Development of sugar-induced blood pressure elevation after uninephrectomy in a resistant rat strain

Effects of high sugar diets on renal fluid, electrolyte and mineral handling in rats: relationship to blood pressure

OBJECTIVE

We examined whether sugar-induced systolic blood pressure (SBP) elevations in rats may develop, in part, through a mechanism common to salt-induced hypertension, i.e., renal retention of water and salt.

DESIGN

Spontaneously hypertensive rats (SHR) ate four diets: two high (> 50% of calories) and two low (< 12% of calories) in sugar (sucrose). SBP, various urinary parameters, and the renal angiotensin and prostaglandin systems were assessed.

RESULTS

SHR consuming diets high in sugar showed significantly decreased urinary volume and excretion of electrolytes, which coincided with increasing SBP. When low sugar diets replaced high sugar diets, SBP and urinary parameters rapidly returned to baseline. SHR received captopril while consuming high sugar diets, and both SBP and urinary parameters assumed baseline values, comparable to ones seen in SHR consuming low sugar diets. A direct angiotensin II receptor antagonist (DuPont 753) did not influence SBP. However, we found decreased PGE2 excretion in SHR consuming excess sugar.

CONCLUSIONS

Salt and water retention occur early during sugar-induced hypertension due to reduced renal excretion, consistent with some part in the pathogenesis. The effects of high sugar diets on SBP were not due to angiotensin II inhibition, however, decreased availability of vasodilatory prostaglandins may play a role in the renal events and sugar-induced hypertension in SHR.

Effects of canrenone on RRM-sucrose hypertension in WKY

Ingestion of a diet high in sucrose content by WKY rats having reduced renal mass (RRM) via a unilateral nephrectomy causes a significant elevation of BP--greater than might be expected from either condition alone. The same findings occur whether the added sucrose calories replace protein or fat. The elevated BP differential remained throughout the 6 months of the study. In some ways, these results resemble a well recognized model of hypertension produced by the removal of 70-80% of renal mass plus excess salt consumption (RRM-salt). When the RRM-sucrose WKY were given canrenone, an agent which is a digoxin antagonist, the BP decreased significantly simulating previous findings in RRM-salt. Therefore, like the RRM-salt model, evidence suggests that the RRM-sucrose model is also caused, at least in part, by a digoxin-like factor (DLF).