Question

1. Your next patient is Mr. Johnson, who also has congestive heart failure. He is taking furosemide (Lasix®) as part of his drug regimen. He says, “These are my water pills, the doctor tells me. They make me go and go!” Furosemide acts in the ascending limb of the Loop of Henle to block the NKCC transporter (ie, prevent it from transporting Na+, K+, and 2Cl- from the tubular fluid into the tubular epithelial cells).

Why does the furosemide (Lasix®) make Mr. Johnson urinate so much?

Answer 1

Furosemide, like other loop diuretics inhbits the luminal Na-K-Cl cotransporter or (NKCC transporter) on the acsending loop of henle.

By inhibiting this cotransporter, the ions are not reabsorbed into the tubular epithelial cells. they stay in the tubular fluid itself, This causes a pull of the water molecules from the tubular epithelial cells into the tubular fluid as to maintain osmotic pressure.

So, more water is drawn into the tubular fuild and hencce more amount of urine is produced, which makes Mr Johnson urinate so much.

Furosemide is usually given in patients with heart failure as they usually develop pedal endema, this water retension in the extremities is reduced by furosemide as it eleminates fluid (water) from the body in the form of urine.