Kidney threshold

The other major class of extracellular LBPs of mammals is the lipocalins (Flower, 1996). These are approximately 20 kDa, P-sheet-rich proteins, performing functions such as the transport of retinol in plasma or milk, the capture of odorants in olfaction, invertebrate coloration, dispersal of pheromones, and solubilizing the lipids in tears (Flower, 1996). The retinol-binding protein (RBP) of human plasma is found in association with a larger protein, transthyretin, the complex being larger than the kidney threshold and thus not excreted, although the RBP itself may dissociate from the complex to interact with cell surface receptors in the delivery of retinol (Papiz et al., 1986 Sundaram et al., 1998). 

Testosterone itself has been isolated in very small amounts from urine, and then only after administration of large doses of the hormone " — an indication that it is rapidly and completely metabolized in the normal male. The hormone disappears rapidly from the blood after intravenous injection and the metabolites appear promptly in the urine. As yet, testosterone has not been detected in the peripheral circulation although A -androstene-3,17-dione (LV) and testosterone are present in the spermatic venous blood of the dog. The transformation of the hormone by tissues, especially the liver, must be quite rapid and the kidney threshold for the metabolites must be extremely low. 

Most of the low molecular substances that are flushed into the primary urine during ultrafiltration are reabsorbed to a large extent. This is true even for such typical excretion products as urea and uric acid, but especially for free amino acids and glucose, which are reabsorbed completely so long as the blood sugar level stays normal. If the level exceeds 0.16%, some of the sugar is excreted in the urine. Reabsorption is active transport (Chapt. XXI-3) and the enzymic apparatus of active transport can no longer cope with the amounts delivered by the blood. Similar conditions prevail for other substances the capacity for reabsorption (formerly called kidney threshold ) differs widely for various substances. 

Repeated exposures of animals to high (near-lethal) concentrations of vapors result in inflammation of the respiratory tract, as weU as degenerative changes in the Hver, kidneys, and heart muscle. These effects arise at concentrations far above those causing irritation. Such effects have not been reported in humans. The low odor threshold and irritating properties of acrylates cause humans to leave a contaminated area rather than tolerate the irritation. 

Phenol. Phenol monomer is highly toxic and absorption by the skin can cause severe blistering. Large quantities can cause paralysis of the central nervous system and death. Ingestion of minor amounts may damage kidneys, Hver, and pancreas. Inhalation can cause headaches, dizziness, vomiting, and heart failure. The threshold limit value (TLV) for phenol is 5 ppm. The health and environmental risks of phenol and alkylated phenols, such as cresols and butylphenols, have been reviewed (66). 

The most serious ha2ard of repeated exposure to chloroform inhalation is injury to the Hver and kidneys. Evidence indicates that in humans, repeated exposure to atmospheric concentrations well below the odor threshold may cause such injury. Industrial experience has shown that daily exposure to concentrations below 100 ppm may result in a variety of nervous system and alimentary tract symptoms, in the absence of demonstrable evidence of injury (39). Injury to the Hver is similar to but somewhat less severe than that caused by carbon tetrachloride. Kidney injury is usually associated with but less severe than Hver injury. 

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