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Biomedical subjects

R Coulson

Publications and source records attributed to R Coulson.

At least 37 records · Page 2Linked to original sources
PubMed1984

Adenosine transport in perfused rat kidney and renal cortical membrane vesicles.

Adenosine is a modulator of renal function but little is known about transport of this compound by renal tubular cells. Transport of exogenous adenosine was studied in isolated perfused rat kidney and in luminal (L) and antiluminal (AL) membrane vesicles isolated from rat renal cortex. Most experiments were performed in the presence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine. Kidneys were perfused in a recirculating system with Krebs-Henseleit bicarbonate buffer containing 6 g albumin/dl and adenosine. Net secretion of adenosine occurred at perfusate adenosine concentrations greater than 40 microM, and net reabsorption was seen at concentrations less than 40 microM. N6-(L-2-phenylisopropyl)adenosine (PIA), a nondeaminated adenosine receptor agonist, also showed net reabsorption when unbound PIA concentrations were 10-20 microM. Influx or efflux of [3H]adenosine in vesicles was measured using a rapid filtration technique. Transport into both L and AL vesicles was saturable. L vesicles demonstrated both high Km (43 +/- 4 microM) and low Km (4.4 +/- 0.6 microM) transport systems. Only a low Km (5 +/- 1 microM) system could be demonstrated in AL vesicles. Results indicate that at concentrations in the physiological range (less than 1 microM) adenosine undergoes mediated transport across both L and AL membranes and that net transport across the L membrane is in the direction of reabsorption.

Adenosine↗
PubMed1984

Effect of perfusate phosphate concentration on responses to PTH in isolated rat kidney.

We studied the excretion of electrolytes and adenosine 3',5'-cyclic monophosphate (cAMP) by rat kidneys perfused for 2 or 3 h at several concentrations of phosphate (Pi). Fractional phosphate excretion increased with higher perfusate Pi concentrations (up to 4.0 mM Pi) without parathyroid hormone (PTH), but no tubular maximum for phosphate reabsorption was reached. The addition of synthetic bovine 1-34 PTH (bPTH) gave a dose-related phosphaturia that depended on the perfusate Pi level. The urinary cAMP response to doses of bPTH was highly dependent on perfusate Pi concentration: with 20 nM bPTH, urinary cAMP was 211 +/- 94 pmol/ml glomerular filtration rate at 1.2 mM Pi and was 3,998 +/- 711 at 4.0 mM Pi (P less than 0.001). Without bPTH, cAMP excretion did not differ among Pi levels. Calcium-to-sodium clearance ratio rose with time in kidneys perfused without bPTH but fell with the addition of as little as 0.02 nM bPTH, regardless of Pi concentration. Variations in Pi or bPTH did not affect fractional magnesium excretion, which fell by 68% through 3 h of perfusion (P less than 0.001). These data suggest that the effects of Pi concentration on renal electrolyte excretion are consistent with changes in the filtered Pi load but that extracellular Pi concentrations dramatically alter the renal cAMP response to bPTH in the isolated perfused kidney.

Animals↗
PubMed1983

Transport and metabolism of N6- and C8-substituted analogs of adenosine 3',5'-cyclic monophosphate and adenosine 3'5'-cyclic phosphorothioate by the isolated perfused rat kidney.

The clearance and metabolism of N6-substituted (N6-dimethyl-), C8-substituted (8-bromo-, 8-p-chlorophenylthio- (PCPT-)), and exocyclic oxygen substituted phosphorothioate diastereomers (cAMPS(Sp)) and cAMPS (Rp)) of adenosine 3':5'-monophosphate (cyclic AMP, cAMP) has been studied in an isolated perfused rat kidney. The N6- and C8-substituted analogs of cyclic AMP (10-100 microM) were not cleared as rapidly as exogenous cyclic AMP and were metabolized: N6- and C8-substituted analogs of adenosine accumulated in perfusate and urine. All analogs exhibited net transtubular secretion, i.e. their urinary excretion rate greater than glomerular filtration rate. Probenecid (0.9 mM) included in the perfusate abolished transtubular secretion and inhibited the metabolism of PCPT-cyclic AMP, suggesting that cyclic AMP analogs, like cyclic AMP itself, penetrate the renal cell at the peritubular membrane by an organic acid transport system. The phosphorothioate diastereomers of cyclic AMP: cAMPS(Sp) and cAMPS(Rp) were cleared as rapidly from the perfusate as cyclic AMP, were extensively secreted (urinary excretion/ glomerular filtration greater than or equal to 10) and exhibited no metabolism. The latter analog would seem most suitable as an intracellular agonist for cyclic AMP-mediated phenomena in the rat kidney.

Animals↗
PubMed1982

Further studies on the mechanism by which chlorpropamide alters the action of vasopressin.

The injection of chlorpropamide into Brattleboro homozygous rats (di/di) has previously been shown to result in enhanced activation of renal medullary adenylate cyclase activity and increased renal medullary content of cAMP in response to 1-desamino-8-D-arginine vasopressin (dDAVP). In contrast, in vivo chlorpropamide did not alter GTP, guanylylimidodiphosphate, or fluoride-stimulated adenylate cyclase activities in these renal membranes. We have now found that the effect of in vivo chlorpropamide in enhancing dDVAP-stimulated adenylate cyclase activity involves lowering the Km for ATP. We have also found that dDAVP increases urinary prostaglandin E2 (PGE2) excretion, and treatment with chlorpropamide causes an even greater PGE2 response to dDAVP. In contrast, in vivo chlorpropamide treatment did not increase vascular responses to arginine vasopressin (AVP) in the perfused kidney preparation and, in fact, inhibited the AVP-induced decrease in the glomerular filtration rate. Chlorpropamide, therefore, enhances the renal responses to dDAVP in terms of the cAMP and PG systems, while not increasing responses to postreceptor stimuli of the adenylate cyclase system or vascular responses to AVP. These observations support the concept that in vivo chlorpropamide acts at the receptor of the vasopressin-sensitive part of the tubule to augment responsiveness to vasopressin. In addition, in vivo chlorpropamide may inhibit certain vascular responses to AVP.

Adenylyl Cyclases↗
PubMed1981

Dextran-bound inhibitors of carbonic anhydrase.

High molecular weight inhibitors of carbonic anhydrase were synthesized and tested in isolated perfused rat kidneys. One such inhibitor, dextran-bound inhibitor (DBI), had a mean molecular mass of 6700 daltons. Its renal clearance was equal to the clearance of inulin and its intrarenal volume of distribution was close to that of inulin. The maximal effect of DBI on bicarbonate excretion was the same as that of acetazolamide. This action could not be attributed to breakdown products of DBI. DBI does not enter erythrocytes. Another inhibitor, extra-large inhibitor, had a mean molecular mass of 99,000 daltons. It was scarcely filterable. It did not increase bicarbonate excretion when added to perfusates in concentrations greater than effective concentrations of DBI. It is concluded that activity of carbonic anhydrase bound to luminal membranes of renal cells is critical for normal reabsorption of bicarbonate.

Animals↗
PubMed1980

Elevated insulin/glucagon ratios and decreased cyclic AMP levels accompany the glycogen and triglyceride storage syndrome in the hypothyroid chick.

The role of endogenous glucagon and insulin on the hepatic glycogen and triglyceride storage syndrome in propylthiouracil (PTU)-induced hypothyroidism was investigated in the chick. PTU feeding in the diet resulted in a progressive increase in liver glycogen concentration associated with a concomitant decrease in hepatic glucose-6-phosphatase (G-6-Pase) activity. Plasma glucagon level was significantly decreased and insulin significantly increased after two days of PTU administration. These enzyme and hormone changes were associated with a significant increase in hepatic glucose-6-phosphate (G-6-P) and a decrease in cyclic AMP levels. Although our results do not directly prove, the data does suggest that the hepatic glycogen storage syndrome observed in the PTU-induced hypothyroidism in the chick is mediated through changes in pancreatic glucagon and insulin secretion. The extent of glycogen accumulation was inversely related to G-6-Pase which is a rate limiting glycogenolytic enzyme. A significant increase in the plasma insulin/glucagon ratio, along with a significant decrease in the hepatic cyclic AMP concentration, could most likely also account for the excessive hepatic triglyceride accumulation in the PTU-treated chicks.

Animals↗
PubMed1980

Augmentation by chlorpropamide of 1-deamino-8-D-arginine vasopressin-induced antidiuresis and stimulation of renal medullary adenylate cyclase and accumulation of adenosine 3',5'-monophosphate.

The effect of chlorpropamide was determined in Brattleboro diabetes insipidus (DI) rats that were injected with 1-deamino-8-D-arginine vasopressin (dDAVP). Chlorpropamide augmented the antidiuretic responses to 0.78 and 1.56 ng dDAVP but not to larger doses. In an effort to explain this observation we investigated the effect of chlorpropamide on renal medullary adenylate cyclase activation by dDAVP and on phosphodiesterase activity. We found that the injection of chlorpropamide increased adenylate cyclase activation by dDAVP added in vitro to renal medullary cell membrane preparations from Brattleboro DI rats but had no effect on phosphodiesterase activity. When kidneys from Brattleboro DI rats, treated and not treated with chlorpropamide, were perfused in vitro, we found that 10(-4) M dDAVP increased the concentration of cAMP in comparison to untreated and chlorpropamide-treated groups, and that chlorpropamide plus dDAVP resulted in a greater concentration of renal cAMP than was found with dDAVP alone. We believe that treatment with chlorpropamide increases dDAVP-stimulated renal medullary adenylate cyclase activity without altering phosphodiesterase activity and that this leads to increased renal cAMP concentrations. This, in turn, causes an augmented antidiuresis in response to dDAVP.

Adenylyl Cyclases↗
PubMed1979

Renal metabolism of N6,O2'-dibutyryl adenosine 3',5'-monophosphate.

Metabolism of dibutyryl cyclic AMP was studied by including the 3H- or C-labeled nucleotide (0.1 mM, 5 mumol) in the recirculating perfusate of the isolated rat kidney. Kidneys were perfused with nucleotide for 60 min. Dibutyryl cyclic AMP was almost completely cleared from the perfusate, about one-quarter as urinary excretion principally by probenecid-sensitive secretion and about one-half as metabolism beyond 3'-phosphate bond cleavage. The principal metabolite, N6-monobutyryl adenosine, accounted for one-third of added dibutyryl cyclic AMP. The remaining metabolites were ATP, ADP AMP, and N6-monobutyryl AMP. Dibutyryl cyclic AMP (0.1 or 1.0 mM) elevated renal ATP but did not alter uricogenesis. Both dibutyryl cyclic AMP and cyclic AMP at 0.2 mM produced similar activation and subcellular redistribution of renal protein kinase. N6-monobutyryl adenosine, unlike adenosine, had no effect on the renal activity of adenylate cyclase, low Km cyclic AMP phosphodiesterase, and protein kinase. Dibutyryl cyclic AMP is like exogenous cyclic AMP in that it penetrates the rat kidney, activates protein kinase, and is metabolized to ATP (R. Coulson, J. Biol. Chem. 251: 4958-4967, 1976), but is unlike cyclic AMP in its extent of secretion and metabolism to ATP and urate and in its formation of the unique metabolites N6-monobutyryl AMP and N6-monobutyryl adenosine.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1976

Metabolism and excretion of exogenous adenosine 3':5'-monophosphate and guanosine 3':5'-monophosphate. Studies in the isolated perfused rat kidney and in the intact rat.

Isolated rat kidneys were perfused with a recirculating medium containing exogenous adenosine 3':5'-monophosphate (cyclic AMP) or guanosine 3':5'-monophosphate (cyclic GMP) at an initial concentration of 0.1 mM. Both cyclic nucleotides were rapidly removed from the perfusate. Urinary excretion accounted for about 20% and 40% of the respective cyclic AMP and cyclic GMP lost from the perfusate. The metabolism of the cyclic nucleotides was studied by 14C-labeled cyclic nucleotides in the perfusate. During 60 min, 30% of added cyclic [14C]AMP was metabolized to renal [14C]adenine nucleotides (ATP, ADP, and AMP) and 30% to perfusate [14C]uric acid. Similarly, 20% of cyclic[14C]GMP was metabolized to renal [14C]guanine nucleotides (GTP, GDP, and GMP) and 30% to perfusate [14C]uric acid. Urine contained principally unchanged 14C-labeled cyclic nucleotide. Addition of 0.1 mM cyclic AMP to the perfusate elevated the renal ATP and ADP contents 2-fold. Addition of 0.1 mM of either cyclic AMP or cyclic GMP to the perfusate also elevated the renal production of uric acid 2- to 3-fold. The production and distribution of metabolites of exogenous cyclic nucleotides were also studied in the intact rat. Within 60 min after injection, 3.3 mumol of either 14C-labeled cyclic AMP or cyclic GMP was cleared from the plasma. Kidney cortex and liver were the principal tissues for 14C accumulation. Urinary excretion accounted for about 20 and 45% of the cyclic [14C]AMP and cyclic [14C]GMP lost from the plasma, respectively. The 14C found in the kidney and liver was present almost entirely as the respective purine mono-, di-, and trinucleotides. The other principal metabolite was [14C]allantoin, found in the urine and, to a lesser extent, the liver. The urine contained mostly unchanged 14C-labeled cyclic nucleotide. Unlike the findings with the perfused kidney, [14C]uric acid was not a significant metabolite of the 14C-labeled cyclic nucleotides in these in vivo experiments.

Adenine Nucleotides↗
PubMed1976

Renal responses to PTH in patients with hormone-resistant (pseudo) hypoparathyroidism.

Five patients with pseudohypoparathyroidism were compared to normal subjects and patients with hypoparathyroidism in their ability to respond to the infusion of parathyroid hormone (PTH) by altering excretion of calcium, sodium, potassium, phosphate and bicarbonate. In patients with pseudohypoparathyroidism, impairment in renal responses to PTH was more generalized than has been recognized. The patterns of response varied from patient to patient. The most commonly observed abnormality, aside from lack of increase in urinary cyclic adenosine 5'-monophosphate (AMP) was failure to decrease the calcium to sodium clearance ratio, and indication of impaired renal calcium reabsorption. The responses which most closely approximated normal, including a normal decrease in the calcium to sodium clearance ratio, occurred in a patient (Case 1) who had the largest, although impaired, response in cyclic AMP excretion. Conversely, the most abnormal responses occurred in three patients (Cases 2, 4 and 5) who had the smallest increases in cyclic AMP excretion after the administration of PTH. The impaired renal reabsorption of calcium after the administration of PTH (lack of decrease in calcium to sodium clearance ratio) may, when present, be in part responsible for hypocalcemia.

Absorption↗
PubMed1975

Effect of chlorpropamide on renal response to parathyroid hormone in normal subjects and in patients with hypoparathyroidism and pseudohypoparathyroidism.

Chlorpropamide inhibited by 35 to 65% the increase in the urinary excretion of adenosine 3',5'-monophosphate (cyclic AMP) following a large dose (250 U) of parathyroid hormone (PTH) in normal subjects and patients with hypoparathyroidism and pseudohypoparathyroidism. By contrast, in normal subjects, the response of urinary cyclic AMP excretion to smaller amounts of PTH (15 and 30 U) was not decreased by chlorpropamide. Chlorpropamide did not decrease the phosphaturic response to any dose of PTH. The probable explanation for the discrepant effects of chlorpropamide on urinary cyclic AMP and phosphate excretions is that phosphaturia results from a minimal elevation of cyclic AMP and that chlorpropamide does not decrease cyclic AMP production to such a low level. Chlorpropamide decreased the accumulation of renal cyclic AMP in response to PTH in the parathyroidectomized rat, suggesting that this may be the mechanism of action for this drug in decreasing the urinary excretion of cyclic AMP in response to PTH in man. Tolazamide, another sulfonylurea, did not inhibit the elevation of urinary cyclic AMP excretion after PTH. Therefore, the sulfonylurea part of the molecule is probably not involved in the inhibition produced by chlorpropamide.

Adult↗