermogenesis, but there was little improvement in response to insulin. GLUT4 was present in membranes from BAT of both warm- and cold-acclimated guinea pigs. Insulin is known to have an antilipolytic effect on both BAT and white adipose tissue of guinea pigs. Thus there is a selective lack of insulin-regulated glucose transport that is not improved by cold acclimation. Guinea pigs may have a mutated component of the translocation mechanism for GLUT4. beta 3-Adrenoceptors appear to be absent in brown adipocytes of adult guinea pigs, as in white adipocytes of guinea pigs, yet are known to be present in the gut. Tissue-specific expression of beta 3-adrenergic receptors in guinea pigs may differ from that in rats, in which receptors are expressed in the adipose tissues and gut.

Optimized radiolabelling of pig granulocytes with indium-111 tropolonate.

Standard labelling methods using 111In-tropolonate in plasma resulted in lower labelling efficiency (LE) with pig granulocytes than with human cells. Addition of acid-citrate-dextrose (ACD) to cell-free plasma in a ratio of 1:10 tripled the LE to a value which was not significantly different from that obtained in saline. Under optimized conditions, LE was 67 +/- 2% (mean +/- SE) with pig granulocytes, which remained lower than that obtained with human cells but was adequate for nuclear imaging studies of granulocyte deposition in the pig.

Colchicine lesions of ventromedial hypothalamus: effects on regulatory thermogenesis in the rat.

Experiments were carried out to test whether the ventromedial hypothalamus (VMH) is the site of a pathway that stimulates thermoregulatory heat production in brown adipose tissue (BAT). Adult Sprague-Dawley rats received bilateral 50 nl microinjections of colchicine solution into the VMH (0.1, 0.32, 1.0 or 3.2 micrograms per side). Beginning a day later, hyperphagia developed consistently with 0.32 microgram colchicine; and with higher doses there appeared the additional effect that for several days rats developed hypothermia when placed temporarily at 6 degrees C. The degree of hypothermia was limited by activation of nonshivering thermogenesis (NST) in BAT, as evidenced by increased shivering after propranolol injection to block NST, and by increased GDP binding measured in IBAT mitochondria after cold exposure. The findings suggest that chemical lesioning to induce the VMH hyperphagia syndrome does not produce an obligatory impairment of thermoregulation against cold unless the dose of neurotoxin and lesion area extends beyond that which underlies the overeating response. Furthermore, when tolerance to cold is thus compromised, the effect is not readily explained in terms of simply disconnecting a proposed stimulatory pathway from the VMH to BAT.

Absence of increased oxygen consumption in brown adipose tissue of rats exhibiting "cafeteria" diet-induced thermogenesis.

Young male Sprague-Dawley rats were induced to overeat (approximately 45%) by provision of a "cafeteria" (CAF) diet of palatable human foods. Normophagic rats fed a commercial chow or a semisynthetic diet served as controls. The CAF rats exhibited (a) the reduced food efficiency and the propranolol-inhibitable elevation in resting metabolic rate (resting VO2) that are indicative of a facultative diet-induced thermogenesis (DIT) by which excess energy gain is resisted, and (b) certain changes in brown adipose tissue (BAT) that are among those taken as evidence for BAT as the effector of DIT, e.g., increased protein content and increased mitochondrial binding of GDP. To assess directly and quantitatively the contribution by BAT to the elevation in VO2 (apparent DIT) of the CAF rats, BAT O2 consumption was determined (Fick principle) from measurements of tissue blood flow (microsphere method) and the arteriovenous difference in blood O2 across interscapular BAT (IBAT). To obtain the measurements, the animals were fitted under halothane anesthesia with vascular cannulas for intraventricular injection of microspheres and sampling of arterial blood and the venous effluent of IBAT. After recovery from anesthesia and rewarming to normal body temperature the animals were placed singly in a temperature-controlled metabolic chamber and the measurements, which also included determination of resting VO2, were made 1.5-2 h later about 11:30 h. As determined from measurements made at 28 degrees C (thermoneutrality) mean values of resting VO2 for the cannulated rats were unchanged from those of intact (unoperated) CAF or control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Defective trophic response of brown adipose tissue of myopathic hamsters.

Hamsters with muscular dystrophy (BIO 14.6) have a smaller than normal amount of brown adipose tissue. Two stimuli that promote growth of brown adipose tissue in normal hamsters, short photoperiod and eating a high-fat diet, are here shown to be without effect on brown adipose tissue of myopathic hamsters. Cold-induced growth of brown adipose tissue occurs normally [Am. J. Physiol. 239 (Cell Physiol. 8): C18-C22, 1980]. There is a normal rate of turnover of norepinephrine in brown adipose tissue of the myopathic hamster but a failure of the tissue to hypertrophy in response to norepinephrine is unlikely since norepinephrine does not appear to mediate the trophic response [Am. J. Physiol. 247 (Endocrinol. Metab. 10): E793-E799, 1984]. Denervation results in a marked reduction in size (protein content) of brown adipose tissue of normal hamsters but has very little effect on the size of brown adipose tissue of myopathic hamsters. A central, possibly hypothalamic, defect in the myopathic hamster is postulated to underlie its abnormal control of brown adipose tissue hypertrophy.

Trophic response of hamster brown adipose tissue: roles of norepinephrine and pineal gland.

The objective was to find out whether the reduced amount of brown adipose tissue in myopathic hamsters [Am. J. Physiol. 239 (Cell Physiol. 8): C18-C22, 1980] was secondary to a refractoriness to the trophic influence of norepinephrine. However, no evidence for any trophic influence of norepinephrine on brown adipose tissue of either normal or myopathic hamsters could be detected under experimental conditions that have demonstrated such an influence in rats. A mediator other than norepinephrine, melatonin, secreted by the pineal gland, is known to mediate the control of brown adipose tissue growth induced in hamsters by short photoperiod. Further studies of intact or pinealectomized hamsters showed that the pineal gland was not required for either cold- or diet-induced growth of brown adipose tissue. It is concluded that the defect in control of brown adipose tissue size in the hamster with muscular dystrophy is not due either to abnormal control by norepinephrine or to the pineal gland since neither of these appears to participate in the normal regulation of brown adipose tissue size in relation to environmental temperature or to diet.

Brown adipose tissue in genetically obese (fa/fa) rats: response to cold and diet.

Young genetically obese (fatty, fa/fa) rats (7-8 wk old) maintained on a chow diet at 28 degrees C have a relatively normal amount of brown adipose tissue (BAT) (normal protein content, normal noradrenaline content, normal or slightly reduced cytochrome oxidase content, 30% reduction in DNA content) with cells grossly hypertrophied by accumulation of lipid. The binding of purine nucleotides by BAT mitochondria is lower in fa/fa rats than in lean rats, suggesting a lesser thermogenic activation of this tissue. Acute exposure to cold (24 h at 4 degrees C) activates BAT thermogenesis (visible hyperemia, marked increase in mitochondrial binding of purine nucleotides, depletion of noradrenaline content) in fa/fa rats as in lean rats. In contrast, feeding a cafeteria diet to young fa/fa rats fails to activate BAT (no increase in mitochondrial binding of purine nucleotides) as it does in lean rats, and these rats accumulate more extra fat (increase in weight of gonadal white adipose tissue) than do cafeteria diet-fed lean rats. It is concluded that the young fa/fa rat has normal cold-induced nonshivering thermogenesis in BAT but defective diet-induced thermogenesis in BAT and that the consequent reduction in energy expenditure, coupled with hyperphagia, contributes to the development of its obesity. The most probable location for the defect is suggested to be associated with the hypothalamus.

Growth of interscapular brown adipose tissue in cold-acclimated hypophysectomized rats maintained on thyroxine and corticosterone.

Brown adipose tissue (BAT) of rats is known to grow in response to acclimation to cold. The growth is accompanied by changes in mitochondrial polypeptide composition (an increase in the relative proportion of a polypeptide of molecular weight 32,000, known to be associated with the thermogenic proton conductance pathway). The mediator of the change in mitochondrial polypeptide composition is unknown. The objective of these experiments was to find out whether any of the pituitary hormones might be the mediator. Treatment of rats with growth hormone failed to alter BAT size or mitochondrial polypeptide composition. BAT grew and the change in BAT mitochondrial polypeptide composition occurred in cold-acclimated hypophysectomized rats, maintained on thyroxine and corticosterone to ensure their survival in the cold. It is concluded that none of the pituitary hormones is the mediator for the cold-induced change in BAT mitochondrial polypeptide composition or is required to exert a direct effect on BAT for cold-induced BAT growth to occur. It also seems unlikely that more than a maintenance amount of glucocorticoids is required for normal cold-induced growth of BAT; these hormones are thus also unlikely to mediate the change in BAT mitochondrial polypeptide composition. The requirement for no more than a maintenance amount of thyroxine for BAT growth and for the cold-induced change in BAT mitochondrial polypeptide composition confirms previous conclusions drawn from studies on cold-acclimated thyroidectomized rats.

Brown adipose tissue of cafeteria-fed rats.

Feeding a "cafeteria" diet for 2 wk to male Holtzman rats resulted in a weight gain that was, on average, only slightly more than that of control rats fed a regular chow diet. Wet weight, DNA, and total protein content of interscapular brown adipose tissue were more than doubled in the cafeteria-fed rats and proliferation of mitochondria paralleled tissue growth. After 2 wk of recovery from cafeteria feeding, the expanded size of the tissue had completely regressed to a normal level. Brown adipose tissue mitochondria of cafeteria-fed rats bound 3 times more purine nucleotides than mitochondria of chow-fed control rats, but no change in the proportion of polypeptides with molecular weight in the region of 32,000 could be detected. The changes in brown adipose tissue and its mitochondria in cafeteria-fed rats correspond to those seen previously in noradrenaline-treated rats, i.e., tissue growth accompanied by mitochondrial proliferation and an unmasking of proton conductance pathways. The increase in 32,000-mol-wt polypeptides seen in brown adipose tissue mitochondria of cold-acclimated rats does not occur in the cafeteria-fed rats. Control mechanisms are presumed to differ, either quantitatively or qualitatively, in the two situations, cold exposure and overeating, which both cause growth of brown adipose tissue.