Carbon Dioxide Trapping by Alkaline Solutions in Tube Absorber

Commercially gas emission purification at thermoelectric power stations, ferrous and non-ferrous metallurgy enterprises, and cement and chemical plants is performed by multistage system with filters and cyclones, which trap solid particles, as well as by using different absorptive and adsorptive methods. A possibility of use a tubular absorption column for carbon dioxide trapping is considered in this work.

Urinary Albumin and Low Molecular Weight Protein Excretion in the Nephrotic Syndrome—Sequential Studies during Corticosteroid Treatment

In a preliminary investigation into the behaviour of low molecular weight proteins in the nephrotic syndrome, we have measured urinary concentrations of albumin, α-1-microglobulin (α1-m) and retinol-binding protein (RBP) in six children for up to 11 days during the course of steroid therapy for nephrotic syndrome. The results in part support the concept of independent proximal tubular absorption of albumin and low molecular weight proteins, and indicate that in the nephrotic syndrome the excretion of RBP and α1-m, two generally accepted markers of tubular proteinuria, is anomalous.

Kinetics, competition, and selectivity of tubular absorption of proteins

Tubular absorption (T) of two cationic proteins, lysozyme (LZM) and cytochrome c (CYT c), and two anionic proteins, beta 2-microglobulin (beta 2M) and 125I-labeled human growth hormone (hGH), was studied in the isolated perfused rat kidney. All four proteins are extensively filtered and, at low loads, almost completely absorbed by the tubular epithelium. TLZM and TCYT c is a saturable process of high capacity (Tm) and low apparent affinity. (Tm)LZM was two orders of magnitude larger than (Tm)CYT c. LZM inhibited TCYT c in a dose-dependent and reversible manner. Saturating loads of CYT c failed to inhibit T beta 2M and ThGH. Saturation, selectivity, and competition is explained on the basis of a model that incorporates adsorption of protein to microvilli as well as geometric and electrical constraints on the access of filtered proteins to endocytic sites at the base of the microvilli. Tubular absorption of all proteins is decreased by inhibitors of the formation and/or internalization of endocytic vesicles (iodoacetate and cytochalasin B). However, lysine (5 mM) and low perfusate calcium concentration (0.5 mM) inhibited T beta 2M but not TCYT c and ThGH. The selective effect of 5 mM lysine, which causes morphologic damage in initial portions of the proximal convoluted tubule, may be due to preferential or exclusive absorption of beta 2 M in this portion of the nephron. The results as a whole demonstrate that in addition to net charge other structural features of the protein molecule and of the luminal wall of proximal tubules may be important determinants of the efficiency and capacity of the tubular absorption of filtered proteins.

Amino acids enhance renal tubular absorption of the los-molecular-weight proteins insulin and growth hormone

The effect of amino acids(AA) on the tubular absorption of low-molecular-weight (LMW) proteins was studied in isolated rat kidneys. Kidneys were perfused with an albumin-electrolyte solution that contained insulin or human growth hormone (hGH) and, unless otherwise stated, the following L-amino acids: glycine, isoleucine, serine, alanine, methionine, proline, arginine, and aspartic acid. In kidneys perfused without AA, fractional urinary insulin clearance (FCi) averaged 7.4 +/- 1.54%, whereas in the presence of multiple AA the FCi was significantly lower (0.68 +/- 0.2%, P less than 0.01). Addition of glycine or alpha-aminoisobutyric acid (AIB) alone also reduced the FCi significantly (1.79 +/- 0.66 and 1.59 +/-1.06%, respectively). By contrast, perfusion with the other AA individually did not alter the FCi. The fractional urinary hGH clearance was also significantly lower in kidneys perfused with multiple AA (0.94 +/- 0.47%) than in those perfused without AA (9.07 +/- 1.2%). We conclude that tubular absorption of filtered insulin and hGH is enhanced by the presence of AA. The mechanism is unclear, but enhancement of insulin absorption can be produced by glycine and AIB alone. This raises the possibility of a link between the absorption of insulin and the glycine and AIB shared transport system, but excludes a primary metabolic effect because AIB is nonmetabolizable.

The Handling of Macromolecules by the Kidney of the River Lamprey, Lampetra Fluviatilis

Micropuncture and renal clearance techniques have been used to investigate the effect of molecular size on glomerular permeability in the river lamprey, Lampetra fluviatilis, and to investigate tubular absorption of native and foreign macromolecules. Polyvinyl pyrrolidone (PVP) molecules of 16 Å in molecular radius were freely filterable but there was significant retention of 37 Å molecules. The estimated sieving coefficients for PVP of 160 000 and 360 000 in molecular weight (molecular radii > 100 Å) were 0.06 and 0.01 respectively, indicating that the glomerular barrier is relatively leaky. Up to 50% of microinjected protein was absorbed by the nephron and the results with bovine serum albumin demonstrated that protein uptake occurs chiefly in the proximal brush border segment. The relative rates of uptake for different proteins and different concentrations of injected solutions indicated that the uptake mechanism is easily saturated and unable to distinguish between native and foreign proteins of high molecular weight. Most lamprey plasma proteins are > 100 000 in molecular weight. This, together with other factors such as molecular charge and tubular reabsorption, could account for the low urinary protein concentration of 0.05 mg/ml.

Removal and excretion of immunoreactive rat growth hormone by the isolated kidney

The renal uptake of immunoreactive rat growth hormone (rGH), molecular weight 21,500 daltons, was examined in the isolated perfused rat kidney to determine whether peritubular removal of a protein greater than 12,000 daltons occurs and to assess the functional characteristics of renal GH uptake. Organ clearance of rGH (OCGH) in control kidneys was 1,039 +/- 99 microliters/min and was unaffected by an excess of insulin but markedly depressed by col (10 degrees C( and KCN. Although glomerular filtration rate (GFR) did not differ significantly from OCGH in the control rats, we suspected that filtration could not account for all the rGH removed because of glomerular protein sieving. However, GFR was significantly less than OCGH with cold and KCN treatment, indicating the occurrence of peritubular removal. In nonfiltering kidneys, rGH removal exceeded that of [14C]inulin (P less than 0.05), demonstrating peritubular rGH removal. Tubular absorption of rGH was unaffected by insulin but markedly depressed by cold and KCN. We conclude that rGH is removed from the renal circulation mainly by the glomerular filtration-tubular absorptive pathway, but, in addition, as with smaller proteins, that peritubular removal occurs.

Comparative nephron function in reptiles, birds, and mammals

Volume and osmolarity of urine produced by kidneys of reptiles, birds, and mammals depend on anatomic relationships among nephrons, epithelial permeability to water controlled by antidiuretic hormone, and, for reptiles and birds, probably on volume flow rate through collecting ducts and excretion of uric acid. Urine volume and volume flow rate through collecting ducts in reptiles and birds depend on number of filtering nephrons controlled by antidiuretic hormone. Mammalian nephrons do not filter intermittently but control of nephron filtration rates in all three vertebrate classes may have important similarities and differences. Uric acid excretion by birds and many reptiles permits excretion of inorganic cations in excess of amounts permitted by osmolarity of urine. This process may require tubular absorption of water without sodium. Such absorption, which has been found in reptilian proximal tubules, may be very important for osmoregulation in all birds and uricotelic reptiles and may provide insight into the mechanism of fluid absorption in mammals. Urea excretion in mammals may be important for enhancing concentrating ability. Much more must be learned about these processes, but similarities and differences among them in the three vertebrate classes may help illuminate details of each.