Localization and characterization of binding sites for endothelin in Harder's gland in rabbits

Endothelin-1 as a central mediator of LPS-induced fever in rats

Fever induced by E. coli lipopolysaccharide (LPS) in rats is substantially reduced by blockade of central endothelin ET(B) receptors. This study explores the role of endothelin-1 as a central mediator of fever in rats, by investigating the effect of a pyrogenic dose of LPS on the levels of big endothelin-1 and endothelin-1 in the cerebrospinal fluid (CSF) and endothelin-1 in the plasma. We further assessed whether the increase in body temperature caused by central injection of endothelin-1 constitutes solely a hyperthermia or a true integrated febrile response. LPS (5 mug kg(-1), i.v.) induced fever which peaked at 1.16 +/- 0.24 degrees C within 2 h and remained stable up to 5 h. CSF levels of immunoreactive (ir) big endothelin-1 decreased to undetectable levels at 3 h after LPS, returning only partially at 5 h post-injection. CSF ir-endothelin-1 levels were undetectable in saline-treated animals, but reached 21.9 +/- 5.2 fmol ml(-1) at 3 h after LPS treatment. Plasma ir-endothelin-1 levels were unchanged after saline or LPS. Central injection of endothelin-1 (1 pmol, i.c.v.) caused long-lasting increases in body temperature (0.81 +/- 0.17 degrees C, 3 h), but simultaneously decreased tail skin temperature (-1.10 +/- 0.26 degrees C), indicating cutaneous vasoconstriction. Moreover, endothelin-1 induced fever (1.0 +/- 0.3 degrees C, 3 h) when injected into the preoptic area of the anterior hypothalamus (100 fmol), but not i.v. (1 or 10 pmol). These data suggest that endothelin-1 is produced in the brain and acts centrally as a mediator of LPS-induced fever.

Effects of a dual endothelin-1 receptor antagonist on airway obstruction and acute lung injury in sheep following smoke inhalation and burn injury

Studies have suggested that ET-1 (endothelin-1) is associated with lung injury, airway inflammation and increased vascular permeability. In the present study we have tested the hypothesis that treatment with a dual ET-1 receptor antagonist will decrease airway obstruction and improve pulmonary function in sheep with combined S+B (smoke inhalation and burn) injury. Twelve sheep received S+B injury using the following protocol: six sheep were treated with tezosentan, an ETA and ETB receptor antagonist, and six sheep received an equivalent volume of vehicle. Physiological and morphological variables were assessed during the 48 h study period and at the end of the study. There was no statistically significant difference in the PaO2/FiO2 (partial pressure of O2 in arterial blood/fraction of O2 in the inspired gas) ratio of the tezosentan-treated animals compared with controls; however, lung lymph flow was significantly higher (P<0.05) in the treated animals. PVRI (pulmonary vascular resistance index) was significantly reduced (P<0.05) in the tezosentan-treated animals. Assessment of NOx (nitric oxide metabolite) levels in plasma and lymph showed significantly elevated (P<0.05) levels in the tezosentan-treated animals compared with levels in untreated sheep. The degree of bronchial obstruction was similar in both treated and control sheep; however, bronchiolar obstruction was reduced in sheep treated with tezosentan. Histopathologically, no difference in the degree of parenchymal injury was detected. In conclusion, administration of a dual ET-1 receptor antagonist prevented an increase in PVRI after injury and reduced the degree of bronchiolar obstruction in sheep with S+B; however, treated sheep showed higher levels of NOx and increased lung lymph flow. Tezosentan treatment was ineffective in protecting against acute lung injury in this model.

Endothelin protein expression in tear glands of the rabbit

PURPOSE

Endothelin-1 (ET-1) has been found to accelerate rabbit corneal epithelial wound healing in vivo and proliferation of rabbit and bovine epithelial cells in vitro. We have now determined that endothelin-like immunoreactivity (ET-LI) is present in the tear fluid of New Zealand white rabbits, and we have addressed the question of whether it is produced by the tear glands (lacrimal gland and Harderian gland).

METHODS

Tears were obtained with capillary pipettes and lacrimal gland fluid was collected by cannulation. ET-LI was determined with a sandwich-enzyme immunoassay. The reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to determine if there are gene transcripts for prepro ET-1 in tear glands. ET-LI in the tear glands was evaluated using immunohistochemistry.

RESULTS

The tears contained 13.85 +/- 3.94 pg/ml (mean +/- SEM, n = 6) ET-LI and the lacrimal gland fluid had 24.90 +/- 6.00 pg/ml (n = 6). The plasma contained 0.89 +/- 0.20 pg/ml (n = 6). Gene transcripts were identified for prepro ET-1 in the lacrimal and Harderian glands. Specific staining for ET-LI was found in the epithelial cells of the ducts of the lacrimal gland and the acinar cells of the Harderian gland.

CONCLUSIONS

The higher concentrations of ET-LI in the tears and the lacrimal gland fluid than in plasma along with prepro ET-1 gene transcripts in the tear glands suggest that they secrete ET-1.

Immunohistochemical and histochemical characterisation of epithelial cells of rabbit lacrimal glands in tissue sections and cell cultures

The purpose of this study was to establish conditions for isolation and long term culture of acinar cells from the Harderian gland, and superior and inferior lacrimal glands of the rabbit and to compare the in vitro growth patterns of cultured cells from these glands. In order to determine the predominant cell type in the cultures, cells and tissue sections were stained using a variety of antibodies to cytokeratins, smooth muscle actin, and neuron specific enolase. Similarly, PAS and alcian blue histochemistry were used to test for the presence of mucins. The glands were excised and cells isolated using enzymatic digestion and then established in long term culture. Different media and substrata were trialed for suitability. When cultured on uncoated Costar plastic in DMEM/10%FBS, the pattern of cell growth was similar for all glands with distinct phases involving aggregation and migration out from the aggregates before cells died between 20 to 30 days. Immunohistochemical staining indicated that the cultures were of acinar cells with a small percentage of ductal cells. The acinar cells of the lacrimal glands in situ and in vitro stained with antibody MNF116 directed against cytokeratins 5, 6, 8 and 17 but did not stain for antibodies to cytokeratin 18. The reverse staining pattern was true for the Harderian gland. Sections from the white lobe of the Harderian gland showed islets of serous secreting cells which showed positive staining when MNF116 was used. In situ, PAS positive cells were found in a small number of demilunes in the superior and inferior lacrimal glands and also in cells of the intercalated ducts. Surprisingly, in culture nearly all cells, including those isolated form the Harderian gland became PAS positive. In this study we have demonstrated that acinar cells from the Harderian and lacrimal glands of rabbit can be isolated and maintained in culture for 20 to 30 days, and that despite dramatic morphological changes, these cells retain their distinctive phenotype as indicated by antibody staining to specific cellular structural proteins such as cytokeratins and actin. However, the cultured cells also begin to produce mucins as indicated by PAS staining.