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Biomedical subjects

M Schwartzman

Publications and source records attributed to M Schwartzman.

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

Arachidonic acid metabolism in a cell suspension isolated from rabbit renal outer medulla.

We studied arachidonic acid (AA) metabolism by a cell suspension containing principally cells of the thick ascending limb of the loop of Henle (TALH) obtained from the inner stripe of the outer medulla of the rabbit kidney. Based on comparison of specific activities of enzymes before and after separation, alkaline phosphatase, Na+-K+-adenosine triphosphatase, as well as Tamm-Horsfall glycoprotein and electron microscopic appearance, 80% of these cells were estimated to be TALH in origin. TALH cells had low activity of cyclooxygenase and did not show evidence of lipoxygenase activity. However, they selectively converted exogenous AA to oxygenated metabolites by a cytochrome P-450 related mechanism. AA metabolites were produced in large amounts (30-40% conversion of [14C]AA, 1 to 5 micrograms/mg of protein/30 min) and were increased 5-fold after separation of TALH cells from a suspension of outer medullary cells, suggesting that TALH cells synthesized these metabolites. Induction of cytochrome P-450 by pretreatment of rabbits with beta-naphthoflavone and 3-methylcholanthrene increased formation of the AA metabolites by almost 2-fold in the separated cells and correlated with cytochrome P-450 content of the renal outer medulla. Additionally, SKF 525A and carbon monoxide inhibited product formation in these renomedullary cells, supporting a role for a cytochrome P-450-like monooxygenase in TALH cell function.

Animals↗
PubMed1983

Bradykinin-stimulated differential incorporation of arachidonic acid into lipids of kidney cortex and medulla.

We investigated bradykinin-induced changes in the turnover of arachidonate in renal lipids of the perfused rabbit kidney. Upon hormone stimulation, this cellular system undergoes only transient dynamic changes in arachidonic acid metabolism; no loss of bradykinin effect on arachidonate release and prostaglandin generation is shown upon repeated hormone administrations during 8-9 hr of perfusion. Ureter-obstructed rabbit kidneys were perfused for 5-6 hr and then saline or bradykinin in saline was administered, followed after 10 sec by pulse labelling with [14C]arachidonate. The pattern of distribution of [14C]arachidonate in lipid fractions of the cortex showed that bradykinin caused a 2 to 2.5-fold increase in the relative incorporation of arachidonic acid into phosphatidylinositol (PI), phosphatidic acid (PA), diglyceride (DG) and triglyceride (TG) fractions and a concomitant decrease in its incorporation into phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In contrast, in the medulla hormone administration caused a marked increase of arachidonate incorporation into PI and PC, and a decrease in incorporation into PE, PA, DG and TG. This differential arachidonate labelling of cortical vs medullary lipids following bradykinin stimulation suggests that the hormone activates different lipolytic processes in cortex and medulla, and promotes hydrolysis of arachidonic acid from different phospholipid pools.

Animals↗
PubMed1981

Evidence for different purinergic receptors for ATP and ADP in rabbit kidney and heart.

ATP and ADP stimulated the release of specific prostaglandin products from the perfused rabbit kidney heart. The two nucleotides produced the same qualitative profile of prostaglandin products. In kidney, prostaglandin E2 was the major product, whereas in heart 6-keto prostaglandin F1 alpha and prostaglandin E2 predominated. ATP was a slightly more potent than ADP. ATP administered into the perfused heart to kidney was rapidly hydrolyzed to ADP and AMP. The prostaglandin E2 generating activity of ATP was increased 6-10 fold when ATP was given together with AMP-PCP or AMP-PNP which competitively inhibit the activity of vascular ATPase. Thus, the rapid hydrolysis of ATP reduces its agonistic activity for prostaglandin release. ATP and ADP administered together at maximal stimulating doses produced an additive response for prostaglandin E2 release. These results and the results of tachyphylaxis experiments indicate that ATP and ADP interact independently with different types of purinergic receptors.

Adenosine Diphosphate↗
PubMed1981

Selective induction of de novo prostaglandin biosynthesis in rabbit kidney cortex.

Ureter-obstructed kidney develops during perfusion an enhanced responsiveness to bradykinin-stimulated prostaglandin release. This enhanced prostaglandin generation results from de novo synthesis of prostaglandin synthetase and acylhydrolase enzymes during the perfusion and is therefore unaffected by acetylsalicylic acid (aspirin) inhibition of prostaglandin synthesis prior to initiation of perfusion. Studies were carried out to identify the renal cellular site in which the newly synthesizing prostaglandin generating system is localized. Kidneys with or without aspirin treatment were perfused for either 1 or 5 h. Following perfusion, medullary and cortical slices were incubated and prostaglandin E2 production measured. Medullary slices showed similar prostaglandin E2 biosynthetic activity in kidneys perfused for 1 or 5 h. Furthermore, medullary prostaglandin generation was inhibited (90-95%) by aspirin pre-treatment and did not increase during subsequent perfusion for 5 h. In contrast, cortical slices from kidneys pretreated with aspirin regained their full activity after 5 h or perfusion, this regeneration being abolished by infusion of the protein synthesis inhibitor, cycloheximide. The same differences in activities between medulla and cortex were also seen when microsomal fractions were compared. The perfusion-induced formation of prostaglandin synthetase activity is thus specifically localized in the cortex and can be detected in cortical microsomes. This cortical activity is unique in that endogenous arachidonic acid released from esterified lipids is converted to prostaglandins, whereas exogenous added arachidonic acid is not. It thus appears that the induced cortical acylhydrolase and prostaglandin synthetase activities are tightly coupled and that the true molecular form or precursor arachidonate for this prostaglandin generating system is esterified and not free arachidonate.

Animals↗
PubMed1980

Biochemical actions of vasoactive peptide hormones. Time-synchronized activation of lipolysis and decreased fatty-acid release by bradykinin and angiotensin in the perfused rabbit kidney.

Bradykinin and angiotensin administered to the isolated perfused rabbit kidney activate two sequential processes: (1) a selective release of the prostaglandin precursor arachidonate with concomitant partial conversion of the arachidonate into prostaglandin E2; (2) activation of a process that leads to decreased release of all fatty acids in the perfusate. There is a time lag of approx. 1 min between the initial activation of the arachidonate-specific deacylation reaction that is coupled to prostaglandin generation, and the subsequent decrease in the release of all fatty acids. This synchronized cycle provides for instant generation of required amounts of prostaglandins and at the same time serves to conserve cellular arachidonate.

Angiotensin II↗
PubMed1980

Indomethacin but not aspirin inhibits basal and stimulated lipolysis in rabbit kidney.

The concurrent effect of indomethacin or aspirin on prostaglandins (PGs) biosynthesis and on cellular fatty acid efflux were compared. Studies with rabbit kidney medulla slices and with isolated perfused rabbit kidney showed a marked difference between the two non-steroidal anti-inflammatory drugs, with regard to their effects on fatty acid efflux from kidney tissue. While aspirin effect was limited to inhibition of PGs biosynthesis, indomethacin also reduced the release of free fatty acids. In medullary slices, indomethacin inhibited the Ca2+ stimulation of phospholipase A2 activity and the resulting release of arachidonic and linoleic fatty acids. In the isolated perfused rabbit kidney, indomethacin inhibited the basal efflux of all fatty acids as well as the angiotensin II--induced selective release off arachidonate. Indomethacin also blunted the angiotensin II--induced temporal changes in the efflux of all other fatty acids. Neither indomethacin nor aspirin affected significantly the uptake and incorporation of exogenous (14C)-arachidonic acid into kidney total lipid fraction. Our tentative conclusion is that indomethacin inhibits basal as well as Ca2+ or hormone stimulated activity of kidney lipolytic enzymes. This action of indomethacin reduces the pool size of free arachidonate available for conversion to oxygenated products (both prostaglandin and non-prostaglandin types). The non-steroidal anti-inflammatory drugs can therefore be divided into two groups: a) aspirin-type compounds which inhibits PGs formation only by interacting with the prostaglandin endoperoxide synthetase and b) indomethacin-type compounds which inhibit PG generation by both reduction in the amount of available arachidonate and direct interaction with the enzyme.

Animals↗
PubMed1980

Time-synchronized activation of lipolysis and fatty acids reacylation by bradykinin and angiotensin II in the perfused rabbit kidney.

BK and AII administered to the isolated perfused rabbit kidney activate two sequential enzymatic processes: 1) a selective release of the PG precursor, AA with concomitant, partial conversion of arachidonate to PGE2. 2) Activation of a reacylation process which leads to decreased release of all fatty acids in the perfusate. There is a lag time of approximately 1 min between initial activation of the arachidonate-specific deacylation reaction that is coupled to PG generation, and subsequent activation of the reacylation process.

Angiotensin II↗
PubMed1979

Prostaglandin generation in rabbit kidney. Hormone-activated selective lipolysis coupled to prostaglandin biosynthesis.

The endogenous release of prostaglandins and free fatty acids from the isolated perfused rabbit kidney in the absence or presence of stimulation by bradykinin or angiotensin-II was investigated. Basal (nonstimulated) release of prostaglandin-precursor arachidonic acid was 15-20-fold higher than that of prostaglandin E2 indicating a low conversion of released arachidonate to prostaglandins. Addition of bovine serum albumin to the perfusion medium caused a substantial (50-250%) increase in the release of all fatty acids except myristic and arachidonic acids, and no significant change in prostaglandin E2 generation. In contrast, administration of bradykinin (0.5 microgram) or angiotensin-II (1 microgram) caused a 10-15-fold increase in prostaglandin E2 release, and with albumin present, also a 2-3-fold selective increase in arachidonic acid release. Thus, unlike what was observed under basal conditions, arachidonic acid released following hormone stimulation is efficiently converted to prostaglandin E2. We conclude that administration of bradykinin or angiotensin-II into the perfused kidney activates a lipase which selectively releases arachidonic acid, probably from a unique lipid entity. This lipase reaction is tightly coupled to a prostaglandin generating system so that the released arachidonate is first made available to the prostaglandin cyclooxygenase, resulting in its substantial conversion to prostaglandins.

Angiotensin II↗
PubMed1978

Prostaglandin biosynthesis in rabbit kidney medulla: inhibition in-vitro vs. in-vivo by aspirin, indomethacin and meclofenamic acid.

The non-steroidal anti-inflammatory drugs aspirin, indomethacin and meclofenamic acid were compared for their potency and duration of inhibition of prostaglandin biosynthesis in rabbit kidney medulla. Indomethacin and meclofenamic acid showed equal potency of inhibition in-vitro (IC50 0.88 micron and 0.85 micron respectively) while aspiring was a much weaker inhibitor (IC50 120 micron). In-vivo, indomethacin was the most powerful inhibitor (ID50 0.034 mg/kg) followed by meclofenamic acid (0.45 mg/kg) and aspirin (2.35 mg/kg). Studies on the duration of in-vivo inhibition by these compounds showed the effect of indomethacin and meclofenamic acid to be completely reversed within 4-6 hours. In contrast, return of kidney prostaglandin biosynthetic activity following aspirin inhibition is very slow and significant inhibition is still present 48 hours after a single aspiring injection. The inhibitory effect of aspirin in-vivo could be blocked by pretreatment with indomethacin, indicating that both drugs interact with related sites on the cyclo-oxygenase enzyme. The irreversible inhibition of the cyclo-oxygenase by aspirin as demonstrated in studies of other investigators suggests that the return of kidney prostaglandin synthetase activity after aspirin inhibition represents synthesis of new cyclo-oxygenase protein.

Animals↗
PubMed1977

Effect of organic sulfur compounds on the chemical and enzymatic transformations of prostaglandin endoperoxide H2.

The effects of several sulfur organic compounds on the enzymatic and non-enzymatic transformations of prostaglandin endoperoxide H2 to prostaglandins were studied. Mercaptoethanol, methional alpha-lipoic acid and dimercaptopropanol increased the chemical (i.e. non-enzymatic) reduction of prostaglandin H2 to prostaglandin F2alpha but except for alpha-lipoic acid, had no effect on the enzymatic conversion of prostaglandin H2 to prostaglandin. In contrast, reduced glutathione showed no effect on the chemical conversion of prostaglandin H2, but exerted a marked and specific stimulation on the enzymatic isomerization of prostaglandin H2 to prostaglandin E2. This specific effect of gluthione may serve to regulate the overall intracellular activity of prostaglandin synthetase as well as the particular ratio of prostaglandins produced.

Animals↗
PubMed1976

Chemical and enzymatic transformations of prostaglandin endoperoxides: evidence for the predominance of the 15-hydroperoxy pathway.

Cyclic prostaglandin endoperoxides prostaglandin G2 and H2 are intermediates formed in the biosynthesis of prostaglandins from arachidonic acid. These endoperoxides can be converted chemically or enzymatically to prostaglandins E2, D2 and F2alpha. The effects of several reducing compounds on the chemical and enzymatic transformations of prostaglandins G2 and H2 were studied in order to determine the possible existence of two alternative enzymatic pathways for the conversion of prostaglandin G2 to prostaglandins. The chemical transformation of prostaglandin H2 to prostaglandins by cleavage of the 9,11-cycloendoperoxide ring was unaffected by the presence of reduced glutathione, heme or tryptophan while hydroquinone and mercaptoethanol promoted the chemical reduction to prostaglandin F2alpha. In contrast the enzymatic transformation of prostaglandin H2 to prostaglandins by a solubilized prostaglandin synthetase from sheep vesicular gland was unaffected by hydroquinone or mercaptoethanol, but was markedly stimulated by reduced glutathione to yield mainly prostaglandin E2. Prostaglandin G2 transformation to prostaglandins involves cleavage of the 9,11-endoperoxide ring and a reduction of the 15-hydroperoxy group. The chemical reduction in buffer in the 15-hydroperoxy group is not affected by the presence of reduced glutathione, hydroquinone, heme or tryptophan. In contrast, the enzymatic reduction of the 15-hydroperoxy group is catalyzed by the solubilized prostaglandin synthetase and is further stimulated by reduced glutathione and hydroquinone. Results are presented which indicate that the enzymatic conversion of prostaglandin G2 to prostaglandins can proceed via two alternative pathways, one involving the intermediate formation of prostaglandin H2 and the other the formation of 15-hydroperoxy prostaglandins. The latter pathway appears to be the major pathway for the enzymatic conversion of prostaglandin G2 to prostaglandins.

Animals↗
PubMed1976

Properties of prostaglandin synthetase of rabbit kidney medulla.

The formation in vitro of prostaglandins E2, D2, and F2alpha from arachidonic acid by rabbit kidney medulla homogenate or microsomal fraction is markedly affected by the composition of the incubation medium employed. Optimal biosynthesis is obtained in 0.1 M potassium phosphate buffer, with the optimum pH being 8.0--8.8. Under these conditions prostaglandin formation is linear up to arachidonic acid concentration of 30 muM. The initial rate of formation of prostaglandin E2 + prostaglandin D2 is 3--4 times higher than that of prostaglandin F2alpha. Reduced glutathione (1 mM) did not affect the biosynthesis by medulla homogenate and produced only small stimulation of the biosynthesis by microsomal powder. Hydroquinone produced a small stimulation at a low concentration of 0.005 mM, and a strong inhibition at concentrations of 0.1 mM or higher. Addition of bovine serum albumin (0.1%) reduced the microsomal biosynthesis of prostaglandins by approximately 80%. Addition of boiled homogenate or boiled 140 000 X g supernatant produced small stimulation of microsomal biosynthesis while 140 000 X g supernatant (not boiled) caused small inhibition which was not dose-related. It appears that rabbit kidney prostaglandin-synthetase converts arachidonic acid to prostaglandins E2 and F2alpha in comparable amounts, without apparent need for a cytoplasmic soluble cofactor or specific reducing agents.

Animals↗