The effect of intraarterial infusion of prostacyclin on the tubuloglomerular feedback control in the rat

Neuronal nitric oxide synthase inhibition sensitizes the tubuloglomerular feedback mechanism after volume expansion

BACKGROUND

In the kidney the neuronal isoform of nitric oxide synthase (nNOS) is located in the macula densa cells. These cells are known to be the sensor in the tubuloglomerular feedback. During volume expansion (VE), the tubuloglomerular feedback response is attenuated, allowing increased water and salt excretion. This study addressed the question whether inhibition of nNOS reestablishes the tubuloglomerular feedback response caused by acute extracellular VE.

METHODS

In rats, VE was achieved by infusion of isotonic saline solution at 50 mL/hour x kg body weight. When urine flow was stabilized, the tubuloglomerular feedback response was evaluated by measuring changes in proximal tubular stop-flow pressure (PSF) in response to various loop of Henle perfusion rates. The loop of Henle was perfused with artificial ultrafiltrate and with addition of 1 mol/L non-specific NOS inhibitor, Nomega-nitro-l-arginine methyl ester (L-NAME). In additional rats the nNOS inhibitor, 7-nitro indazole (7-NI), was given intraperitoneally. Single nephron glomerular filtration rate (SNGFR) was also measured. GFR was determined after VE and nNOS inhibition.

RESULTS

Acute VE decreased DeltaP(SF) and DeltaSNGFR while increasing the turning point, indicating decreased sensitivity of tubuloglomerular feedback response. After administration of L-NAME or 7-NI, DeltaP(SF) was maximally sensitized and the turning point and DeltaSNGFR were restored. GFR decreased after VE and nNOS inhibition compared to that after VE alone.

CONCLUSION

These results suggest that a functioning nitric oxide system, especially through the nNOS, is important in mediating normal renal responses and that increased production of and/or sensitivity to nitric oxide during sustained VE plays an important role in the adaptive mechanism of the tubuloglomerular feedback.

Altered expression of prostacyclin synthase in a subset of the thick ascending limb cells and mesangial cells in 5/6-nephrectomized rats

The aim of this study was to evaluate the possible role of prostacyclin (PGl2) in the onset and development of hypertension and chronic renal failure in 5/6-nephrectomized rats (5/6NX). We measured the systolic blood pressure, 24-h urinary excretion levels of 6-keto-PGF1alpha, which was a stable metabolite of PGI2, and levels of PGI2 synthase (PCS) mRNA in the kidneys. Immunostaining for PCS in the kidneys was also evaluated. Systolic blood pressure was higher in 5/6NX than in sham-operated rats. The 24-h urinary excretion levels of 6-keto-PGF1alpha in 5/6NX at 1 week postsurgery were lower than in sham-operated rats. In renal morphology, tubulointerstitial injury was observed at 2 weeks postsurgery, and glomerulosclerosis at 4 weeks. Levels of PCS mRNA in 5/6NX decreased significantly at 1 and 2 weeks postsurgery compared with those in sham-operated rats, but at 8 weeks these levels showed a tendency to increase. Immunostaining for PCS was positive in a subset of the cortical thick ascending limb of Henle's loop cells, including macula densa in both groups. Moreover, in 5/6NX at 8 weeks postsurgery, mesangial cells also stained positive for PCS. In conclusion, our findings suggest that PCS might play an important role in mitigating glomerular hemodynamic changes associated with reduction of renal mass.

Effect of calcium antagonist, manidipine hydrochloride, on renal hemodynamics and tubuloglomerular feedback in spontaneously hypertensive rats

The effects of a calcium antagonist, manidipine, on renal hemodynamics and the tubuloglomerular feedback (TGF) mechanism were examined in 7- to 8-week-old spontaneously hypertensive rats (SHRs) and age-matched normotensive Wistar-Kyoto rats (WKYs). Manidipine, 10 micrograms/kg intravenously, reduced blood pressure only in SHRs. A greater increase in renal plasma flow occurred in SHRs, but effects on GFR were observed in both SHR and WKY rats. Filtration fraction decreased only in SHRs. The TGF response curve in SHRs was shifted to the left compared with that in WKY rats, indicating a more active TGF in hypertensive rats. Manidipine infusion produced a right and upward shift of the feedback curve in SHRs and only an upward shift in WKY rats. We conclude that manidipine corrects hyperactivity of the TGF mechanism in SHRs.

A new technique for the cannulation of small lymph vessels

A method is described which allows rapid cannulation of small lymph vessels using a modified, in-dwelling cannula and a tissue glue. The method was used to cannulate hilar lymph vessels of the kidney but should but appropriate to cannulate small lymph vessels at other locations as well.

Renal vasoconstrictor response to hypertonic saline in the dog: effects of prostaglandins, indomethacin and theophylline

The role of prostaglandins in the mechanism of the tubuloglomerular feed-back was examined in the anaesthetized dog using the infusion of hypertonic saline to increase renal plasma sodium concentration by 30 mmol/l as the stimulus to activate the tubuloglomerular feed-back. Two sequential infusions of hypertonic saline into the renal artery for 10 min separated by 90 min resulted in equivalent reductions in renal blood flow (264 +/- 32 to 174 +/- 20 ml/min first time; 280 +/- 29 to 200 +/- 15 ml/min second time). Administration of indomethacin, 8 mg/kg, between the two infusions did not alter the renovascular response to hypertonic saline (319 +/- 26 to 226 +/- 35 ml/min vs. 288 +/- 32 to 202 +/- 24 ml/min). Infusion of either prostaglandin E2 (PGE2) or prostaglandin I2 (PGI2) during the second hypertonic saline infusion period also resulted in no change in the renovascular response (251 +/- 37 to 141 +/- 31 ml/min vs. 297 +/- 53 to 184 +/- 51 ml/min; and 223 +/- 31 to 162 +/- 35 ml/min vs. 254 +/- 33 to 186 +/- 39 ml/min, respectively). Intrarenal theophylline, to a concentration of 40 micrograms/ml, however, totally abolished the renovascular response to hypertonic saline (279 +/- 20 to 209 +/- 13 ml/min control vs. 390 +/- 26 to 402 +/- 17 ml/min during theophylline). The systemic hypertensive response during the infusion of hypertonic saline was unaltered by indomethacin or prostaglandins but was totally abolished by theophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal vasodilation after unilateral renal ablation

Renal blood flow was studied in rats 120 minutes after unilateral renal ablation. The influence of endogenous prostaglandin formation was evaluated by indomethacin treatment prior to the ablation. Radioactive microspheres were used for estimation of the total renal and cortical blood flow, and the renal medullary blood flow was determined with the 86-Rb chloride extraction method. The total blood flow in the remaining kidney was increased by 80% following contralateral ablation, with augmentation in all areas, particularly in the deep medullary region. Indomethacin treatment in intact rats evoked increased blood flow as compared with the indomethacin control group. The results indicated that the renal blood vessels respond to ablation of the contralateral kidney with dilation in all kidney regions, and that this vascular dilation may be prostaglandin-mediated.

Tubuloglomerular feedback response in the contralateral kidney after 24-hour unilateral ureteral obstruction

Reduction of the functioning renal mass by unilateral nephrectomy or unilateral ureteral occlusion (UUO) leads to increased function of the remaining nephrons, an important factor being the glomerular filtration rate (GFR). GFR can be modified via the tubuloglomerular feedback control (TGF), which senses the distal delivery of fluid and alters the tonus of the glomerular arterioles. The aim of the present study was to investigate the TGF sensitivity in the intact left kidney of rats after 24 hours of right ureteral occlusion. Using a micropuncture technique, proximal tubular stop-flow pressure (Psf), as a relative index of glomerular capillary pressure, was measured upstream to the block, while late proximal segments were perfused with Ringer solution (rates 0-40 nl/min). The maximal drop in Psf and the tubular flow rate at which 50% of this response was achieved, the turning point (TP), were determined. Considerable decrease in the sensitivity of the TGF system in the contralateral kidney during UUO was indicated by a significantly higher TP as compared with control rats (sham operation), viz. 29 v. 19 nl/min. Maximal Psf drop after UUO was significantly less than in the controls (6 v. 12 mm Hg). Reduced TGF sensitivity in the contralateral kidney after protracted UUO is a prerequisite for that kidney's increased excretion of salt and water to compensate for the loss of functioning renal mass.