Athletes who use anabolic steroids should be aware that such drugs increase insulin resistance and negatively affect glucose tolerance. As
such, concurrent use of steroids and insulin can make a hypoglycemic episode induced by insulin far worse than if the person is using only
INSULIN AS MEDICINE: A BRIEF HISTORY
Insulin was first administered to a diabetic patient in January 1922 by scientists Frederick Banting and Charles Best. (Banting and another
researcher, John J.R. Macleod, later shared a Nobel prize in medicine for their isolation of insulin.) The insulin given to this first
patient - a 11-year-old boy who weighed 65 pounds - was described as a "thick, brown muck." By 1923, the extraction of insulin from animal
sources had greatly improved. The polypeptide protein structure of insulin was discovered in i960; commercial forms of bovine (beef)- and
porcine (pig)-derived insulin were developed in 1963.
But neither bovine nor porcine insulin are identical to human insulin. Human insulin is a polypeptide hormone; bovine-derived insulin differs
from it by three amino acids in its configuration; porcine insulin differs by one amino acid. These subtle structural differences in the
hormone, however, are detectable by the immune system, resulting in allergic reactions in some people.
A recently approved synthetic insulin analogue, Humalog (insulin lispro), differs from regular insulin in that two amino acids, lysine and
proline, have their normal positions in the insulin configuration reversed. This produces a more rapid onset of action and shorter duration
of activity, thus helping to offset the major side effect of insulin - hypoglycemia, or low blood glucose. Humalog is generally taken 15
minutes before a meal.
The newest form of insulin is an oral version trademarked as Macrulin. It's now in phase-one human drug trials in England, and preliminary
studies show that it does survive degradation in the gut, providing full insulin activity. All current insulin drugs are injectable because
the amino-acid structure of insulin would otherwise be broken down by the digestive system; the same holds true for growth hormone (GH).
New research presented at the Joint Meeting of the European Society for Pediatric Endocrinology, held last June 22-26 in Stockholm, Sweden,
shows that a deficiency of a CH-like protein during childhood may set the stage for later development of type II diabetes during adulthood.
Replacement therapy with this new hormone may prevent later development of this type of diabetes, but right now insulin and oral drugs to
increase insulin output constitute the primary therapies for type II diabetes.
HOW INSULIN WORKS
Insulin is anabolic, and it fosters increased amino-acid entry into muscle, stimulating protein synthesis. Also, it works in tandem with
other anabolic hormones in the body, such as testosterone and GH. Some people attribute the massive muscle increases of some athletes over
the past few years to a multidrug combination of insulin, testosterone and GH.
Insulin and GH, however, cancel out each other to a degree. GH in-creases blood-glucose levels, while insulin rapidly lowers them. Insulin
blocks muscle-protein breakdown induced by Cortisol. GH, however, may interfere with this anticatabolic activity of insulin. GH serves as
a late-onset, counterregulatory hormone secreted by the body to offset hypoglycemia (low blood glucose), which can be produced by insulin.
Insulin also affects testosterone synthesis and release. Insulin helps raise levels of active or free testosterone circulating in the
blood. Insulin may also increase testosterone output by stimulating a testic-ular enzyme called hydroxysteroid dehydrogenase.
Scientists, however, still argue over whether insulin has an anti-catabolic or a protein-synthesizing upgrade effect in muscles. Other
research shows that insulin must be present for protein synthesis to occur at an optimal rate, although exercise-induced muscle growth is
an insulin-independent process.
More recent studies show that insulin may influence muscle-protein synthesis through an upgrade in cellular hydration. It does this by
promoting an increase in cellular mineral-transport systems, allowing nutrients such as potassium, sodium and chloride to enter the cell.
This leads to cellular "swelling," which turns on the protein-synthesizing process. In experiments on rats, insulin receptors have also been
found in the Leydig's cells of the testes, where testosterone is synthesized in males. This points to a possible direct influence of insulin
on testosterone synthesis in human males.
Insulin also inhibits the activity of a peripheral tissue enzyme called aromatase, which converts androgens such as testosterone into
estrogen. This, too, would have the effect of increasing free or active blood-testosterone levels.
Insulin favors increased bodyfat synthesis by activating a fat-cell enzyme called lipoprotein lipase and decreasing the activity of a
fat-mobilizing enzyme called hormone-sensitive lipase. Insulin is also a potent cause of water retention because it promotes the secretion of
aldosterone, an adrenal hormone that causes the kidneys to conserve sodium while excreting potassium. Insulin is also known to blunt the
thermic effect of epinephrine, which would also favor increased bodyfat deposition.