Hypertension

ReportRepeatRevise******Phenotypic Expression of Hypertension in Rodent
Models through Dietary Manipulation

The pathogenesis of hypertension in humans is not fully understood.
This disease of persistent elevation of blood pressure is a multifactorial
combination of genetic and environmental factors. To better
understand the specific mechanisms involved, as well as to researchtreatments for prevention of hypertension, various animal models
have been developed to mimic the hypertensive responses seen
in humans.
Historically, the preferred small animal model for hypertension
research has been the rat. This may be due to the amount of publishedphysiological data, relative small size, and robust responses seen insome genetic strains. Because of the polygenic nature of hypertension,
numerous rat models have been developed including selective bredhomozygous hypertensive rat strains (e.g. spontaneously hypertensive
rat [SHR] and Dahl salt sensitive [Dahl SS]) and outbred strains (e.g.
Sprague Dawley) to elucidate the desired hypertensive phenotype.
As the form of hypertension can differ between strains, researchers
need to not only be aware of the form of hypertension that theindividual strain exhibits but also the impact that a particular typeof diet may have on the phenotypic response.

Sodium Induced Hypertension
High sodium diets are commonly used to study diet induced
hypertension, since increasing levels of circulating sodium cause
cells to release water (due to osmotic pressure) which elevates thepressure on blood vessel walls.
Lewis Dahl developed, from selectively inbred Sprague Dawley rats,
the Dahl salt-sensitive (Dahl SS) and Dahl salt-resistant (Dahl SR)
rats based on their response to an 8% NaCl diet (1). Weaned Dahl SS
can rapidly develop elevated blood pressure (>180 mm Hg) when
fed an 8% NaCl diet in as little as 2 weeks for some individuals,
though the average for the strain is usually closer to 4-6 weeks (1-4).
When fed a lower levels of NaCl, hypertension along with vascularand renal lesions develop though the length of time is typicallylonger (5, 6). The age of the animal also seems to play a role in thedevelopment of salt induced hypertension. Dahl SS rats placed ona high salt diet (8%) at 3 or 6 months after weaning developed
elevated blood pressure at a slower rate compared to those placed on
the diet at weaning. None of the animals typically survive beyond 8
months on the diet regardless of the age at which they start (5).
In contrast, the Dahl SR rat fails to exhibit elevated hypertension
or vascular and renal lesions even after being placed on a high salt
diet for several months (1, 6-8).

250

SBP (mmHg)

A Brief Review of the Scientific Literature- October 2008
by Matthew Barker, M.S. Project Manager & Scientist, Research Diets, Inc.

**
200

150

100
CC

CC+S

FAT

FAT+S

FRU

FRU+S

WES

WES+S

FIGURE 1. Systolic blood pressure (SBP) measured by tail–cuff method. Black bars
represent pretreatment, green bars represent 5 weeks of treatment, orange bars
represent 11 weeks of diet. DIETS: (CC)= complex carbohydrate, (CC+S)= complex
carbohydrate + NaCl (FAT)= high fat, (FAT+S)= high fat + NaCl, (FRU)= highfructose, (FRU+S)= high fructose + NaCl, (WES)= western diet, (WES+S)= western
diet + NaCl. Data are the mean ± SEM. *P < .05 compared to the same dietary groupwith low salt at 5 and 11 weeks. †P < .05 compared to baseline measurement.
Graphic representation - for details see reference (25).

As the name implies the SHR develops hypertension spontaneouslywith increases in blood pressure beginning early in life (5-6 weeks) (9).
As the peripheral resistance and normal cardiac output exhibited by
the SHR are similar to human hypertension, this strain has been
considered a good model of essential hypertension (10). Increasing
the vascular resistance with the addition of NaCl (~7%) to the dietand/or saline solution of 1% NaCl provides an additive effect on
increasing blood pressure in the SHR (11, 12).
As a model of diet-induced hypertension, the mouse is not widelyused. Inbred mice such as the C57BL/6 can develop elevated bloodpressure on purified diets high in NaCl (8%), though the time frame
for this appears to be on the order of several months (13). Sequencingof the mouse genome coupled with the successful development oftransgenic and knockout mouse lines allows researchers to investigate
the roles that individual genes play within specific mechanisms ofrenal physiology under both normal and pathologic conditions (14).

Other Dietary Factors that can Influence
the Hypertensive Phenotype
Dietary factors other than sodium can play a role in the degree andonset of hypertension in rodents. When 4% NaCl was added toboth a chow diet and a purified ingredient diet, Dahl SS rats fed
the purified diet had higher blood pressure and more renal damage
compared to chow-fed rats (15). Of equal interest is the finding that
offspring from parents who were fed the 4% NaCl purified diet had
higher blood pressures regardless of the diet they were fed after
weaning, suggesting that the diet fed to the mother duringHypertension
pregnancy can promote hypertension in the offspring. How does the
background diet (chow vs. purified) affect the outcome in this case?
The reasons are not clear but may be related to fundamental
differences between chows and purified diets in the levels of mineralssuch as sodium and potassium, protein sources, presence or absenceof phytochemicals, carbohydrate type, and/or the level and type offiber. Typical purified ingredient diets contain about 0.1% Na (0.25%
NaCl), while chow diets contain about 0.3-0.4% Na (0.75-1.0%
NaCl). Soy protein in chow based diets (a common protein source inchows) has been shown to attenuate the development of hypertension
in the spontaneous hypertensive rat (SHR) in comparison to diets
containing casein (the primary protein source used in purified diets)(16). Soy protein does contain the phytoestrogen, genistein, which has
been shown to blunt the increase in blood pressure due to NaCl
induced hypertension (17). As casein contains no phytoestrogens, thedifferences seen in blood pressure between animals fed chows andpurified diets may be partially due to the variable levels of genisteinand other phytoestrogens within chow (18).
Diets containing normal levels of NaCl but high in fructose or
sucrose (around 60% of calories) can increase blood pressure invarious rodent models (e.g. Dahl SS, SHR) of hypertension (19-23)
and allow researchers to evaluate numerous factors of metabolic
syndrome, including hypertriglyceridemia and insulin resistance(21, 22). Although Dahl rats fed high sucrose or fructose diets exhibit
hypertension, it is not until a high level of salt (6%) is combined withhigh sucrose/fructose that there is an exacerbation of the hypertension
and a pronounced increase in mortality (24, 25) FIG. 1. Outbred rats
strains such as the Sprague-Dawley and Wistar rats (which are inwidespread use for obesity research) can also develop numerous
components of metabolic syndrome (hypertension, insulin resistance,and hypertriglyceridemia) on diets high in fructose (60%) (21, 26) as
well as hypertension concurrent with the development of obesity(27-29).
As one might expect not only can one elevate blood pressure throughdietary measures, but hypertension can be attenuated by way of thediet. Similar to findings in humans, hypertension resulting fromfeeding an 8% NaCl diet can be prevented by supplementing thediet with extra potassium (2, 30). Dietary supplementation withantioxidants (such as vitamins E and C) has been shown to lower
blood pressure in the stroke-prone, SHR or the Dahl SS rat (3133)Therefore, this suggests that low intake of these micro-nutrients
could promote hypertension.

Where NutriPhenomics® Begins

We have briefly covered some of the disease models that can beused to study diet induced hypertension. What should be clear isthat while some dietary factors promote one phenotype (i.e. sodium
induces hypertension), others may promote multiple phenotypes(high fructose diets to promote insulin resistance, hypertriglyceridemia,
and hypertension). As the specific goals and needs for each researcher
will vary, the careful selection and control of both the strain and dietare of immense importance in the development of a consistent anduseful phenotype.

References
1. Dahl LK: Salt and hypertension. Am. J. Clin. Nutr. 25: 231-244, 1972
2. Ogihara,T, Asano,T, Ando,K, Sakoda,H, Anai,M, Shojima,N, Ono,H, Onishi,Y,Fujishiro,M, Abe,M, Fukushima,Y, Kikuchi,M, Fujita,T: High-salt diet enhancesinsulin signaling and induces insulin resistance in Dahl salt-sensitive rats.
Hypertension 40:83-89, 2002
3. Tian,N, Thrasher,KD, Gundy,PD, Hughson,MD, Manning,RD, Jr.: Antioxidant
treatment prevents renal damage and dysfunction and reduces arterial pressure insalt-sensitive hypertension. Hypertension 45:934-939, 2005
4. Cowley,AW, Jr., Stoll,M, Greene,AS, Kaldunski,ML, Roman,RJ, Tonellato,PJ,
Schork,NJ, Dumas,P, Jacob,HJ: Genetically defined risk of salt sensitivity in anintercross of Brown Norway and Dahl S rats. Physiol Genomics 2:107-115, 2000
5. Dahl LK, Knudsen KD, Heine MA, Leitl GJ: Effects of chronic excess salt ingestion.
Modification of experimental hypertension in the rat by variations in the diet.
Circulation Research. 22:11-18, 1968
6. Rapp JP, Dene H: Development and characteristics of inbred strains of Dahl
salt-sensitive and salt-resistant rats. Hypertension 7: 340-349, 1985
7. Rapp JP: Dahl salt-susceptible and salt-resistant rats: A review.
Hypertension 4: 753-763, 1982
8. Inoko M, Kihara Y, Morii I, Fujiware H, Sasayama S: Transition from compensatory
hypertrophy to dilated failing left ventricles in Dahl salt-sensitive rats.
Am. J. Physiol. 267 (Heart Circ. Phsyiol. 36): H2471-H2482, 1994
9. Okamoto K, Aoki K: Development of a strain of spontaneously hypertensive rats.
Jap Circ J 27: 282-293, 1963
10. Ferrone R, Walsh G, Tsuchiya M, Frohlich E: Comparison of hemodynamics inconscious spontaneous and renal hypertensive rats.
Am. J. Physiol. 236(3): H403-H408, 1979

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Hypertension
References

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11. Aoki K, Yamori Y, Ooshima A, Okamotoa K: Effects of high or low sodium intakein spontaneously hypertensive rats. Jap Circ J 36: 539-545, 1972
12. Chyrsant SG, Walsh GM, Kem DC, Frohlich ED: Hemodynamic and metabolic
evidence of salt sensitivity in spontaneously hypertensive rats.
Kidney International 15: 33-27, 1979
13. Yu,Q, Larson,DF, Slayback,D, Lundeen,TF, Baxter,JH, Watson,RR: Characterizationof high-salt and high-fat diets on cardiac and vascular function in mice.
Cardiovasc.Toxicol. 4:37-46, 2004
14. Cvetkovic B, Sigmund CD: Understanding hypertension through genetic
manipulation in mice. Kidney International 57: 863-74, 2000.
15. Mattson,DL, Kunert,MP, Kaldunski,ML, Greene,AS, Roman,RJ, Jacob,HJ,
Cowley,AW, Jr.: Influence of diet and genetics on hypertension and renal disease in
Dahl salt-sensitive rats. Physiol Genomics 16:194-203, 2004
16. Nevala R, Vaskonen T, Vehniainen J, Korpela R, Vapaatalo H: Soy based dietattenuates the development of hypertension when compared to casein based diet inspontaneously hypertensive rat. Life Sci 66(2): 115-124, 2000
17. Cho TM, Peng N, Clark JT, Novak L, Roysommuti S, Prasain J, Wyss JM: Genistein
Attenuates the Hypertensive Effects of Dietary NaCl in Hypertensive Male Rats.
Endocrinology 148(11):5396-5402, 2007
18. Jensen MN, Ritskes-Hoitinga M: How isoflavone levels in common rodent diets caninterfere with the value of animals models and with the experimental results.
Laboratory Animals 41: 1-18, 2007
19. Melancon S, Bachelard H, Badeau M, Bourgoin F, Pitre M, Lariviere R, Nadeau A:
Effects of high-sucrose feeding on insulin resistance and hemodynamic responses toinsulin in spontaneously hypertensive rats. Am. J. Physiol. Heart Circ Physiol 290:
H2571-H2581, 2006
20. Pitre M, Nadeau A, Bachelard H: Insuilin sensitivity and hemodynamic responses toinsulin in Wistar-Kyoto and spontaneously hypertensive rats. Am. J. Physiol. 271(Endocrinol. Metab. 34): E658-E668, 1996
21. Oron-Herman M, Kamari Y, Grossman E, Yeger G, Peleg E, Shabtay Z, Shamiss A,
Sharabi Y: Metabolic Syndrome: Comparison of the two commonly used animals
models. Am. J. Hypertens. 21: 1018-1022, 2008
22. Sanchez-Lozada,LG, Tapia,E, Jimenez,A, Bautista,P, Cristobal,M, Nepomuceno,T,
Soto,V, Avila-Casado,C, Nakagawa,T, Johnson,RJ, Herrera-Acosta,J, Franco,M:
Fructose-induced metabolic syndrome is associated with glomerular hypertension
and renal microvascular damage in rats.
Am J Physiol Renal Physiol 292: F423-F429, 2007
23. Vasudevan,H, Xiang,H, McNeill,JH: Differential regulation of insulin resistanceand hypertension by sex hormones in fructose-fed male rats.
Am J Physiol Heart Circ Physiol 289:H1335-H1342, 2005
24. Sharma N, Okere IC, Duda, MK, Johnson J, Yuan CL, Chandler MP, Ernsberger P,
Hoit BD, Stanley WC. High fructose diet increases mortality in hypertensive rats
compared to a complex carbohydrate or high fat diet.
Am J Hypertens 20: 403-409, 2007
25. Sharma N, Okere IC, Barrows BR, Lei B, Duda, MK, Yuan CL, Previs SF, Sharov
VG, Azimzadeh AM, Ernsberger P, Hoit BD, Sabbah H, Stanley WC. High-sugardiets increase cardiac dysfunction and mortality in hypertension compared to
low-carbohydrate or high-starch diets. J Hypertens 26: 1402-1410, 2008
26. Hwang IS, Ho H, Hoffman BB, Reaven GM: Fructose-Induced Insulin Resistanceand Hypertension in Rats. Hypertension 10: 512-516, 1987
27. Dobrian,AD, Davies,MJ, Prewitt,RL, Lauterio,TJ: Development of hypertension ina rat model of diet-induced obesity. Hypertension 35:1009-1015, 2000
28. Dobrian,AD, Schriver SD, Lynch T, Prewitt,RL: Effect of salt on hypertension andoxidative stress in a rat model of diet-induced obesity.
Am J Physiol Renal Physiol 285: F619-F628, 2003
29. Yamakawa T, Tanaka S, Tamura K, Isoda F, Ukawa K, Yamakura Y, Takanashi Y,
Kiuchi Y, Umemura S, Ishii M, Sekihara H: Wistar fatty rat is obese andspontaneously hypertensive. Hypertension 25: 146-150, 1995
30. Dahl LK, Letil G, Heine M: Influence of dietary potassium and sodium/potassium
molar ratios on the development of salt hypertension. J Exp Med 136: 318-330, 1972
31. Kopilas,MA, Dang,LNT, Anderson HDI: Effect of dietary chromium on resistanceartery function and nitric oxide signaling in the sucrose-fed spontaneously
hypertensive rat. J Vasc Res 44:110-118, 2007
32. Vasdev,S, Gill,V, Parai,S, Gadag,V: Dietary vitamin e supplementation attenuates
hypertension in Dahl salt-sensitive rats.
J Cardiovasc Pharmacol Ther 10:103-111, 2005
33. Noguchi,T, Ikeda,K, Sasaki,Y, Yamamoto,J, Yamori,Y: Effects of vitamin e andsesamin on hypertension and cerebral thrombogenesis in stroke-prone spontaneously
hypertensive rats. Clin Exp Pharmacol Physiol 31 (Suppl 2): S24-S26, 2004