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L Axelrod

Publications and source records attributed to L Axelrod.

At least 19 recordsLinked to original sources
PubMed1992

Coordinate control of lipolysis by prostaglandin E2 and prostacyclin in rat adipose tissue.

PGE2 is a potent antilipolytic agent produced by adipose tissue, but its role as a physiological regulator of triglyceride lipolysis is controversial because inhibitors of prostaglandin synthesis have not enhanced hormone-stimulated lipolysis in adipose tissue consistently. Adipose tissue also produces PGI2, but this eicosanoid has not had a demonstrated effect on lipolysis under physiological conditions previously. We investigated both PGE2 and PGI2 production and their effects on lipolysis in rat adipose tissue. We found that 1) EPI-stimulated PGE2 production (like PGI2 production) requires the cooperation of adipocytes and endothelial cells, 2) adipose tissue produces PGE2 and PGI2 at comparable rates, 3) indomethacin inhibits EPI-induced PGE2 and PGI2 production and has no effect on EPI-stimulated lipolysis when added to a mixture of adipocytes and endothelial cells or to intact epididymal fat pads, 4) PGI2 is a potent lipolytic agent when added to isolated adipocytes in the absence of endothelial cells under physiological conditions, 5) the magnitudes and the ED50s of the antilipolytic effect of PGE2 and the lipolytic effect of PGI2 in isolated adipocytes in the absence of endothelial cells are comparable, 6) PGI2 antagonizes the antilipolytic effect of PGE2 in isolated adipocytes in the absence of endothelial cells in a dosage-related manner, and 7) the antilipolytic effect of added PGE2 in isolated adipocytes is greater in the absence of endothelial cells than in their presence, suggesting that endogenous eicosanoid production reduces the effectiveness of added PGE2. These studies demonstrate that catecholamine-induced lipolysis is under the coordinate control of PGE2, a potent antilipolytic agent, and PGI2, a potent lipolytic agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1991

Insulin, prostaglandins, and the pathogenesis of hypertension.

Hypertension is associated with hyperinsulinemia in the presence or absence of obesity or glucose intolerance. Physiological concentrations of insulin decrease the catecholamine-induced production of prostaglandin I2 (PGI2; prostacyclin) and PGE2, two potent vasodilators, in adipose tissue, one of the largest organs in the body. This finding suggests that hyperinsulinemia increases peripheral vascular resistance and blood pressure by inhibiting the stimulatory effect of adrenergic agonists (and perhaps other agonists) on the production of PGI2 and PGE2 in adipose tissue (and perhaps other tissues). This concept is supported by evidence that PGI2 and PGE2 modulate vascular reactivity in states of health and disease. For example, during insulin deficiency, i.e., in diabetic ketoacidosis, PGI2 and PGE2 production by adipose tissue are increased, and peripheral vascular resistance and blood pressure are decreased. This hypothesis is also supported by evidence that blood flow through rat and human adipose tissue is decreased in obesity and that insulin decreases the blood flow through adipose tissue in nonobese rats. Thus, insulin may regulate PGI2 and PGE2 production by adipose tissue (and possibly other tissues) through a wide range of concentrations with important physiological and clinical consequences.

Adipose Tissue↗
PubMed1989

Increased insulin-like growth factor II production and consequent suppression of growth hormone secretion: a dual mechanism for tumor-induced hypoglycemia.

We investigated the pathophysiology of fasting hypoglycemia associated with large tumors of mesenchymal origin. We studied two patients with symptomatic fasting hypoglycemia (plasma glucose, 1.92 and 2.03 mmol/L) and a large mesenchymal neoplasm. Before therapy, the plasma insulin-like growth factor II (IGF-II) level measured by RIA was elevated (1879 and 1084 micrograms/L; normal range, 358-854 micrograms/L), the serum GH response to hypoglycemia was impaired, and the plasma IGF-I level was low in both patients. After treatment of the tumor, all of these abnormalities resolved in both patients. Northern blot analysis of tumor RNA revealed extremely high levels of IGF-II mRNA (greater than 100-fold higher than those in normal adult liver). Tumor fragments released IGF-II into tissue culture medium (2.1 and 7.2 micrograms IGF-II/g tissue.24 h). These findings indicate that secretion of IGF-II into the circulation by the tumor was the likely source of the elevated plasma IGF-II levels. We suggest that the primary event in tumor-induced hypoglycemia is overproduction of IGF-II by the tumor, which gives rise to hypoglycemia by a dual mechanism: increased glucose utilization mediated by the insulin-like actions of IGF-II and inhibition of GH secretion.

Aged↗
PubMed1989

Prostacyclin and pathogenesis of hemodynamic abnormalities of diabetic ketoacidosis in rats.

The pathogenesis of the hemodynamic abnormalities of diabetic ketoacidosis (DKA) is not well understood. Previous studies suggest that prostacyclin (PGI2) production by adipose tissue is increased in DKA. We investigated the role of PGI2 in the pathogenesis of the reduced vascular resistance in DKA. Rats with streptozocin-induced DKA were anesthetized with pentobarbital sodium, and flow was measured with an electromagnetic probe on the infradiaphragmatic aorta. The plasma level of 6-keto-PGF1 alpha (stable derivative of PGI2) was higher (mean +/- SE 0.91 +/- 0.05 ng/ml) and vascular resistance lower (4.9 +/- 0.2 mmHg.ml-1.min-1.100 g-1 [resistance units, RU]) in 67 rats with DKA than in 21 normal rats (0.34 +/- 0.03 ng/ml, P less than .01, and 9.0 +/- 0.7 RU, P less than .01, respectively). Inhibition of cyclooxygenase activity with either indomethacin or meclofenamic acid reduced the plasma 6-keto-PGF1 alpha level but failed to raise vascular resistance. Infusions of PGI2 in rats with DKA demonstrated that the vasculature was responsive to PGI2. Inhibition of cyclooxygenase activity not only reduced PGI2 production but also suppressed renin release. When the effects of the renin-angiotensin system were excluded by bilateral nephrectomy, indomethacin caused a significant increase (P less than .05) in vascular resistance. Thus, the failure of cyclooxygenase inhibitors to raise vascular resistance in DKA was a result of concurrent suppression of vasodilator (PGI2) and vasoconstrictor (renin-angiotensin system) mechanisms that are activated in DKA. Insulin administration increased vascular resistance (P less than .01) and decreased the level of plasma 6-keto-PGF1 alpha (P less than .01). Combined administration of PGI2 and insulin did not alter vascular resistance, suggesting that the increase in vascular resistance with insulin was predominantly due to the reduction of circulating PGI2. Thus, vascular resistance is decreased in DKA primarily as a result of the vasodilator effects of PGI2 produced by adipose tissue. The activation of the renin-angiotensin system represents a partial compensation. The increase in PGI2 production may contribute to the hypotension and mortality of DKA.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

Cooperation of adipocytes and endothelial cells required for catecholamine stimulation of PGI2 production by rat adipose tissue.

Disturbances of prostaglandin I2 (PGI2, prostacyclin) production by adipose tissue contribute to the pathogenesis of diabetic ketoacidosis and may contribute to the pathogenesis of hypertension and vascular disease. We studied the cellular basis of PGI2 production in adipose tissue, measured as release of 6-keto-PGF1 alpha in response to epinephrine. Adipocytes did not produce PGI2 when nonfat cells were removed by repeated washing. The nonadipocyte cellular constituents of adipose tissue (nonfat cells) did not produce PGI2 in the absence of adipocytes. Both adipocytes and nonfat cells were required for PGI2 production in response to epinephrine. Adipocytes pretreated with 0.2 mM aspirin to inhibit PGH synthase nevertheless promoted PGI2 production when mixed with nonfat cells. Nonfat cells preincubated with aspirin did not produce PGI2 when mixed with adipocytes. The nonfat cells converted arachidonic acid to PGI2 but adipocytes did not. Epinephrine stimulated lipolysis and PGI2 production in a dose-dependent parallel manner, but the responses were distinct above 10(-6) M. Characterization of the nonfat cells by fractionation on a Percoll density gradient followed by measurement of angiotensin-converting enzyme activity and 6-keto-PGF1 alpha production indicated that the nonfat cells were predominantly vascular endothelial cells. We conclude that catecholamine-stimulated PGI2 production in adipose tissue results from the cooperation of adipocytes and vascular endothelial cells. The adipocytes provide arachidonic acid, which is converted to PGI2 by the vascular endothelial cells. Because adipose tissue is located near blood vessels throughout the body, adipocytes may be an important source of arachidonic acid for vascular endothelial cells in various circumstances in health and disease. Our findings raise the possibility that adipocytes may, under some circumstances, release arachidonic acid into the systemic circulation where it is used by vascular endothelial cells throughout the body to produce PGI2 and other eicosanoids.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

Omega-3 fatty acids in diabetes mellitus. Gift from the sea?

The potential role of omega-3 fatty acids in the prevention of atherosclerotic disease in the nondiabetic population currently engenders interest, enthusiasm, and controversy. Some apparently beneficial effects of omega-3 fatty acids on platelet function, eicosanoid formation, plasma triglyceride levels, and blood pressure have been described in patients with diabetes mellitus. However, enthusiasm for the use of omega-3 fatty acids in diabetes has been dampened by reports of potentially deleterious effects of these agents, including increased plasma glucose, glycosylated hemoglobin, plasma total cholesterol and LDL cholesterol, and serum apolipoprotein B levels. These adverse effects have been achieved with large, perhaps excessive, doses of omega-3 fatty acids, in the range of 4-10 g/day. The magnitude of these adverse effects has been small (typically 10-36%). It cannot be assumed that the effects of omega-3 fatty acids are the same in patients with diabetes mellitus as in nondiabetic subjects or patients with primary hyperlipidemia. First, the biosynthesis and composition of fatty acids is abnormal in diabetic animals and possibly in diabetic patients. Second, many potential mechanisms implicated in the pathogenesis of atherosclerosis are present in diabetic but not necessarily in nondiabetic subjects. Third, the mechanisms of many of the risk factors in diabetic patients differ from the mechanisms of these abnormalities in nondiabetic subjects, reflecting the effects of insulin deficiency, hyperglycemia, and their sequelae. Finally, because diabetes is a heterogeneous group of diseases, the effects of omega-3 fatty acids must be addressed separately for patients with insulin-dependent diabetes mellitus, non-insulin-dependent diabetes mellitus, and possibly other forms of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriosclerosis↗
PubMed1986

Prostacyclin production by isolated rat adipocytes: evidence for cyclic adenosine 3',5'-monophosphate-dependent and independent mechanisms and for a selective effect of insulin.

The rat adipocyte contains two separate mechanisms for prostaglandin (PG) production. Norepinephrine stimulates prostacyclin (PGI2) and PGE2 production and triglyceride lipolysis in isolated rat adipocytes. In contrast, the vasoactive peptides angiotensin II, vasopressin, and bradykinin stimulate PGI2 production, but not PGE2 production or triglyceride lipolysis, in these cells. In this study, we characterized the two separate mechanisms of PG production with respect to the time course, the role of cAMP, the identity of the adrenergic receptor, and the effects of insulin and glucocorticoids. Angiotensin II stimulated PGI2 production rapidly (at 5 min) and independently of cAMP. beta-Adrenergic stimulation with isoproterenol produced a rapid 11-fold increase in the cAMP concentration and stimulated PGI2 production more slowly (at 120 min). The phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine (0.2 and 0.5 mM) and the adenylate cyclase activator forskolin (10 microM) also stimulated cAMP production rapidly and PGI2 production more slowly. 1-Methyl-3-isobutylxanthine (5.0 mM) further stimulated cAMP levels, but prevented the increase in PGI2 production and blunted the increase in glycerol release seen at lower concentrations. beta-Adrenergic blockade with propranolol or timolol completely inhibited the norepinephrine- or isoproterenol-stimulated production of PGI2 and triglyceride lipolysis, respectively. Insulin selectively inhibited isoproterenol-stimulated PGI2 production and triglyceride lipolysis at physiological concentrations, but had no effect on angiotensin II-stimulated PGI2 production. In contrast, dexamethasone inhibited PGI2 production induced by both isoproterenol and angiotensin II. We conclude that: angiotensin II stimulates PGI2 production rapidly and independently of cAMP, but isoproterenol stimulates PGI2 production more slowly, an effect that is cAMP dependent; insulin inhibits the cAMP-dependent beta-adrenergic stimulation of PGI2 production (and triglyceride lipolysis), but not the cAMP-independent angiotensin II-induced stimulation of PGI2 production (this suggests that the former effect is mediated by a decrease in cAMP levels in the adipocyte); and dexamethasone inhibits both mechanisms of PGI2 production. Both mechanisms of PGI2 production by rat adipocytes are exquisitely sensitive to hormonal regulation.

1-Methyl-3-isobutylxanthine↗
PubMed1977

The treatment of the hepatorenal syndrome with intra-renal administration of prostaglandin E1.

Three patients with the hepatorenal syndrome were treated with prostaglandin E1 administered through a selective renal arterial catheter. Prostaglandin E1 was given in progressively increasing doses (2 to 100 ng/kg/min) over a 60-minute period. Control plasma prostaglandin E levels were elevated in all three patients, 0.98, 0.91, and 0.83 ng/ml, respectively. At the end of the infusion, plasma prostaglandin E levels had risen to 10.4, 2.63, and 10.3 ng/ml in the three patients respectively. Plasma renin activity increased during the course of the infusion in two of the patients. The plasma aldosterone concentration did not change during the prostaglandin E1 infusion. Intrarenal prostaglandin E1 failed to increase urine volume or urinary sodium concentration in three patients with the hepatorenal syndrome.

Adult↗