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Biomedical subjects

B J Morris

Publications and source records attributed to B J Morris.

At least 217 records · Page 12Linked to original sources
PubMed1978

Activation of human inactive ("pro-") renin by cathepsin D and pepsin.

Inactive human renin is found in amniotic fluid, plasma, and kidney and may be a renin precursor ("prorenin"). The mechanism of activation of inactive renin in vivo is not known. The present study examined the hypothesis that cathepsin D, a lysosomal pepsin-like endopeptidase may be capable of eliciting activation. Cathepsin D was incubated with inactive renin in human amniotic fluid at pH 4.8 and 22 C for 0-5 h. Marked activation occurred and the reaction displayed first order kinetics with respect to the concentration of cathepsin D. The initial velocity of conversion of inactive renin to active renin by cathepsin D was 0.007%/min/microgram cathepsin D. Under identical conditions, the initial velocity of conversion by pepsin was 0.18%/min/microgram pepsin. The 25-fold higher potency of pepsin compared with cathepsin D is in accordance with the recognized relative substrate affinities and catalytic efficiencies of the two enzymes. Inactive renin in human amniotic fluid seems to be similar to that found in human kidney and since cathepsin D is present in juxtaglomerular cells, this activation process may have physiological importance.

Amniotic Fluid↗
PubMed1977

Mechanism of interference by chelating agents and sucrose in radioimmunoassay of angiotensin I.

EDTA, 2,3-dimercaptopropanol and sucrose were shown by Scatchard analysis to interfere in the radioimmunoassay of angiotensin I by altering the affinity, but not the capacity, of antibody for antigen. It is stressed that when interfering reagents are present in samples the assay result must be obtained from a standard curve in which each standard contains the interfering reagent(s) at a similar concentration as present in each sample mixture.

Angiotensin II↗
PubMed1977

The renin-angiotensin-aldosterone system in rabbits with congestive heart failure produced by aortic constriction.

Severe constriction of the suprarenal abdominal aorta of 3-kg rabbits to 3.7+/-0.2 mm2 and maintenance of a daily sodium intake of 10 mE q by infusion of 0.9% sodium chloride resulted in a progressive increase in central ear arterial pressure to 106+/-3 (SEM) mm Hg (control=79+/-1). This was accompanied by a progressive increase in left ventricular end-diastolic pressure to 22+/-2 mm Hg (control=3+/-1), plasma renin activity to 21+/-5 ng of angiotensin/hour per ml (control=5+/-1), plasma aldosterone concentration to 99+/-23 pg/ml (control=14+/-4), and plasma sodium concentration to 142+/-1 mEq/liter (control=136+/-1). Urinary excretion of sodium decreased to 3.9+/-0.7 mEq/day and marked fluid retention occurred. We also found that these changes were accompanied by a decrease in hematocrit to 24+/-2% (control=40+/-1), formation of 36+/-9 ml of fluid in the thoracic cavity, 33+/-9 ml of ascites, pulmonary congestion and edema, hepatic congestion, and enlargement and hypertrophy of both the left and right ventricles. All rabbits died of ventricular failure at a time that was partly related to the degree of aortic constriction and that ranged from 2 to 12 days. The model we have established is chronic, highly reproducible, easy to produce, and inexpensive, and resembles the clinical syndrome of right and left congestive heart failure in man. Furthermore, the studies provide evidence for an important role of the renin-angiotensin-aldosterone system in the fluid retention that leads to pulmonary and systemic venous congestion after suprarenal aortic constriction.

Aldosterone↗
PubMed1977

Identification of "angiotensin immunoreactive material" in rat kidney.

The reported presence of large quantities of a high molecular weight form of angiotensin I and II in renin granules from rat kidney cortex was investigated. Subcellular fractionation by differential centrifugation and isopycnic gradient centrifugation confirmed the presence of 'angiotensin I immunoreactive material,' but the distribution resembled that of lysosomes rather than renin granules, mitochondria or protein. The material did not possess pressor properties, was stable to incubation at 37 C and was precipitated by ethanol. Incubation of subcellular fractions with peptidase inhibitors known to inhibit the activity of renal angiotensinases (EDTA, diisopropyl phosphorofluoridate and 2,3-dimercaptopropanol) decreased the level of 'angiotensin I immunoreactive material' in kidney fractions treated by radioimmunoassay. By paper chromatography it was apparent that subcellular fractions were capable of degrading 125I-labelled angiotensin I used as tracer in the radioimmunoassay. The degree of degradation followed the distribution of lysosomes among the fractions and was decreased by the angiotensinase inhibitors. The apparent molecular weight of the major portion of angiotensinase activity persisting despite the presence of angiotensinase inhibitors was 75,000, a value similar to that of 'angiotensin immunoreactive material'inkidney fractions treated with non-ionic detergent. On the basis of the present findings it is suggested that 'angiotensin immunoreactive material' may be largely artifactual, beingcreated by the hydrolysis of tracer by angiotensinase enzymes during radioimmunoassay to form fragments that are no longer capable of binding to the specific antibody. This would produced results that would appear the same as those produced had genuine angiotensin immunoreactivity indeed been present in the samples. Such an effect could, in principle, occur in any competitive protein binding assay and should be tested.

Angiotensin II↗
PubMed1976

Renin substrate in granules from rat kidney cortex.

1. Subcellular fractions of rat kidney cortex generated angiotensin I continuously over 2h when incubated at 37degreesC with rat renin, indicating the presence of renin substrate within cells in the renal cortex. 2. Renin substrate was located in highest specific concentration in particulate fractions. The particles containing renin substrate had a sedimentation velocity slightly lower than mitochondria and renin granules but greater than the microsomal fraction. 3. Isopycnic gradient centrifugation indicated a density of 1.190g/ml for the particles containing renin substrate, compared with 1.201 for renin granules, 1.177 for mitochondria, and 1.170 and 1.230 for lysosomes in the heavy-granule fraction. 4. In the liver, renin substrate was also found in particles, but these had a lower sedimentation rate than those from the kidney. 5. The molecular weights of renin substrate in kidney and liver granules and rat plasma were similar, namely 61000-62000. 6. On the basis of these biochemical findings, a mechanism for the intrarenal production of angiotensin, incorporating a subcellular reaction scheme, is proposed.

Angiotensin II↗
PubMed1976

Renin release from isolated rat glomeruli.

1. By the use of a mechanical graded sieving technique a high yield of isolated glomeruli has been obtained from rat kidny. 2. Microscopy and renin assay have shown the presence of renin-containing juxtaglomerular cells attached to these glomeruli. 3. The viability of isolated glomeruli has been confirmed by the ability of the cells to survive and divide in tissue culture and by their exclusion of vital dyes. 4. In superfusion after washout of extracellular renin, the glomeruli actively release constant amounts of renin over 3 h in direct proportion to the number of superfused. 5. Decreasing sodium concentration from 140 to 110 mol/l with constant osmolarity of 305 mosmol/l stimulated renin release by a direct effect on juxtaglomerular cells. 6. Catecholamines stimulated renin release in vitro in proportion to the potency of their action on beta-adrenoreceptors. 7. The system of superfusion of isolated glomeruli provides a technique for studying the influence of mediators leading to renin release acting directly on juxtaglomerular cells, independent of pressure change, tubular sodium, the sympathetic nervous system and circulating hormones.

Animals↗
PubMed1976

Isolation of renin granules from rat kidney cortex and evidence for an inactive form of renin (prorenin) in granules and plasma.

Renin was demonstrated in particles having a sedimentation velocity similar to that of mitochondria during differential centrifugation separated renin granules from the bulk of mitochondria and lyosomes, as well as from microsomes and cytoplasm. The density of renin granules was 1.202, which differed from the mean equilibrium densities of mitochondria (1.175) and lysosomes (1.170 and 1.230) in the heavy granule fraction. In studies involving gel filtration and polyacrylamide gel electrophoreis, renin granules appeared to contain an inactive form of renin that could be activated by acid treatment, had a higher apparent molecular weight than renin, and may be a more basic molecule. Inactive renin was also studied in plasma by electrophoresis and may originate from renin granules after exocytosis by the juxtaglomerular cells. Inactive renin may be a biosynthetic precursor (prorenin) and may be activated within the cell by a specific protease consequent upon the fusion of renin granules with lysosomes, thus providing a mechanism for the rapid regulation of renin activity prior to secretion.

Animals↗
PubMed1975

Clearance and metabolism of neurophysins by rat kidney.

The half-life in the circulation of 125I-labelled porcine neurophysins, injected intravenously into rats, was determined. The radioactivity in blood collected at intervals after injection was characterized as neurophysin by polyacrylamide gel electrophoresis. The half-life of neurophysin I was 1-5 plus or minus 0-1 (S.E.M.) min and that of neurophusin II was 1-7 plus or minus 0-1 min. The metabolic clearance rate of neurophysin I and neurophysin II was 1-9 plus or minus 0-1 and 1-3 plus or minus 0-2 ml/min/200 g respectively. Clearance from the circulation was due to both equilibration with the extravescular space and rapid specific accumulation by the kidney. The neurophysins were filtered at the glomerulus. Most of the neurophysin takken up by the kidney was incorporated into lysosomes, probably in the proximal tubule and degraded to low-molecular-weight metabolites which appeared in urine and which represented the principle mode of excretion of neurophysins.

Animals↗
PubMedDate not supplied

Control of receptor sensitivity at the mRNA level.

Neurons are able to adjust the sensitivity of receptor-mediated processes according to the level of receptor activation. Extrapolating from our knowledge of other cellular proteins, regulation of receptor mRNA availability would provide a highly economical means of achieving this objective. Epidermal growth factor is able to induce long-lasting increases in its receptor binding by increasing receptor mRNA levels, and similar effects have been shown for other growth factors. Studies on G-protein-coupled receptors, in particular using adrenoceptor clones transfected into cultured cell lines, have shown that changes in receptor number are generally associated with an alteration in receptor mRNA content. At the neuromuscular junction, dramatic increases in nicotinic acetylcholine receptor number are achieved by activating receptor subunit gene transcription. Less information is available concerning the regulation of ligand-gated ion channels in the brain. Overall, the evidence suggests that receptor mRNA levels are frequently controlled by the degree of receptor stimulation. Receptor mRNA levels are therefore likely to be one of the most important control points for both homologous and heterologous regulation of receptor sensitivity.

Animals↗
PubMedDate not supplied

Dynamic changes in NADPH-diaphorase staining reflect activity of nitric oxide synthase: evidence for a dopaminergic regulation of striatal nitric oxide release.

In fixed tissue, neuronal NADPH-diaphorase staining results from nitric oxide synthase (NOS) activity. Neuronal NOS only synthesizes nitric oxide once activated by the binding of Ca2+/calmodulin. We show here that neuronal NADPH-diaphorase staining is also dependent on Ca2+/calmodulin, implying that only activated NOS is detected. In addition, in bovine pulmonary endothelial cells, carbachol and bradykinin dramatically and rapidly increase the intensity of NADPH-diaphorase staining. Furthermore, administration of MK801, an NMDA antagonist, decreases neuronal NADPH-diaphorase staining. This suggests that the intensity of the NADPH-diaphorase staining is related to the level of enzyme activation at the moment of tissue fixation. The potential of exploiting this observation to detect cellular activation of NOS is illustrated by the observations that the intensity of NADPH-diaphorase staining in rat striatal neurones is decreased following systemic treatment with the D1-like dopamine receptor antagonist SCH23390, and increased by the D2-like antagonist eticlopride. These results therefore provide strong evidence that the NADPH-diaphorase reaction can be used to monitor NOS activity at a cellular level of resolution, and reveal a dopaminergic regulation of NOS activity in the striatum mediated by D1-like and D2-like dopamine receptors.

Animals↗
PubMedDate not supplied

Clearance from the circulation of the rat and whole-body autoradiography in the mouse of 125I-labelled neurophysins.

1. The rate of clearance of 125I-labelled porcine neurophysins I and II from the circulation of the rat has an initial fast component followed by a slower component. 2. In the initial phase of clearance the half-life of neurophysin I was 1.50 min (s.e.m. = 0.03) and for neurophysin II was 1.74 min (s.e.m. = 0.05). In the slower phase of clearance the half-life of neurophysin I was 22.6 min (s.e.m. = 2.2) and for neurophysin II was 27.3 min (s.e.m. = 5.8). 3. The first component had a volume of distribution similar to the blood volume and the second component had a volume of distribution similar to the volume of extracellular fuid of the rat. 4. The metabolic clearance rates per 200 g of body weight were 1.94 ml/min (s.e.m. = 0.12) for neurophysin I and 1.29 ml/min (s.e.m. = 0.15) for neurophysin II. 5. Using whole-body autoradiography, the kidney was shown to be the major site of uptake of radioactivity in both virgin female and lactating mice.

Animals↗
PubMedDate not supplied

Release of renin from glomeruli isolated from rat kidney.

1. Glomeruli free from renal tubules and cell debris were isolated in large numbers from rat kidney cortex by a rapid, simple process of graded sieving on stainless steel meshes. 2. Glomeruli were viable, had fragments of the arterioles attached and contained renin. 3. Glomeruli, when incubated, released renin into the medium. Using a super-fusion technique this was shown to be time dependent until a basal secretion level was achieved. 4. Release of renin was directly proportional to the number of glomeruli and could be stimulated by isoprenaline, adrenaline and noradrenaline in order of the potency of their action on beta-adrenoreceptors. 5. Isolated glomeruli were therefore established as a useful model system for studying the release of renin by direct influences on the juxtaglomerular cells where haemodynamic, tubular and extrarenal influences are removed.

Animals↗