Studies on the Mechanism of Reduced Urinary Osmolality after Exposure of the Renal Papilla

A B S T R A C T Urine was observed to flow intermittently in the collecting ducts of the extrarenal papilla of antidiuretic rats. The purpose of this investigation was to test Reinking and Schmidt-Nielsen's hypothesis that intermittent flow plays an important role in the production of maximally concentrated urine. Samples of collecting duct fluid were obtained from the base and tip of the papilla by micropuncture through the intact ureter. Fluid osmolality rose sharply from base, 894±120 mosmol/kg H20-' (mean±SE), to tip, 1,667±114 (P<0.001), a distance of only 2 mm, and was due exclusively to reabsorption of water. After excision of the ureter, which abolished intermittent flow, osmolality fell modestly at the base to 723±82 mosmol/kg H20-' (P < 0.02), but strikingly at the tip to 1,012±103 (P < 0.001). The pelvic ureter was paralyzed by topical verapamil and dimethylsulfoxide, which abolished intermittent flow. Osmolality of urine at the tip was not changed (1,959±184 mosmol/kg H20-1 before, vs. 1,957±126 after paralysis). The ureter was severed just beyond the papillary tip, a maneuver which preserved intermittent flow but abolished urinary reflux over the papilla. Urinary osmolality fell from 1,876±134 mosmol/kg H20-1 to 1,284±115 (P < 0.005). These findings demonstrate that when the ureter is intact, over half of the increase in urinary osmolality above isotonicity occurs in the terminal onefourth of the medullary collecting duct and is due exclusively to water reabsorption (no net solute addition). It is the continuity of the ureter, rather than intermittent flow due to ureteral peristalsis, which is essential for the formation of a maximally concentrated urine.

Section: Discussionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Urinary Concentration in the Papillary Collecting Duct of the Rat

Oliver¹,

Roy²,

Jamison³

1982

“…Thus, while a prostaglandin E-mediated decrease in collecting duct water permeability may have played a role, other factors may also be important. Recent studies from our laboratory have demonstrated that increased medullary blood flow can be associated with a decrease in urine osmolality (13). Since previous studies have noted that the medullary solute falls during bradykinin and acetylcholine administration, it may be that the decrease in medullary solute associated with the increase in papillary flow is the primary explanation for the decrease in urine osmolality observed during bradykinin administration.…”

Section: Discussionmentioning

confidence: 89%

“…Mongrel dogs, [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] kg, were deprived of food and water for 12 h before study. Anesthesia was induced with intravenous sodium pentobarbitol, 30 mg/kg and a constant level of anesthesia was maintained by using additional 5-mg injections as needed.…”

Section: Methodsmentioning

confidence: 99%

Studies on the Mechanism of Sodium Excretion during Drug-induced Vasodilatation in the Dog

Fadem¹,

Hernandez-Llamas²,

Patak³

et al. 1982

Self Cite

A B S T R A C T The administration of vasodilating agents such as bradykinin and acetylcholine cause an increase in urinary sodium excretion. Yet the mechanisms involved in this natriuretic effect are not clear. Recent studies with another renal vasodilator, secretin have shown this drug also causes a profound increase in renal blood flow but without major changes in sodium excretion. To attempt to delineate the basis of this difference in sodium excretion with these drugs, the renal functional effects of secretin and bradykinin were compared at an equivalent vasodilating dose. Bradykinin increased renal blood flow from 222 to 342 ml/min, urine volume from 0.2 to 1.2 ml/min, and urine sodium excretion from 28 to 115,ueq/min. Urine osmolality fell from 1,230 to 401 mosmol/kg. Secretin caused a comparable increase in renal blood flow (216 to 325 ml/min) while changes in urine flow, sodium excretion, and urine osmolality were significantly less.In further studies papillary plasma flow was estimated using the albumin accumulation technique. Control papillary plasma flow was 29 ml/min per 100 g. Bradykinin increased urinary sodium excretion 108 seq/min and decreased urinary osmolality from 1,254 to 516 mosmol/kg in association with a rise in papillary plasma flow to 62 ml/min per 100 g. Urine sodium excretion, urinary osmolality, and urine flow rate, as well as papillary plasma flow rate (32 ml/min per 100 g) were unchanged from control when secretin was administered. Studies with acetylcholine were qualitatively similar to those of bradykinin. Renal blood flow increased from 150 to 248 ml/min, urinary sodium excretion increased from 20 to 243 geq/min, urinary osmolality decreased from 1,237 to 411 mos-

“…Chuang and co-workers (17) suggested that exposure of the papilla stimulates the synthesis of prostaglandin E2, which increases papillary blood flow, causing washout of papillary solute. Reinking and Schmidt-Nielsen (18) that in antidiuresis, the papillary collecting ducts regularly open and close with a periodicity coincident with ureteral peristalsis and proposed that ureteral contraction stops flow periodically not only in the collecting ducts but in the loops of Henle and vasa recta as well.…”

Section: Discussionmentioning

confidence: 99%

Examination of transepithelial exchange of water and solute in the rat renal pelvis.

Bargman¹,

Leonard²,

McNeely³

et al. 1984

Abstract. Severance of the ureter beyond the renal papilla causes a fall in urinary osmolality, which suggests that exchange of water or solute between urine and renal parenchyma normally occurs in the intact renal pelvis. We examined water and solute flux in the renal pelvis with micropuncture and microcatheterization techniques. Four groups of antidiuretic rats were studied. Group I (n = 17) underwent micropuncture through the intact contracting ureter. Urine samples were obtained at the papillary tip, and in the pelvis beside the base of the extrarenal papilla. Urinary osmolality at the base, 880±97 mosmol/kg H20 (mean±SE), was less than that at the tip, 1,425±104i mosmol/kg H20 (P < 0.005). In group II (n = 24), samples were analyzed for inulin and osmolality. In 15 rats (group IIA), comparison was made between base and tip samples. In thei other nine animals (group IIB), comparisons were made among base, tip, and bladder samples and urea was also measured. In group II (A and B combined) urine-to-plasma (U/P) osmolality was lower at the base, 4.31±0.27, than at the tip, 6.08±0.23 (P < 0.001), and U/P inulin was lower at the base, 192±25, than at the tip, 306±16 (P < 0.001). In group IIB, the bladder urine had a lower U/P osmolality, 5.27±0.25, than the tip, 6.01±0.31 (P < 0.02). The U/P urea was 59±10.6 (base), 98±9.4 (tip) (base vs. tip, P < 0.05), and 81±6.5 (bladder, P < 0.005, compared with tip). In group III (n = 8), samples were A preliminary report of these findings has been published in abstract form: Leonard, S., and R. Jamison. 1983 obtained by microcatheter from the fornices, the deepest intrarenal extensions of the pelvis, and compared with samples at the tip. Urinary osmolality was lower in the fornix, 646±106 mosmol/kg H20, than at the tip, 1,296±99 mosmol/kg H20 (P < 0.001). Similarly, U/P inulin was lower in the fornix, 48±14, than at the tip, 128±12 (P < 0.001). The lower U/P inulin in the pelvic urine is the result of either the addition of fluid to the pelvis, or the backleak of inulin across the epithelium lining the pelvis. To verify that the pelvic epithelium was impermeable to inulin, in group IVA (n = 4) the left renal pelvis was superfused with a solution of chemical inulin. Cumulative absorption of inulin from the left kidney was 0.15±0.08% of that superfused. Using ['4C]inulin in group IVB (n = 3), similar results were obtained (0.05±0.02%).These findings indicate that in the renal pelvis, fluid is added to urine after it emerges from the collecting ducts. We suggest that reflux of hyperosmotic urine over the renal papilla creates a transepithelial gradient for the flux of water into the pelvis. A model that incorporates diffusive and convective forces for water and solute transport is proposed to account for these findings.