It has no definite melting point and no
tendency to crystallize.
resin is used to give gloss, flow, adhesion, and water resistance to cosmetics. This is a brittle substance, usually translucent or transparent, that can be found in nature or synthetically manufactured. Among the natural resins are dammar, elemi, and sandarac, which are formed from the hardened secretions of these plants. Toxicity and allergenicity depend on the source used.
A yellowish insoluble organic compound exuded by trees as a viscous liquid that gradually hardens on
exposure to air to form a brittle amorphous solid. Synthetic resins are artificial
polymers used in making adhesives, insulators and paints. See also rosin.
A semisolid or solid complex amorphous
mix of organic compounds.
resin: A synthetic or naturally occurringpolymer. Synthetic resins areused in making plastics. Naturalresins are acidic chemicals secretedby many trees (especially conifers)into ducts or canals. They are foundeither as brittle glassy substances ordissolved in essential oils. Their functionsare probably similar to those ofgums and mucilages.
Originally a category of vegetable substancessoluble in ethanol but insoluble in water, resinin modern technology is generally an organicpolymer of indeterminate molecular weight.The class of flammable, amorphous secretionsof conifers or legumes are considered true resins,and include kauri, copal, dammar, mastic,guaiacum, jalap, colophony, shellac, andnumerous less well-known substances. Waterswellablesecretions of various plants, especiallythe Burseraceae, are called gum resinsand include myrrh and olibanum The officialresins are benzoin, guaiac, mastic, and resin.Other natural resins are copal, dammar,dragon’s blood, elaterium, lac, and sandarac.The natural vegetable resins are largely polyterpenesand their acid derivatives, which find application in the manufacture of lacquers,adhesives, varnishes, and inks.
Prior to the introduction of the statins in the mid to
late 1980s, the bile acid–sequestering drugs cholestyramine
(Questran) and colestipol (Colestid) were primary
drugs for lowering plasma cholesterol. Today they are
second-line drugs that can safely be given with a statin
to enhance cholesterol lowering or as an alternative for
patients intolerant to a statin or concerned with statin’s
potential for toxicity.Alone, the resins can achieve 20 to
25% reductions in LDL cholesterol, but when used with
a statin, such as lovastatin, reductions of 50% and more
can be seen.
These drugs are basically anion exchange resins that
remain in the gut, bind intestinal bile acids, and greatly
increase their fecal excretion.
The lowered concentration of bile acids returning to the
liver by the enterohepatic circulation results in derepression
of 7-α-hydroxylase, the rate-limiting enzyme
for conversion of cholesterol to bile acids.This results in
increased use of cholesterol to replace the excreted bile
acids and lowering of hepatic cholesterol. Thus, similar to the statins, the ultimate
actions of the bile acid–sequestering resins are upregulation
of transcription of the LDL receptor gene,
increased hepatic receptor activity, and lowering of
plasma LDL cholesterol.
The bile acid sequestering resins lower elevated
LDL cholesterol and therefore are useful in the treatment
of type IIa hyperlipoproteinemia. However, because
the resins can raise plasma VLDL in some patients,
they are not recommended for treatment of
combined hyperlipidemias when both LDL
cholesterol and VLDL triglycerides are high or in other
conditions of elevated triglycerides.
The resins are interesting drugs because they have
profound metabolic effects without truly entering the
body. Perhaps for this reason they are relatively safe,
with constipation being the chief complaint. Because the
resins are given as the chloride salt and the chloride is
exchanged for the negatively charged bile salt, bile acid
resins can lead to hyperchloremic acidosis in vulnerable
patients (children and patients with kidney failure).
