Histomorphology of the hamster cheek pouch

Histomorphology of the cheek pouch was studied in 14 hamsters by light and transmission electron microscopy. The cheek pouch wall was devoid of any lymphatic tissue and dense subepithelial tissue (i.e. the lamina propria) would render lymph drainage almost impossible and might constitute impermeable morphological barrier for non-recognition of transplants evoking a host immune response. Because in the literature it was reported that there is absence of any arteriovenous anastomoses on the pouch wall, and interruption of arterial supply failed to alter the growth rate of tissue grafts, we speculated that epidermal growth factors present in the saliva could play a role in maintaining the growth of tissue transplants.     

Experimental paracoccidioidomycosis of hamster inoculated in the cheek pouch

We compared the granuloma morphology and immune response of hamsters inoculated withParacoccidioides brasiliensis (Pb) into the cheek pouch, which lacks lymphatic drainage, and into the footpad, which is rich in lymphatics. Our objective was to better understand the modulation ofPb granuloma in an immunocompetent animal inoculated in an immunologically privileged site. The humoral immune response (ELISA) and cell mediated immunity (footpad test) became positive on days 7 and 14, respectively in animals inoculated into footpad and on days 35 and 60 in animals inoculated into the pouch. Typical epithelioid granulomas were observed at both sites on day 14. The number of fungi gradually decreased from the beginning of the experiment in footpad lesions, but only after day 35 in pouch granulomas, when cell mediated immunity was detectable. The results indicate that typical epithelioid paracoccidioidomycotic granulomas may develop in the absence of a detectable immune response; however, they are incapable of controlling fungal reproduction. Lack of lymphatic drainage delays the appearance of a detectable immune response, but with time fungi escape from the pouch, elicit an immune response and reach other organs. Our results further indicate the importance of the lymphatics in the pathogenesis of paracoccidioidomycosis.Abbreviations HCP hamster cheek pouch - Pb Paracoccidioides brasiliensis - Pbmycosis Paracoccidioidomycosis     

Tyrosine kinase inhibitors modulate agonist-induced vasodilation in the hamster cheek pouch.

The purpose of this study was to determine whether inhibitors of tyrosine kinase attenuate vasodilation elicited by endogenously elaborated and exogenously applied nitric oxide in the in situ peripheral microcirculation. Using intravital microscopy, we found that pretreatment with genistein (1.0 microM) and tyrphostin 25 (10.0 microM), two structurally unrelated tyrosine kinase inhibitors, significantly attenuated acetylcholine-, bradykinin- and nitroglycerin-induced dilation of second-order arterioles (51 +/- 1 microm) in the in situ hamster cheek pouch (P < 0.05). Both inhibitors nearly abrogated acetylcholine-induced responses but only partially blocked bradykinin- and nitroglycerin-induced vasodilation. Genistein and tyrphostin 25 alone had no significant effects on resting arteriolar diameter and on adenosine-induced vasodilation in the cheek pouch. On balance, these data indicate that tyrosine kinase inhibitors attenuate endogenously elaborated and exogenously applied nitric oxide-induced vasodilation in the in situ hamster cheek pouch. However, the extent of tyrosine kinase inhibitor-sensitive pathway involvement in this response appears to be agonist dependent.     

Free-radical inhibition of ATPase in hamster cheek pouch homogenates

The effects of free-radicals generated by either the oxidation of hypoxanthine by xanthine oxidase (HX/XO) or the lipoxidation of arachidonic acid (AA) on the ATPase of the hamster cheek pouch has been studied. Cheek pouches were removed from female golden syrian hamsters and homogenized. ATPase activity was measured by the production of Pi at 37 degrees. HX/XO and AA were added at a final concentration of 9.6 X 10(-5) M HX with 5 X 10(-2) units HX and 5 X 10(-5) M AA with and without 1 X 10(-4) M ouabain. HX/XO produced a 24.7% inhibition alone and 35.0% when combined with ouabain. Ouabain alone produced a 7.1% inhibition. AA produced a 23.6% inhibition alone and 24.3% inhibition when combined with ouabain. Ouabain alone produced a 5.4% inhibition in this series. When AA was added in doses ranging from 1 X 10(-5) to 2 X 10(-3) M, a plot of percent inhibition versus log dose followed a typical sigmoid type curve. The IC50 was 1.5 X 10(-4) M. These results suggest that free-radicals are capable of inhibiting the ATPase found in the hamster cheek pouch tissues. The possible modes of action of the free-radicals in producing this inhibition are discussed.     

Ultrastructural and autoradiographic observations of hamster cheek pouch epithelium grown in vitro.

Epithelial outgrowths from hamster cheek pouch explants were cultured for varying periods of time up to 22 days. Growth of the epithelial sheets was monitored, employing colcemid for demonstrating mitotic activity and tritiated thymidine for DNA synthesis. Mitoses and thymidine uptake were observed among epithelial outgrowths at a considerable distance form the original explant. The epithelial nature of the growing cell sheets was confirmed, employing electron microscopic techniques. The cells exhibited the presence of tonofilaments, desmosomes, ribosomes, Golgi, mitochondria, and rough endoplasmic reticulum. The cultured explants were treated with cyclic nucleotides in order to investigate their modulatory effects on epithelial cell differentiation. Dibutyryl cAMP induced marked mitotic inhibition (46.3%) in our assay, which was increased to 57% with the addition of theophylline. Dibutyryl cGMP showed only a mild (5%) stimulatory effect on mitotic activity. Dibutyryl cAMP enhanced keratinization in the epithelial cell outgrowths with the biogenesis of keratohyalin granules, whereas dibutyryl cGMP did not produce any observable alterations.     

Iron deficiency depresses cell proliferation in hamster cheek pouch epithelium

Iron deficiency anaemia was induced in hamsters by feeding a low iron diet coupled with weekly bleeding. To assess cell proliferation, the stathmokinetic agent vinblastine sulphate was administered and cell birth rates were calculated from cumulative mitotic indices. The rate was significantly reduced in epithelium from iron-deficient animals. The uptake of tritiated thymidine [( 3H]TdR) was also significantly reduced in these animals. Results of both stathmokinetic and labelling experiments indicate that cell production in the cheek pouch epithelium of iron-deficient animals is impaired.     

Hog barn dust extract increases macromolecular efflux from the hamster cheek pouch.

The purpose of this study was to determine whether short-term exposure to an aqueous extract of hog barn dust increases macromolecular efflux from the intact hamster cheek pouch and, if so, to begin to determine the mechanism(s) underlying this response. By using intravital microscopy, we found that suffusion of hog barn dust extract onto the intact hamster cheek pouch for 60 min elicited a significant, concentration-dependent leaky site formation and increase in clearance of FITC-labeled dextran (molecular mass, 70 kDa). This response was significantly attenuated by suffusion of catalase (60 U/ml), but not by heat-inactivated catalase, and by pretreatment with dexamethasone (10 mg/kg iv) (P < 0.05). Catalase had no significant effects on adenosine-induced increase in macromolecular efflux from the cheek pouch. Suffusion of hog barn dust extract had no significant effects on arteriolar diameter in the cheek pouch. Taken together, these data indicate that hog barn dust extract increases macromolecular efflux from the in situ hamster cheek pouch, in part, through local elaboration of reactive oxygen species that are inactivated by catalase. This response is specific and attenuated by corticosteroids. We suggest that plasma exudation plays an important role in the genesis of upper airway dysfunction evoked by short-term exposure to hog barn dust.     

Iron deficiency depresses cell proliferation in hamster cheek pouch epithelium

Abstract. Iron deficiency anaemia was induced in hamsters by feeding a low iron diet coupled with weekly bleeding. To assess cell proliferation, the stathmokinetic agent vinblastine sulphate was administered and cell birth rates were calculated from cumulative mitotic indices. The rate was significantly reduced in epithelium from iron-deficient animals. The uptake of tritiated thymidine ([³H]TdR) was also significantly reduced in these animals. Results of both stathmokinetic and labelling experiments indicate that cell production in the cheek pouch epithelium of iron-deficient animals is impaired.     

Effects of tetraiodothyronine and triiodothyronine on hamster cheek pouch microcirculation

The aim of the present study was to assess the effects of topically applied triiodothyronine (T(3)) and thyroxine (T(4)) on the arterioles of hamster cheek pouch microcirculation in vivo. Microvessels were visualized using a fluorescent microscopy technique. Topical application of T(3) (3.08, 30.8, 61.5, 307, 615, and 6,150 nM/l) consistently induced dose-dependent dilation of arterioles within 2.0 +/- 0.5 min of administration. The application of T(4) (150, 257, 514, and 5,140 nM/l) caused different dose-dependent effects: dilation at the three lower doses within 16 +/- 2 min and rhythmic diameter changes at the highest dose. Aging of hamsters did not alter the arteriolar responses to T(3) and T(4). T(3)-induced dilation was countered by the inhibition of nitric oxide synthase with N(G)-nitro-L-arginine-methyl ester or N(G)-nitro-L-arginine. Iopanoic acid (IPA), which inhibits types I and II 5'-deiodinase, abolished the dilation elicited by 514 nM T(4) but did not affect T(3)-dependent dilation. 6-Propyl-2-thiouracil (PTU), which inhibits type I 5'-deiodinase only, did not affect the dilation induced by T(4). IPA and PTU did not impair arteriolar dilation induced by acetylcholine or sodium nitroprusside. These results indicate that T(3) induces arteriolar dilation, likely through nitric oxide release. The local conversion of T(4) to T(3) appears to be crucial for the dilation induced by T(4).     

A modified technique for permeability studies in the superfused hamster cheek pouch

We report here a modification of the superfused hamster cheek model for use in vascular permeability studies. Radio-iodine labeled serum albumin (I-125 RISA) is injected prior to the superfusion period. Plasma content is calculated on a μ1/100mg wet weight basis and compared to the contralateral (non-superfused) cheek pouch. Water content is calculated on a percentage basis and compared in the same manner. Results demonstrate that superfusion causes an increase in permeability of protein and water. Plasma content is reduced by catalase, indomethacin or FPL 55712 pretreatment, suggesting that free-radicals, prostaglandis and leukotrienes are released during superfusion. Water content increase is refractory to pretreatment. The advantages of this system and its application are discussed.     

Regulation of flow and wall shear stress in arteriolar networks of the hamster cheek pouch.

Our purpose was to define arteriolar network hemodynamics during moderate increases in interstitial adenosine or nitric oxide in the hamster (n = 34, pentobarbital sodium 70 mg/kg) cheek pouch tissue. The network consists of a feed arteriole (approximately 12-microm diameter, approximately 800-microm length) with three to six branches. Observations of diameter, red blood cell flux, and velocity were obtained at the feed before the branch and within the branch. A comparison of baseline with suffused adenosine or sodium nitroprusside (SNP) 10(-9) to 10(-5) M showed the following. First, diameter change was heterogeneous by agonist, did not reflect the expected dilatory response, and was related to location within the network. With adenosine, upstream branch points constricted and those downstream dilated, even at 10(-5) M. With SNP, upstream branch points dilated, whereas those downstream constricted. Second, with adenosine, changes in diameter, flux, and velocity together resulted in no change in wall shear stress until 10(-5) M. Wall shear stress was not maintained at a constant level with Nomega-nitro-L-arginine (10(-5) M), suggesting a role for flow-dependent diameter changes with adenosine. With SNP, diameter change correlated with the baseline (before SNP) shear stress conditions.     

Ultrastructural and autoradiographic observations of hamster cheek pouch epithelium grown in vitro

Summary Epithelial outgrowths from hamster cheek pouch explants were cultured for varying peroids of time up to 22 days. Growth of the epithelial sheets was monitored, employing colcemid for demonstrating mitotic activity and tritiated thymidine for DNA synthesis. Mitoses and thymidine uptake were observed among epithelial outgrowths at a considerable distance from the original explant. The epithelial nature of the growing cell sheets was confirmed, employing electron microscopic techniques. The cells exhibited the presence of tonofilaments, desmosomes, ribosomes, Golgi, mitochondria, and rough endoplasmic reticulum. The cultured explants were treated with cyclic nucleotides in order to investigate their modulatory effects on epithelial cell differentiation. Dibutyryl cAMP induced marked mitotic inhibition (46.3%) in our assay, which was increased to 57% with the addition of theophylline. Dibutyryl cGMP showed only a mild (5%) stimulatory effect on mitotic activity. Dibutyryl cAMP enhanced keratinization in the epithelial cell out-growths with the biogenesis of keratohyalin granules, whereas dibutyryl cGMP did not produce any observable alterations.     

Bradykinin- and substance P-induced edema formation in the hamster cheek pouch is tyrosine kinase dependent.

The purpose of this study was to determine whether protein tyrosine kinase, a ubiquitous family of intracellular signaling enzymes that regulates endothelial cell function, modulates bradykinin- and substance P-induced increase in macromolecular efflux from the intact hamster cheek pouch microcirculation. Using intravital microscopy, I found that suffusion of bradykinin or substance P (each, 0.5 and 1.0 microM) onto the cheek pouch elicited significant, concentration-dependent leaky site formation and increase in clearance of fluorescein isothiocyanate-dextran (FITC-dextran; molecular mass, 70 kDa; P < 0.05). These responses were significantly attenuated by suffusion of genistein (1.0 microM) or tyrphostin 25 (10 microM), two structurally unrelated, nonspecific protein tyrosine kinase inhibitors (P < 0.05). Conceivably, the kinase(s) involved in this process could be agonist specific because genistein was more effective than tyrphostin 25 in attenuating bradykinin-induced responses while the opposite was observed with substance P. Both inhibitors had no significant effects on adenosine (0.5 M)-induced responses (P > 0.5). Collectively, these data suggest that the protein tyrosine kinase metabolic pathway modulates, in part, the edemagenic effects of bradykinin and substance P in the intact hamster cheek pouch microcirculation in a specific fashion.     

Effects of antioxidant enzyme overexpression on the invasive phenotype of hamster cheek pouch carcinoma cells.

To examine the role of reactive oxygen species on the invasive phenotype of cancer cells, we overexpressed manganese- and copper-zinc-containing superoxide dismutases (MnSOD, CuZnSOD) and catalase (Cat) in hamster cheek pouch carcinoma (HCPC-1) cells in vitro using adenoviral vector-mediated gene transfer. Hamster cheek pouch carcinoma cells were transduced with these adenoviral vector constructs alone, or in combination, at concentrations [i.e., multiplicity of infectivity (MOI)] of 100 MOI each. The Escherichia coli beta-galactosidase reporter construct was used as a control virus. Protein expression was examined by Western blot analysis and enzymatic activities were measured using spectrophotometry. To observe the effects of transgene overexpression on in vitro tumor cell invasion, we used the membrane invasion culture system, an accurate and reliable method for examining tumor cell invasion, in vitro. This assay measures the ability of tumor cells to invade a basement membrane matrix consisting of type IV collagen, laminin, and gelatin. MnSOD overexpression resulted in a 50% increase in HCPC-1 cell invasiveness (p < .001); co-overexpression of MnSOD with Cat partially inhibited this effect (p < .05). Moreover, co-overexpression of both SODs resulted in a significant increase in invasiveness compared with the parental HCPC-1 cells (p < .05). These changes could not be correlated with the 72 kDa collagenase IV or stromolysin activities using zymography, or the downregulation of the adhesion molecules E-cadherin or the alpha4 subunit of the alpha4beta1 integrin. These results suggest that hydrogen peroxide may play a role in the process of tumor cell invasion, but that the process does not rely on changes in matrix metalloproteinase activity in the cells, or the expression of cell adhesion molecules.