Glomerular epithelial cells synthesize endothelin peptides.

Glomerular mesangial and endothelial cells have been reported to synthesize and secrete endothelin-1 (ET-1). Whether glomerular epithelial cells (GEC) have the ability to synthesize ET-peptides is not known. Employing immunocytochemistry we report that the GEC in vitro constitutively express ET-1 and ET-3. ET-1 synthesis by the GEC was further confirmed by detection of a specific 2.3kb mRNA that hybridizes with rat prepro ET-1 genomic DNA on Northern blot analysis. ET-1 is secreted into the medium in a time-dependent manner as measured by radioimmunoassay and radiobinding assay. Synthesis of endothelin peptides by the GEC may have important implications in the pathogenesis of glomerular diseases where GEC injury figures prominently.

Effect of Ringer infusion on ischemic acute renal failure: caution on interpreting the results of short-term studies.

The effect of a 4.5 mL/h Ringer infusion on the recovery from a unilateral 40-min renal artery occlusion was investigated in Sprague-Dawley rats. The inulin clearance measured in the experimental kidney 24 and 48 h after the insult in control animals that did not receive the Ringer infusion was 0.14 +/- 0.10 (mean +/- SE) and 0.11 +/- 0.05 mL/min, respectively. In animals that received 24 h of Ringer infusion begun at the time of the renal artery occlusion the inulin clearance was 0.81 +/- 0.07 mL/min, a value significantly higher than either of the control groups (p less than .05). If, however, the Ringer infusion was stopped at 24 h and the inulin clearance measured at 48 h, it had decreased significantly (0.27 +/- 0.09 mL/min) and was no longer greater than the control groups. Similarly, if the infusion was continued for 48 h there was no longer a significant difference between the inulin clearance (0.37 +/- 0.11), when compared with 48 h of no infusion (0.11 +/- 0.05). The histology of the different groups corresponded with the functional data. We conclude that 24 h of Ringer infusion leads to functional and histological protection when measured at 24 h; however, if measured at 48 h, protection is no longer evident. These studies suggest that caution should be exercised in extrapolating from the results of protective maneuvers in ischemic acute renal failure investigated by short-term studies.

Measurement of renin secretion in single perfused rabbit glomeruli.

A new technique is presented that allows the measurement of the renin secretion rate of single rabbit glomeruli during in vitro perfusion at controlled afferent arteriolar perfusion pressure. Rabbit glomeruli with intact afferent arteriole and Bowman's capsule are obtained by microdissection and cannulated with a pipette system that allows continuous afferent arteriolar pressure measurement. The renin secretion rate of 10 glomeruli, perfused at 40 mmHg, was measured in 15-min intervals with an antibody-trapping microassay. Renin secretion rate was low relative to total renin content (1.2-2.0% of content/perfusion h) and increased three- to fivefold in response to isoproterenol (10(-5) M). The afferent arteriole contracted to norepinephrine (10(-5) M) in each instance. This novel, although difficult, technique allows the study of renin release in vitro at controlled perfusion pressure, without the interfering effects of the macula densa, arterial angiotensin II, and the adrenergic nervous system. It should allow a new perspective on issues such as the pressure-flow dependence of renin release and the interaction of the afferent arteriolar endothelium with the renin-secreting juxtaglomerular cells.

Effect of atriopeptin II on Ca influx, contractile behavior and cyclic nucleotide content of cultured neonatal rat myocardial cells.

The present study was carried out to evaluate the effects of biologically active atriopeptin II (APII) in synchronously contracting monolayer cultures of rat ventricular myocytes. The effects of 10 nM APII on Ca influx, contractile behavior and cyclic nucleotide content of the cells were measured. Applied acutely APII had no effect on Ca influx. There was however a time-dependent effect such that after 30 min Ca influx (pmol/cm2/s) had declined from a control (mean +/- S.E.M.) of 1.53 +/- 0.16 to 1.02 +/- 0.07 (P less than 0.001; n = 6). There was parallel decline in both the magnitude and velocity of cell edge motion which was maximal in 30 min at which time cell edge motion measured 65.3 +/- 4.4% of control. Treatment with APII for 30 min decreased cAMP (pmol/mg protein) from 5.35 +/- 0.17 to 2.86 +/- 0.24 (P less than 0.001; n = 5). At the same time cGMP (pmol/mg protein) increased from 0.86 +/- 0.21 to 2.14 +/- 0.33 (P less than 0.001; n = 5). Further studies elucidated the fact that the decline in Ca influx and contractile behavior was dependent on the decrease in cAMP rather than the increase in cGMP. Pre-treatment of the cells with 5 ng/ml of pertussis toxin to ADP-ribosylate the Gi protein abolished the effects of APII on cAMP, Ca influx and contractile behavior. The results indicate that in myocardial cells, as in other cells, APII stimulates guanylate cyclase and inhibits adenylate cyclase. The resultant fall in cAMP decreases Ca influx and negatively influences the contractile behavior of the cells.

Tubular site(s) of action of atrial natriuretic peptide in the rat.

With micropuncture techniques, the present study examined the delivery of chloride to the superficial late distal tubule and the base and tip of the papillary collecting duct in rats treated with either Wy 47663, a synthetic analogue of atrial natriuretic peptide (ANP), or vehicle alone. Whole kidney glomerular filtration rate (GFR) and single-nephron glomerular filtration rate were not significantly different between the two groups. Late distal tubule chloride delivery was also not different between ANP- (5.71 +/- 1.15%) and vehicle- (6.28 +/- 1.12%) treated animals. However, fractional delivery to the base of the papillary collecting duct was significantly greater in the ANP-treated rats (14.37 +/- 1.98%) compared with vehicle-treated rats (7.32 +/- 1.47%). Tip papillary collecting duct delivery was also significantly greater in the ANP-treated rats (1.97 +/- 1.96 vs. 3.09 +/- 0.60%). In addition, the percent of chloride delivered that was reabsorbed along the papillary collecting duct was significantly less in the ANP-treated rats. In conclusion, ANP inhibits reabsorption in some tubular segments between the superficial late distal tubule and papillary collecting duct base as well as in the accessible portion of the papillary collecting duct.

Atrial natriuretic peptide, right atrial pressure, and sodium excretion rate in the rat.

This study examined the relationship between right atrial pressure (RAP), urine flow rate, sodium excretion rate, and plasma atrial natriuretic peptide (ANP) levels after an acute Ringer expansion. Two groups of rats had their RAP monitored and balloon catheters placed in their thoracic inferior venae cavae. In one group the balloon remained deflated, and in the second group the balloon was inflated during the volume expansion in an attempt to prevent the rise in RAP. The peak RAP was 7.3 +/- 0.8 mmHg when the balloon remained deflated and 3.5 +/- 0.6 mmHg in the group with the balloon catheter inflated (P less than 0.005). The corresponding peak ANP levels were 682 +/- 140 and 223 +/- 40 pg/ml. There was a significant correlation between the peak RAP and ANP levels (r = 0.754; P less than 0.05). The inflation of the balloon catheter significantly decreased the urine flow rate and the urine sodium excretion rate. A final group of animals had 200 microliters of rabbit serum containing antibody to ANP infused before the volume expansion. The antibody-treated animals had significantly lower urine flow and sodium excretion rates than nonantibody-treated control rats. We conclude that ANP is one of the factors which allows the rat to excrete an acute Ringer expansion.

Effect of atriopeptin II on determinants of glomerular filtration rate in the in vitro perfused dog glomerulus.

Atrial natriuretic factor (ANF) is a peptide originally found to be present in extracts of mammalian atria that possess marked natriuretic and diuretic qualities. A number of mechanisms have been suggested to explain these properties. Recently, it has been suggested that ANF may enhance glomerular filtration. In this report, we describe a series of experiments designed to investigate if atriopeptin II, a 23-amino acid synthetic analogue of ANF, increases glomerular filtration rate (GFR) and, if so, the mechanism for this increase. We used the isolated perfused glomerulus technique (n = 6), which allows a single isolated glomerular unit to be perfused and the determinants of single-nephron GFR (SNGFR) to be measured. Two periods were performed in each experiment, the control followed by the experimental. The only difference between the two periods was the addition of atriopeptin II to the experimental perfusate at a final concentration of 5 X 10(-7) M. There was indeed a significant increase in the SNGFR (78 +/- 27 to 108 +/- 29 nl/min, P less than 0.01). This increase was associated with a significant increase in the glomerular capillary hydrostatic pressure (PGC) from 31 +/- 3 to 35 +/- 3 mmHg (P less than 0.05). The filtration fraction also increased in each experiment (from 0.16 +/- 0.3 to 0.25 +/- 0.03, P less than 0.005). Neither the afferent flow nor the efferent arteriolar flow changed, although there was a tendency for both to decrease.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of albumin on glomerular ultrafiltration coefficient in isolated perfused dog glomerulus.

To evaluate the direct effect of albumin concentration on the glomerular capillary ultrafiltration coefficient (Kf), we compared the effect of "normal" (3.4 g/100 ml), "low" (0.1 g/100 ml), and "no albumin" (less than 0.005 g/100 ml) concentration on the determinants of single-nephron glomerular filtration rate (SNGFR) as measured with the isolated perfused glomerulus technique. When the albumin concentration was decreased from normal to low concentrations, the afferent flow rate increased from 318 +/- 147 (mean +/- SE) to 450 +/- 174 nl/min, the filtration fraction increased from 0.19 +/- 0.04 to 0.35 +/- 0.08, and the SNGFR increased from 49 +/- 21 to 126 +/- 34 nl/min. These changes were associated with a small though significant increase in Kf from 2.79 +/- 1.01 to 3.74 +/- 0.98 nl/(min X mmHg) (P less than 0.05). When the albumin concentration was decreased from low to no albumin the filtration fraction and SNGFR increased even further and were associated with a marked increase in Kf to a value of 27.04 +/- 11.43 nl/min X mmHg). We conclude that there is very little effect of decreases in albumin concentration on Kf until extremely low levels are reached, and at that point there is a marked increase in the ultrafiltration coefficient. Furthermore, when these extremely low concentrations of albumin are reached an important role for albumin in the basic function of the ultrafiltration barrier is demonstrable.

Intrarenal localization of angiotensinogen mRNA by RNA-DNA dot-blot hybridization.

The renal renin-angiotensin system plays an important role in the control of renal hemodynamics and in the etiology of some types of hypertension. Angiotensinogen is the prohormone for angiotensins I and II. In the present communication, we report for the first time the presence of mRNA coding for angiotensinogen in the kidney. Indeed, the intrarenal location appears to be predominantly in the renal medulla. Additionally, an investigation of the effect of uninephrectomy on the intrarenal angiotensinogen mRNA suggests that regulation of mRNA levels in the kidney does occur.

Experimental models of nephrotoxic acute renal failure.

Table 1 summarizes the findings in these three models of nephrotoxic acute renal failure. As can be noted, leakage of filtrate across damaged tubular epithelium is a factor in each instance. Some degree of tubular obstruction is probably present in each model but is of major importance only with severe tubular injury. Hemodynamic alterations and a change in the ultrafiltration coefficient may also play a role in the renal functional impairment. It is not presently possible to quantitatively determine the significance of each of these abnormalities in a given experimental model.

Ischemic acute renal failure in the rat: protective effect of uninephrectomy.

Experiments were performed to investigate the effect 2-wk prior nephrectomy has on the recovery from a 40-min renal artery occlusion. Two groups were initially examined. Group 1 animals underwent sham nephrectomy and group 2 animals right nephrectomy 14 days prior to a 40-min left renal artery clamp. The percent recovery of inulin clearance in group 2 (33 +/- 6%) was not significantly different from that in the group 1 (36 +/- 8%) when measured 3 h after reflow. At 24 and 48 h of reflow, however, group 2 animals had a significantly higher percent recovery of inulin clearance (24 h: 31 +/- 5%; 48 h: 50 +/- 11%) than group 1 animals (24 h: 1 +/- 1%; 48 h: 8 +/- 4%). Similarly the histology was better preserved at 24 and 48 h in group 2. To further investigate this enhanced recovery, three additional groups were studied. Group 3 underwent right nephrectomy at the time of renal artery occlusion. Group 4 had right uretero-venostomies created immediately prior to the ischemic insult, and group 5 had their aortas rather than left renal arteries clamped. Each group shared with group 2, ischemia to all functioning excretory tissue. The percent recovery of inulin clearance in group 3 (48 +/- 9%), group 4 (54 +/- 5%), and group 5 (42 +/- 6%) were each significantly (P less than 0.005) higher than in group 1 (8 +/- 4%) when measured at 48 h. We conclude that the protection offered by uninephrectomy is not a consequence of hypertrophy but that alterations in the environment which follow ischemia to all functioning excretory renal tissue are responsible for the enhanced recovery seen.

Glomerular dynamics.

The kidney glomerulus produces an essentially protein-free filtrate of blood that is converted to urine as it traverses the remainder of the nephron. Recent studies, largely carried out in animals, have provided new information on the determinants of glomerular function. These findings, briefly summarized herein, are also related to clinical conditions.