Encyclopedia of Health and Medicine

290 The Immune System and Allergies
AGGREGATION to aid COAGULATION (BLOOD clotting).
Other prostaglandins facilitate calcium transport to
and from cells, the onset and progression of labor
during CHILDBIRTH, and the functions of other hormones.
Prostaglandins are also responsible for discomforts
related to their release, such as after
injury when inflammation results or when menstrual
cramps (DYSMENORRHEA) occur.
Prostaglandin activity is autocrine (affects only
cells that secrete it) or paracrine (affects cells
within immediate proximity of the secreting cells).
Prostaglandin activity is also intense but short
lived, though the symptoms of the resulting
inflammation continue for some time after
prostaglandin release stops. Mast cells are the
main source of prostaglandin synthesis and secretion.
Epithelial cells (surface cells of the SKIN and
mucous membranes) and platelets also produce as
well as respond to prostaglandins.
PROSTAGLANDINS AND THE PROSTATE GLAND
The researchers who discovered prostaglandins
in the 1930s isolated the first member of this biochemical
family from SEMEN—the secretions of
the PROSTATE GLAND. They named it for this connection.
Over the following decades further
research identified a number of prostaglandins
and determined that nearly every cell in the
body contains some form of prostaglandin.
Aspirin was the first DRUG to block the synthesis
of prostaglandins.
The enzymes cyclooxygenase 1 (COX-1) and
COX-2 facilitate the synthesis of prostaglandins
from arachidonic acid, an essential fatty acid (a
fatty acid the body requires for health but cannot
synthesize from other substances so must obtain
from dietary sources) found in red meats and
peanuts. Arachidonic acid is also the foundation
for LEUKOTRIENES, other biochemicals also involved
in the inflammatory response. The enzyme lipoxygenase
facilitates the conversion of arachidonic
acid to leukotrienes. COX-1 is primarily in the
STOMACH, KIDNEYS, and walls of the blood vessels; it
maintains the prostaglandins necessary for the
body’s normal functioning. COX-2 is present in
the tissues and becomes active during an inflammatory
response.
NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS),
including aspirin, block the action of COX, preventing
prostaglandin production. This action
provides pain relief, reduces fever, and mitigates
the swelling associated with inflammation.
Though much therapeutic focus is on blocking
prostaglandin production, there are numerous
therapeutic applications for synthetic
prostaglandins. Therapeutic administration of synthetic
prosta-glandin E 1 (PGE 1 ) maintains a patent
ductus arteriosus in infants born with serious congenital
heart defects. Prostaglandin E 2 (PGE 2 ) and
prostaglandin F 2 (PGF 2 ) cause the UTERUS to contract,
either initiating or strengthening labor.
See also CONGENITAL HEART DISEASE; CRAMP; HOR-
MONE; IMMUNE
CELL; PLATELET.
RESPONSE; IMMUNOGLOBULIN; MAST
psychoneuroimmunology The interrelationships
between emotions, neurologic function, and the
IMMUNE SYSTEM. In the 1970s researchers discovered
receptors for neuropeptides on cells throughout
the body, including the immune system. The
BRAIN produces neuropeptides, protein-based
structures that convey biochemical messages
related to cognition (thought and logic) and emotion.
Neuropeptides include endorphins and
enkephalins, substances connected to perceptions
of SATIETY and pleasure.
Though researchers do not yet understand how
neuropeptides affect IMMUNE RESPONSE, they do
know emotional stress affects physical health.
They also know that the immune system affects
neurologic functions, which is one reason people
feel irritable and cranky when they are sick. It
appears that the primary messengers for immuneto-neural
communication are the CYTOKINES
immune cells produce during the immune
response, notably INTERLEUKINS, which are capable
of activating NERVE impulses that convey signals to
the brain. Researchers continue to explore ways to
use these connections for health, HEALING, and disease
prevention.
See also MIND–BODY CONNECTION.
reticuloendothelial system See MONONUCLEAR
PHAGOCYTE SYSTEM.