Regulation of leptin secretion from white adipocytes by free fatty acids

Norepinephrine stimulates lipolysis and concurrently inhibits insulin-stimulated leptin secretion from white adipocytes. To assess whether there is a cause-effect relationship between these two metabolic events, the effects of fatty acids were investigated in isolated rat adipocytes incubated in buffer containing low (0.1%) and high (4%) albumin concentrations. Palmitic acid (1 mM) mimicked the inhibitory effects of norepinephrine (1 microM) on insulin (10 nM)-stimulated leptin secretion, but only at low albumin concentrations. Studies investigating the effects of the chain length of saturated fatty acids [from butyric (C4) to stearic (C18) acids] revealed that only fatty acids with a chain length superior or equal to eight carbons effectively inhibited insulin-stimulated leptin secretion. Long-chain mono- and polyunsaturated fatty acids constitutively present in adipocyte triglyceride stores (oleic, linoleic, gamma-linolenic, palmitoleic, eicosapentanoic, and docosahexanoic acids) also completely suppressed leptin secretion. Saturated and unsaturated fatty acids inhibited insulin-stimulated leptin secretion with the same potency and without any significant effect on basal secretion. On the other hand, inhibitors of mitochondrial fatty acid oxidation (palmoxirate, 2-bromopalmitate, 2-bromocaproate) attenuated the stimulatory effects of insulin on leptin release without reversing the effects of fatty acids or norepinephrine, suggesting that fatty acids do not need to be oxidized by the mitochondria to inhibit leptin release. These results demonstrate that long-chain fatty acids mimic the effects of norepinephrine on leptin secretion and suggest that they may play a regulatory role as messengers between stimulation of lipolysis by norepinephrine and inhibition of leptin secretion.     

The effect of high dose of cortisol on glucose-6-phosphatase and fructose-1,6-bisphosphatase activity,and glucose and fructose-2,6-bisphosphate concentration in carp tissues (Cyprinus carpio L.)

The effect of a high dose of cortisol (200 mg kg(-1) body mass) on juvenile carp was investigated. The activity of glucose-6-phosphatase in liver and of fructose-1,6-bisphosphatase in liver, kidney and muscle, the serum glucose and fructose-2,6-bisphosphate concentration as well as the serum concentration of the injected hormone were measured after 24, 72 and 216 h after intraperitoneal cortisol injection. The activities of fructose-1,6-bisphosphatase in liver and kidney and glucose-6-phosphatase in liver were elevated in comparison with the control, while the fructose-1,6-bisphosphatase activity in the muscle tissue was unchanged. After cortisol injection, the serum glucose level was nearly two times higher after 24 and 72 h and was still 50% higher after 216 h compared with controls. In contrast, the liver fructose-2,6-bisphosphate concentration was unchanged after 24 h. More than two times higher fructose-2,6-bisphosphate concentration was observed in liver after 72 h and it was still elevated after 216 h after the cortisol injection.     

Role of calcium in the secretion of leptin from white adipocytes

The mechanism by which calcium regulates leptin secretion was studied in adipocytes isolated from rat white adipose tissue. Incubation of adipocytes in a medium containing glucose, but no calcium, markedly inhibited insulin-stimulated leptin secretion (ISLS) and synthesis, without affecting basal leptin secretion or lipolysis. However, when pyruvate was used as a substrate, ISLS was insensitive to the absence of calcium. Likewise, the stimulatory effects of insulin were completely prevented by phloretin, cytochalasin B, and W-13 (3 agents that interfere with early steps of glucose metabolism) in the presence of glucose, but not in the presence of pyruvate. Thus calcium appears to be specifically required for glucose utilization. On the other hand, (45)Ca uptake and leptin secretion were not affected by insulin or by inhibitors of L-type calcium channels. However, agents increasing plasma membrane permeability to calcium (high calcium concentrations, A-23187, and ATP) increased (45)Ca uptake and concomitantly inhibited ISLS. Similarly, release of endogenous calcium stores by thapsigargin inhibited ISLS in a dose-dependent manner. ATP, A-23187, calcium, and thapsigargin inhibited ISLS, even in the presence of pyruvate. These results show that 1) extracellular calcium is necessary for ISLS, mainly by affecting glucose uptake, 2) insulin does not affect extracellular calcium uptake, and 3) increasing cytosolic calcium by stimulating its uptake or its release from endogenous stores inhibits ISLS at a level independent of glucose metabolism. Thus calcium regulates leptin secretion from adipocytes in a manner that is markedly different from its role in the exocytosis of many other polypeptidic hormones.     

Diversity of the Bialowieza Forest avifauna in space and time

The Biaowiea Forest (BF) is an extensive and relatively little changed forest complex on the Polish-Belarussian border. Data on the structure and diversity of its breeding avifauna have mostly been collected in primeval old-growth stands, preserved within the Biaowiea National Park (BNP). Mapping censuses repeated in space (plots, replicated in riverine, oak-lime-hornbeam and coniferous stands) and time (permanent plots, 28 years) reveal that the breeding bird assemblages are rich in species (29–52/season in a 25 to 33-ha plot), but of moderate overall density (40–120 pairs/10 ha). The latter is due to low, lower than in man-transformed areas, densities of the majority of particular species. Despite marked changes in vegetation structure, the composition of the breeding bird assemblage does not vary much across different primeval forest types, with a single breeding bird community inhabiting all of them, including treefall gaps. High richness of the BF avifauna stems from the Forests geographical locality, as well as from a high level of the primeval avifauna retention. Over 95% of the 135–140 pristine species still breed there. Especially species-rich groups are birds of prey, owls, woodpeckers and Sylvinae warblers. Bird communities in the BNP and primeval tropical rain forests share many features, suggesting that natural differences between temperate and tropical forests were less pronounced in the past. The combination of high species richness with low densities of individual species is probably a feature of all pristine forests, independent of climatic zone. The BF avifauna must once have been typical of the ancient European forests and it has become so exceptional chiefly because it has preserved most of its pristine features. The BF thus constitutes an indispensable reference site for future studies of woodland bird biology. To ensure its survival should become a priority. Commercial logging, taking place over 80% of the Polish BF part, severely changes the Forests structure and strongly affects the birds, especially species which depend on dead wood (Dendrocopos leucotos, Picoides tridactylus) and on old-growth stands. The small area protected as the BNP becomes an increasingly isolated island, in which preservation of the primeval forest features seems to be impossible. In order to retain them, it is necessary to protect the whole BF area.     

Sex differences in adrenocortical structure and function

Summary The zonation and cellular composition of the adrenal cortex of intact mature male and female rats of different strains (Chbb Thomm, CFY) and three strains of Wistar rats (W1, W2 and W3) at the age of 84–90 days were compared using morphometry.Both absolute and relative adrenal gland weights were higher in female than male rats. Rats of W3 and Chbb Thomm strains had the largest adrenals. These differences depended upon the higher volume of the zona fasciculata (ZF) and zona reticularis (ZR) in the W3 and Chbb Thomm strains than in the remaining animals. Females had larger adrenocortical zones than corresponding males. The average volume of the ZF cell ranged in males from 1589 m³ (W1 strain) to 2111 m³ (Chbb Thomm) and in females from 2249 m³ (W1 strain) to 2894 m³ (W3 strain). The average nuclear volume of the ZF cells was higher in female rats whereas there were no strain-and sex-differences in the size of zona glomerulosa (ZG) and ZR cells.The total number of parenchymal cells per pair of adrenals varied markedly among the studied strains, with the highest number in W3 and Chbb Thomm females. W3, Chbb Thomm and CFY females had larger number of parenchymal cells than males; the reverse was true for W1 strain whereas no differences were found among W2 male and female rats.     

Gestational changes in hamster adrenal cortex: Morphometric and ultrastructural stereologic studies

Summary In the hamster, the weight of the adrenal glands increases during the course of gestation, with the highest value at day 5. In comparison to non-pregnant control animals, there were no changes in the volume of the zona glomerulosa (ZG) and zona fasciculata (ZF), while the volume of the zona reticularis (ZR) increased notably. The average volume of ZG-cells rose at day 5 of pregnancy and thereafter gradually decreased to that of control hamsters. A marked drop in the volume of ZF-cells was seen at days 5 and 10 of pregnancy, whereas at day 15 the cells were larger than in controls. At day 5 of pregnancy, a conspicuous increase in the cell volume was found in ZR, followed by lower values at day 10 and again higher than in control hamsters at day 15. The total number of parenchymal cells in hamster adrenal cortex increased at day 10 of gestation, then underwent a marked decrease, reaching the control value at the final day of pregnancy; this drop was mainly due to a reduction in the number of ZF-cells. The changes in the cell volume were paralleled by rather proportional changes in the volume of the mitochondrial compartment and in the quantity of smooth endoplasmic reticulum. The volume of the lipid-droplet compartment significantly rose in the course of gestation in both ZF- and ZR-cells. The cortisol output by adrenal homogenates gradually decreased during pregnancy.Study performed in partial fulfillment of the Ph.D. Thesis of Magdalena Nowak     

The effects of ageing on the morphology and function of the zonae fasciculata and reticularis of the rat adrenal cortex

Summary The morphological counterpart of the well-known age-dependent marked impairment of glucocorticoid secretion of rat adrenals was investigated by use of morphometric techniques. For this purpose 4-, 8-, 16- and 24-month-old rats were studied. Despite the notable lowering of both basal and ACTH-stimulated production of corticosterone by collagenase-dispersed inner adrenocortical cells, ACTH and corticosterone plasma concentrations displayed significant increases with ageing. Zona fasciculata (ZF) and zona reticularis (ZR) showed a notable hypertrophy in aged rats, which was due to rises in both the average volume and number of their parenchymal cells. The hypertrophy of ZF and ZR cells was in turn associated with increase in the volume of the mitochondrial compartment and proliferation of smooth endoplasmic reticulum, i.e., the two organelles involved in steroid-hormone synthesis. All these morphologic changes, conceivably due to the chronic exposure to high levels of circulating ACTH, are interpreted as a response enabling ZF and ZR to compensate for their age-dependent lowering in glucocorticoid secretion. Stereology also demonstrated that ZF and ZR cells underwent a striking age-related lipid-droplet repletion. Lipid droplets are the intracellular stores of cholesterol esters, the obligate precursors of steroid hormones in rats. This finding is in keeping with the contention that the mechanism underlying the age-dependent decline in rat-adrenal glucocorticoid secretion mainly involves impairments of the utilization of intracellular cholesterol previous to its intramitochondrial transformation to pregnenolone.