Commercial rodent diets contain more sodium than rats need

Abstract

The dietary sodium requirements for rats have been a matter of debate. Our hypothesis was that normal commercial rodent chow contains sodium in excess of dietary needs and that this could have a significant impact on cardiovascular and renal physiology. To investigate dietary sodium requirements, 3-wkold weanling Sprague-Dawley rats were fed a custom pelleted diet containing no sodium that was isocaloric to normal commercial rodent chow. These rats were provided with two drinking bottles; one contained water, and the other contained 0.5% NaCl. Thus they could choose and consume sodium as needed. Age-matched controls received normal pelleted Harlan Teklad 22/5 rodent diet (0.5% sodium content) and water ad libitum. Body weight and liquid intake were monitored over 7 wk until the rats were 10 wk old. At the end of the study, blood pressure was recorded. Weekly sodium intake in the experimental group was only 15% of that reported for rats fed normal rodent chow beginning in the first week postweaning. Growth was identical in the two groups (7.8 Ϯ 0.1 vs. 7.6 Ϯ 0.1 g/day), as was the total fluid volume intake. Blood pressure was significantly lower in the experimental rats compared with controls (96 Ϯ 4 vs. 122 Ϯ 4 mmHg, P Ͻ 0.05). These data suggest that, when given the choice, rats will consume significantly less sodium than provided in commercial chow, without any alteration in their growth rate. Rats fed standard commercial rodent chow may consume at least seven times more sodium than is necessary. This suggests commercial rodent diets may force excess sodium to accommodate caloric intake.calories; growth; metabolic requirements; blood pressure DIETARY SODIUM INTAKE IS AN important element in fluid balance, renal function, and blood pressure. In the wild, the rat is a scavenger and its sodium intake is very limited, but in the domesticated or laboratory rat dietary salt is abundant. Manipulation of dietary sodium intake is an important experimental paradigm for studying renal physiology or pathophysiology. High salt intake has been found to influence a wide variety of physiological parameters in otherwise normal rats, including blood pressure (7,11,17,18,22), renin secretion (2, 20, 21), plasma aldosterone (7,20), angiotensin receptors (20), nitric oxide synthase (2, 21), cyclooxygenase (9, 22), endothelin (18), insulin resistance (17), and vascular adaptation (22). Commercial "normal" rat chows contain 0.3-0.5% sodium, while experimental "high-salt" diets contain 2-8% sodium (2, 7, 11, 17, 18, 20 -22). It has been proposed that the daily nutritional sodium requirement for normal growth and reproduction is 0.05% of dietary intake (19) and that an adult 400-g rat will consume at least 15-20 g of rat chow/day, which translates to a daily intake of 7.5-10 mg sodium. However, commercial rodent diets have been modified, altering nutritional factors to promote growth, in keeping with the guidelines for nutrient requirements published by the National Research council (NRC) (15). These guidelines push the range of sodi...

Retinal Vasculopathy Is Reduced by Dietary Salt Restriction

“…This was not because of poor nutrition, which may exacerbate OIR in mice and rats, 43,44 but reduced water intake mostly likely as a result of the mothers previous preference for a diet higher in salt content. 45 With respect to retinal neovascularization in OIR, we found a marked improvement with an LS diet, as well as normalization of mRNA and protein levels of VEGF and erythropoietin in retina. 20,29 Enhanced activity of ERK1/2 has been linked to both VEGF and erythropoietin signaling and to retinal angiogenesis.…”

Hyperphosphorylation of Na-K-2Cl Cotransporter in Thick Ascending Limbs of Dahl Salt-Sensitive Rats

“…Male DSS and DSR rats (8-9 weeks old) weighing 200 to 250 g (Harlan, Indianapolis, IN) were maintained on a diet containing 0.22% sodium (which provides excess Na 27 and has been widely used in tubule perfusion experiments to stabilize baseline Na + transport) and 1.1% potassium (Purina, Richmond, IN) with water ad libitum for ≥14 days after arrival to our facility. All animal protocols were approved by the Henry Ford Hospital Institutional Animal Care Committee.…”

Metabolic effects following periconceptional alcohol exposure in rat adult offspring: modulations by a postnatal western diet

“…While this demonstrates how a certain food pattern might be the preferred one (and therefore a likely change of the postnatal environment), it is important to emphasize that the dosage used in animal studies are not always comparable to a human scenario. For example, the 8% sodium diet used in the study by Yan et al (2014) has 16-fold higher sodium levels compared with the recommended rodent diet of 0.5% sodium (Martus et al, 2005).…”

“…For example, EtOH selectively acetylates histone H3 at lysine residue 9 (H3Ack9) (via an alcohol metabolism dependent process) in both cultured rat hepatocytes (Martus et al, 2005) and in vivo (Powles et al, 2013, Muzio et al, 2012. As a consequence, Adh1 gene expression increases (Martus et al, 2005); EtOH metabolism increases, and this in turn intensifies this cycle (Yan et al, 2014). Although maternal livers were not collected during the exposure period, unpublished data from our lab demonstrate such increase by which dams consuming EtOH had a ~40% increase in hepatic Adh1 gene expression on E20 compared with untreated dams (P < 0.05).…”

“…While this demonstrates how a certain food pattern might be the preferred one (and therefore a likely change of the postnatal environment), it is important to emphasize that the dosage used in animal studies are not always comparable to a human scenario. For example, the 8% sodium diet used in the study by Yan et al (2014) has 16-fold higher sodium levels compared with the recommended rodent diet of 0.5% sodium (Martus et al, 2005).For a human, that would be equivalent to a daily intake of 32g sodium (recommended intake is <2g/d). The mean sodium intake (globally) was however estimated to 3.95g daily in 2010 (Powles et al, 2013) and therefore the physiological relevance of such experiment is limited.…”