Calcium Carbonate Exacerbates Glomerular Capillary Hypertension and Injury in Rats With Desoxycorticosterone-salt Hypertension

Abstract

To examine the effects of dietary calcium supplementation on systemic and renal hemodynamics and glomerular injury in experimental hypertension, rats with desoxycorticosterone-salt hypertension were fed either standard chow, containing 1% calcium by weight, or chow supplemented with calcium carbonate to achieve a calcium content of 2% by weight. Ingestion of calcium carbonate failed to reduce systemic blood pressure, but was associated with increased proteinuria and morphologic evidence of glomerular injury. Micropuncture studies revealed that afferent arteriolar resistance was reduced and glomerular capillary pressure further increased in the high calcium group. Thus, calcium carbonate, in moderate amounts, not only failed to ameliorate systemic hypertension but, paradoxically, worsened intrarenal hypertension and injury in rats with mineralocorticoid-induced hypertension.

Renal impairment in deoxycorticosterone acetate‐salt hypertensive rats

“…Calcium supplementation leads to a relaxation of the afferent arterioles but glomerular pressure is increased, thus increasing glomerular injury. 31 This would support the failure of the normalization of calcium intake to attenuate renal hypertrophy or renal dysfunction in our study.…”

“…Intrarenal hypertension is in fact probably worsened by calcium supplementation. Micropuncture studies have shown that capillary pressure in superficial glomeruli is increased; 31 this probably applies to all glomeruli, deep as well as superficial. Calcium treatment did not restore the pressure natriuresis responses in the isolated kidneys of DOCA‐Ca treated rats, whereas it does in the in situ perfused kidney of Dahl rats.…”

“…DOCA administration probably directly causes the decrease in renal function. DOCA‐salt rats develop an elevated glomerular transcapillary hydraulic pressure gradient as a result of afferent arteriolar vasodilatation; this leads to glomerular injury 31 possibly due to angiotensin II 32 or endothelin. 33 DOCA‐salt hypertension may be caused by high systemic endothelin levels with increased endothelin receptor density.…”

“…Dietary calcium supplementation to DOCA‐salt hypertensive rats has produced contradictory results: significant attenuation of hypertension in this and some studies 10,11 or no effect on the degree of hypertension. 31,36 These studies are difficult to compare because different calcium salts were given either in the food or water and neither calcium nor sodium consumptions are reported in the literature studies. Our study showed that DOCA‐salt rats have a reduced dietary calcium intake as their food consumption was decreased; normalization of calcium intake in DOCA‐Ca rats maintained blood pressure at approximately normotensive levels while significantly attenuating the increased water intake of the DOCA‐salt rats.…”