Robert O. Banks

Renal glucose reabsorption during hypertonic glucose infusion in female streptozotocin-induced diabetic rats

Information regarding the renal glucose transport capacity in diabetes mellitus is limited. These data are needed because two weeks following injection of streptozotocin (STZ), mRNA and protein levels of the glucose transporter, GLUT2, are upregulated in the proximal tubule of the rat. Therefore, we measured renal glucose transport and GLUT2 protein levels in female control rats, and in rats one (STZ-1), two (STZ-2), and three weeks (STZ-3) after STZ injection (65 mg kg(-1), i.p.). Progressive amounts of glucose were infused into anesthetized rats via the femoral vein and renal clearances collected. The amount of glucose reabsorbed, factored by the glomerular filtration rate (GFR) was significantly greater in STZ-3 rats compared with all other groups. In addition, the amount of glucose reabsorbed factored by the amount of glucose filtered was decreased in STZ-1 and STZ-2 compared with controls but was increased in STZ-3. By contrast, renal GLUT2 levels were elevated in all the STZ-treated rats. These data suggest that other factors, functioning either in conjunction with or independent of GLUT2, are required to support an elevated renal glucose transport capacity.

Failure of Atrial Myocardial Extract to Inhibit Renal Na+, K+-ATPase

The effects of a natriuretic factor contained in extracts of the atrial myocardium on an isolated renal Na+, K+-ATPase enzyme system were evaluated. Ultrafiltrates (molecular weight less than 30,000) of boiled extract of rat atria and ventricles were prepared. Infusion of 100 microliters of the atrial ultrafiltrate into bioassay rats resulted in a prompt, short-lived natriuresis and diuresis. However, addition of 100 microliters of the atrial ultrafiltrate to 900 microliters of a suspension containing Na+, K+-ATPase had no significant effect on enzymatic activity. Similarly, ultrafiltrates of ventricular extract also had no significant effect on Na+, K+-ATPase activity. These results indicate that the atrial natriuretic factor does not alter renal tubular sodium reabsorption by directly inhibiting the Na+, K+-ATPase enzyme system.

Renal Function and Glucose Transport in Male and Female Mice with Diet-Induced Type II Diabetes Mellitus

The aim of this study was to measure cardiovascular and renal function, including the renal transport capacity for glucose, in male and female C57BL/6J mice with diet-induced Type II diabetes mellitus. Typical of Type II diabetes, mice fed a high-fat, high-simple carbohydrate diet for 3 months were obese (45-65 g), hyperglycemic (138-259 mg%), and hyperinsulinemic (1.8-15.06 ng/ml); significant gender differences were observed in all cases. Based on systolic pressure measurements in conscious mice and arterial blood pressure measurements in anesthetized mice, no diet-induced hypertension was observed in either male or female mice. Urine flow rate, sodium, potassium, osmolar, and protein excretion rates were significantly increased (P < 0.05) in male mice fed the high-fat, high-simple carbohydrate diet compared with female mice fed the same diet. However, no differences in the excretion variables existed between male and female mice fed the control diet. The glomerular filtration rate (ml min-1 g kw-1), determined by FITC-inulin, in male and female mice fed the control diet (0.87 +/- 0.01 and 0.90 +/- 0.1, respectively) and high-fat, high-simple carbohydrate diet (0.96 +/- 0.1 and 0.93 +/- 0.2, respectively) was not different between the groups. These hyperglycemic mice were also not glucosuric. Infusions of progressive amounts of glucose in male mice fed either diet for 3 or 6 months demonstrated that the renal threshold for glucose was 400 mg% for all these mice, well above the fasting plasma glucose concentrations observed in this study. Thus, C57BL/6J mice were valuable tools for studying diet-induced obesity, hyperglycemia, and hyperinsulinemia; however, no hypertension or kidney dysfunction was apparent within the time frame of the current study.

Age-related changes in Na+ excretion in saline-loaded spontaneously hypertensive rats.

The ability of 6- to 7-, 12- to 13-, and 16- to 17-wk-old spontaneously hypertensive rats (SHR) to excrete an acutely administered, isotonic saline load (equivalent to 4.5% body wt) was evaluated. Female SHR from two different colonies were studied. Age-matched female Wistar (W) and Wistar-Kyoto (WKY) rats served as controls. At age 6 wk, the fraction of administered Na+ load excreted by either SHR colony after 60 min was significantly lower than in the Wistar rats but not significank, one colony of SHR excreted significantly more sodium after 60 min than the other rats. Glomerular filtration rate during control periods was positively correlated with age in one SHR colony; no age-related changes were observed in glomerular function in the other groups. These data 1) suggest that WKY rats are more appropriate than the Wistar rats as controls for renal function in the SHR, 2) demonstrate that the ability of the SHR to excrete an acutely administered sodium load is equal to or greater than normotensive WKY controls, and 3) demonstrate that with respect to renal function parameters, the SHR is not a homogenous strain.

Cardiorenal actions of endothelin, part I: Effects of converting enzyme inhibition

We have evaluated the effects of endothelin-1, with and without captopril administration, on the circulating concentration of aldosterone in pentobarbital (60 mg/kg) anesthetized rats. Following surgery, rats (N = 5/group) were infused with saline intravenously, at a rate of 0.024 ml/min, with or without captopril (5 mg kg-1 hr-1) administration throughout the entire experiment. All rats were allowed 60 min to stabilize and 3 X 20 min control clearances collected. Endothelin-1 (100 eta kg-1 min-1) was then added to the infusate for 30 min. Plasma aldosterone concentration increased from 60 +/- 7 eta/dl to 171 +/- 14 eta/dl (p less than 0.01) with endothelin alone and from 101 +/- 6 eta/dl to 210 +/- 54 eta/dl (p less than 0.01) in rats treated with endothelin plus captopril. The endothelin-induced increment in blood pressure was not altered by captopril treatment. However, the endothelin-induced decrement in renal function was markedly attenuated in rats treated with captopril. These data demonstrate that endothelin stimulates the release of aldosterone from the rat adrenal and that the angiotensin II is not involved in this response. These data also demonstrate that the endothelin-induced systemic vasoconstriction is not affected by captopril whereas the endothelin-induced changes in renal function are abolished by captopril.

Segmental Nephron Sodium and Potassium Reabsorption in Newborn and Adult Dogs during Saline Expansion

Abstract Studies were carried out in 23 anesthetized neonatal dogs aged 2 to 20 days and in 16 adult dogs to compare the effects of saline volume expansion on renal tubular Na and K reabsorption between newborn and adult animals. Proximal- and distal-tubule function was estimated by the distal-nephron-blockade technique using ethacrynic acid and amiloride. During saline infusion, which increased extracellular volume by approximately 30% for both age groups, total nephron fractional Na reabsorption was 0.91 for the adult but 0.98 for the puppy (P < 0.01). However, proximal tubule fractional Na reabsorption was greater in the adult (0.64) than in the puppy (0.48, P < 0.01) whereas distal nephron fractional Na reabsorption was much greater in the newborn (0.51) than in the adult (0.26, P < 0.01). Sodium reabsorption normalized to kidney weight was lower in all segments of the neonatal kidney than in the adult kidney. The filtered sodium load was lower in the newborn (27.0 μeq min–1g–1) than in the adult (105.0, P < 0.01), and the Na load to the distal nephron was also lower in the newborn (14.0 μeq min–1g–1) than in the adult (37.2, P < 0.01). Fractional K excretion was similar in both age groups even though the fraction of filtered K escaping proximal-tubule reabsorption was greater in the newborn than in the adult, indicating greater net K fractional reabsorption in the distal nephron of the newborn than in the adult kidney. These results indicate that in response to saline expansion there is a greater proximal tubule natriuresis in the neonate than in the adult but overall renal Na excretion is less in the newborn animal due to enhanced fractional Na reabsorption in the neonatal distal nephron, particularly in Henles Loop.

Actions of Nicotine on Renal Function in Dogs

Abstract Renal excretory and circulatory responses to nicotine were investigated in anesthetized dogs under three sets of conditions: (a) infusion of nicotine into the left renal artery (ia) at a dose of 0.5 μg·min−1 ·kg body wt−1 × 15 min; (b) ia nicotine after 1.0 mg/kg ia propranolol; and (c) ia nicotine after bilateral adrenalectomy. Measured and calculated left and right renal excretory variables included sodium, potassium, and chloride excretion rates (UNaV, UKV, and UClV, respectively), total solute excretion (UOsV), glomerular filtration rate (GFR), fractional sodium excretion (FENa), and urine flow rate. Systemic arterial pressure and left renal artery blood flow (RBF) were also measured. In seven intact dogs administered nicotine alone, there were significant increases in UNaV, UClV, UOsV, GFR, and urine flow rates from both kidneys. However, nicotine did not significantly affect UKV, FENa, arterial pressure, or RBF. The lack of circulatory effects of nicotine was also observed after either propranolol or adrenalectomy. However, when nicotine was administered after propranolol, the drug evoked significant decreases in UOsV, UNaV, UClV, and GFR, compared with prenicotine values. When nicotine was administered after bilateral adrenalectomy, the drug evoked decreases in the excretory parameters similar to those observed after propranolol. These findings seem to support several inferences: (a) nicotine stimulates renal excretory functions—the alkaloid is saluretic and diuretic; (b) the action of nicotine on the kidney is mediated mainly by the release of catecholamines from the adrenal medulla; (c) catecholamines released by nicotine act mainly on β-adrenergic receptors; and (d) the saluresis prompted by the release of catecholamines in response to nicotine is due to a subsequent increase in GFR.

Cardiorenal actions of endothelin, Part II: Effects of cyclooxygenase inhibitors.

The effects of cyclooxygenase inhibitors (meclofenamate and indomethacin) on endothelin-induced changes in renal function were evaluated in pentobarbital anesthetized female rats. Two groups (n = 5/group) of rats were evaluated: one group received a continuous intravenous infusion of meclofenamate (0.03 mg kg-1 min-1) and the second group received a bolus injection of indomethacin (5 mg/kg). Following surgery, rats were allowed 60 min to stabilize and 3 X 20 min control clearances collected. Endothelin-1 (100 eta kg-1 min-1) was then added into the infusate for 30 min. Neither meclofenamate nor indomethacin caused significant changes on endothelin-induced systemic vasoconstriction; blood pressure increased from 107 +/- 3 to 136 +/- 2 mmHg (p less than 0.01) with endothelin alone, from 103 +/- 6 to 135 +/- 6 mmHg (p less than 0.01) with endothelin plus meclofenamate, and from 105 +/- 6 to 131 +/- 10 mmHg (p less than 0.01) with endothelin plus indomethacin. Similarly, endothelin-induced decreases in glomerular filtration rate (GFR) were not affected by either meclofenamate or indomethacin; GFR decreased from 2.7 +/- 0.2 to 0.8 +/- 0.3 ml/min (p less than 0.01) with endothelin alone, from 2.3 +/- 0.5 to 0.7 +/- 0.4 ml/min (p less than 0.01) with endothelin plus meclofenamate, and from 2.6 +/- 0.4 to 0.6 +/- 0.4 ml/min (p less than 0.01) with endothelin plus indomethacin. Baseline excretion rates of sodium, potassium and urine volume were also not affected by the inhibitors of cyclooxygenase. These data demonstrate that, under the conditions of the current study, endothelin-induced changes in renal and cardiovascular function are not affected by inhibiting prostaglandin production.

Influence of Antidiuretic Hormone on Intrarenal Blood Flow Distribution in Diabetes Insipidus Dogs and Rats

Summary The distribution of labeled mi-crospheres within the renal cortex was used to evaluate the influence of physiological amounts of antidiuretic hormone on intra-renal blood flow distribution in hypophysec-tomized dogs and in rats with hereditary diabetes insipidus. In both species, intravenous infusions of ADH caused a significant decrease in the ratio of inner to outer cortical blood flow. The change in blood flow distribution observed in the hypophysecto-mized dog with ADH was primarily a consequence of a decrease in inner cortical blood flow. No consistent changes in outer cortical blood flow were found. Also in the dog, glomerular filtration rates and electrolyte excretion rates (Na and K) increased following ADH. In contrast, ADH infusion into Brattleboro rats caused no change in glomerular filtration rate or excretion of Na and K. I would like to thank Dr. Carl Hansen of NIH for kindly supplying our Brattleboro breeders. The excellent technical assistance of Mrs. Christine Eldon is gratefully acknowledged.

Hemodynamic Actions of Nicotine on the Canine Stomach

Abstract Acute effects of nicotine were determined in the circulation of the stomach in which measurements of gastric blood flow, systemic arterial and portal venous blood pressures, and the arteriovenous oxygen content difference were made. From these measurements gastric vascular resistance and oxygen consumption were calculated. Nicotine was infused for 10-min periods in two doses intraarterially (ia) and intravenously (iv) alone and following adrenergic receptor blockade with either propranolol or phentolamine or both agents. With ia nicotine alone, gastric blood flow and oxygen consumption increased. The effect of nicotine on blood flow was enhanced by prior treatment with phentolamine. The effects of nicotine on both blood flow and oxygen consumption were abolished in the presence of combined phentolamine plus propranolol. With iv nicotine alone, gastric blood flow, oxygen consumption, and arterial pressure increased transiently. Phentolamine enhanced the effect of nicotine on oxygen uptake and prevented the pressor response. Propranolol enhanced the pressor effect of nicotine but abolished the blood flow and oxygen consumption responses. Combined treatment with both adrenergic antagonists abolished nicotine effects on blood flow and oxygen consumption. These findings indicate that nicotine alters gastric hemodynamics and oxygen consumption during acute intravascular infusions of the drug. The vasodilator and metabolic effects of nicotine appear to be mediated via β-adrenergic receptors. These findings provide little basis for implicating a local ischemic mechanism in the ulcerogenic effects of nicotine on the stomach.