Search PubMed⌕ Search

Biomedical subjects

K Poulsen

Publications and source records attributed to K Poulsen.

At least 163 records · Page 9Linked to original sources
PubMed1977

Direct measurement of high molecular weight forms of renin in plasma.

Gel filtration of normal mouse serum revealed the presence of high molecular-weight forms of renin, in addition to the well-recognized 40 000 dalton form. The distribution of renin was measured by using both the antibody trapping method, which measures renin's enzymatic reactivity, and by a direct radio-immunoassay, which detects the renin molecule by its antigenic properties. A well characterized and distinct peak corresponding to a molecular weight of 200 000 or greater was always present. A less distinct peak was seen between 70 000 and 140 000 daltons. The well separated and symmetrical peak at 40 000-45 000 daltons was secreted from both kidneys and submaxillary glands and disappeared almost completely after combined nephrectomy and sialoadenectomy in contrast to the forms of higher molecular weight. The higher the molecular weight the lower was the specific enzymatic reactivity found to be. The 200 000-dalton peak was mainly detectable by the direct assay, although it was demonstrated to contain enzymatic reactivity to a small extent. The 40 000-dalton peak had a specific enzymatic reactivity and molecular weight identical to that of pure submaxillary renin.

Animals↗
PubMed1977

Cause of the continuous rise in plasma renin concentration after removal of manipulated submaxillary glands in nephrectomized mice.

After gentle manipulation with subsequent removal of the submaxillary glands in nephrectomized mice there is a vast increase in the concentrations of high molecular weight renin ("prorenin"?) as well active renin in plasma. The increase in active renin is continuous even after removal of glands as well as kidneys. Using in vitro incubation and replacement transfusion experiments, the continuous rise was found not to be due to activation of the high molecular weight renin. The continous increase could instead be shown to be due to a rapid transfer of submaxillary lymph and (or) interstitial fluid to the surrounding tissues, with a subsequent slower release from these tissues to the blood. Continued release of renin from extra-submaxillary tissue-depots is probably also the cause of the continuance of the high plasma renin concentrations for several hours after the removal of the manipulated glands, which contrast with the much more rapid decline in the concentration after injection of extracts of submaxillary glands as well as after injection of pure submaxillary renin.

Animals↗
PubMed1977

Cause of the disproportion between the vast increase in plasma renin and the only small (if any) increase in blood pressure after manipulation of the submaxillary gland.

The cause of the disproportion between the vast increase in plasma renin concentration and the small, if any increase in blood pressure after manipulation of the submaxillary glands in mice is complex. The increase in plasma renin was found to cause a marked depletion of renin substrate, which however, was relatively so much less than the increase in renin that the (calculated) renin activity was markedly increased. The sensitivity of the vessels to angiotensin had only decreased in about half the animals studied, and even here the tachyphylaxis could not cope with the pronounced increase in plasma renin activity, as shown by a marked decrease in the blood pressure after blockade of the renin system. The finding that blockade of the renin system lowered the blood pressure below the pre-manipulation level made it probable that the vast release of submaxillary renin is followed by release of a depressor substance. The glands are known to contain kallikrein, but with the methods used it was neither proved nor disproved that the manipulation causes a release of kallikrein. Besides the factors studied, compensatory cardiovascular reflexes can play a role for the disproportion between plasma renin and blood pressure.

Angiotensin II↗
PubMed1976

On the specificity of human renin. Studies with peptide inhibitors.

The amino acid sequence around the renin substrate site is known to be identical to the N-terminal tetradecapeptide: Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser. Renin (EC 3.4.99.19) from both primates and non-primates cleaves this peptide at the leucylleucine bond. Several analogs of the octapeptide segment: His-Pro-Phe-His-Leu-Leu-Val-Tyr of this tetradecapeptide act as competitive inhibitors for human renin with inhibition constants down to 1 muM. The same peptides were shown, however, to have no or only slight affinity for non-primate renin. The substrate site has been preserved throughout evolution whereas the enzyme site for human renin is different from that of non-primate renins. The findings suggest that species-specific peptides must be developed for both studies of renin inhibition and for renin purification.

Animals↗
PubMed1976

Vast and apparently paradoxical continuous rise in plasma renin after removal of gently manipulated submaxillary glands in nephrectomized mice.

Gentle manipulation of the submaxillary glands of previously nephrectomized mice results in a vast increase in plasma renin concentration. The concentration reaches 1 to 7 G.U. renin/ml, which is 1,000-fold higher than normal plasma concentrations. The rise is much less pronounced if the glands are removed after the manipulation, confirming the site of the release. However, an apparent paradox is seen: the renin concentration continues to rise even after removal of submaxillary glands as well as kidneys, indicating that a bound a form of renin is also released. The bound renin can be in the form of exocytosed granules or (and) in the form of "protein", the renin of which is activated with time. In spite of the very high renin concentrations the blood pressure is normal or only moderately increased. This disproportion between plasma renin and blood pressure can be caused by a simultaneous release of submaxillary kallikrein and renin, which have conteracting effects on the blood pressure.

Animals↗
PubMed1976

Participation of renal, but not of submaxillary renin in the homeostasis of the blood pressure after experimentally induced hypotension in mice.

While hypotension elicited a marked increase in plasma renin concentration in conscious normal mice, no increase was provoked in previously nephrectomized mice in spite of the high renin content of their submaxillary glands. The role of the increased release of renal renin for the homeostasis of the blood pressure was shown by the decrease in pressure which followed blockade of the renin system. Contrary to Saralasin which did not change the blood pressure in nephrectomized mice, injections of SQ 20.881 did in some mice result in a decrease in blood pressure, which was probably caused by its ability to inhibit bradykininases. Both Saralasin and SQ 20.881 elicited marked increases in plasma renin in normal, but not in nephrectomized mice, showing that, while renal renin release is controlled by the plasma angiotensin II concentration, this does not apply to submaxillary renin release.

Animals↗
PubMed1976

Competitive inhibitors of renin. A review.

This review describes some of the characteristics for renin's substrate specificity and also some features of its species specificity. It describes how competitive inhibitors were synthesized and how the solubility was increased in order to make them effective at physiological pH. Their use for in vitro and in vivo inhibition of renin is discussed and their use for purification of renin demonstrated.

Animals↗
PubMed1975

Competitive inhibitors of renin. Inhibitors effective at physiological pH.

Previously we reported the development of competitive inhibitors of renin effective at pH 5.5 (Poulsen, K., Burton, J., and Haber, E. (1973), Biochemistry 12, 3877). At physiologic pH (7.5), the inhibitory constants (Ki) increased and solubility decreased to the point that inhibition could not be demonstrated with these peptides. Modification of the octapeptide sequence, His-Pro-Phe-His-Leu-Leu-Val-Tyr, either by addition of serinol to the carboxyl terminus or by replacement of valine-7 with an isosteric threonyl residue failed to yield peptides active at pH 7.5. Attachment of polyproline sequences to the amino terminus increased solubility from threefold to tenfold and decreased Ki so that competitive inhibition was demonstrable at physiologic pH. In addition, if leucine-6 was replaced in these peptides with a phenylalanyl or tyrosyl residue, Ki decreased (3-12 muM) to give effective competitive inhibitors at physiologic pH in both buffer and in plasma.

Binding Sites↗
PubMed1975

Purification of hog renin by affinity chromatography using the synthetic competitive inhibitor (D-Leu6)octapeptide.

The renin substrate analog His-Pro-Phe-His-Leu-D-Leu-Val-Tyr ([D-Leu6]-octapeptide) acts as a potent inhibitor of renin because of the D-amino acid substitution at the cleavage site. This inhibitor was coupled to CNBr-activated Sepharose 4B to yield a support for affinity chromatography. Hog renin with a specific activity of 1.2 Goldblatt units/mg was in one step purified 195-fold to a final specific activity of 234 Goldblatt units/mg. Application of a pH gradient from 5.0 to 7.5 to the support was found to be the most successful elution program, probably because the [D-Leu6]-octapeptide is not an inhibitor for renin at neutral pH.

Animals↗
PubMed1975

Time course of changes in plasma renin after blockade of the renin-system. Studies of conscious and anaesthetized, normal, adrenalectomized and spontaneously hypertensive rats.

Inhibition of the angiotensin I converting enzyme with SQ 20.881 results in a 2 to 35 fold increase in plasma renin concentration in normal rats and in spontaneously hypertensive rats. The effect is transient, lasting for 1 to 3 hours even in the presence of prolonged blockade. The relative increase is independent of the pretreatment plasma renin concentration. The blood pressure is unchanged in conscious rats in which the effect of SQ 20.881 on plasma renin is believed to be due to a blockade of the negative feedback of angiotensin II on renin release. In anaesthetized rats, SQ 20.88) has an additional hypotensive effect which augments the increase in plasma renin. Saralasin is without effect on blood pressure and plasma renin in conscious normal rats and in spontaneously hypertensive rats, while it causes a transient 3 to 27 fold increase in plasma renin concentration in anaesthetized rats. It is suggested that this increase is hardly due to an interception of the feedback, but to the concomitant fall in blood pressure, as a similar hypotension and increase in plasma renin is produced by dihydralazine. It is furthermore found that Saralasin blocks renin release induced by SQ 20.881. This demonstrates that Saralasin is bound to the receptors in the juxtaglomerular cells and has slight, agonistic properties there. Both in conscious rats and in anaesthetized adrenalectomized rats substituted with DOCA and salt, SQ 20.881 as well Saralasin causes transient increases in plasma renin concentration. If such rats are only substituted with salt and not with DOCA, the effects of both blockers are in the form of severe hypotension and a permanent elevation of plasma renin.

Adrenalectomy↗
PubMed1975

Different effects on renal and submaxillary renin release after blockade of the renin system in mice.

Ingibition of the angiotensin I converting enzyme with SQ 20,881 results in a rapid marked increase in plasma renin concentration in mice. The maximum effect is short-lasting, but the values are still elevated 2 hours after the injection, the time course being similar to that previously found in rats. The relative increase is the same in normal and sialo-adenectomized mice. The plasma renin concentration of nephrectomized mice with their submaxillary glands intact is, however, totally uninfluenced by injection of the blocker. This finding indicates that renin release from the submaxillary glands is not controlled by the plasma angiotensin II concentration as is that of the renin release from the kidneys.

Angiotensin II↗
PubMed1975

Characteristics of renin release from isolated superfused glomeruli in vitro.

1. A method is described for studying renin release from superfused rat glomeruli following their rapid isolation by a magnetic iron-oxide technique. 2. Microscopically selected glomeruli were free of tubular components. Some possessed vascular pole protrusions of up to 20 mum, unrelated to renin content. 3. Renin content of 102 batches, each of 400 glomeruli, was 1.34 plus or minus 0.08 times 10-4 Goldblatt hog units per 100 glomeruli (plus or minus S.E. of mean). Different osmolarities (305, 355 and 400 m-osmole/1.), sodium concentrations (110 and 135 mM) and buffer compositions of the preparation solution did not alter this value. Renin content per glomerulus in intact kidney was 100-fold higher. 4. At 30 degrees C the contained juxtaglomerular cells released renin at consistent but decreasing rates over 4-6 hr. Initial release rate in 110 mM sodium, 305 m-osmole/1. solutions were 0.86 plus or minus 0.068 times 10-6 units per 100 glomeruli per 30 min (plus or minus S.E. of mean, n = 42) or 0.546 plus or minus 0.046 percent of content per 30 min. In 135 mM sodium, 305 m-osmole/1. solutions, release was 2.4-fold higher (P less than 0.001) and remained elevated for at least 3 hr. When related to renin content per glomerulus resting release rate in vitro was higher by at most one order of magnitude than calculated in vivo values. 5. Release was augmented by gentle physical agitation of the glomeruli. 6. Release rate was inversely ralated to temperature. On reducing temperature from 30 degrees C, release increased 2.6-fold at 20 degrees C and 6.7-fold at 10 degrees C (P less than 0.001, n = 11). The response was reversible. 7. 3 mM sodium cyanide plus 3 mM sodium iodoacetate caused a variable release of renin associated with depletion of content within 4 hr. The response was progressive and reached a peak after 60 min. 8. Sensitivity of renin release to temperature and metabolic blockade indicates that energy is required for retention of renin by the cell. This, together with the release observed with increased sodium concentration at constant osmolarity, suggests a dependence of renin release upon the mechanism controlling the volume of the juxtaglomerular cell or its organelles.

Animals↗