Before earlier 50s., it was generally
believed that adipose tissue was a simple repository of fat. The first report
suggesting fat was an active metabolic tissue was published by Von
who noted that glycogen accumulation in adipose tissue took place if an animal had been
fasted and re-fed or else overfed from the start. He concluded that the adipose tissue had
its own internal metabolism.
However it was not until 1965 that an
acceptable review on the subject was published, comprising 894 pages, 69 chapters and
about 4.100 references on adipose tissue metabolism.
Now it is widely recognized that the main
function of the fat cells is to act as a reservoir of energy, as tryglicerides, but it has
also been implicated in sex hormones metabolism. (473)
The fat cell is one of the most metabolic-
active tissues all over the human body, nearly triplicating the blood circulation of any
Adipocytes from living species are
specially adapted for the uptake and release of energy in the form of fatty acids. Fatty
acids accumulate in the form of triglycerides inside the fat cell, and released as fatty
acids back to the circulation as needed.(13-298-393-467).
Depending on its localization, adipocytes
show different metabolic turnovers (307)
The mature fat cell contains a large lipid
vacuole, which stretches the cytoplasm and displaces the cell nucleus to the periphery of
the cell, showing the classic "signet-ring" appearance .
For these metabolic purposes the fat cells
have two poles: a lipogenic, where fatty acids are taken up form the circulation, and a
lipolytic, where triglycerides accumulated in the fat cell are released back into the
Both poles are, in turn, subjected to
different metabolic regulation, which we will briefly discuss.
Fatty acids for tryglicerides
synthesis are derived from hydrolysis of circulating lipoproteins by LPL (lipoprotein
Lipase), an enzyme that hydrolyzes chylomichrons and very Low Density Lipoproteins to
fatty acids.(197-221-222-348-384-413) .
Since potentiality for blood fatty acids
synthesis from capillaries is minimal, the former represents the most important metabolic
pathway for triglyceride synthesis and later deposition into the fat cell.
The activity of LPL (and consequently the
apposition of fat into the fat cell) exhibits different activity levels depending
1. Nutritional status: It decreases during
fasting or diabetes, and rises in the fed state.(261-374)
2. Fat topography and sex: During fertile
life women tend to accumulate fat (LPL High) preferentially in the femoral region compared
to the abdominal, which is difficult to mobilize.(59-375-376-377-378-465).
3. During pregnancy the above mentioned
findings are even more pronounced than while lactancy. In the latter condition,
triglycerides are no longer taken up preferentially in the femoral region.(Fat
4. Age: LPL Activity decreases in
womens femoral region during menopause. The same phenomena can be observed in males
abdominal region after their sixties .
The lipolytic pole of the fat cell has been
more researched, and obviously is more understood than the lipogenic one.(212-215-439) (
A complex system of hormones and enzymes
controls fatty acids release from adipocytes: insulin, adrenergic receptors, thyroid
hormones, adrenal steroids. Phosphodiesterase activity, Proteinkinase, Hormone sensitive
Activation of the adenylate cyclase by
different substances generates cyclic AMP, which provokes a cascade of protein
phosphorilations, the final step being the phosphorylation and activation of the Hormone
sensitive Lipase, which proceeds in turn to the enzymatic attack of stored
An interesting, and beneficial aspect from
the therapeutic viewpoint, is the finding that human adipose tissue possesses both Alfa
and beta-cell membrane adrenoreceptors. Binding of agonist to the beta receptor enhances
lipolysis, where an agonist that bind to alfa2 receptors inhibits
lipolysis.(16-17-18-19-20-21-22-23- 88- 148- 149- 153- 284- 292 - 303-394-498-499-500)
Lipolytic response to epinephrine (both
betal and alpha 2 adrenoreceptors) is more marked in abdominal than in gluteal or femoral
tissues. Moreover, it has been suggested that the male pattern of body fat distribution
(fat mainly located in the abdominal region), may reflect greater alpha2 activity in the
abdominal tissue of men.
Recent reports have demonstrated the
possibility to locally modulate those adrenoreceptors, to improve Body Contour
When compared obese patients managed with a
Standard Hypochaloric Diet submitted (or not) to adrenergic agents (lipolytic), regions
treated with Adrenergic drugs showed greater circumference reduction in treated areas, as
related to control sites.
It may be possible that these
Investigations bear some relevance to the treatment of Obesity.
This approach could hit both targets at the
same time: rapid weight loss and a pleasant body contour remodeling after