Thymus involution in alloxan diabetes: analysis of mast cells

We previously reported that alloxan-induced diabetes results in reduction in the number and reactivity of mast cells at different body sites. In this study, the influence of diabetes on thymic mast cells was investigated. Thymuses from diabetic rats showed marked alterations including shrinkage, thymocyte depletion, and increase in the extracellular matrix network, as compared to those profiles seen in normal animals. Nevertheless, we noted that the number and reactivity of mast cells remained unchanged. These findings indicate that although diabetes leads to critical alterations in the thymus, the local mast cell population is refractory to its effect. This suggests that thymic mast cells are under a different regulation as compared to those located in other tissues.

A novel hot-plate test sensitive to hyperalgesic stimuli and non-opioid analgesics

It is widely accepted that the classical constant-temperature hot-plate test is insensitive to cyclooxygenase inhibitors. In the current study, we developed a variant of the hot-plate test procedure (modified hot-plate (MHP) test) to measure inflammatory nociception in freely moving rats and mice. Following left and right hind paw stimulation with a phlogogen and vehicle, respectively, the animals were placed individually on a hot-plate surface at 51°C and the withdrawal latency for each paw was determined simultaneously in measurements performed at 15, 60, 180, and 360 min post-challenge. Plantar stimulation of rats (250 and 500 æg/paw) and mice (125-500 æg/paw) with carrageenan led to a rapid hyperalgesic response of the ipsilateral paw that reached a plateau from 15 to 360 min after challenge. Pretreatment with indomethacin (4 mg/kg, ip) inhibited the phenomenon at all the times analyzed. Similarly, plantar stimulation of rats and mice with prostaglandin E2 (0.5 and 1 æg/paw) also resulted in rapid hyperalgesia which was first detected 15 min post-challenge. Finally, we observed that the MHP test was more sensitive than the classical Hargreaves' test, being able to detect about 4- and 10-fold lower doses of prostaglandin E2 and carrageenan, respectively. In conclusion, the MHP test is a simple and sensitive method for detecting peripheral hyperalgesia and analgesia in rats and mice. This test represents a low-cost alternative for the study of inflammatory pain in freely moving animals.

Histamine-potentiating activity in rat anaphylactic pleural fluid: role of serotonin

The identity of the histamine-potentiating activity detected in the rat anaphylactic pleural washing was investigated. Wistar rats of both sexes, weighing 150-200 g, were sensitized by injecting subcutaneously (sc) a mixture of ovalbumin and Al(OH)3 14 days before allergen challenge. In sensitized rats, intrapleural (ipl) injection of ovalbumin (l2 mug/cavity) caused an intense protein exudation. A single ipl administration of compound 48/80 (l2 mug/cavity) exhausted the resident mast cell population and turned the pleural cavity hyporeactive to the allergen challenge performed 5 days later. Allergen-induced exudation occurred in parallel to a dramatic decrease in the amount of cell-stored histamine (from 9.6 ñ 1.4 (N = 8) to 1.3 ñ 0.1 (N = 6) mug/cavity, P<0.001) in the pleural fluid within 10 min. The anaphylactic cell-free pleural washing obtained at this time, as well as histamine at a concentration equivalent to that stored in pleural mast cells (10 mug/cavity), did not induce pleural exudation when injected into normal rats. In contrast the combined administration of histamine and anaphylactic pleural washing led to remarkable pleural exudation, comparable to that obtained with a high dose of histamine (200 mug/cavity) alone. It is noteworthy that the anaphylactic washing from compound 48/80 pretreated rats failed to synergize with histamine. Also, synergism was not reproduced when recipient rats were pretreated with methysergide (50 mug/cavity). Consistently, serotonin (5 mug/cavity) acted synergistically with histamine (1O mug/cavity), producing a greater exudative response than observed with the sum of the effects of each vasoactive amine alone. The results indicate that serotonin accounts for the histamine-potentiating activity noted in the anaphylactic pleural washing, confirming that the synergistic interaction between these vasoactive amines plays a critical role in the rat allergic pleurisy.

Endotoxin induces eosinophil accumalation in the rat pleural cavity

Changes in eosinophil counts after intrathoracic (it) injection of endotoxin (LPS) were investigated in Wistar rats (150 - 180 g). Increasing doses of endotoxin (62.5 - 500 ng/cavity) induced a dose-dependent increase in the number of eosinophils recovered from the rat pleural cavity 24 h later. The eosinophilia was apparent within 24 h, peaked within 48 h (from 0.76 ñ 0.12 to 3.68 ñ 0.51 eosinophils x 10**6/cavity, P < 0.001) and returned to basal levels 120h after the it inection of endotoxin (250 ng/cavity). Endotoxin (3 ng - 4 µg/ml) failed to attract eosinophilis in vitro under conditions in which PAF-acether induced a dose-related response. These findings indicate that endotoxin-induced eosinophil migration in vivo is mediated by a secondary mechanism

Pleural eosinophil infiltration induced by PAF-acether is not a desensitizable phenomenon

This study investigated the effect of successive daily intrathoracic (it) injections of PAF-acether upon its demonstrated ability to generate eosinochemotaxin(s). Repeated administration of PAF-acether led to a selective state of desensitization, characterized by a gradual reduction of its ability to induce exudation. Concomitantly, however, there was a progressive pleural accumulation of eosinophilis leading to a 7-fold increase in the eosinophil counts after the 4th restimulation. The generation of eosinochemotaxin(s) elicited by PAF-acether was not modified by desensitization, as detected by transferring the cell-free pleural fluid from donor to recipient animals. We conclude that, in contrast to exudation, eosinophil tissue infiltration induced by PAF-acether is not a desensitizable phenomenon

Kinetics of pleural exudation and cellular alterations induced by antigen in actively sensitized rats

This study was undertaken to characteize the different phases of the allergic pleurisy induced by ovalbumin in actively sinsitized rats. The reaction was triggered by the intrathoracic injection of ovalbumin (12 microng/cavity) into animals sensitized 14 days before. The challenge caused, at 30 mjin, a drastic mast cell degranulation and exudation which peaked within 4h. At this time, an intense pleural leucocyte recruitment also occurred, accounted for by an increase in the mononuclear cell counts and by a predominant influyx of neutrophils. After 24h, the mast cell counts stated to reover, accompanied by a long-lasting (96 h) accumaltion of pleural eosinophils. Forty-eight hour later, the exudation and neutrophils were at basal levels, whereas mast cell counts increased progressively to reach control values at 120 h. This study describes the time course of the exudatory and cellular alterations observed during pleural inflammation induced by low antigen concentrations

Late eosinophil mobilization induced by PAF-acether in the pleural cavity of rats

In view of the rapid degradation of PAF in biological fluids, this study was designed to determine if late eosinophil infiltration induced in rats by PAF was deriived from its direct chemotatic action. A significant and selective 5-fold increase in the pleural eosinophil counts was detected 24 h after intrapleural PAF injection. The transfer of 6-h PAF washings to the pleural cavity of recipient rats also induced a 3-fold selective accumulation of eosinophils. The protein synthesis inhibitor cycloheximide abolished the pleural eosinophil migration and the generation of transferable chemotactic activity when administered to donor but not to recipient rats. These findings suggest that a secondary protein mediator accounts for the late eosinophil mobilization induced by PAF

Adrenalectomy exacerbates paw edema without interfering with desensitization induced by PAF-acether in rats

Subcutaneous injection of PAF-acether into rat's paw to a local inflammatory response (edema) followed by desensitization after repeated injections of the substance. The desensitizing effect was not modified by previous adrenalectomy, whereas the inflammatory response observed after the first injection of PAF-acether was exacerbated. This finding suggests that adrenal hormones may act as modulators of PAF-induced inflammatory reactions. Because LY 171883, an LTD4 blocker, inhibited the edema which follows the first injection of PAF-acether, we suggest that leukotrienes may play an important role in the phenomenon