Aminohippuric acid
Encyclopedia
Aminohippuric acid or para-aminohippuric acid (PAH), a derivative of hippuric acid
, is a diagnostic agent useful in medical tests involving the kidney
used in the measurement of renal plasma flow. It is an amide
derivative of the amino acid
glycine
and para-aminobenzoic acid.
. PAH is completely filtered from plasma
in the nephron
and not reabsorbed by the tubules, in a manner identical to inulin
. PAH differs from inulin in that the fraction of PAH that bypasses the glomerulus and enters the nephron's tubular cells (via the peritubular capillaries
) is completely secreted. Thus, renal clearance
of PAH is useful in calculation of renal plasma flow (RPF), which empirically is (1 − hematocrit
) × renal blood flow
. Of note, the clearance of PAH is reflective only of RPF to portions of the kidney that deal with urine formation, and thus underestimates actual RPF by about 10%.
The renal extraction ratio of PAH in a normal individual is approximately 0.92.
salt sodium para-aminohippurate. During World War II, para-aminohippurate was given along with penicillin in order to prolong the time penicillin circulated in the blood. Because both penicillin and para-aminohippurate compete for the same transporter in the kidney, administering para-aminohippurate with penicillin decreased the clearance of penicillin from the body by the kidney, providing better antibacterial therapy. Transporters found in the kidney eliminate organic anions and cations from the blood by moving substances, in this case, drug metabolites, from blood into urine.
s, the NSAID diclofenac
, which is extraordinarily toxic to vulture
s, interferes with the renal transport of uric acid
via the PAH channel.
pKa = 3.83
Hippuric acid
Hippuric acid is a carboxylic acid found in the urine of horses and other herbivores. Hippuric acid crystallizes in rhombic prisms which are readily soluble in hot water, melt at 187 °C and decompose at about 240 °C...
, is a diagnostic agent useful in medical tests involving the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
used in the measurement of renal plasma flow. It is an amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
derivative of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...
and para-aminobenzoic acid.
Diagnostics
PAH is useful for the measurement of renal plasma flow because it is secreted primarily by the renal tubules; only 20-30% is filtered by the glomerulusGlomerulus
A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...
. PAH is completely filtered from plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
in the nephron
Nephron
The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....
and not reabsorbed by the tubules, in a manner identical to inulin
Inulin
Inulins are a group of naturally occurring polysaccharides produced by many types of plants. They belong to a class of fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes...
. PAH differs from inulin in that the fraction of PAH that bypasses the glomerulus and enters the nephron's tubular cells (via the peritubular capillaries
Peritubular capillaries
In the renal system, peritubular capillaries are tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron....
) is completely secreted. Thus, renal clearance
Clearance (medicine)
In medicine, the clearance is a measurement of the renal excretion ability. Although clearance may also involve other organs than the kidney, it is almost synonymous with renal clearance or renal plasma clearance. Each substance has a specific clearance that depends on its filtration characteristics...
of PAH is useful in calculation of renal plasma flow (RPF), which empirically is (1 − hematocrit
Hematocrit
The hematocrit or packed cell volume or erythrocyte volume fraction is the percentage of the concentration of red blood cells in blood. It is normally about 45% for men and 40% for women...
) × renal blood flow
Renal blood flow
In the physiology of the kidney, renal blood flow is the volume of blood delivered to the kidneys per unit time. In humans, the kidneys together receive roughly 22% of cardiac output, amounting to 1.1 L/min in a 70-kg adult male...
. Of note, the clearance of PAH is reflective only of RPF to portions of the kidney that deal with urine formation, and thus underestimates actual RPF by about 10%.
The renal extraction ratio of PAH in a normal individual is approximately 0.92.
Pharmaceuticals
Aminohippuric acid is often used as the sodiumSodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
salt sodium para-aminohippurate. During World War II, para-aminohippurate was given along with penicillin in order to prolong the time penicillin circulated in the blood. Because both penicillin and para-aminohippurate compete for the same transporter in the kidney, administering para-aminohippurate with penicillin decreased the clearance of penicillin from the body by the kidney, providing better antibacterial therapy. Transporters found in the kidney eliminate organic anions and cations from the blood by moving substances, in this case, drug metabolites, from blood into urine.
Other
In vultureVulture
Vulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...
s, the NSAID diclofenac
Diclofenac
Diclofenac is a non-steroidal anti-inflammatory drug taken to reduce inflammation and as an analgesic reducing pain in certain conditions....
, which is extraordinarily toxic to vulture
Vulture
Vulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...
s, interferes with the renal transport of uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...
via the PAH channel.
pKa = 3.83