# Preliminary evidence of extrarenal sodium storage in a large mammal: implications for comparative physiology and hypertension research: Running: Sodium storage in cattle

## TL;DR

This study finds evidence that cattle can store and later release excess sodium outside the kidneys, which could help manage blood pressure in large mammals.

## Contribution

The study provides the first preliminary evidence of extrarenal sodium storage in large mammals like cattle.

## Key findings

- Cattle excreted excess sodium in urine and feces after a high-sodium dose, with a delayed release pattern.
- Sodium storage does not appear to involve potassium exchange in urine, but fecal excretion suggests some intestinal exchange.
- The findings suggest cattle could serve as a model for studying sodium regulation in large mammals.

## Abstract

Under conditions of dietary sodium (Na+) excess, the kidneys may fail to adequately excrete Na+, potentially compromising blood pressure homeostasis. Body tissues, such as skin, can offer sites of short-term extrarenal Na+ storage and previous research has shown that this can help guard against hypertension in small mammals (e.g., rodents). Large mammals have relatively greater Na+ storage potential, but whether extrarenal Na+ storage occurs for this group is unknown. Here, we report preliminary evidence of extrarenal Na+ storage in cattle. We provided a large pulse-dose of NaCl to four cattle (body mass: ~720 kg) and measured excretion of Na+ and potassium (K+) in urine and faeces for a period of 7-days. Following NaCl administration, Na+ excretion spiked in both urine and faeces for ~ 48 h before returning to baseline measurements. After ~ 96 h, however, Na+ excretion increased again; a consistent physiological phenomenon across all individuals studied. We did not observe a pattern in urinary K+ excretion, indicating that the mechanism of Na+ storage does not appear to involve exchange for K+. However, faecal K+ excretion was reciprocal to that of Na+, presumably reflecting exchange of Na+/K+ across the walls of the large intestine. We infer that during the initial period of Na+ stress, short-term extrarenal Na+ storage occurred and the stored Na+ was later released only when the body had returned to Na+ homeostasis. Additional experiments are required to understand how patterns of Na+ regulation changes across body sizes and the specific body compartments involved. Cattle may be a useful model system for examining the impact of high Na+ intake in mammals larger than humans.