Effects of Chronic Excess Salt Ingestion

341

210

strain)* to the hypertensive effect of high salt diet. In this review "salt" will always mean NaCl.t Selective BreedingIn the 1950s, Meneely and coworkers studied the effects of high salt diet on the blood pressure of rats. Meneely and Ball 5 reviewed the work, showing that for a large group of rats the average blood pressure of the group was positively and linearly related to the percentage of NaCl in the diet between 0 and 10% NaCl. Moreover, they remarked that "there was quite a marked degree of individual variation" in the response of blood pressure to salt. This work was carried out on Sprague-Dawley rats that were presumably randombred.•A nomenclature committee of the International Society of Hypertension has stated that Dahl salt-sensitive (or salt-susceptible) rats should be designated DS and Dahl salt-resistant rats should be designated DR (see ref. I). This nomenclature is specifically not used in this review, and its use. except as noted below, is discouraged. In DahTs original work in 1962 and for 14 years until his death. Dr. Dahl called the strains S and R. There is no need to replace that historic precedent. The nomenclature committee specifically states that they were naming "hypertensive rat strains with stable hypertension which had been inbred (brother-sister mating) for at least 20 generations" (ref. \>. Apparently they were naming inbred strains under development at Brookhavcn National Laboratory since Dr. Dahl's death in November, 1975. No fully inbred rats were supplied to investigators from the Brookhaven colony because they do not exist (yet). What was supplied were rats from colonies of S and R rats separate from the inbreeding program and maintained as Dahl had done for many years by selective breeding, avoiding inbreeding where possible. Thus, the use of DS and DR implies the use of specific inbred strains which do not exist. If and when such strains from Brookhavcn become available, these specific strains of inbred S and R rats can be referred to as DS and DR. tSodium in the diet is expressed in two ways in the literature, either as % Na+ or % NaCl The latter assumes that all the Na+ is present as NaCl, % NaCl means grams of NaCl per 100 grams of food. In most of the literature reviewed, sodium was expressed as % NaCl, and so this will be used throughout the review. Where the original article gave data in % N a + . this will be given followed by the % NaCl so that diets can always be compared on the same basis (% NaCl = 2.54 times % Na + ).A survey of commercial rat chows shows that they contain close to 1% NaCl, and so "normal salt diet" will refer to l%NaCl in the food. Two diets were introduced by Dahl during his work with S and R rats: 8% NaCl diet referred to as "high salt diet"; and 0.3 to 0.4% NaCl diet referred to as "low salt diet." Note that with this arbitrary nomenclature, low salt diet has only somewhat less than half the salt content of normal diet. Where a diet was fed that contained insufficient salt for optimum growth, this will be called sodium-deficient diet. The m...

Section: Selective Breedingmentioning

confidence: 99%

Dahl salt-susceptible and salt-resistant rats. A review.

Rapp¹

1982

341

210

“…The current analysis uses the estimates of genetic variance according to criteria established by Christian et al 1 " The equality of total variance was evaluated by an F' test. When the total variance of MZ and DZ twins was equal, the presence of genetic variance was tested using the F ratio (Within DZ/Within MZ).…”

Section: Studies In Twinsmentioning

confidence: 99%

An approach to the evaluation of genetic influences on factors that regulate arterial blood pressure in man.

Grim¹,

Luft²,

Miller³

et al. 1980

SUMMARY To assess the influence of heredity on factors that help regulate the arterial blood pressure in man, we conducted sodium-loading and depletion studies in monozygotic and dizygotic twins, normotensive first-degree relatives of essential hypertensives, and in nonnotenslve control subjects matched for age, sex, and race. Following sodium-loading, we found evidence for the influence of genetic variance on the natriuretic responses, plasma renin activity (PRA), plasma aldosterone concentrations (PA), and plasma and urinary norepinephrine. Relatives of hypertensives differed from controls in that they had higher blood pressures, greater renin values, and relatively sluggish natriuretic responses. Since renin and fractional sodium excretion values were inversely correlated in all subject groups, it is possible that the heritable influences we observed on sodium excretion were mediated by the renin-angiotensin-aldosterone system. 79 the nature of these influences has not been defined clearly. To examine inherited mechanisms that may contribute to the development of essential hypertension in some individuals, or the resistance to hypertension in others, we conducted detailed studies of monozygotic and dizygotic normotensive twins, normotensive firstdegree relatives of essential hypertensives, and large numbers of normotensive white and black subjects by means of a standardized protocol incorporating both sodium-loading and depletion. "14 In these studies we examined electrolyte balance, components of the renin-angiotensin-aldosterone system, and humoral indicators of sympathetic nervous system activity. The studies in twins 1-34fluences in each of these areas. The studies in normotensive, first-degree relatives of essential hypertensives indicated the existence of important differences in electrolyte excretion and peripheral renin values that may contribute to the susceptibility to hypertension of this high-risk group." We present these findings in light of their bearing on the importance of heredity in regulating blood pressure in man. Methods Studies in TwinsData from monozygotic (MZ) and dizygotic (DZ) twins provide a unique opportunity to test for the existence of genetic variation in traits. Since MZ twins are genetically identical and DZ twins are related as full siblings, a given trait would be expected to exhibit smaller twin-pair differences for MZ than DZ twins if genetic influences are present. On the other hand, if the trait is only influenced by environmental variability, the MZ and DZ twin-pair differences should be approximately equal.The statistical methods involved in the analysis of MZ and DZ twin data have been recently reviewed by Christian. 16 We chose the comparison of MZ and DZ twins as the most efficient method for the initial investigation of heritable components in quantitative by guest on May 11, 2018 http://hyper.ahajournals.org/ Downloaded from

mentioning

confidence: 98%

“…This suggests that some individuals will respond to dietary sodium intake with an increase in blood pressure (BP) while others are relatively resistant to the pro-hypertensive effects of sodium. Indeed, Dahl et al 4 have been able, through selective inbreeding, to produce genetically salt-sensitive and salt-resistant strains of rats. At present, other than through the clue provided by a positive family history, there are no ways to identify individuals with potentially salt-sensitive hypertension who might benefit from early dietary counseling.…”

mentioning

confidence: 99%

Hemodynamic effects of dietary sodium in man: a preliminary report.

Sullivan¹,

Ratts²,

Taylor³

et al. 1980

100

SUMMARY The effect of dietary sodium manipulation was studied In 27 normal subjects and 19 patients with borderline hypertension. Sodium-loading caused an Increase in blood pressure (BP) in 14 of 19 borderline hypertensive patients but in only 4 of 27 normal subjects (X* = 13.85, p < 0.01). In the normal subjects, a 10 mEq sodium diet resulted in a fall in supine mean blood pressure (MBP) of 43% after 4 days (p < 0.05). Cardiac index (CI) measured by echocardiography fell by 4.0%, while total peripheral resistance (TPR) remained unchanged. After the subjects had followed a 200 mEq sodium diet for 4 days, CI rose 6.9%, TPR fell 13%, and MBP fell 3.9%. Six normal subjects also receired a 400 mEq sodium diet, which resulted in a 16% increase in MAP (p < 0.01). This was accompanied by an 11.1% increase in CI and an 11.5% increase in TPR. When subjected to sodium depletion, the 19 hypertensive subjects displayed a similar 4. Epidemiologic studies have shown that the frequency with which hypertension is found in a population rises in relation to the quantity of habitually used sodium by that population. 13 However, the majority of individuals, about 60%, remain normotensive even in those populations that consume the highest amounts of sodium.' This suggests that some individuals will respond to dietary sodium intake with an increase in blood pressure (BP) while others are relatively resistant to the pro-hypertensive effects of sodium. Indeed, Dahl et al. 4 have been able,