Dr.Claudio Brovida, Dr. Stefania Ceretto
In the dynamic stage renal disease, the progressive loss of function that leads to renal failure, is characterized by an evolution compensating survivors of nephrons, which are subject to hypertrophy (mega nephrons). This evolution is the body’s natural response to the need to compensate the increase of blood hydrostatic pressure of capillaries, of the glomerular filtration rate (GFR) index due to a reduction of kidney filtering surface. In addition to the already mentioned hypertrophy, hypertension and glomerular hyper filtration also occur.
As is now well known, when the damage exceeds the fateful percentage of 75% or 3/4 of nephrons is established stage of kidney failure that inevitably evolves towards the uremic state, i.e. the final failure of kidney function that can lead to death of the subject.
At this stage of renal filtration surface reduction, i.e. the number of functioning nephrons, particular attention should be paid to the hemodynamic that is accompanying the disease status, particularly to all the physio-pathological mechanisms that control the vascular tone of the renal vessels, afferent and efferent arterioles of glomeruls.
These mechanisms can be or not associated with inflammatory processes, however, they depend on the biological modulators that act on blood vessels.
In fact intra-glomerular pressure is regulated by eicosanoids, vasoactive substances derived from the processing of some polyunsaturated fatty acids, which play a role in the genesis of glomerular hypertension.
The eicosanoids are compounds derived from unsaturated fatty acids localized at the cell membrane and include prostaglandins, prostacyclins, leukotrienes and thromboxanes.
The vegetable fats are rich in linoleic acid (ω – 6 polyunsaturated fatty acids), while oil derived from fish feed with plankton is rich of eicosapentaenoic and docosahexaenoic (polyunsaturated fatty acid ω- 3).
The main eicosanoids that play a role in the genesis of glomerular hypertension, resulting from arachidonic acid that can be converted from linoleic acid easily in the dog but not in the cat due to poor effect of the specific enzyme (delta-6-desaturase).
Specifically, studies done recently by Scott Brown et al.(2000) (2,3) have shown that renal failure in dogs is characterized by an increased production of these eicosanoids.
In fact a ω – 6 rich diet can bring to an increase of prostaglandin E2 and / or thromboxane A2 production, inducing glomerular hypertension, with worsening proteinuria, renal structural damage with decreased glomerular filtration rate and progressive uremia evolution.
On the contrary a diet supplemented with ω – 3, which interfere with the production of these eicosanoids, can lower the glomerular pressure.
In particular it was noticed that a diet with ω – 3 ratio, ω – 6 equal to 5: 1 decreases the production of inflammatory eicosanoids, reduces the intra-glomerular pressure and allows to keep under control glomerular hypertension.
It follows that an integration of this type of food, can have long-term positive effects in the evolution of chronic renal failure.
The introduction of polyunsaturated ω – 3 fats in the diet has other benefits; In fact, in animals with CRF (chronic renal failure) we will show abnormalities of lipid metabolism characterized by high plasma cholesterol levels.
High levels of lipids in the blood stimulate the proliferation of kidney mesangial cells inside the glomerular, the consequence is a surplus production of mesangial matrix in the long run due to glomerulosclerosis.
Reducing the dietary intake of saturated fat and favor unsaturated ω – 3 to decrease serum cholesterol and even pathological effect of its excess.
In the progression of renal disease occurs in some cases a platelet induced coagulopathy, favored by the action of thromboxane (A2); It is of considerable aid the selective inhibition of this molecule, or the competition with the functionality of thromboxane produced by eicosapentaenoic acid, with lesser platelet aggregating ability.
The last effect of fatty acids polyunsaturated ω- 3 is the protection of the cell from the peroxidative damage caused by free radicals.
Bibliography:
- Brenner BM, Meyer TW, Hostetter TH. Dietary protein intake and the progressive nature of renal disease. N Engl J Med 1982; 307:652-659.
- Brown SA, Brown CA, Crowell WA, Barsanti JA, Kang C, Allen T, Cowell C, Finco DR. Effects of dietary PUFA supplementation in dogs with early renal insufficiency. J.Lab.Cin.Med. 2000.
- Brown SA, Pazak HE, Laflamme DP, Cowan LA, Finco DR, Barsanti JA. Dietary fatty acid composition affects renal function in cats. J Vet Int Med 1988; 12: 223.
NBF-Lanes thank Dr. Claudio Brovida and Dr. Stefania Ceretto for their cooperation.
