Dahl salt-sensitive rats provide a useful model of salt-sensitive hypertension. What if we used something besides NaCl to give them sodium? What happens with sodium bicarbonate, for example?
Bicarbonate Therapy Alleviates Hypertension-Induced Renal Injury in Dahl Salt-Sensitive Rats Independent of System Blood Pressure. D Irsik et al.
Telemetry-monitored rats were treated with NaCl of equimolar NaHCO3 in their drinking water. Blood pressure rose identically in the two groups of rats, so sodium really seems to be the drive of that response. A variety of indices of kidney damage, including glomerulosclerosis tubular casts, and interstitial fibrosis, were significantly reduced in the rats receiving bicarbonate.
Na excretion was similar in both groups, although net acid excretion rose dramatically in the NaCl rats. This consisted of both NH4+ as well as a significant component of titratable acids.
Some of the numbers are rather preliminary, but serum pH and bicarbonate levels were similar in the two groups (7.49 for pH and ~27 for bicarbonate). Potassium was reduced in both groups, although lower with NaCl (3.59 vs 3.33). Numbers in each group are too small for statistical comparisons, but that should be corrected in the near future.
For a clinician, this work from Paul O'Connor's lab raises many interesting points. First, the groups had essentially identical pH and bicarbonate. If these results hold up as they expand their numbers, it has human implications. I would not have targeted either group for bicarbonate therapy based on serum levels.
I would like to see them do a clinically relevant experiment. When we give base (usually as NaBicarbonate) to patients, we are not generally substituting it for NaCl. Rather, we are adding another 30-50% of daily Na intake to their usual NaCl intake. How would doing that in this model change the outcomes? Would the additional sodium have any untoward effects?
As those of us at the Gottschalk lecture know, there are complex interactions between Na, H+, and K+ at the epithelial Na Channel in salt-sensitive states. Reducing the presence of acid (H+) in the filtrate may be beneficial, both in preserving potassium levels and, perhaps, other yet unidentified effects.