Mechanisms of renal hemodynamic regulation in response to protein feeding

The purpose of these studies was to compare the effects of proximally and distally acting diuretics on the renal hemodynamic response to protein feeding to determine the importance of the proximal tubule in postprandial renal vasodilation. In chronically instrumented conscious dogs, a meat meal (10 g/kg raw beef) caused glomerular filtration rate (GFR) to increase from 63 +/- 5 to 87 +/- 10 ml/min and effective renal plasma flow (ERPF) to increase from 189 +/- 20 to 249 +/- 20 ml/min, while plasma alpha-amino nitrogen levels rose from 4.0 +/- 0.1 to 6.8 +/- 0.4 mg/dl. Administration of amiloride (0.2 mg/kg + 0.003 mg.kg-1.min-1) or potassium canrenoate (1.76 mg/kg + 1.76 mg.kg-1.h-1), diuretics that act in the distal tubule, had no effect on the renal hemodynamic responses to a meat meal. However, the normal renal hemodynamic responses to protein feeding were abolished during administration of a diuretic that acts in the proximal tubule, acetazolamide (20 mg/kg + 20 mg.kg-1.h-1), although plasma alpha-amino nitrogen levels increased after the meat meal in all experiments. These data suggest that normal proximal tubular sodium reabsorptive function is necessary for acute protein-stimulated renal vasodilation and are consistent with the hypothesis that a tubuloglomerular feedback mechanism may mediate postprandial renal vasodilation.

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Impaired renal hemodynamic response to protein feeding in dogs with experimental Fanconi syndrome

AJP Renal Physiology ◽

10.1152/ajprenal.1991.261.1.f14 ◽

1991 ◽

Vol 261 (1) ◽

pp. F14-F21 ◽

Cited By ~ 1

Author(s):

L. L. Woods ◽

E. W. Young

Keyword(s):

Maleic Acid ◽

Fanconi Syndrome ◽

Amino Nitrogen ◽

Hemodynamic Response ◽

Nitrogen Excretion ◽

Tubular Function ◽

Renal Hemodynamic ◽

Proximal Tubular ◽

Protein Feeding ◽

Proximal Tubular Function

These studies were designed to test the hypothesis that intact proximal tubular function is required for protein-stimulated renal vasodilation. In normal chronically instrumented conscious dogs, a meal of raw beef (10 g/kg) caused glomerular filtration rate (GFR) to increase significantly from 63 +/- 5 to 94 +/- 10 ml/min after 90 min, while plasma alpha-amino nitrogen rose from 3.9 +/- 0.2 to 6.7 +/- 0.6 mg/dl. In another group of dogs experimental Fanconi syndrome (generalized proximal tubular dysfunction) was induced with maleic acid (25 mg/kg iv, pH 7.3). GFR fell slightly but significantly from 91 +/- 18 to 66 +/- 9 ml/min after maleic acid, while Na+ excretion rose from 24 +/- 8 to 176 +/- 24 mu eq/min, alpha-amino nitrogen excretion rose from 82 +/- 40 to 148 +/- 47 micrograms/min, and glucose excretion rose from 0.2 +/- 0.1 to 6.1 +/- 1.0 mg/min. In response to a subsequent meat meal, plasma alpha-amino nitrogen rose significantly from 3.8 +/- 0.4 to 6.2 +/- 0.5 mg/dl, but GFR did not change, averaging 66 +/- 9 ml/min over the next 120 min. These results suggest that normal proximal tubular function is necessary for protein-stimulated renal vasodilation to occur. This finding is consistent with the hypothesis that the tubuloglomerular feedback mechanism may be involved in mediating the normal renal hemodynamic response to protein feeding.

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Mechanisms of renal vasodilation after protein feeding: role of the renin-angiotensin system

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1993.264.3.r601 ◽

1993 ◽

Vol 264 (3) ◽

pp. R601-R609 ◽

Cited By ~ 2

Author(s):

L. L. Woods

Keyword(s):

Sodium Intake ◽

Renal Plasma Flow ◽

Renin Angiotensin System ◽

Plasma Renin ◽

Hemodynamic Response ◽

Angiotensin System ◽

Renin Angiotensin ◽

Renal Hemodynamic ◽

Meat Meal ◽

Protein Feeding

These studies were designed to determine the importance of the renin-angiotensin system (RAS) in the renal hemodynamic response to acute protein feeding. In chronically instrumented conscious dogs on a normal (80 meq/day) sodium intake, a 10 g/kg meal of raw beef caused glomerular filtration rate (GFR) to increase from 68 +/- 6 to 86 +/- 6 ml/min and effective renal plasma flow (ERPF) to increase from 211 +/- 14 to 263 +/- 15 ml/min. Plasma renin activity (PRA) was 0.44 +/- 0.14 ng ANG I.ml-1 x h-1 and did not change significantly. When the protocol was repeated during infusion of captopril, GFR increased from 67 +/- 11 to 97 +/- 10 ml/min, and ERPF rose from 264 +/- 74 to 392 +/- 82 ml/min after the meat meal. The dogs were then placed on a low-salt diet (approximately 7 meq/day) to physiologically activate the RAS. In sodium-restricted dogs, GFR increased from 71 +/- 7 to 104 +/- 10 ml/min and ERPF increased from 226 +/- 15 to 299 +/- 21 ml/min after the meat meal. PRA was 3.1 +/- 1.0 ng ANG I.ml-1 x h-1 and did not change. Thus neither blockade of the RAS with captopril nor activation of the RAS by salt restriction reduced the renal hemodynamic response to a meat meal. These data indicate that the RAS is relatively unimportant in the renal hemodynamic response to acute protein feeding.

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