PRINCIPLES OF TOXICOLOGY

570 GLOSSARY
porphyrin Any of a group of iron-free or magnesium-free cyclic tetrapyrrole derivatives occurring
universally in protoplasm. They form the basis of the respiratory pigments of animals and plants.
potency A comparative expression of chemical or drug activity measured in terms of the dose
required to produce a particular effect of given intensity relative to a given or implied standard of
reference. If two chemicals are not both capable of producing an effect of equal magnitude, they
cannot be compared with respect to potency.
potentiation A condition whereby one substance is made more potent in the presence of another
chemical that alone produces no response.
pressure, static The potential pressure exerted in all directions by a fluid at rest.
pressure total The algebraic sum of static and velocity pressures, representing the total energy in
the system.
pressure, velocity The kinetic pressure exerted in the direction of flow necessary to cause a fluid at
rest to flow at a given velocity.
primary carcinogens Chemicals that act directly and without biotransformation. Also called direct
carcinogens.
primary irritants Chemicals that induce local, minor to severe inflammatory response, or even
extreme necrosis, of cells of a tissue, in direct relation to the concentration available to the tissue.
This is termed a nonspecific chemical action, the toxicity of which may be manifested at the site
of exposure (e.g., skin or in the respiratory tract). Examples of these types of chemicals are strong
acids or bases, ammonia, and acrolein.
Probenecid A white, odorless crystalline powder, with the formula C13H19NO4S, soluble in dilute
alkali, alcohol, and acetone; used to increase serum concentrations of certain antibiotics, as well as
being an agent to promote uric acid secretion in the urine.
procarcinogen Chemicals that require metabolism to another, more reactive or toxic chemical form
before their carcinogenic action can be expressed.
proerythropoietin A precursor of erythropoietin.
psoriasis A chronic, hereditary, recurrent, papulosquarnous dermatitis, the distinctive lesion of
which is a vivid red macula, papule, or plaque covered almost to its edge by silvery lamellated
scales. It usually involves the scalp and extensor surfaces of the limbs, especially the elbows, knees,
and shins.
pyrethroid Any of several synthetic insecticidal compounds similar to the nature pyrethrums
extracted from crushed chrysanthemums.
Raynaud’s phenomenon Intermittent attacks of severe pallor of the fingers or toes and sometimes
of the ears and nose, brought on characteristically by cold and sometimes by emotion.
receptors See specific receptor; nonspecific receptor.
renal osteodystrophy A condition resulting from chronic kidney disease. The onset early in
childhood is characterized by impaired renal function, elevated serum phosphorus and low or
normal serum calcium levels, and stimulation of parathyroid function. The resultant bone disease
includes a variety of symptoms, including osteitis fibrosa cystica, osteomalacia, osteoporosis, and
osteosclerosis. Renal dwarfism may result from childhood onset.
reproduction tests Tests that determine (or estimate) the effects of an agent on fertility, gestation,
and offspring; usually conducted on more than one generation of test animals. Toxicity in either
parent may affect fertility as the direct result of altered gonadal function, estrus cycle, mating
behavior, and conception rates. Effects on gestation concern the development of the fetus. Effects
on offspring concern growth, development, and sexual maturation; and effects on the mother
concern lactation and acceptance of the offspring.
resorption The loss of substance in the mucous lining of the uterus.
reticuloendothelial system Phagocytic macrophages present in linings of sinuses and in reticulum
of various organs and tissues. A functionally important body defense mechanism; the phagocytic