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A L Loeb

Publications and source records attributed to A L Loeb.

30 records · Page 2Linked to original sources
PubMed1988

Potentiation of platelet aggregation by atrial natriuretic peptide.

Atrial natriuretic peptide (ANP) has binding sites on a variety of tissues, including human platelets. We have used a new, quenched-flow approach coupled to single-particle counting to investigate the effects of ANP (rat, 1-28) on the initial events (within the first several seconds) following human platelet activation. While ANP alone (1 pM-100 nM) had no effect, ANP significantly potentiated thrombin (0.4 units/ml)-, epinephrine (15 microM)- and ADP (2 or 10 microM)-induced aggregation. Maximum stimulation occurred between 10 to 100 pM. ANP had no influence on the thrombin or ADP-induced increase in platelet volume associated with the "shape change." Since ANP receptors are coupled to a particulate guanylate cyclase and some ANP-induced effects may be mediated through cyclic GMP, we studied how another activator of platelet guanylate cyclase, sodium nitroprusside, affected platelet activation and cyclic nucleotide levels. Sodium nitroprusside (1 microM) inhibited ADP, but not thrombin or epinephrine-induced aggregation. Both sodium nitroprusside (1 microM) and ANP (10 nM) increased cyclic GMP levels by 80% and 37%, respectively, within 60 sec in washed platelets. ANP had no effect on platelet cyclic AMP, while sodium nitroprusside induced a 77% increase. These data suggest that the platelet ANP receptor may be coupled to guanylate cyclase and the rise in cyclic GMP may potentiate platelet function.

Atrial Natriuretic Factor↗
PubMed1988

Use of cultured cells to study the relationship between arachidonic acid and endothelium-derived relaxing factor.

We have used mixed- and co-cultures of endothelial and vascular smooth muscle cells to investigate the role of phospholipase activation and arachidonic acid metabolites in the production of endothelium-derived relaxing factor (EDRF). Inhibition of phospholipase A2 with para-bromophenacyl bromide, dexamethasone or quinacrine, alone or in combination, blocked arachidonate release by 50%-60% but had no effect on EDRF production as assessed by cyclic GMP accumulation in mixed- or co-cultures of endothelial and vascular smooth muscle cells. Inhibition of the phospholipase C-diacylglycerol (DAG) lipase pathway of arachidonate release by the DAG lipase inhibitor RHC-80267 also caused partial inhibition of arachidonate release and had no effect on EDRF. When both phospholipase A2 and phospholipase C pathways for arachidonate mobilization were inhibited (dexamethasone + RHC 80267), arachidonate release was totally inhibited while EDRF release remained intact. We conclude that neither phospholipase activation nor arachidonate mobilization is required for EDRF release from cultured bovine endothelial cells.

Acetophenones↗
PubMed1988

Endothelium-dependent relaxation is independent of arachidonic acid release.

Endothelium-dependent relaxation is mediated by the release from vascular endothelium of an endothelium-derived relaxing factor (EDRF). It is not clear what role arachidonic acid has in this process. Inhibition of phospholipase A2, and diacylglycerol lipase in cultured bovine aortic endothelial cells caused a marked reduction in agonist-induced arachidonic acid release from membrane phospholipid pools, and complete inhibition of prostacyclin production. EDRF release, assayed by measuring endothelium-dependent cGMP changes in mixed endothelial-smooth muscle cell cultures, was not inhibited under these conditions. In fact, EDRF release in response to two agonists, melittin and ATP, was actually increased in cells treated with phospholipase A2 inhibitors. In addition, pretreatment of rats with high-dose dexamethasone, an inhibitor of PLA2, did not attenuate endothelium-dependent relaxation in intact aortic rings removed from the animals, or depressor responses in anesthetized animals induced by endothelium-dependent vasodilators. In summary, inhibition of arachidonic acid release from membrane phospholipid pools does not attenuate endothelium-dependent relaxation in rats, or the release and/or response to EDRF in cultured cells.

Adenosine Triphosphate↗
PubMed1987

Changes in vascular endothelium and its function in systemic arterial hypertension.

The various functions of arterial endothelium may be altered during pulmonary and arterial hypertension. Changes in the endothelium (or function) associated with hypertension are described. In both acute and chronic hypertension, permeability of the endothelium is enhanced. During the acute phase of hypertension, hyperplasia (cell replication) of the endothelium occurs while cell hypertrophy (enlarged cell size) and an increase in homocellular tight junctions are associated with sustained elevations of blood pressure. Endothelium may contribute to the increase in smooth muscle mass or cell number reported with various models of hypertension. Increased endothelial uptake or metabolism of norepinephrine and serotonin occurs during hypertension. The biotransformation of adenine nucleotides and various peptides by the endothelium is not altered by hypertension. Synthesis of prostacyclin is enhanced in the spontaneously hypertensive and Goldblatt hypertensive rat. Metabolism of prostaglandin E2, prostaglandin F2 alpha and prostacyclin by prostaglandin 15-hydroxydehydrogenase is impaired in the genetic models. Responses to endothelium-dependent vasodilators are impaired in acute and chronic models of hypertension. Production of relaxing factor by the endothelium is not inhibited, but rather the vascular smooth muscle fails to respond. Acute, severe hypertension potentiates the response to serotonin, presumably by attenuating the release or response to relaxing factor(s). In the aorta of the spontaneously hypertensive rat, the endothelium releases a constricting factor in response to acetylcholine. Pulmonary arterial endothelium (and other vessels) releases a vasoconstrictor that is blocked by inhibitors of cyclooxygenase. It is not clear whether this pressor factor is thromboxane A2. Cultured endothelial cells release a polypeptide that contracts arteries; however, any relation to hypertension is not known.

Acute Disease↗
PubMed1987

Role of calcium in endothelium-dependent relaxation of arterial smooth muscle.

Endothelium-dependent relaxation was studied in rings of rabbit thoracic aorta. Relaxation responses were induced with methacholine, the calcium ionophore A23187 and maitotoxin before and after removal of Ca++ from the external medium; in the presence of calcium-channel entry blockers (verapamil and nifedipine); or with trifluoperazine. Deletion of Ca++ greatly impaired responses to all 3 agonists while trifluoperazine only blocked cholinergic-induced relaxation. The calcium-channel blockers had effects that were concentration- and time-dependent, but their action included blockade of A23187. Cytosolic-free Ca++ concentrations were measured in cultured endothelial cells after incubation of the cells with 10 microM Fura-2/AM or 50 microM Quin 2/AM. Bradykinin (1 X 10(-10) to 1 X 10(-7) M) and melittin (0.5 to 5 micrograms/ml) caused dose-dependent increases in intracellular Ca++ with maximal responses at 3 X 10(-8) M and 3 micrograms/ml, respectively. Both agents were able to induce an increase in cytosolic-free Ca++ in the presence of EGTA (1.5 X 10(-3) M) or verapamil (1 X 10(-5) M). The plateau phase of the Ca++ transient appeared to be modified slightly by verapamil, while the peak responses and plateau were attenuated by '0' Ca++/EGTA. To assess a function of the endothelium, production of endothelium-derived relaxing factor (EDRF) was studied in cells grown on microcarrier beads superfused in a column, and the column effluent was bioassayed on aortic rings.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Endothelium-derived relaxing factor in cultured cells.

Many vasoactive agents stimulate release of an endothelium-derived relaxing factor (EDRF). EDRF stimulates cyclic guanosine 3',5'-monophosphate (cGMP) accumulation and relaxation of vascular smooth muscle in a manner similar to that produced by sodium nitroprusside. Endothelium and vascular smooth muscle were isolated from porcine, bovine, and rat thoracic aorta. The capacity of sodium nitroprusside to stimulate cGMP accumulation in cultured bovine, porcine, and rat vascular smooth muscle was found to increase with time in culture to a maximum of 12 to 14 days after plating. In addition, bovine and porcine vascular smooth muscle, but not rat vascular smooth muscle, lost the sodium nitroprusside-stimulated cGMP response after the fifth passage. Cultured endothelial cells did not respond to endothelium-dependent vasodilators or sodium nitroprusside with increased cGMP levels. Vascular smooth muscle cells responded only to sodium nitroprusside. Mixed cultures of porcine and bovine endothelium and vascular smooth muscle and bovine endothelium and rat vascular smooth muscle responded to endothelium-dependent vasodilators with increased cGMP levels. Short-term (4 hours) coculture experiments using bovine endothelium grown on microcarriers to assess the need for long-term contact between the two cell types produced similar results. Release of EDRF from bovine endothelium was studied by loading endothelium-covered microcarrier beads into a column superfused with physiological buffer. Treatment of the column with bradykinin, the calcium ionophore A23187, melittin, and arachidonate released EDRF from the column as measured by cGMP changes in denuded aortic rings and vascular smooth muscle cells and by relaxation of rings when bathed in column effluent. The time course of cGMP changes and relaxation were similar and could be reversed by hydroquinone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Antihypertensive drugs inhibit hypertension-associated aortic DNA synthesis in the rat.

The effect of antihypertensive drug treatment on aortic DNA synthesis was examined in rats with two-kidney, one clip renal hypertension and in spontaneously hypertensive rats (SHR). In two-kidney, one clip hypertensive rats, hypertension developed over a 2-week period. Four days after clipping the renal artery, during the onset of hypertension, there was an increase in aortic DNA synthesis. Aortic DNA synthesis was also increased 3 weeks later, when hypertension had been established. Captopril, hydralazine, and verapamil were each able to prevent the increase in aortic DNA synthesis and the rise in blood pressure when given throughout the first 5 days of the developing phase of hypertension, or when given to rats with established hypertension. Drug treatment of sham-operated rats had no significant effect on DNA synthesis, although blood pressure was decreased. There were no differences in blood pressure or aortic DNA synthesis in 4-week-old SHR, as compared with age-matched Wistar-Kyoto (WKY) controls or normal Wistar rats. At 17 weeks of age, when hypertension was established, aortic DNA synthesis was significantly enhanced in the SHR. Captopril or hydralazine treatment was able to reduce blood pressure and DNA synthesis to levels seen in the WKY. At 21 weeks of age, DNA synthesis in the SHR had declined to the same levels as in the WKY. Captopril, hydralazine, and verapamil may have a common ability to reduce intracellular calcium and therefore inhibit DNA synthesis. In support of this, ouabain treatment, which increases intracellular calcium by inhibiting the Na+-K+ pump, produced a significant increase in the rate of DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Increased aortic DNA synthesis precedes renal hypertension in rats. An obligatory step?

The rate of DNA synthesis was determined in rats with developing and established two-kidney, one clip renal hypertension. Rate of DNA synthesis was measured as [3H]thymidine incorporation into DNA per hour. After stenosis of the renal artery, blood pressure increased over a 2-week period. Five days after clipping, there was an increase in the rate of aortic DNA synthesis before an increase in blood pressure was detected, whereas there was no DNA effect in sham-operated animals. This difference in [3H]thymidine incorporation into aortic DNA could not be accounted for by alterations in thymidine pool sizes. The increase in DNA synthesis was still present 3 weeks after renal artery stenosis, although by that time blood pressure had plateaued. The role of DNA synthesis in the development of renal hypertension was investigated by determining whether inhibition of DNA synthesis with cytosine arabinoside could prevent the increase in blood pressure. Treatment of clipped rats with cytosine arabinoside for 5 days delayed the increase in blood pressure for more than 4 days, as compared with the effect of saline treatment in clipped rats. Although the possibility remains that some effect of cytosine arabinoside other than its effect on DNA synthesis could have influenced blood pressure, there were no differences in body weight, food intake, water intake, or urine output between cytosine arabinoside-treated and saline-treated rats with renal artery clips, and cytosine arabinoside treatment had no effect on blood pressure or body weight in normal rats. These results suggest that an increase in DNA synthesis may be an obligatory step in the genesis of renal hypertension.

Animals↗
PubMed1981

Antagonism of acrylamide neurotoxicity by supplementation with vitamin B6.

The effect of vitamin B6 supplementation on acrylamide induced neurotoxicity was examined in rats chronically dosed for 3 weeks. Using the inclined screen test, the onset of neurotoxicity developed on day 12 in all rats given 30 mg/kg acrylamide per day on day 16 in the rats supplemented with 5 mg/day of vitamin B6. On day 21 all animals given only acrylamide were severely affected compared to only 4 of 7 rats receiving acrylamide + vitamin B6. Another behavioral index, the foot spread test, did not detect any alteration in the development of acrylamide toxicity by vitamin B6. Weight loss was seen in both acrylamide treated groups and was not altered by vitamin B6 supplementation. The data show that vitamin B6 supplementation can delay the onset and reduce the severity of the neurotoxicity caused by chronic acrylamide administration to rats and suggest that acrylamide toxicity may be caused by an interaction of acrylamide with enzymes involved in supplying energy to the neuron. Vitamin B6 supplementation may be able to increase the amount of energy available to the neuron via alternate metabolic pathways.

Acrylamides↗
PubMedDate not supplied

Endothelium-derived vascular relaxing factor.

A large number and variety of compounds (acetylcholine, adenosine diphosphate, adenosine triphosphate, arachidonic acid, bradykinin, Ca2+ ionophores, calcitonin gene-related peptide, histamine, hydralazine, substance P, thrombin, and vasoactive intestinal polypeptide) have been shown to relax arterial smooth muscle indirectly. The endothelium in muscular arteries from several species appears to have receptors for these vasodilators. Binding of one of these compounds to its endothelial receptors results in the release (and presumably synthesis) of substance(s) that act on arterial smooth muscle to cause relaxation. The name endothelium-derived relaxing factor (EDRF) has been proposed for the substance or substances responsible for inhibition of contraction. Studies to determine additivity of endothelium-dependent relaxing agents and sensitivity of EDRF-mediated responses to a variety of inhibitors suggest that a single factor or a single common mechanism induces relaxation of vascular smooth muscle. Pharmacological studies have been equivocal with regard to the postulated involvement of phospholipases or arachidonic acid and to the suggestion that EDRF is an oxidative, non-cyclooxygenase product of arachidonate. Experiments on transfer of EDRF and reversal of endothelium-dependent relaxation consistently indicate that EDRF is quite labile. There is convincing evidence that EDRF activates smooth muscle guanylate cyclase, which results in an increase in intracellular cyclic guanosine 3',5'-monophosphate levels. The stimulation of guanylate cyclase by EDRF provides a valuable and sensitive parameter for studies with arteries as well as cells in culture. At present, the identity of EDRF and its role in cardiovascular homeostasis are unknown.

Animals↗
PubMedDate not supplied

Evidence for endothelium-derived relaxing factor in cultured cells.

Intracellular cyclic GMP concentration was used as a biochemical indicator of endothelium-dependent and organonitrate-induced responses to these vasodilators in cultured porcine aortic smooth muscle and endothelial cells. Sodium nitroprusside (10(-6) M) caused a rapid increase in cyclic GMP levels in confluent smooth muscle cell cultures but not in confluent endothelial monolayers. Adenosine triphosphate (10(-4) M) and methacholine (10(-5) M), two agents that elicit endothelium-dependent relaxation in intact vessels, failed to raise cyclic GMP concentrations in muscle or endothelial cultures alone. When the cell types were grown together in mixed culture, however, treatment with adenosine triphosphate or methacholine induced an elevation in intracellular cyclic GMP levels. These findings suggest that mixed cultures of arterial smooth muscle and endothelial cells can be used to study the phenomenon of endothelium-dependent responses in arterial smooth muscle.

Animals↗