Einfluß verschiedener Aktivatoren und Inhibitoren auf die Lokalisation von unspezifischen Esterasen in der normalen sowie unter Wirkung von BeCl2 stehenden Leberzelle

Zusammenfassung Es wurde der Einfluß verschiedener Aktivatoren und Inhibitoren auf die Lokalisation unspezifischer Esterasen in der normalen sowie in der nach Gaben von BeCl₂ veränderten Leberzelle untersucht.Die Ergebnisse weisen darauf hin, daß in den perikanalikulären Granula der Hepatozyten A- und C-Esterasen auftreten, — jedoch ist es nicht möglich die letzteren spezifisch nachzuweisen. Die im Zytoplasma der Leberzellen lokalisierten unspezifischen Esterasen wurden am stärksten durch F^–, Hg⁺⁺, Cu⁺⁺, Be⁺⁺-Ionen, sowie E 600 inhibiert. Hg⁺⁺, Cu⁺⁺und-Be⁺⁺Ionen bewirkten eine beträchtliche Schwächung der Esterasen in den perikanalikulären Granula. Nach Behandlung der Schnittpräparate mit Diisopropylfluorophosphat erfolgte ein vollständiges Schwinden der Enzymaktivität. 72 Std nach BeCl₂-Injektion (3 mg pro Ratte), wurden große, saure Phosphatase-positive Kugeln beobachtet, die Zytolysomen entsprechen. Diese enthielten auf E 600 widerstandsfähige unspezifische Esterasen. Hg⁺⁺ und Cu⁺⁺-Ionen hemmten deren Aktivität sehr stark, F^– und Be⁺⁺-Ionen, sowie Natriumtaurocholat und Cystein dagegen in geringem Maße. Eserin hatte keinen Einfluß auf die Aktivität der unspezifischen Esterasen, pCMB dagegen bewirkte deren Steigerung.Auf Grund unserer Beobachtungen kann angenommen werden, daß die unter den besprochenen Bedingungen in den Zytolysomen auftretenden Esterasen u.a. A- und C-Esterasen sind.

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Summary The influence of different activators and inhibitors on the localization of the activity of nonspecific esterases in the liver cells of intact rats and after intoxication with BeCl₂ was examined.It was found that esterases A and C occur in pericanalicular granules of liver cells but the specific activity of the latter enzyme cannot be demonstrated histochemically. The activity of nonspecific esterases in the cytoplasma of liver cells is most inhibited after treatment with F^–, Hg⁺⁺, Cu⁺⁺, Be⁺⁺ and E 600. Effect of Hg⁺⁺, Cu⁺⁺ and Be⁺⁺ reveals itself by the inhibition of esterasic activity also in pericanalicular granules. The inhibition of this activity is complete after treatment with di-isopropyl-fluorophosphate. 72 hours after the injection of 3 mg BeCl₂ large balls positive to test for acid phosphatase, corresponding to cytolysomes, was observed in some liver cells. They show the E 600 resistant nonspecific esterase activity. Ions of Hg⁺⁺ and Cu⁺⁺ inhibit considerable the above mentioned activity, however, it is markedly less inhibited by the F^–, Be⁺⁺, sodium taurocholate and cysteine. Eserine does not affect the activity of esterases within cytolysomes but after treatment with pCMB this activity becomes more intensive.These findings show that nonspecific esterasic activity which occur in the above mentioned condition within the cytolysomes can be ascribed to esterases A and C.

     

Nest sites,nest depredation,and productivity of avian broods in a primeval temperate forest: do the generalisations hold?

Data on nest success and brood productivity of three ground-nesting, three canopy-nesting and four hole-nesting (non-excavator) passerines were gathered in a primeval lowland temperate forest (Bialowieza National Park, E Poland). Natural holes were superabundant and the birds had to cope with a heavy pressure of a diverse assemblage of nest predators. We tested whether in such conditions nesting in holes is more productive, and whether nesting on the ground is most risky, as expected from some earlier generalisations. The nesting success varied significantly across the nest types. As predicted, the success of hole-nesters (51–74%) and their brood productivity were the highest. Contrary to expectations, the ground-nesters (27–40%) did not breed less successfully than the canopy-nesters (22–33%). Nest predators, responsible for 64–94% of nest losses in individual species, were the major cause of the differences among nest types. The Bialowieza results confirm the long-held view that holes tend to be the safest breeding places, but lend no support for the idea that nesting on the ground is more dangerous than in tree crowns.     

Neuropeptide B and W regulate leptin and resistin secretion, and stimulate lipolysis in isolated rat adipocytes

Neuropeptide B (NPB) and W (NPW) regulate food intake and energy homeostasis in humans via two G-protein-coupled receptor subtypes, termed as GPR7 and GPR8. Rodents express GPR7 only. In animals, NPW decreases insulin and leptin levels, whereas the deletion of either NPB or GPR7 leads to obesity and hyperphagia. Metabolic and endocrine in vitro activities of NPW/NPB in adipocytes are unknown. We therefore characterize the effects of NPB and NPW on the secretion and expression of leptin and resistin, and on lipolysis, using rat adipocytes. Isolated rat adipocytes express GPR7 mRNA. NPB and NPW are expressed in macrophages and preadipocytes but are absent in mature adipocytes. Both, NPB and NPW reduce the secretion and expression of leptin from isolated rat adipocytes. NPB stimulates the secretion and expression of resistin, whereas both, NPB and NPW increase lipolysis. Our study demonstrates for the first time that NPB and NPW regulate the expression and secretion of leptin and resistin, and increase lipolysis in isolated rat adipocytes. These effects are presumably mediated via GPR7. The increase of resistin secretion, stimulation of lipolysis and the decrease of leptin secretion may represent mechanisms, through which NPB and NPW can affect glucose and lipid homeostasis, and food intake in rodents.     

A theoretical study of zinc(II) interactions with amino acid models and peptide fragments

Density functional theory calculations have been employed to study the interaction between the Zn²⁺ ion and some standard amino acid models. The highest affinities towards the Zn²⁺ ion are predicted for serine, cysteine, and histidine. Relatively high affinities are reported also for proline and glutamate/aspartate residues. It was found that the zinc complexes with cysteine adopt a tetrahedral conformation. Conversely, complexes with one or two histidine moieties remain in an octahedral geometry, while those with three or more histidine groups adopt a square-planar geometry. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Orexins and adipoinsular axis function in the rat

Orexin A and B are recently identified as peptides that are derived from the same precursor and their expression is highly specifically localized in neurons located in the lateral hypothalamic area, a region implicated in the feeding behaviour. These peptides appear to be a part of a complex circuit that integrates the aspects of energy metabolism, cardiovascular function, hormone homeostasis and sleep/wake behaviours. The functional linking of orexins with leptin and insulin suggests the possibility of its involvement in the regulation of the adipoinsular axis, and the present investigation was designed to examine the potential role of orexins in this axis regulation. In all the tested doses (8, 16 and 40 nmol/kg body weight (b.w.)), subcutaneous (s.c.) injections of orexin A caused the significant increase in insulin and leptin blood levels. These elevations were observed 60 and 120 min after peptide administration. On the other hand, after the orexin B administration, elevated insulin and leptin blood concentrations were found only at 60 min of the experiment, and in that time point, the increases were comparable to that evoked by orexin A. In comparison with the control animals, the administration of orexins for 7 days resulted in a significant gain in body weight. Prolonged administration of either orexin A or orexin B significantly elevated insulin and leptin blood concentrations. Under these conditions, the orexin A effect on the leptin secretion was more marked than on the insulin secretion, and this difference is reflected by the lowered insulin/leptin molar ratio. These results suggest that orexins play an important role in the adipoinsular axis function and may be a significant regulator of both insulin and leptin secretion. In this regard, we suggest the updated functional model of Kieffer and Habener [Am. J. Physiol.: Endocrinol. Metab. 27 (2000) E1] that proposed the adipoinsular axis. Our model is extended by the probable humoral links between orexins and leptin and orexins and insulin and points on the dependence of the effects evoked by orexins, leptin and insulin on the blood glucose levels.     

Simulated microgravity impairs aldosterone secretion in rats: possible involvement of adrenomedullin

The prolonged exposure to microgravity (MG) or simulated MG (SMG) has been reported to cause hypotension, mainly due to reduced vascular contractility, and dysregulation of fluid and electrolyte balance. However, the mechanism(s) involved in these MG- or SMG-induced effects is not yet completely elucidated. Hence, we investigated in the rat the effect of prolonged (15 day) SMG, in the form of hindlimb unweighting, on the renin-angiotensin-aldosterone system (RAAS), as well as on atrial natriuretic peptide (ANP) and adrenomedullin (ADM), two hypotensive peptides that play a major role in the regulation of RAAS activity by inhibiting adrenal aldosterone secretion. SMG caused a mild hypotension in rats, associated with the blockade of body weight gain. Plasma aldosterone concentration and basal and agonist-stimulated in vitro aldosterone secretion from adrenal slices were decreased, and plasma renin activity was moderately increased. Neither Na(+) and K(+) serum concentrations nor ACTH and corticosterone blood levels were significantly affected. Plasma ANP concentration did not display significant alterations, while ADM blood concentration underwent a marked rise. The administration of the ADM-receptor antagonist ADM-(22-52) during the last 3 days of hindlimb unweighting reversed the SMG-induced hypotension and hypoaldosteronism. Collectively, these findings allow us to suggest that prolonged SMG impairs RAAS activity in rats, through a mechanism probably involving upregulation of the ADM system. Both hypoaldosteronism and increased ADM secretion may contribute to the development of hypotension during prolonged exposure to SMG.     

Mechanisms of leptin secretion from white adipocytes

The mechanisms regulating leptin secretion were investigated in isolated rat white adipocytes. Insulin (1-100 nM) linearly stimulated leptin secretion from incubated adipocytes for at least 2 h. The adrenergic agonists norepinephrine, isoproterenol (two nonselective beta-agonists), or CL-316243 (potent beta3) all inhibited insulin (10 nM)-stimulated leptin release. The inhibitory effects of norepinephrine and isoproterenol could be reversed not only by the nonselective antagonist propranolol but also by the selective antagonists ICI-89406 (beta1) or ICI-118551 (beta2), the beta2-antagonist being less effective than the beta1. Insulin-stimulated leptin secretion could also be inhibited by a series of agents increasing intracellular cAMP levels, such as lipolytic hormones (ACTH and thyrotropin-stimulating hormone), various nonhydrolyzable cAMP analogs, pertussis toxin, forskolin, methylxanthines (caffeine, theophylline, IBMX), and specific inhibitors of phosphodiesterase III (imazodan, milrinone, and amrinone). Significantly, antilipolytic agents other than insulin (adenosine, nicotinic acid, acipimox, and orthovanadate) did not mimic the acute stimulatory effects of insulin on leptin secretion under these conditions. We conclude that norepinephrine specifically inhibits insulin-stimulated leptin secretion not only via the low-affinity beta3-adrenoceptors but also via the high-affinity beta1/beta2-adrenoceptors. Moreover, it is suggested that 1) activation of phosphodiesterase III by insulin represents an important metabolic step in stimulation of leptin secretion, and 2) lipolytic hormones competitively counterregulate the stimulatory effects of insulin by activating the adenylate cyclase system.