In a study of salt intake's effect on renal function, which change is most likely to occur in an animal on a low-salt diet?

When an animal is on a low-salt diet, the body responds by attempting to conserve sodium to maintain homeostasis and ensure adequate sodium levels for physiological functions. One key response is the upregulation of epithelial sodium channels (ENaC) in the renal tubules, particularly in the distal nephron. This increase in ENaC expression leads to enhanced sodium reabsorption from the urine back into the renal interstitium, which ultimately helps to prevent sodium loss.

This adaptation is crucial because sodium is essential for maintaining extracellular fluid volume, normal blood pressure, and various cellular functions. As the ENaC transcription increases, it reflects the body’s effort to adapt to the low-salt intake by improving sodium retention mechanisms.

The other potential changes indicated in the options are less likely to be directly associated with the immediate physiological response to a low-salt diet. For instance, extracellular fluid volume might not change significantly at first due to compensatory mechanisms. Plasma levels of atrial natriuretic peptide typically decrease in response to low sodium intake as this peptide is released when the body has excess sodium and volume, functioning to promote natriuresis. Lastly, serum potassium concentration tends to be more stable, as potassium homeostasis is tightly regulated and