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Don Prashad - One of the best experts on this subject based on the ideXlab platform.

  • the avian Renal Portal System a model for studying nephrotoxicity of xenobiotics
    Toxicology Letters, 1990
    Co-Authors: Richard Blackburn, Don Prashad
    Abstract:

    In avian species, there is a dual afferent blood supply to the kidney via a ‘high pressure’ (160/120 mmHg) Renal artery and in addition a ‘low pressure’ (25 mmHg) supply via a Renal Portal System (RPS). Glomerular areas of the kidney are supplied by the Renal artery; peritubular areas partly by efferent glomerular arterioles and also by venous return from the legs communicating with the RPS. The magnitude of the Renal Portal supply reaching the peritubular areas appears to be controlled by an autonomically innervated smooth muscle valve [l], the Renal Portal valve. When the valve contracts and closes, either naturally or as a result of treatment with exogenous substances, blood perfuses the peritubular areas of the kidney finally returning to the posterior vena cava via the Renal vein. When the valve is open, blood is shunted directly to the posterior vena cava. The existence of two effectively separate circulations, one mainly for glomerular areas and one for peritubular tissue, confers some advantages over mammalian Systems in studies on Renal ‘handling’ of nephrotoxic substances and pha~acolo~cally active agents. Unilateral injection of an exogenous substance, together with markers for filtration and tubular secretion can be made directly into the peritubular circulation of one kidney (homolateral) and excretion patterns from both kidneys monitored separately using indwelling ureteral cannulae. This enables the response of the homolateral kidney to be simultaneously compared with the uninjected (contralateral) kidney which acts as a control within the same individual. Using this System, the excretion patterns of phenol red [2] and bipyridinium compounds [3] have been investigated. In these studies, homolateral excretion of these compounds, which are

Peter H Holz - One of the best experts on this subject based on the ideXlab platform.

  • Anatomy and Physiology of the Reptile Renal System.
    Veterinary Clinics of North America: Exotic Animal Practice, 2020
    Co-Authors: Peter H Holz
    Abstract:

    Reptile kidneys maintain a constant extracellular environment within the body. They excrete waste products, maintain normal concentrations of salt and water, regulate acid-base balance, and produce hormones and vitamins. The kidneys contain nephrons consisting of glomeruli designed to filter the plasma, Bowman capsules that collect the filtrate, and tubules that resorb most of the filtered water and nutrients while excreting waste metabolites. A Loop of Henle is absent. Therefore, reptile kidneys cannot produce a hypertonic urine. The urinary bladder (if present) and cloaca excrete and absorb additional fluids and electrolytes. A Renal Portal System is present in all reptiles.

  • Effect of Injection Site on Carbenicillin Pharmacokinetics in the Carpet Python, Morelia spilota
    Journal of herpetological medicine and surgery, 2020
    Co-Authors: Peter H Holz, John P. Burger, Kirby Pasloske, Rupert T. Baker, Sam Young
    Abstract:

    ABSTRACT The premise that drugs should not be injected into the caudal body of reptiles because they will be carried by the Renal Portal System to the kidneys and rapidly excreted was tested by comparing the pharmacokinetics of carbenicillin in carpet pythons, Morelia spilota, injected anteriorly with those injected posteriorly. Seven carpet pythons were treated with 200 mg/kg carbenicillin administered intramuscularly. Three were injected anteriorly and four posteriorly. Serial blood samples were withdrawn over a period of 120 hr. Carbenicillin blood levels were measured over each time period and results used to calculate maximum carbenicillin plasma level, time of maximum plasma level, terminal half-life, area under the curve, volume of distribution and total body clearance. The study was repeated five months later with those snakes that were previously injected anteriorly now being injected posteriorly and vice versa. Blood was taken and the same parameters calculated. Following all calculations no sig...

  • the reptilian Renal Portal System a review
    Bulletin of the Association of Reptilian and Amphibian Veterinarians, 1999
    Co-Authors: Peter H Holz
    Abstract:

    ABSTRACT The anatomy of the reptilian Renal Portal System is reviewed. Its structure is fundamentally similar in all species examined. The Renal Portal System functions to provide blood to tubule cells during periods of dehydration to prevent them undergoing ischaemic necrosis. Blood flows from the tail and hindlimbs through the kidneys and then on to the heart. However, anastomoses exist capable of shunting blood around the kidneys to the liver. Current data suggests that the Renal Portal System does not affect drug kinetics.

  • the anatomy and perfusion of the Renal Portal System in the red eared slider trachemys scripta elegans
    Journal of Zoo and Wildlife Medicine, 1997
    Co-Authors: Peter H Holz, Ian K Barker, Graham J Crawshaw, Howard Dobson
    Abstract:

    The anatomy of the Renal Portal System of the red-eared slider (Trachemys scripta elegans) is described, based on dissection of six double latex-injected specimens (three males, three females). The anatomy of these vessels, which had not previously been described in this species, was found not to differ significantly from the fundamental chelonian pattern. Fluoroscopic radioangiography revealed that venous blood returning from the hindlimbs flowed predominantly to the liver and bypassed the kidneys. Blood from the tail either flowed to the kidneys or bypassed them and flowed directly to the liver. A putative valve is described that governs venous blood flow from the caudal body to or around the kidneys.

  • The effect of the Renal Portal System on pharmacokinetic parameters in the red-eared slider (Trachemys scripta elegans).
    Journal of Zoo and Wildlife Medicine, 1997
    Co-Authors: Peter H Holz, Ian K Barker, Graham J Crawshaw, John P. Burger, Peter D. Conlon
    Abstract:

    The premise that drugs not be injected into the caudal body of reptiles because they will be carried by the Renal Portal System to the kidneys, where they may be nephrotoxic or rapidly excreted, was tested by comparing the pharmacokinetics of gentamicin (excreted via glomerular filtration in mammals) and carbenicillin (excreted partly via Renal tubular secretion in mammals) following injection into the forelimb or hindlimb of red-eared sliders (Trachemys scripta elegans). Ten sliders received intramuscular gentamicin (10 mg/kg) in a forelimb (n = 5) or a hindlimb (n = 5), and plasma levels of the drug were assayed over time. Following drug clearance, the experiment was repeated with the site of injection reversed so that each animal acted as its own control. Another 10 sliders were similarly treated, using intramuscular carbenicillin (200 mg/kg). Injection site of gentamicin had no effect on any pharmacokinetic parameter (time to maximum plasma concentration, maximum plasma concentration, half-life, area under the curve, clearance, and volume of distribution). However, the area under the curve of plasma carbenicillin concentration vs. time was significantly lower following hindlimb injection, in comparison with forelimb injection, at 1, 4, and 8 hr, which may reflect reduced bioavailability of the drug, as would be expected with Renal Portal perfusion and tubular excretion on first pass through the kidney. This effect on carbenicillin likely is not clinically important because plasma levels remained above recommended minimum inhibitory concentrations. Because blood draining the caudal body of reptiles passes through the kidneys or the liver before reaching the central circulation, the effect on the pharmacokinetics of a drug injected in that region will vary with its Renal or hepatic extraction rate. Generally, this effect is unlikely to be significant.

Richard Blackburn - One of the best experts on this subject based on the ideXlab platform.

  • the avian Renal Portal System a model for studying nephrotoxicity of xenobiotics
    Toxicology Letters, 1990
    Co-Authors: Richard Blackburn, Don Prashad
    Abstract:

    In avian species, there is a dual afferent blood supply to the kidney via a ‘high pressure’ (160/120 mmHg) Renal artery and in addition a ‘low pressure’ (25 mmHg) supply via a Renal Portal System (RPS). Glomerular areas of the kidney are supplied by the Renal artery; peritubular areas partly by efferent glomerular arterioles and also by venous return from the legs communicating with the RPS. The magnitude of the Renal Portal supply reaching the peritubular areas appears to be controlled by an autonomically innervated smooth muscle valve [l], the Renal Portal valve. When the valve contracts and closes, either naturally or as a result of treatment with exogenous substances, blood perfuses the peritubular areas of the kidney finally returning to the posterior vena cava via the Renal vein. When the valve is open, blood is shunted directly to the posterior vena cava. The existence of two effectively separate circulations, one mainly for glomerular areas and one for peritubular tissue, confers some advantages over mammalian Systems in studies on Renal ‘handling’ of nephrotoxic substances and pha~acolo~cally active agents. Unilateral injection of an exogenous substance, together with markers for filtration and tubular secretion can be made directly into the peritubular circulation of one kidney (homolateral) and excretion patterns from both kidneys monitored separately using indwelling ureteral cannulae. This enables the response of the homolateral kidney to be simultaneously compared with the uninjected (contralateral) kidney which acts as a control within the same individual. Using this System, the excretion patterns of phenol red [2] and bipyridinium compounds [3] have been investigated. In these studies, homolateral excretion of these compounds, which are

L Forrest - One of the best experts on this subject based on the ideXlab platform.

Howard Dobson - One of the best experts on this subject based on the ideXlab platform.

  • the anatomy and perfusion of the Renal Portal System in the red eared slider trachemys scripta elegans
    Journal of Zoo and Wildlife Medicine, 1997
    Co-Authors: Peter H Holz, Ian K Barker, Graham J Crawshaw, Howard Dobson
    Abstract:

    The anatomy of the Renal Portal System of the red-eared slider (Trachemys scripta elegans) is described, based on dissection of six double latex-injected specimens (three males, three females). The anatomy of these vessels, which had not previously been described in this species, was found not to differ significantly from the fundamental chelonian pattern. Fluoroscopic radioangiography revealed that venous blood returning from the hindlimbs flowed predominantly to the liver and bypassed the kidneys. Blood from the tail either flowed to the kidneys or bypassed them and flowed directly to the liver. A putative valve is described that governs venous blood flow from the caudal body to or around the kidneys.