Renovascular Responses to High and Low Perfusate Calcium Steady-State Experiments in the Isolated Perfused Rat Kidney with Baseline Vascular Tone

• Published in: The Journal of surgical research 1996-02, Vol.61 (1), p.51-57
• Main Authors: Castelli, I., Steiner, L.A., Kaufmann, M.A., Drop, L.J.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calcium - pharmacology; Calcium Channel Blockers - pharmacology; Dose-Response Relationship, Drug; Fundamental and applied biological sciences. Psychology; Glomerular Filtration Rate - drug effects; Homeostasis; In Vitro Techniques; Male; Natriuresis - drug effects; Osmolar Concentration; Perfusion; Rats; Rats, Sprague-Dawley; Renal Circulation - drug effects; Verapamil - pharmacology; Vertebrates: urinary system
• ISSN: 0022-4804; 1095-8673
• DOI: 10.1006/jsre.1996.0080

Acute hypercalcemia is commonly observed in surgical patients after calcium infusion while acute hypocalcemia is common during rapid citrated blood transfusion. Although high and low ionized calcium ([Ca2+]) within the clinical range produce an increase or decrease in cardiac performance and systemic vessel resistance, respectively, their effects on renal vessels have not been quantified. A possible renal vasoconstriction that might occur with high [Ca2+] is of clinical interest because it is a factor which may contribute to impaired renal circulation and decreased function. In this study we examined the renovascular responses to [Ca2+], which was varied within the clinical range under hemodynamically controlled conditions. We instituted high and low [Ca2+] in the per fusate, which consisted of Krebs–Henseleit buffer containing albumin, 60–65 g/liter. Stable high (n= 10) or low (n= 7) [Ca2+] (1.93 ± 0.02 and 0.59 ± 0.01 mM,respectively) was instituted for 10 min and preceded and followed by normal [Ca2+] of the same duration. In a separate protocol (n= 8) verapamil (10−5M) was added to the perfusate 10 min before high [Ca2+] was tested. We measured changes in renal flow at a constant perfusion pressure of 110 mm Hg and also characterized the renal vessels over a range of pressures by pressure vs flow plots. High [Ca2+] was associated with a small decrease in flow (from 28.8 ± 2.4 to 26.9 ± 2.6 ml/min/g,P< 0.02), indicating a small vasopressor effect. This effect was also shown by a leftward shift in the pressure vs flow plots. These changes were prevented by verapamil. GFR decreased (from 0.35 ± 0.04 to 0.28 ± 0.06 ml/min/g,P< 0.01) without a significant change in sodium excretion or fractional sodium excretion. Low [Ca2+] was associated with increased renal flow (from 30.8 ± 2.1 to 35.2 ± 2.7 ml/min/g,P< 0.02), indicating a vasodilator effect. This effect was also shown by a rightward displacement of the pressure vs flow plots. GFR increased from 0.51 ± 0.03 to 0.56 ± 0.04 ml/min/g,P< 0.01, as did sodium excretion (from 2.32 ± 0.22 to 3.87 ± 0.49 μEq/min,P< 0.01) and fractional sodium excretion (from 2.33 ± 0.26 to 3.61 ± 0.49%,P< 0.01). We conclude, first, that in the isolated perfused rat kidney, high [Ca2+] is a weak vasopressor while low [Ca2+] has vasodilator action. Second, high [Ca2+] effects are abolished by verapamil pretreatment. These findings illuminate mechanisms of high [Ca2+] effects on renovascular tone.