Prostaglandin synthesis inhibition during volume expansion: collecting duct function

Methods for imaging Renin-synthesizing, -storing, and -secreting cells

Renin-producing cells have been the object of intense research efforts for the past fifty years within the field of hypertension. Two decades ago, research focused on the concept and characterization of the intrarenal renin-angiotensin system. Early morphological studies led to the concept of the juxtaglomerular apparatus, a minute organ that links tubulovascular structures and function at the single nephron level. The kidney, thus, appears as a highly "topological organ" in which anatomy and function are intimately linked. This point is reflected by a concurrent and constant development of functional and structural approaches. After summarizing our current knowledge about renin cells and their distribution along the renal vascular tree, particularly along glomerular afferent arterioles, we reviewed a variety of imaging techniques that permit a fine characterization of renin synthesis, storage, and release at the single-arteriolar, -cell, or -granule level. Powerful tools such as multiphoton microscopy and transgenesis bear the promises of future developments of the field.

Blunted pressure natriuresis in the Brattleboro diabetes insipidus rat

Antidiuretic hormone is known to stimulate the renal synthesis of prostaglandins. These autacoids, in turn, modulate the pressure natriuresis phenomenon. Accordingly, the present study was done to test the hypothesis that, in the absence of antidiuretic hormone and antidiuretic hormone-dependent prostaglandin synthesis, the pressure natriuresis response is blunted. Experiments were performed on Brattleboro diabetes insipidus rats (n = 7) and Long Evans control rats (n = 14). A change in perfusion pressure in the Long Evans rats from 89.3 +/- 1.0 to 108.7 +/- 1.1 mm Hg (p less than 0.05) was associated with significant increases in the fractional excretion of sodium (1.1 +/- 0.2 to 2.3 +/- 0.3%) and the urinary prostaglandin excretion (32.6 +/- 6.8 to 56.6 +/- 10.0 pg/min). In contrast, a similar change in perfusion pressure in the diabetes insipidus rat from 88.6 +/- 1.4 to 106.2 +/- 1.5 mm Hg (p less than 0.05) resulted in no significant increases in either sodium or prostaglandin excretions. Treatment of a third group of diabetes insipidus rats (n = 9) with 1-desamino-8-D-arginine vasopressin (1 microgram/day) restored the natriuretic response to increases in renal perfusion pressure. Treated diabetes insipidus and Long Evans control rats had comparable natriuretic responses to increases in renal perfusion pressure. Untreated diabetes insipidus rats, on the other hand, had blunted responses. In summary, the pressure natriuresis response in diabetes insipidus rats is blunted compared with Long Evans control rats. We conclude that antidiuretic hormone is necessary for the complete expression of the pressure natriuresis response.

Effect of NSAIDS on serum electrolytes and osmolality

Rabbits and rats were injected two Nonsteroidal anti-inflammatory drugs (aspirin 300 mg/kg or indomethacin 3 mg/kg) intraperitoneally. One hour after injection blood was analyzed for serum electrolytes and osmolality. Administration of both aspirin and indomethacin in rabbits and rats caused increase in serum sodium, potassium, calcium, chloride, magnesium, phosphorus and osmolality. Results suggest the marked similarity in the action of aspirin and indomethacin on electrolytes and osmolality. It is concluded that the ingestion of aspirin and indomethacin can have a major effect on serum electrolytes and osmolality that may influence the interpretation of clinical data in patients taking these drugs.

Fractional excretion of magnesium and renal concentrating capacity in refluxing renal units

To evaluate renal function in kidney units exposed to vesicoureteral reflux we quantified the fractional renal excretion of magnesium and the maximal renal concentrating capacity in 22 renal units of infants and children who presented with grade III to V vesicoureteral reflux on standard voiding cystourethrography. The lowest normal value for maximal concentrating capacity and the highest normal value for fractional excretion of magnesium were set at 800 mOsm. per kg. and 8 per cent, respectively. Concentrating capacity was abnormal in all 22 renal units and the excretion of magnesium was abnormal in 5. Failure of a renal unit to retain magnesium normally was always associated with an inability to concentrate urine. We conclude that in cases of vesicoureteral reflux function of the distal part of the nephron is the first to become abnormal and concentrating capacity is a more sensitive indication of dysfunction than fractional excretion of magnesium.

Papillary collecting tubule synthesis of prostaglandin E2 in Dahl rats

Isolated kidneys of Dahl salt-sensitive rats (DS) excrete sodium less readily than those of Dahl salt-resistant rats (DR). The collecting tubule is an important source of papillary prostaglandin E2 and is a site of significant sodium reabsorption. We cultured renal papillary collecting tubule cells from 5-week-old, prehypertensive DS and DR on a low salt diet and also after 14 weeks of high salt feeding, and we measured prostaglandin E2 synthetic capacity. Unstimulated renal papillary collecting tubule cells from 5-week-old DS produced 62 +/- 5% less prostaglandin E2 than did comparable cells from DR (p less than 0.001). The cells from DS also synthesized less prostaglandin E2 after stimulation with the calcium ionophore A23187 (67 +/- 6% of control; p less than 0.001) or the addition of exogenous arachidonate (74 +/- 7% of control; p less than 0.01). Urinary prostaglandin E2 excretion was also diminished in the 5-week-old DS compared with their salt-resistant counterparts (18.1 +/- 1.3 vs 23.9 +/- 1.7 ng/24 hr; p less than 0.025). After high salt feeding, the DS became hypertensive but the DR remained normotensive. Renal papillary collecting tubule cells cultured from these DS continued to produce less prostaglandin E2 than those from control rats, both in the basal state (60 +/- 12% of control; p less than 0.09) and after stimulation with ionophore (62 +/- 2% of control; p less than 0.002). In these older animals, the DS continued to underexcrete prostaglandin E2 compared with the DR (29.7 +/- 3.2 vs 42.2 +/- 6.1 ng/24 hr; p less than 0.08). The underproduction of prostaglandin E2 in the papillary collecting tubule of DS may play a role in their inadequate renal natriuretic capacity and contribute to the onset and maintenance of salt-induced hypertension in this strain.

Pressure natriuresis and prostaglandin secretion by perfused rat kidney

Isolated rat kidneys respond to elevations of perfusion pressure with an increase in glomerular filtration rate (GFR), filtration fraction (FF), and sodium excretion (UNaV) and a fall in fractional sodium reabsorption (FRNa). Significant linear correlations exist between each of these dependent variables and the renal artery pressure (P). In control kidneys, pressure natriuresis is seen to result both from an increase in filtered sodium load and a decrease in FRNa. In kidneys treated with indomethacin in doses which curtail the release into the perfusate of prostaglandin E2 (PGE2) and the prostacyclin metabolite, 6-keto-PGF1 alpha, the regression lines relating GFR, FF, and UNaV to P are shifted to the right. Thus, prostaglandin-inhibited kidneys require higher pressures than control kidneys to maintain comparable rates of filtration and sodium excretion. Total renal vascular resistance (RVR) is also higher in inhibited kidneys. These findings suggest that in the isolated perfused rat kidney, prostaglandins promote pressure natriuresis by maintaining afferent arteriolar dilation. Their inhibition leads to afferent constriction, which raises RVR, lowers FF and GFR, and reduces sodium excretion.