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Biomedical subjects

R L Jamison

Publications and source records attributed to R L Jamison.

At least 73 records · Page 4Linked to original sources
PubMed1980

Diabetes insipidus: a physiologic approach to diagnosis.

Diabetes insipidus can be delineated in the context of the normal physiology of water metabolism. This approach highlights the common pathway taken by the variety of diseases that can progress to an insufficiency of antidiuretic hormone (ADH) and to diabetes insipidus. A simple diagnostic approach uses homeostatic pathways to separate diabetes insipidus from the other polyuric states. New developments in the biochemical alteration of ADH have improved the ability to individualize hormonal replacement and promise better therapy in the near future.

Deamino Arginine Vasopressin↗
PubMed1980

Terminal papillary collecting duct reabsorption of water, sodium, and potassium in Psammomys obesus.

Micropuncture studies were performed to assess the contribution of the terminal collecting duct to reabsorption of water, sodium, and potassium in the desert rodent, Psammomys obesus. Tubule fluid was collected at base and tip of the exposed papilla before (period I) and after (period II) administration of furosemide. In period I, a significant rise occurred in tubule fluid-to-plasma (TF/P) ratios of inulin, osmolality, and sodium and potassium from base to tip; 2.3 +/- 0.8% of filtered water and 5.1 +/- 1.7% of filtered sodium were reabsorbed by the collecting duct. In period II water, sodium, and potassium delivery to the collecting duct was significantly increased. Although TF/P ratios for inulin, osmolality, and sodium and potassium were lower at base and tip in period II than corresponding values in period I, all ratios increased between base and tip. Approximately 3 times as much water (7.4 +/- 1.8%) and twice as much sodium (10.1 +/- 3.0%) were reabsorbed by the exposed collecting duct in period II. These results reveal a remarkable reabsorptive capacity and suggest that the terminal collecting duct plays an important role in regulation of water and sodium excretion in Psammomys obesus.

Animals↗
PubMed1979

Editorial review. Recent formulations of the urinary concentrating mechanism: a status report.

The status of the purely passive mode of solute concentration as of 1979 appears to be similar to that of the original countercurrent hypothesis 10 years ago. The passive mode concept has advanced our understanding of the concentrating process by qualitatively incorporating the permeability characteristics of tubule segments and the lack of an active transport process in the thin loop of Henle into a mechanism which has attractive economy and explanatory value. But in the final analysis some assumptions are not borne out by experimental findings (for example, the high urea concentration of fluid in the rat and hamster end-descending limb; the likelihood of net transepithelial addition of sodium chloride to the Psammomys descending limb; the removal of sodium chloride from the hamster ascending limb against an apparent electrochemical gradient under certain circumstances; and the osmotic lag between vasa recta blood and interstitium in the rat). Furthermore, when the known permeability and transport characteristics of the renal tubule are incorporated into a mathematic model of the passive operating mode, numerical simulations fail to establish a progressively hyperosmotic inner medulla. This does not rule out the applicability of the more general model (Eq. 1), particularly if evidence for some form of active transport in the inner medulla, heretofore lacking, is forthcoming.

Animals↗
PubMed1979

Suppression of potassium-recycling in the renal medulla by short-term potassium deprivation.

Recently we proposed that potassium, like urea, normally undergoes medullary recycling from collecting tubule to the pars recta or descending limb of the juxtamedullary nephron and suggested that the extent of recycling is a function of the concentration of potassium in collecting tubule fluid. To test this hypothesis further, we fed young rats a potassium-free diet for 3 days and then prepared them for micropuncture of the left renal papilla. Compared to findings in normally fed animals, potassium deprivation caused a significant fall in plasma potassium and urinary excretion of potassium. There was a striking decrease in the fraction of filtered potassium remaining at the end of the justamedullary descending limb for 94 +/- 11% to 38 +/- 3% (P less than 0.001). The latter value is not significantly different from the fraction of filtered sodium remaining (36 +/- 4%) and suggests that net addition of potassium to the pars recta or descending limb was completely abolished. A correlation was observed between the fraction of filtered potassium remaining at the end of the descending limb and either urinary potassium excretion (P less than 0.001) or urinary potassium concentration(P less than 0.001) in the contralateral unexposed kidney. These results lend further support to the hypothesis of medullary recycling of potassium.

Animals↗
PubMed1979

Urinary concentrating mechanism in the desert rodent Psammomys obesus.

The mechanism by which osmolality rises in fluid in the juxtamedullary descending limb was examined in Psammomys obesus by micropuncture of the left renal papilla. The concentration of Na, Cl, K, Mg, and phosphorus was determined by electron probe; Cl concentration by both probe and the microcoulometric technique of Ramsay et al. (J. Exp. Biol. 32: 822--829, 1955). The mean urine-to-plasma ultrafiltrate (U/P) osmolality was 5.5 +/- 0.46 (SE). In 43 samples obtained from the end-descending limb in 16 animals, mean values were: tubule fluid-to-plasma ultrafiltrate (TF/P) osmolality, 3.64 +/- 0.30; (TF/P)In, 6.96 +/- 0.52; (TF/P)Na, 3.53 +/- 0.27; (TF/P)Cl-e, 4.11 +/- 0.37 (-e is electron probe determination); and (TF/P)Cl-r, 4.25 +/- 0.37 (-r is determination by method of Ramsay). In terms of percentage of filtered ion remaining at the end-descending limb, Na was 54 +/- 3.7%, Cl-e was 61 +/- 3.6%, and Cl-r was 63 +/- 4.0%. The percentage of filtered chloride remaining averaged 80% or more in three animals, equalled or slightly exceeded 100% in six individual descending limb samples, and in all animals was a function of loop fluid osmolality (y = 8.61x + 31.9, r = 0.66, P less than 0.01). The results are most consistent with the thesis that both water extraction and transepithelial NaCl addition contribute to the rise in osmolality of fluid in the descending limb of the Psammomys.

Animals↗
PubMed1979

Questions and replies: role of the collecting tubule in fluid, sodium, and potassium balance.

In terms of day-to-day regulation of fluid and electrolyte balance, the collecting tubule system appears to occupy a paramount position among segments of the renal tubule. Controversy has arisen concerning the quantitative contribution by the collecting tubule system to the regulation of individual solute excretion, which in part may be due to differences among the investigative techniques employed. In this Editorial Review, R. L. Jamison summarizes current views on the function of the collecting tubule system, particularly with regard to regulation of sodium and potassium excretion, and then poses seven questions pertaining to this topic. H. Sonnenberg, who has revived the microcatheterization technique, and J. H. Stein, whose group has employed the micropuncture method, respond to these questions. The key issues addressed are: 1) the principal factors that influence transtubular movement of sodium and potassium across the collecting tubule; 2) the limitations and potential artifacts of the microcatheterization and micropuncture techniques when used to examine the function of the collecting tubule; 3) apparent discrepancies among results obtained by micropuncture in vivo, microcatheterization in vivo, and microperfusion in vitro of the collecting tubule; and 4) major unresolved questions concerning the function of the collecting tubule.

Animals↗
PubMed1979

Acute renal failure following cardiac surgery.

In a prospective 6 month study of 204 patients requiring cardiac operations, five (2.5 percent) developed acute renal failure (ARF) and five (2.5 percent) had documented renal dysfunction (RD). Preoperative left ventricular dysfunction and prolonged cardiopulmonary bypass (CPB) were important predictors of subsequent RD/ARF; CPB pressure per se was not. Physiological and clinical studies in 51 selected patients studied over an 18 month period documented the effectiveness of low flow, low pressure CPB in preserving postoperative renal function. Twenty-two patients with nonazotemic postoperative courses demonstrated moderate depression of cardiac function while the glomerular filtration rate (GFR) was normal (98 +/- 30 ml./min/1.73 M.2) within 24 hours of operation. Seventeen high risk patients developed AFF (65 percent mortality rate) and 12 experienced severe RD without ARF (17 percent mortality). ARF (65 percent mortality rate) and 12 experienced severe RD without ARF (17 percent mortality). Eleven patients with ARF and 11 with RD were studied in the early postoperative period; at this time, all 22 patients demonstrated RD with equivalent severe depression of cardiac and renal function. Superposition of further hemodynamic or toxic insults upon ischemic kidneys was usually necessary for ARF to occur.

Acute Kidney Injury↗
PubMed1978

Effect of chronic potassium loading on potassium secretion by the pars recta or descending limb of the juxtamedullary nephron in the rat.

Recently we demonstrated potassium secretion by the pars recta or by the descending limb of the juxtamedullary nephron. The purpose of this present investigation is to study the effect of a chronic high-potassium intake on this phenomenon. Fractional reabsorption of water and sodium by the juxtamedullary proximal nephron was decreased when compared to that in normal hydropenic rats. There was a striking increase in the fraction of filtered potassium at the end of the juxtamedullary descending limb from 94+/11% to 180+/18%, which was principally a result of enhanced potassium secretion. When the concentration of potassium in the collecting tubule fluid of potassium-loaded rats was reduced after the administration of amiloride, a sharp fall was observed in the amount of potassium which reached the end of the descending limb (64+/8%). A direct correlation was observed between the fraction of filtered potassium at the descending limb and the potassium concentration in the final urine (P less than 0.001). The findings suggest that potassium, like urea, normally undergoes medullary recycling, which is enhanced by chronic potassium loading.

Amiloride↗
PubMed1977

Evidence for a concentration gradient favoring outward movement of sodium from the thin loop of Henle.

Recent models of the urinary concentrating mechanism have postulated that urea in the medullary interstitium creates a transtubular concentration gradient for sodium between fluid at the end of the descending limb of Henle's loop and the medullary interstitium, favoring the passive outward movement of sodium from Henle's thin ascending limb. These experiments were designed to determine whether such a gradient normally exists. Young nondiuretic Munich-Wistar rats were prepared for micropuncture of the exposed left renal papilla. Samples of loop of Henle fluid and vasa recta plasma (assumed to reflect the composition of interstitial fluid) were obtained from adjacent sites. Loop fluid values in 21 comparisons from 18 rats (mean +/- SE) were: sodium 344 +/- 12 meq/liter; potassium, 26 +/- 2 meq/liter; osmolality, 938 +/- 37 mosmol/kg H23. Vasa recta plasma values (in corresponding units of measurement) were: sodium, 284 +/- 11; potassium, 34 +/- 2; osmolality, 935 +/- 34. Mean values of paired differences (loop fluid minus vasa recta plasma) were: delta sodium, 60 +/- 11.1 (P less than 0.001); delta potassium, -8.0 +/- 2.1 (P less than 0.001); delta osmolality, 4 +/- 16 (NS). Corrected for plasma water, the loop fluid minus vasa recta differences (in milliequivalents per kilogram H2O) were: delta sodium, 40 +/- 11.4 (P less than 0.005); delta potassium, -9.7 +/- 1.9 (P less than 0.001). We interpret these findings to indicate that in the papilla of nondiuretic rats, a significant difference in sodium concentration exists across the thin loop of Henle favoring outward movement of sodium, which confirms a key requirement of the passive models. A concentration difference for potassium in the reverse direction was also observed.

Animals↗
PubMed1976

Potassium secretion by the decending limb or pars recta of the juxtamedullary nephron in vivo.

Potassium reabsorption by the juxtamedullary nephron up to the hairpin turn was studied by the micropuncture technique in the exposed renal papilla of rats. In 18 nondiuretic rats, the fraction of filtered potassium remaining at the end of the desdending limb averaged 113 +/- 9%, indicating either that potassium is not reabsorbed by the juxtamedullary proximal tubule and descending limb or that potassium is reabsorbed and secreted in those segments. Furosemide, a drug which inhibits NaCl reabsorption in the ascending limb downstream from the descending limb, significantly decreased the potassium remaining at the end of the descending limb from 106 +/- 12 to 72 +/-11% in seven rats. Benzolamide, a drug which inhibits reabsorption of NaHCO3 and water in the proximal tubule upstream from the descending limb significantly increased the potassium remaining from 103 +/- 13 to 177 +/- 32% in eight rats. These findings support the hypothesis that in the rat, potassium is normally reabsorbed by the proximal convoluted tubule and secreted in the pars recta or descending limb of the juxtamedullary nephron.

Absorption↗
PubMed1976

Water extraction from the inner medullary collecting tubule system: a role for urea.

Recent examinations of the inner medullary collecting tubule membrane in vitro have demonstrated that its reflection coefficient to urea (sigma urea) is significantly less than unity and less than sigma NaClhe presence of antidiuretic hormone. Fluid entering the inner medullary collecting tubule has a higher urea concentration and lower NaCl concentration than does the medullary interstitium, although total osmolarity is nearly equal on either side of the membrane. The transtubular difference in solute composition, together with the difference between sigma urea and sigma NaCl, should result in a driving force for extraction of water from the tubule. This hypothesis was examined in a differential analysis of water and solute fluxes across the collecting tubule epitheliu. The results indicate that this driving force contributes significantly to water extraction from the inner medullary collecting tubule.

Animals↗
PubMed1976

An examination of transcapillary water flux in renal inner medulla.

We recently demonstrated that net fluid uptake occurs in the capillary system of the inner medulla. To define the site of fluid uptake, the concentration of protein was determined in plasma from descending vasa recta at the base and tip of the exposed papilla in Munich-Wister rats. The vasa recta plasma-to-arterial plasma protein concentration ratio (VR/P) was 1.43 +/- 0.09 at the base and 1.66 +/- 0.09 at the tip. These results, which indicate fluid loss from the descending vasa recta, are difficult to explain on the basic of hydraulic and oncotic forces alone. The osmolality of the contents of descending vasa recta increased between base and tip (delta = 72 +/- 30 mosmol/kg H2O). If the increase in osmolality of plasma in descending vasa recta lags behind that of the adjacent medullary interstitium, a transcapillary osmotic driving force exists favoring water loss from descending vessels. It is concluded that fluid uptake by the inner medullary circulation occurs beyond descending vasa recta in interconnecting capillaries or ascending vasa recta. In our view the most likely interpretation of these results is that fluid movement across vasa recta in the inner medulla is influenced by three forces: those owing to transcapillary differences in osmotic, oncotic, and hydraulic pressures.

Animals↗