Regulatory mechanisms in inflammation: new aspects of autopharmacology

Acute aerocystitis in Piaractus mesopotamicus: participation of eicosanoids and pro-inflammatory cytokines

A total of 360 pacus (Piaractus mesopotamicus) were used to study vascular permeability (VP) and inflammatory cell component (CC) in induced aerocystitis in P. mesopotamicus through inoculation of inactivated Aeromonas hydrophila, and the effect of steroidal and nonsteroidal anti-inflammatory drugs. It was observed that after inoculation of A. hydrophila, the maximum VP occurred 180 min post-stimulus (MPS). Pretreatment with anti-inflammatory drugs inhibited VP, and the inhibitory effect of dexamethasone was seen earlier than the effects caused by meloxicam and indomethacin. Inoculation of the bacterium caused a gradual increase in the accumulation of cells, which reached a maximum 24 h post-stimulus (HPS). Pretreatment with dexamethasone, indomethacin and meloxicam reduced the accumulation of lymphocytes, thrombocytes, granulocytes and macrophages. There was no significant difference between the different doses of the drugs tested. The results suggest that eicosanoids and pro-inflammatory cytokines participate in chemical mediation in acute inflammation in pacus.

Hormonal control of inflammatory responses

Almost any stage of inflammatory and immunological responses is affected by hormone actions. This provides the basis for the suggestion that hormones act as modulators of the host reaction against trauma and infection. Specific hormone receptors are detected in the reactive structures in inflamed areas and binding of hormone molecules to such receptors results in the generation of signals that influence cell functions relevant for the development of inflammatory responses. Diversity of hormonal functions accounts for recognized pro- and anti-inflammatory effects exerted by these substances. Most hormone systems are capable of influencing inflammatory events. Insulin and glucocorticoids, however, exert direct regulatory effects at concentrations usually found in plasma. Insulin is endowed with facilitatory actions on vascular reactivity to inflammatory mediators and inflammatory cell functions. Increased concentrations of circulating glucocorticoids at the early stages of inflammation results in downregulation of inflammatory responses. Oestrogens markedly reduce the response to injury in a variety of experimental models. Glucagon and thyroid hormones exert indirect anti-inflammatory effects mediated by the activity of the adrenal cortex. Accordingly, inflammation is not only merely a local response, but a hormone-controlled process.

Suppression of allergic inflammatory response in the skin of alloxan-diabetic rats: relationship with reduced local mast cell numbers

BACKGROUND

Diabetic patients are refractory to allergic inflammatory diseases. In this study, the influence of alloxan-induced diabetes on allergic skin inflammation was investigated.

METHODS

Diabetes was induced by intravenous injection of alloxan into male Wistar rats, and the analyses were performed 21 days later. Animals were actively sensitized with a mixture of aluminium hydroxide plus ovalbumin and challenged intradermally with ovalbumin on day 14.

RESULTS

Diabetic sensitized rats exhibited a less pronounced antigen-induced protein extravasation in the dorsal skin when compared with normal animals. Also, fragments of the dorsal subcutaneous tissue from diabetic sensitized rats showed a reduction in histamine release after stimulation with antigen in vitrowhen compared with fragments obtained from nondiabetic sensitized rats. Optical microscopy analysis revealed that the dorsal skin of diabetic rats showed a marked reduction in dermis thickness, as compared with that seen in normal animals. A significant decrease in the number of skin mast cells was also noted, a phenomenon that paralleled with the reduction in the expression of extracellular matrix components laminin, fibronectin and collagen. Administration of insulin into diabetic rats restored basal mast cell numbers as well as the levels of laminin, fibronectin and collagen.

CONCLUSIONS

Our findings show that alloxan diabetes induces downregulation of the skin allergic inflammatory response in rats, and this was correlated with reduction in local mast cell numbers and expression of extracellular matrix components. Lastly, these alterations were reversed with insulin treatment.

Lack of potentiation of bradykinin by angiotensin-(1-7) in a type 2 diabetes model: role of insulin

Considering the growing importance of the interaction between components of kallikrein-kinin and renin-angiotensin systems in physiological and pathological processes, particularly in diabetes mellitus, the aim of the present study was to investigate the interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK), important components of these systems in an insulin resistance model of diabetes, and the effect of insulin on it. For this the response of mesenteric arterioles of anesthetized neonatal streptozotocin-induced (n-STZ) diabetic and control rats was evaluated using intravital microscopy. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in n-STZ rats. Chronic but not acute insulin treatment restored the potentiation. This restorative effect of insulin was abolished by a K+ channel blocker (tetraethylammonium), by nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and by a cyclooxygenase inhibitor (indomethacin). On the other hand, Na(+)-,K(+)-ATPase inhibition (by ouabain) did not abolish the effect of insulin. There was no difference in mRNA and protein expression of B1 and B2 kinin receptor subtypes between n-STZ diabetic and control rats. Insulin treatment did not alter the kinin receptor expression. Our data allow us to conclude that diabetes impaired the interaction between BK and Ang-(1-7) and that insulin restores it. The restoring effect of insulin depends on membrane hyperpolarization, nitric oxide release and cyclooxygenease metabolites but not Na+K+-ATPase. Alteration of kinin receptor expression might not be involved in the restoring effect of insulin on the potentiation of BK by Ang-(1-7).

Effect of Dietary Supplementation with Vitamin E and Stocking Density on Macrophage Recruitment and Giant Cell Formation in the Teleost Fish, Piaractus mesopotamicus

The effect of dietary supplementation with 0, 100 and 450 mg of vitamin E (DL-alpha tocopheryl acetate)/kg of a dry diet on the kinetics of macrophage recruitment and giant cell formation in the pacu, maintained at different stocking densities (5 kg/m(3) and 20 kg/m(3)), was investigated by insertion of round glass coverslips into the subcutaneous connective tissue. After a feeding period of 18 weeks, the coverslips were implanted and later removed for examination at 2, 7 and 15 days post-implantation. Fish fed diets supplemented with 450 mg of vitamin E showed an increase (P<0.05) in the accumulation of macrophages, foreign body giant cells and Langhans type cells. The kinetics of macrophage recruitment and giant cell formation on the glass coverslips appeared to be strongly influenced by vitamin E supplementation, since fish fed a basal diet and held at high stocking densities showed low numbers of adhering cells on the coverslips, and high concentrations of plasma corticosteroids. On the other hand, fish given a diet supplemented with 450 mg of vitamin E did not show a similar difference in plasma cortisol concentrations related to stocking density. The effect of cortisol concentrations on carbohydrate metabolism, analysed by assessment of plasma glycaemia, was not clear. Blood glucose concentrations did not vary substantially with the different treatments examined. These results suggest that vitamin E may contribute to the efficiency of the fish's inflammatory response by increasing macrophage recruitment and giant cell formation in the foreign body granulomatous reaction. Vitamin E appeared to act on the stress response of pacus by preventing a stress-related immunosuppression.

Adoptive transfer of mast cells abolishes the inflammatory refractoriness to allergen in diabetic rats

Mast cells are pivotal secretory cells primarily implicated in allergen-evoked inflammatory responses and are downregulated following experimental chemical diabetes. Here we tested the hypothesis that a decrease in the number and reactivity of mast cells would account for the hyporesponsiveness of diabetic rats to allergen-induced inflammation. We found that the anaphylactic release of histamine from sensitized ileum, trachea and skin tissues was clearly reduced in rats turned diabetic via intravenous administration of alloxan. Likewise, actively and passively sensitized diabetic rats mounted a weaker allergen-evoked pleural mast cell degranulation and protein extravasation, as compared to sensitized nondiabetic animals, which paralleled a marked reduction in the mast cell population in the pleural cavity. The number of mast cells enumerated in the mesentery from diabetic rats was also clearly reduced. The allergen-evoked plasma leakage in diabetic rats was restored by the transfer of mast cells from sensitized nondiabetic rats. Moreover, the adoptive transfer of sensitized mast cells from diabetics to naive animals led to a lower allergen-induced exudation as compared to the response noted after the transfer of sensitized naive mast cells. Purified mast cells from diabetic rats were hyporesponsive to antigen and compound 48/80 stimulation in vitro as attested by histamine release. Thus, our results show that the phenomenon of refractoriness of diabetic animals to allergen challenge appears to be accounted for by a reduction in the number and reactivity of mast cells.

Minalrestat, an aldose reductase inhibitor, corrects the impaired microvascular reactivity in diabetes

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.

Angiotensin-(1-7) and bradykinin interaction in diabetes mellitus: in vivo study

The interaction between angiotensin-(1-7) (Ang-(1-7)) and bradykinin (BK) was determined in the mesentery of anesthetized Wistar alloxan-diabetic and non-diabetic rats using intravital microscopy. Impaired BK vasodilation observed in arterioles of diabetic rats was restored by acute and chronic insulin treatment as well as by enalapril. Though capable of potentiating BK in non-diabetic rats, Ang-(1-7) did not potentiate BK in diabetic rats. Chronic but not acute insulin treatment restored the potentiation, whereas enalapril did not. Potassium channel blockade (by tetraethylammonium (TEA)) but not nitric oxide (NO) synthase inhibition (by N-omega-nitro-L-arginine-methyl-esther (L-NAME)) abolished the restorative effect of insulin. Our data allow us to suggest that the alteration observed is restored by insulin by a mechanism involving membrane hyperpolarization but not NO release. The beneficial effect of enalapril in diabetes might not involve the potentiation of BK by Ang-(1-7).

A new approach to the study of latissimus dorsi muscle vasoreactivity in rats

In this paper we describe a new approach to the study of changes in latissimus dorsi (LD) muscle microcirculation in rats. The experiments were carried out under anesthesia in normal male Wistar rats (C, n = 6) and in diabetes-induced rats (D, streptozotocin, 50 mg/kg, i.v., n = 6). The left LD muscle was exposed in order to preserve the proximal tendon with its thoracodorsal nerve and artery. The animal was kept in lateral decubitus over a heating board attached to the mechanical stage of the intravital microscope. The ventral surface of the muscle was exposed over a transparent plate and fixing. The image of the LD vascularization was transferred to the camera system, which was connected to a microcomputer equipped with software (KS-300, Kontron Elektronik, Munich, Germany) for image storage. The vasoreactivity of LD was analyzed by changes in arteriole diameter after topically administered noradrenaline (0.3 microg/ml) and acetylcholine (300 microg/ml). The microscopic image provided by the described optical setup permitted clear resolution of capillary vessels and a stable preparation over a period of 3-4 h. D rats showed increased vasodilatation (29 +/- 2% vs. 18 +/- 2.6% in C) and similar vasoconstriction (25.5 +/- 3% vs. 27.5 +/- 3.3% in C) as compared to C rats. The method described in this paper is suitable for the study of changes in responsiveness of LD arterioles, vessels which represent the major site of vascular resistance and are most actively involved in the control of tissue perfusion.

Influence of aldose reductase inhibition on the microvascular reactivity in experimental diabetes

1. To verify if tolrestat, an aldose reductase inhibitor, corrects the impaired responses of microvessels to histamine and bradykinin in alloxan-diabetic rats, the mesenteric microcirculation was studied in vivo in anaesthetised animals. 2. The impaired responses were corrected by tolrestat 5 mg/kg/day for 7 days p.o. Similar responses to acetylcholine and sodium nitroprusside were obtained in preparations of diabetic and control rats and were not altered by tolrestat treatment. 3. As in diabetes, galctosemia induced impaired responses to histamine and bradykinin; these altered responses were corrected by tolrestat treatment. 4. These data allow us to suggest that the polyol pathway activity might be involved in the altered responses of microvessels observed in diabetic rats. It is possible that polyol activation may play an important role in the development of vascular dysfunction in diabetes mellitus.

Is bronchial asthma a pancreatic disease?

Bronchial asthma and diabetes mellitus seldom occur in the same patient. The exact mechanism of this mutual exclusion is still unknown and its elucidation can make clear the physiopathology of both diseases. Clinical and experimental evidences suggest that insulin is a proinflammatory hormone and glucagon an antiinflammatory and a bronchodilator one. We hypothesize that the relationship between plasma insulin and glucagon may play an important role in bronchial asthma.

β-Adrenergic Responsiveness of the Gastrointestinal Tract in Diabetic Rats

Recently, decreased gastrointestinal beta-adrenergic responses in experimental diabetes have been demonstrated. Gastrointestinal responses to beta-adrenoceptor agonists are impaired in both insulin-dependent and non-insulin-dependent diabetic rat. Insulin treatment improves the impaired gastrointestinal beta-adrenergic responsiveness of diabetic rats. The improvement seen with insulin treatment on beta-adrenergic responsiveness is closely related to protein biosynthesis. The decreased beta-adrenergic responses in diabetic rat gastrointestinal tract seem to result from a decrease in the number of beta-adrenoceptors. It is most likely that the decreased gastrointestinal beta-adrenergic responsiveness is related to an impairment in the turnover of beta-adrenoceptors as a consequence of diabetes and that insulin has a beneficial effect on the impaired receptor turnover.

Negative endocrine control system for inflammation in rats

Inflammatory processes may be suppressed by endogenous mechanisms such as release of adrenocorticosteroid hormones through stimulation of the hypothalamus-pituitary-adrenal axis. In the present study, the relationship between the temporal development of carrageenan-induced edema in the hindlimb of the rat and release in plasma of the principal endogenous adrenocorticosteroid of the rat corticosterone was investigated. Suplantar injection of carrageenan produced a biphasic increase in basal plasma corticosterone levels that was not attributed to diurnal variation. The plasma level of corticosterone increased rapidly after injection of carrageenan and peaked 12-fold at 20 min. This first phase increase was attributed to the stress of the injection since it was mimicked by subplantar injection of saline. The second phase of corticosterone release was gradual and peaked 12-fold 7 hr after injection of carrageenan. The second phase was not elicited by subplantar injection of saline. When the hypothalamus-pituitary-adrenal axis is impaired via hypophysectomy, carrageenan-induced edema is more intense and lasts longer than in control rats. The results demonstrate that adrenocorticosteroid hormones are released as a result of the stress of injection and by the inflammatory response. Release of adrenocorticosteroids acts as a feedback mechanism to suppress the inflammatory response.

Early inflammatory response to carrageenan in the pleural cavity and paw of rats with altered body temperature

Polymorphonuclear leucocyte (PMNL) migration and oedema induced by carrageenan in the pleural cavity and paw, respectively, of rats made hyper- or hypothermic by physical and chemical means have been investigated. In rats placed in a warm environment to produce a rise in body temperature, carrageenan caused a moderate but significant increase in PMNL migration compared with the control animals. Opposite effects were obtained with hypothermic animals kept in a cold environment. While hyperthermia produced by amphetamine did not alter the PMNL migration, chlorpromazine-induced hypothermia caused a fall in the number of these cells present in the pleural cavity following carrageenan. Both hyper- and hypothermias, whether induced by physical or chemical means, inhibited the carrageenan paw oedema. The observed changes in the PMNL numbers in the pleural cavity did not reflect their numbers in the peripheral circulation. Results indicate that while a rise or a fall in body temperature may have opposite effects on PMNL migration, in carrageenan inflammation both conditions inhibit oedema formation.

Reduced neurogenic inflammation in streptozotocin-diabetic rats due to microvascular changes but not to substance P depletion

The effect of streptozotocin treatment (65 mg/kg i.v.) on plasma protein extravasation, nociception, and the content of substance P immunoreactivity (SP-IR) and somatostatin immunoreactivity (SOM-IR) was investigated in the rat. Twelve days after treatment, the neurogenic plasma extravasation induced by 5% mustard oil was reduced by 67% in the skin of the hind paw. Extravasation caused by SP, a putative mediator of neurogenic inflammation, was also reduced by 61% in the abdominal skin. While calcitonin gene-related peptide (CGRP) potentiated the SP-induced extravasation in control rats, no potentiation was observed in diabetic rats. Thermonociception or chemonociception was unchanged after streptozotocin treatment. The content of SP-IR and SOM-IR in sensory nerves or spinal ganglia was also not altered. These results indicate that the impairment of neurogenic inflammation in diabetic rats is not the result of depletion of neurogenic mediators like SP. Changes of the microvasculature at the leakage site appear to account for the effects observed.

Involvement of lymphocytes in non-immune inflammation: dual effect of glucocorticoids

Leucopenia induced by the administration of methotrexate reduced the volume of inflammatory exudate and the number of cells entering the pleural cavity during a 4-h carrageenin pleurisy when compared with that of non-leucopenic controls. The depressed response was partially but markedly restored when leucopenic animals were intravenously injected, immediately before the initiation of pleurisy, with spleen lymphocytes (or their products) obtained from normal, adrenal-demedullated or mock-operated rats. In contrast spleen lymphocytes (or their products) obtained from adrenalectomized rats or from rats receiving metyrapone, an inhibitor of adrenal glucocorticoid biosynthesis, were completely inactive. It is concluded that in physiologic concentrations glucocorticoids are essential for the production of lymphocyte-derived factors involved in the development of acute, non-immune inflammation. In pharmacologic concentrations, however, glucocorticoids suppress the release of such pro-inflammatory factors.

Vascular reactivity in diabetes mellitus: role of the endothelial cell

The response to vasoactive agents of microvessels in situ and large arteries in vitro was compared in normal and alloxan-diabetic rats. Noradrenaline was equally effective in evoking a constrictor response of mesenteric microvessels in normal and diabetic animals. The constrictor response to a standard amount of noradrenaline in such vessels was fully antagonized by acetylcholine or papaverine, the minimum effective doses being equivalent in normal and diabetic animals. In contrast, the minimum doses of histamine or bradykinin, effective in normal animals, had to be increased about 20 fold to be active in diabetic animals. Increased osmolarity of extracellular fluid caused a significant and equivalent increase in latency of the vasoconstrictor response of microvessels to noradrenaline in normal and diabetic animals. Concentration-effect curves, constructed from the response of isolated aortae to noradrenaline, were similar in normal and diabetic animals, provided the endothelium was removed. Diabetes only affected preparations in which the endothelium was left intact. In these, the median effective concentrations of noradrenaline were greatly increased in comparison with normal values. Precontracted aortae from normal and diabetic animals were equally relaxed by acetylcholine and histamine, provided the endothelium was left intact. Loss of the relaxant response of the preparations in all groups of animals was observed following removal of endothelial cells. It is suggested that different mechanisms may be involved in the effects of vasodilator agents on large arteries in vitro or small vessels in situ. Histamine and bradykinin which are potent permeability-increasing factors, may antagonize the vasoconstrictor response of microvessels to noradrenaline through an action on endothelial cells with increased vascular permeability and temporary changes in composition of extracellular fluid. The reactive process of endothelial cells to permeability factors was affected by diabetes mellitus. However, the response of microvessels to acetylcholine and papaverine which are devoid of permeability-increasing properties, was not influenced by diabetes.

[Cardiovascular reactivity to arachidonic acid, prostaglandin E2, prostacyclin and bradykinin in carrageenan treated rats]

In the rat, during carrageenan-induced peritonitis, the hypotensive activity of arachidonic acid, which depends on PG biosynthesis, is increased during the first hours, and thereafter is not modified. The vasodilator action of PGE2 is reduced during the first day while the actions of PGI2 and bradykinin are not modified. The concentrations of plasma albumin and haptoglobin, two inhibitors of PG biosynthesis are reduced during the first hours. Thereafter the concentration of haptoglobin is increased by 100% while the concentration of albumin remains diminished. During this peritonitis, no plasmatic inhibitory influence on PG synthesis is seen. The anti-inflammatory action of carrageenans does not depend on PG synthesis inhibition.