Vascular perfusion

FIGURE 9.14 Effects of adenosine receptor agonist 2-chloro-adenosine on vascular perfusion pressure of isolated perfused rat kidneys. Minor effects seen in untreated kidneys (filled circles) and pronounced vasoconstriction while vasodilatation in kidneys coperfused with subthreshold concentrations of a-adrenoceptor vasoconstrictor methoxamine and vasodilatatory activation of adenylyl cyclase with forskolin (open circles). Redrawn from [49]. 

Figure 2.8 Effective permeability coefficients (Peff) (xlO-6) of verapamil calculated from appearance in venous blood (P 00 ) and disappearance from lumen (Peff) in the presence and absence of PSC833, midazolam, or ketoconazole in the vascularly perfused intestinal.

Devries MH, Rademaker CM, Geerlings C, Vandijk A and Noordhoek J (1989) Pharmacokinetic Modeling of the Effect of Activated-Charcoal on the Intestinal Secretion of Theophylline, Using the Isolated Vascularly Perfused Rat Small-Intestine. J Pharm Pharmacol 41 pp 528-533. 

McMaster D, Steel L and Love AH (1983) The Isolated, Vascularly Perfused, Small-Intestine of the Rat—A Useful Tool for the Study of Absorption in Nutritional Deficiency. IrJ Med Sci 152 pp 329-335. 

Cong D, Fong AK, Lee R and Pang KS (2001) Absorption of Benzoic Acid in Segmental Regions of the Vascularly Perfused Rat Small Intestine Preparation. Drug Metab Dispos 29 pp 1539-1547. 

Intramuscular and subcutaneous injections are by far the most common means of parenteral drug administration. Because of the high tissue blood flow and the ability of the injected solution to diffuse laterally, drug absorption generally is more rapid after intramuscular than after subcutaneous injection. Drug absorption from intramuscular and subcutaneous sites depends on the quantity and composition of the connective tissue, the capillary density, and the rate of vascular perfusion of the area. These factors can be influenced by the coinjection of agents that alter local blood flow (e.g., vasoconstrictors or vasodilators) or by substances that decrease tissue resistance to lateral diffusion (e.g., hyaluronidase). 

The accessibility may be low if it is located in a tissue, which is distant from the site of exposure or with poor vascular perfusion. Alternatively, it may be in a compartment of the cell, which is protected by membranes, which are not readily permeable to the toxicant mitochondria, for example. The accessibility of DNA will vary with the cell cycle. 

Regulation ofpulmonary vascular perfusion in advanced respiratory disease... 

Kidney tissue is fixed with paraformaldehyde-lysine-periodate by vascular perfusion (Brown et al., 1996). Tissue slices are further fixed overnight at4°C with the same fixative and stored in PBS (pH 7.4) containing 0.02% sodium azide. They are placed in 30% sucrose in PBS for at least 1 hr, and then surrounded by a drop of Tissue-Tek embedding medium on a cryostat chuck before freezing by immersion in liquid nitrogen. Cryostat sections about 5 p,m thick are cut at a chamber temperature of -25°C, collected on Fisher Superfrost Plus charged slides, and stored at —20°C until use. 

Ginkgo Ginkgo biioba Leaf of the gingko tree Improve memory and cognition increase vascular perfusion of brain and other tissues antioxidant antiinflammatory... 

Liu S, Tam D, Chen X, et al. P-glycoprotein and an unstirred water layer barring digoxin absorption in the vascularly perfused rat small intestine preparation induction studies with pregnenolone-16alpha-carbonitrile. Drug Metab Dispos 2006 34 1468-1479. 

The l,25(OH)2D3-stimulated transport of calcium across the intestinal epithelium has been extensively studied in our laboratory. l,25(OH)2D3 can stimulate rapid transport of calcium in vascularly perfused chick duodenal loops [19] before the ap-... 

Zinc Transport by Isolated, Vascularly Perfused Rat Intestine and Intestinal Brush Border Vesicles... 

Studies of zinc transport with isolated, vascularly perfused rat intestine and brush border vescicles fail to support a role for a unique binding ligand in zinc absorption. 

The second step in zinc absorption involves the intracellular interaction of zinc with various compounds which may enhance or impede absorptive processes. In 1969, Starcher noted that radioactive copper, given orally, associated with a low molecular weight protein (25). Subsequently, this mucosal protein was isolated and characterized by Richards and Cousins, who classified it as a metallothionein (26), and who further showed that it was induced in response to zinc administration (5). The appearance of this metallothionein, with properties similar to those described for both rat (27) and human (28) liver metallothionein, appears to be related to changes in both dietary zinc status and plasma zinc levels (5). The synthesis of mucosal metallothionein has been shown to be under transcriptional control (29,30). Menard al. reported that dietary zinc administration resulted in enhancement of metallothionein mRNA transcription and its subsequent translation, to yield nascent metallothionein polypeptides(31). The intestinal metallothionein appearance was correlated to both an increase in mucosal zinc content primarily associated with the protein and with a decrease in serum zinc levels. In addition. Smith e al., using the isolated, vascularly perfused intestinal system, reported an inverse relationship between the synthesis of metallothionein and zinc transfer to the portal system, confirming earlier studies (32). 

In recent experiments, we have employed two approaches to examine specific aspects of zinc absorption. The Isolated, vascularly perfused rat intestine has been employed to examine absorption at the organ level. Isolated brush border membranes from rat intestine have been used to study the transfer of zinc across the intestinal surface. 

The Isolated, vascularly perfused rat intestine system has been used to investigate the influence of various zinc-binding ligands on zinc absorption. With this approach the functional integrity of the intestine with respect to several minerals, including calcium, iron and zinc uptake, and subsequent transfer of these minerals to their respective serum transport proteins is maintained (32,33). The intestinal perfusion system allows the simultaneous measurement of both mucosal zinc uptake (retention) and transfer to the portal circulation (absorption), and thus provides detailed information on the nature of the mechanisms of both uptake from the lumen and transfer to albumin in the portal circulation. 

In addition to factors Influencing luminal uptake of zinc, transfer across the basolateral membrane has been shown to be dependent on the concentration of albumin in the portal circulation (33). These investigations suggest that metabolic factors which affect the albumin concentration in the plasma may also affect the rate of portal zinc transfer. It should be noted that EDTA did not enhance zinc accumulation within the mucosal cells yet it Increased transfer to the vascular perfusate. These results suggest that basolateral membrane transport of zinc is enhanced by EDTA. We have proposed (35), as has Davies (38), that basolateral transport to the circulation is the rate limiting phase of zinc absorption. Since EDTA and zinc might be transported as a complex (42), the latter may transverse this barrier more easily and thus Increase zinc absorption. 

In addition to the vascular perfusion system studies, we have employed brush border membrane vesicles. Isolated from rat mucosa, to determine more closely the parameters of mucosal zinc transport (43). These vesicle preparations represent the best means currently available to delineate the characteristics of zinc transfer into mucosal cells. The technique permits isolation of the microvillous membrane free of other cellular contaminants, as determined by established procedures (44). 

The studies reported here using the isolated, vascularly perfused rat intestine system and isolated brush border membrane vesicles fail to support a role for a specific zinc-binding ligand involved in zinc uptake in the rat. Rather, the extent of zinc uptake involves the interaction of several phenomena, including both extracellular and intracellular reactions. It appears that the major pathway of zinc uptake under normal dietary conditions involves the transfer of zinc from various dietary components to a carrier mediated transport system at the brush border membrane. The net absorption of zinc from the lumen could involve a competition between various dietary components, zinc binding ligands and the membrane carrier for zinc. Thus, in some cases, those compounds in the lumen with a higher affinity for zinc than the membrane component will be less likely to permit transfer of zinc to the carrier, while compounds with a lower affinity for zinc will increase the amount of zinc made... 

During maintenance of the vascular perfusion for approx 10 min, cut away the liver. Cut up either side of the trachea. Remove tissue and membrane overlying the trachea. Insert and tie in the plastic tracheal cannula just below the larynx. 

HBSS (500 mL) used for the vascular perfusion, and the other from a beaker of HBSS/EDTA (150 mL) to which is added the subdiisin for the enzyme perfusion. These are switched to a common tube via the pump to the top of the oxygenator. The oxygenator is enclosed in a water jacket filled fn n the same water bath at 37°C in which the solutions are maintained. Oxygenated effluent from the bottom of the oxygenator goes via the second pump to be connected to either the arterial or the tracheal cannula. 

The isolated vascular perfused liver preparation mimics the liver in vivo and has normal cell-cell topography, vasculature, blood, and bile hows. This model is used to directly measure the contribution of the Uver in the presystemic eUminahon of drugs, and to evaluate factors that affect this process. 

TABLE 16.1 Major Applications of Vascular Perfused Organs in Drug-Candidate Optimization and Development... 

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