Microvascular permeability to IgG in the rat testis at puberty

Immunoglobulin G (IgG) spaces and permeability surface area products (PS) were calculated separately in the testis parenchyma, capsule and interstitial tissue in four age groups of rats to see if there were regional differences in microvascular permeability in the rat testis and if there were changes in PS with age. The results demonstrated a marked increase in PS to IgG at 27 days of age in the testicular interstitial tissue, whereas PS in the capsule did not show such consistent changes. Blood volumes per gram, as indicated by the 3 min IgG spaces, were considerably greater in the testicular capsule than in the interstitial tissue, although the weight of the capsule was only about one-third of the interstitial tissue weight. Maximal IgG spaces were reached at 5 h in the testicular parenchyma, but in most groups only at 20 h in the capsule. IgG was demonstrated immunohistochemically in the testicular interstitial tissue from 33 days of age onwards.     

Effects of haemorrhagic hypotension on the subcapsular artery and microvasculature of the rat testis

Developing germ cells may be sensitive to even moderate reductions in blood flow. Surprisingly, however, experimental evidence suggests that the rat testis may be unable to maintain its blood flow during a decrease in systemic blood pressure. This study was therefore performed in order to answer the following questions: Is the testis able to maintain its blood flow during moderate to major reductions in blood pressure and, if so, at which level of the testicular vasculature (main artery or microcirculation) does this compensatory response take place? Moderate (-20%) and major (-40%) reductions in blood pressure were induced in anaesthetized rats by haemorrhage and the effects on testicular microvascular blood flow and subcapsular testicular artery diameter were examined by using laser Doppler flowmetry and in vivo video-microscopy respectively. Haemorrhagic hypotension led to decreased local testicular blood flow, but the relative reductions in flow were generally only half as large as the reductions in blood pressure. Hypotension also decreased the diameter of the main subcapsular testicular artery. During large reductions in blood pressure the subcapsular testicular artery constricts and testicular blood flow decreases. However, blood flow is reduced proportionally less than the mean arterial pressure, suggesting that local regulatory mechanisms are present in the testicular microvasculature, which may prevent blood flow from falling below a critical level.     

Effects of prolactin on luteinizing hormone-stimulated testosterone secretion in isolated perfused rat testis

The direct peripheral effect of prolactin on LH-stimulated testosterone secretion was re-evaluated using the intact, isolated, perfused rat testis. In paired experiments, one testis was infused with the hormones being studied; the other testis of the same rat was used as the control. A dose-response curve of LH-stimulated testosterone secretion was established first. A dose of 300 ng of LH, which was on the ascending portion of the dose-response curve, was selected so that both stimulatory and inhibitory effects of prolactin could be observed. Prolactin doses ranging from 0 ng to 3000 ng were then tested to determine alterations in LH-stimulated testosterone secretion. Prolactin inhibited LH-stimulated testosterone secretion at low doses (less than 300 ng), but augmented LH action at high doses (greater than 1000 ng). These results showed that prolactin and LH interact with each other in a biphasic dose-dependent manner.     

Triolein-induced pulmonary embolization and increased microvascular permeability in isolated perfused rat lungs.

BACKGROUND: The pathophysiologic mechanism of the fat embolism syndrome is poorly understood. This study was designed to determine the effects of fat emboli on pulmonary vasculature. METHOD: Triolein was infused into isolated rat lungs perfused with Krebs-Henseleit buffer. Pulmonary arterial pressure and microvascular permeability (Kf) were measured at baseline and 20 minutes after the triolein infusion. RESULT: The 99% triolein produced dose-dependent increases in both pulmonary arterial pressure and Kf. The 65% triolein, containing free fatty acid, resulted in a greater increase in Kf. Pretreatment with indomethacin attenuated the increase in Kf after 65% triolein but not after 99% triolein. CONCLUSION: Pure triolein induced mainly embolization in the pulmonary vasculature, and 65% triolein caused embolization and subsequently increased vascular permeability, which are, at least in part, mediated by the action of cyclooxygenase products. Free fatty acids might induce permeability edema by means of a cyclooxygenase-dependent mechanism. We conclude that triolein-induced increases in pulmonary arterial pressure and Kf in isolated rat lungs provides a useful model of acute lung injury by fat embolism.     

Cutaneous thermal injury alters macromolecular permeability of rat small intestine

The intestinal epithelium normally provides a barrier function that prevents absorption of potentially harmful materials from the intestinal lumen. It has been postulated but never demonstrated that a cutaneous thermal injury will result in increased small-intestinal permeability. In a standardized 20% body surface area full-thickness scald injury, with polyethylene glycol 3350 and horseradish peroxidase used as permeability probes, small-intestinal permeability was examined regionally in an everted intestinal sac model. In the normal animals, the upper (proximal) and lower (distal) small intestine were less permeable to these probes than the middle segment. Within 6 hours after the injury, an increase in the mucosal uptake and transmural permeability was seen in all three small-intestinal segments; the most dramatic increase in permeability occurred in the ileum, p less than 0.01. The maximum increase in permeability was seen at 18 hours, and permeability was normal by 72 hours after the injury. This increase in intestinal permeability may represent a transient failure of the intestinal barrier function and may allow absorption of potentially toxic macromolecules from the intestinal lumen into the portal circulation early after thermal injury. Absorption of these macromolecules, such as endotoxin, may be potentially harmful by direct toxic actions or potentially helpful by activation of the immune system.     

Intestinal permeability and bacterial translocation following small bowel transplantation in the rat

In addition to its role in absorbing nutrients, the intestinal mucosa provides an important barrier against toxins and bacteria in the bowel lumen. The present study evaluated gut barrier function following orthotopic (in continuity) intestinal grafting in rats. Graft histology, intestinal permeability, and bacterial translocation to the grafted mesenteric lymph nodes, the host's liver, and the host's spleen were assessed on the 3rd, 5th, and 7th postoperative days. The study group received no immunosuppression after allotransplantation. The two control groups included rats with isografts and rats with cyclosporine-treated allografts. On the 7th POD, the study animals had moderate transmural inflammation due to rejection, with normal histology in the isografts and CsA-treated allografts; increased intestinal permeability, measured by urinary excretion of oral 51Cr-EDTA (P less than 0.01); and increased number of bacteria in the MLN and spleen (P less than 0.05). The number of bacteria in the MLN and spleen of the study group positively correlated with the changes in intestinal permeability (P less than 0.05). Rejection of the orthotopic intestinal graft leads to increased intestinal permeability and bacterial translocation from the lumen of the graft to the host's reticuloendothelial system. Measures to improve gut barrier function and antibiotic therapy during rejection episodes may help reduce the incidence of septic complications after intestinal grafting.     

Increased transcellular permeability of rat small intestine after thermal injury.

The pathway which results in a loss of intestinal barrier function and transepithelial transfer of macromolecules after cutaneous thermal injury is unknown. To determine the enhanced absorption pathway, transepithelial transport of horseradish peroxidase (HRP) was examined ultrastructurally after a thermal injury. Within 6 h after the injury, increased HRP uptake was seen in the portal and systemic blood with the maximal increase in uptake measured at 18 h postinjury; permeability returned to normal by 72 h postinjury. Morphologically, the increased uptake was found to be transcellular through ultrastructurally normal intestinal absorptive cells. Occasional focal regions of enhanced HRP uptake were found and this enhanced uptake was attributed to focal intestinal epithelial disruptions. This increase in intestinal permeability represents a transient loss of intestinal barrier function and potentially allows absorption of macromolecules such as endotoxin from the intestinal lumen into the portal circulation early after thermal injury.     

The importance of the Leydig cells in the vascular response to hCG in the rat testis

The increase in permeability of the testicular blood vessels following an injection of hCG into rats is abolished completely if the animals are treated 3 days earlier with ethane dimethane sulphonate (EDS), a compound that effectively eliminates Leydig cells from the testes. As there is other evidence that androgens or prostaglandins are not involved in this vascular response, further studies will be necessary to determine whether these data mean that another vasoactive substance is secreted by the Leydig cells or whether the EDS also eliminates other cells besides the Leydig cells, for example the mast cells found in the vicinity of the testicular artery.     

Response of rat testis to localized induced hyperthermia.

A method is presented in which the rat testis is extensively mobilized through a low abdominal incision, but in which its blood supply is carefully preserved. Localized hyperthermia is induced in this mobilized testis by water bath immersion. The tissue temperature is measured during and after immersion by means of a thermocouple inserted into the tissue. The relative sensitivity of spermatogenic tissue to increased temperature is confirmed and the relative resistance of Sertoli and Leydig cells is noted. Minimal or absent inflammatory reaction to thermal destruction of testicular cells is found as long as the tubule is intact. A marked peritesticular inflammatory response is noted when the total testicular tissue is destroyed at the highest temperature tested.     

Functional analysis of the cooled rat testis

Direct cooling of the testis results in the depletion of most germ cells in vivo. Germ cell-depleted testes are now commonly used to investigate spermatogenic regeneration and can serve as recipients for germ cell transplantation. The present study explored the effects of cooling rat testes on the depletion of endogenous germ cells, spermatogenic regeneration, and Sertoli cell function. Adult rat testes were cooled with iced Ringer's solution for 60 minutes, which results in the initiation of apoptotic germ cell loss within 8 hours. Pachytene spermatocytes at stages XII-I were the cells most sensitive to cooling. In 46%-67% of seminiferous tubule cross-sections, only Sertoli cells remained in the cooled testes 3-10 weeks after treatment. Germ cell loss was accompanied by a significant decrease in circulating inhibin B and an increase in follicle-stimulating hormone concentrations, which indicated a change in Sertoli cell function. Quantitative analysis of mRNA expression associated with apoptotic signals showed no significant uniform changes among the cooled testes, although some individuals had a distinct up-regulation of FAS mRNA at 24 hours. Attempts to use the cooled testes as recipient testes for mouse-to-rat germ cell transplantation were undertaken, but none of the mouse germ cells transplanted into the testes 15-34 days after cooling appeared to have undergone spermatogenesis 64-92 days after transplantation. These data suggest that modifications to Sertoli cell function resulting from testicular cooling create an environment that is unable to support spermatogenesis by donor germ cells.     

Iron-induced injury of rat testis

Summary. Male Wistar rats were intraperitoneally injected twice with 0.4 mmol kg⁻¹ FeSO₄. One, 2 and 4 days after the second Fe injection, Fe and malondialdehyde (MDA) content in testis was measured, the morphology studied by light and electron microscopy and the number of spermatids counted. After Fe injection, Fe and MDA content had increased in parallel. Light microscopic inspection on days 1 and 2 after Fe injection revealed numerous necroses in the different cell types of the germ epithelium. Four days after Fe injection, fewer alterations were found. Electron microscopic investigations revealed that some spermatids contained up to three nuclei and at least three axonemes. In some sperm tails up to 11 axonemes were found. In some midpieces two or three complexes of axonemes, outer dense fibres and mitochondria were observed. In other midpieces axonemes were absent and replaced by granular and filamentous material. The number of spermatids was reduced 4 days after Fe treatment. The increase in the number of axonemes was similar to that seen in Mg and Zn deficiency, indicating that the increase in Fe content and oxygen free radicals is the major reason for the biochemical and morphological alterations in Mg and Zn deficiency.     

New perspectives on the microvasculature of the islets of Langerhans in the rat

The vasculature of the islets of Langerhans was studied in rats using methacrylate corrosion casts and islet reconstructions from stained serial paraffin sections. In corrosion casts, which allowed a three-dimensional view of the pancreatic vasculature, all islets had one or two afferent arterioles, which gave off numerous capillaries to form a glomerular-like network. Islets could be grouped in three classes on the basis of size. Moreover, these classes had preferential locations within the vascular tree: the smaller the islet, the more peripheral. In small islets (those less than 160 micrometers in diameter) efferent capillaries arose from this network and either coalesced at the periphery of the islet or passed through perinsular exocrine tissue before coalescing into venules. However, in intermediate islets (those 160--260 micrometers in diameter) and large islets (those greater than 260 micrometers in diameter) efferent capillaries usually coalesced at the edge of the islet forming an extensive fingerlike network of collecting venules over the islet. This suggested that at least in the rat a large amount of the islet tissue is directly drained by venules. In serial paraffin sections of islets perfused with India ink and stained alternately for B-cells or for non-B-cells, the relation of the blood vessels and the organized array of different cell types making up the islet was discernible. In islets of all sizes, the afferent arterioles entered the islet of all sizes, the afferent arterioles entered the islet at discontinuities of the mantle of non-B-(glucagon, somatostatin, and pancreatic polypeptide) cells. Entering at the B-cell mass, the arterioles broke into capillaries that traversed the B-cell core before passing through the opposite non-B-cell mantle. The afferent capillaries coalesced into collecting venules outside the islet. In intermediate and large islets, the overlying collecting venule network was closely apposed to the mantle. These anatomic findings indicate that in the rat islet only some of the efferent vessels are part of a insuloacinar portal system and that the afferent vessels reach the B-cell core without passing through the non-B-cell islet tissue.     

Pentoxifylline in the isolated perfused rat kidney

The effects of pentoxifylline, a new methylxanthine with marked hemorrheologic properties, were studied following brief renal artery occlusion in the isolated rat kidney model perfused with cell-free Krebs-Henseleit buffer. Anuria was observed in 3 of 6 control kidneys within 5 min after reperfusion; urine flow was maintained in all rat kidneys perfused with pentoxifylline (2500 ng/ml). Glomerular filtration rate was significantly greater in kidneys administered pentoxifylline compared with controls following 40 min of postocclusion reperfusion (460 +/- 100 vs. 100 +/- 110 microliters/min/gKW; P less than 0.01). Pretreatment of kidneys with indomethacin, a nonspecific cyclooxygenase inhibitor, blocked the protective effects of pentoxifylline in this setting. These data suggest that the addition of pentoxifylline may prevent hypoxia-related changes in renal function of transplanted kidneys. Stimulation of renal prostaglandin synthesis, as well as an interaction at the level of the adenosine receptors, were most likely responsible for the observed beneficial effects of pentoxifylline.     

The effect of ischemia on ascites secretion in the perfused rat liver

The ascites fluid secreted by the isolated perfused liver was studied in rats. The quantity of fluid appearing on the surface of the isolated perfused liver was independent of the pressure in the portal vein and could be raised by the amount of fluid flowing through the liver. Irrespective of the flow conditions, the ischaemic liver will produce more ascites than the intact liver und similar conditions. A rise of hepatic oncotic pressure will not reduce ascites production by the ischaemic liver. With respect to osmolarity there is no difference between the perfusing fluid and ascites. As regards the quantity of bilirubin secreted with ascites no significant difference was found between the control and the ischaemic group. The pertaining literature and the theories of ascites formation are discussed.     

Reconsideration of the lymphatic drainage of the rat testis

Gynogenetic diploid individuals were produced in an anuran amphibian, Xenopus laevis, and their response to skin grafts exchanged among siblings was studied. All skin grafts exchanged among nongynogenetic sibling froglets, as well as those from genetically unrelated donors, were rejected within 30 days. More than half (57%) of the gynogens that received grafts from sibling partners exhibited a prolonged survival (over 30 days), including long-term survival of over 120 days in 13%. The skin grafted from genetically unrelated froglets onto Nieuwkoop and Faber stage 42-56 larvae and onto perimetamorphic stage 58-65 animals was rejected within 30 days. Similarly, most (96%) of the skin grafts from outbred sibling froglets onto larvae at these stages were rejected acutely or subacutely (12-39 days). However, the skin grafted from sibling froglets to gynogens at larval stage 42-56 and perimetamorphic stage 58-61 enjoyed a long-term survival significantly more frequently (81%) than that in the final metamorphic (stage 64-65) counterparts (57%). These results support the view that in the adult Xenopus allograft responses are reactions to a single MHC as well as to cumulative, multiple minor H-locus barriers. The results also suggest that in larval stages the responses against minor H-locus barriers are generated only mildly.     

Glyburide sensitizes perfused rat liver to insulin-induced suppression of glucose output

Glyburide, a second-generation sulfonylurea, is used in the treatment of NIDDM because of its hypoglycemic action. However, the site and mechanism of action of this sulfonylurea remain unclear. We examined the ability of glyburide to enhance insulin's inhibitory effect on glucagon-stimulated hepatic glucose production. The livers of fed male rats were perfused with a Krebs-Henseleit buffer containing washed human red blood cells. After a 60-min control period during which the liver was exposed to both insulin and glucagon (10 microU/ml and 11 pg/ml, respectively), the glucagon concentration was increased to 88 pg/ml in the presence of 0, 10, 40, and 240 microU/ml of insulin. Hepatic glucose output and phosphorylase a activity were monitored during the control and elevated-glucagon periods. The glyburide-infused group received glyburide (1.6 microgram/ml) during both the control and elevated-glucagon periods. As expected, high levels of insulin suppressed glucagon-stimulated glucose production and phosphorylase activation. Insulin at a concentration of 10 microU/ml was unable to suppress glucagon's stimulation of glucose production or its activation of phosphorylase. However, in the presence of glyburide it was able to decrease stimulated hepatic glucose production and phosphorylase activation by 40 and 50% respectively. In the absence of insulin, glyburide was unable to suppress glucagon's glycogenolytic action, suggesting that the drug potentiates insulin's action on the liver rather than exerting an inhibitory effect directly. Insulin at a concentration of 240 microU/ml completely suppressed glucagon action, and glyburide had no additional effect. Therefore, glyburide is able to enhance the sensitivity of the perfused rat liver to insulin without altering maximal insulin responsiveness.