Increased 1,2-diacylglycerol content in myopathic hamster hearts at a prenecrotic stage

Protective effects of carvedilol against doxorubicin-induced cardiomyopathy in rats

Carvedilol (CAR) is a vasodilating beta-blocker which also has antioxidant properties. CAR produces dose-related reduction in mortality in patients with congestive heart failure. In the present study, we tested the hypothesis that CAR protects against doxorubicin (DOX)-induced cardiomyopathy in rats. Sprague-Dawley rats were treated with DOX, CAR, CAR+DOX, or atenolol (ATN)+DOX. DOX (cumulative dose, 15 mg/kg) was administered intraperitoneally, and CAR (30 mg/kg daily) or ATN (150 mg/kg daily) was administered orally. Three weeks after the completion of these treatments, cardiac performance and myocardial lipid peroxidation were assessed. Mortality was observed in the DOX (25%) and ATN+DOX (12.5%) groups. Compared with control rats, DOX significantly decreased systolic blood pressure (104+/-4 vs. 120+/-4 mmHg, P<0.05) and left ventricular fractional shortening (38.8+/-3.1 vs. 55.4+/-1.3%, P<0.01), and resulted in a significant accumulation of ascites (14.4+/-4.9 vs. 0 ml, P<0.01). CAR significantly prevented the cardiomyopathic changes caused by DOX, while ATN did not. The myocardial thiobarbituric acid reactive substances (TBARS) content was significantly higher in DOX-treated rats than in control rats (80.4+/-7.1 vs. 51.5+/-1.2 nmol/g heart, p<0.01). CAR prevented the increase in TBARS content (48.8+/-3.0 nmol/g heart, P<0.01 vs. DOX group), whereas ATN had no significant effect (74.3+/-5.2 nmol/g heart). CAR also significantly prevented the increase in both myocardial and plasma cholesterol concentrations caused by DOX. These data indicate that CAR protects against DOX-induced cardiomyopathy and that this effect may be attributed to the antioxidant and lipid-lowering properties of CAR, not to its beta-blocking property.

Linoleic acid metabolism in primary cultures of adult rat cardiomyocytes is impaired by aging

Many of the changes that occur in the rat cardiac muscle with advancing age are related to modifications in membrane fatty acid composition, polyunsaturated fatty acids decreasing and saturated increasing as the animal develops. In the present study, using cultured adult cardiomyocytes isolated from the hearts of rats of a broad (1-24 months) age range, we demonstrated that the modifications in the fatty acid pattern of cardiomyocytes have to be related to alterations in the mechanism of desaturation/elongation of essential fatty acids. In fact, independent of the age of the animal, heart cells in culture were capable of rapidly metabolizing radiolabeled linoleic acid taken up from the surrounding medium, but to a different extent. The ability of heart cells to metabolize linoleic acid to higher and more unsaturated metabolites decreased with the animal's age. As the age of the animal increased, the pattern of fatty acids of the cultured cardiomyocytes showed a gradual but significant shift, similar to those reported in the whole heart. Data here reported confirm that the basic aging-related process in the cellular model system may also be relevant to aging in the whole animal.

Enalapril reduces the enhanced 1,2-diacylglycerol content and RNA synthesis in spontaneously hypertensive rat hearts before established hypertension

There is evidence that cardiac hypertrophy in spontaneously hypertensive rats (SHR) occurs before the development of hypertension. 1,2-Diacylglycerol, which is thought to be a second messenger activating protein kinase C, is also produced in excess in SHR hearts at 4 weeks of age, before established hypertension. We determined myocardial 1,2-diacylglycerol content in SHR with and without prazosin and enalapril from 3 to 4 weeks of age. Hearts from untreated SHR had greater RNA and DNA synthesis and greater relative weights at 4 weeks of age than those from Wistar-Kyoto (WKY) rats. There was no difference in triglyceride content or phospholipid species between WKY rats and untreated SHR, except for a higher cholesterol content in SHR. Treatment of SHR with enalapril, but not prazosin, lowered not only 1,2-diacylglycerol content but also RNA synthesis to the levels of WKY rats. Moreover, fatty acids involved in 1,2-diacylglycerol were altered by enalapril despite the lack of a difference between WKY rats and untreated SHR. Prazosin did not have any effect on 1,2-diacylglycerol fatty acid composition. Enalapril may decrease cardiac hypertrophy in SHR by lowering myocardial 1,2-diacylglycerol production.

Vasopressin stimulates phospholipase D activity against phosphatidylcholine in vascular smooth muscle cells

It is now clear that various hormones and agonists can stimulate the production of lipid mediators from non-phosphoinositide phospholipids. We have investigated the production of diacylglycerol from nonphosphoinositide sources, and we demonstrated that vasopressin and other vasoactive agents stimulate hydrolysis of phosphatidylcholine in a variety of cultured vascular smooth muscle cells of rat and human origin. We used vasopressin to characterize this response and found that vasopressin stimulates phospholipase D activity against phosphatidylcholine in A-10 vascular smooth muscle cells. The vasopressin-stimulated phosphatidylcholine hydrolysis is both time- and concentration-dependent. The half-maximal dose of vasopressin required for phosphatidylcholine hydrolysis (ED50 approximately 1 nM) correlates well with vasopressin binding to A-10 cells (Kd approximately 2 nM). The phosphatidylcholine in A-10 cells can be preferentially radiolabeled with [3H]myristic acid; subsequent treatment with vasopressin stimulates a rapid increase in 3H-labeled phosphatidate (approximately 4 X control values at 3 min), and after a short lag, 3H-labeled diacylglycerol rises and reaches maximal levels at 10 min (approximately 2 X control values). Similar temporal elevations of phosphatidate and diacylglycerol occur in A-10 cells labeled with [3H] glycerol. In A-10 cells radiolabeled with [3H] choline, the elevation of cellular phosphatidate and diacylglycerol is concomitant with the release of [3H] choline metabolites (predominantly choline) to the culture medium. The temporal production of phosphatidate and diacylglycerol as well as the release of choline to the culture medium are consistent with vasopressin activating phospholipase D. In addition, vasopressin stimulates a transphosphatidylation reaction that is characteristic of phospholipase D. The transphosphatidylation reaction is detected by the production of phosphatidylethanol that occurs when A-10 cells are incubated with ethanol and stimulated with vasopressin. The phospholipase D is active in the absence of extracellular Ca++ whereas the vasopressin-stimulated mobilization of arachidonic acid is dependent on extracellular Ca++. The data indicate that vasopressin stimulates phospholipase D which hydrolyzes phosphatidylcholine to phosphatidate. The phosphatidate is then metabolized, presumably by a phosphatidate phosphohydrolase, to produce sustained levels of cellular diacylglycerol. These sustained levels of diacylglycerol may activate protein kinase C and thereby function in the "sustained phase" of cellular responses.

1,2-diacylglycerol content in myocardium from spontaneously hypertensive rats during the development of hypertension

1,2-Diacylglycerol (DAG) has been considered to play an important role as an activator of protein kinase C in the signal transduction of inositol phospholipid metabolism. To examine the relation of 1,2-DAG in heart tissues to cardiac hypertrophy associated with hypertension, we measured the amount of 1,2-DAG in spontaneously hypertensive rat (SHR) hearts at 4, 10 and 20 weeks of age, and in age-matched normotensive Wistar-Kyoto (WKY) rat hearts using thin-layer chromatography with flame ionization detection (TLC-FID). Significant cardiac hypertrophy was found in 4-week-old SHR, while SHR did not yet have significant hypertension. Major phospholipids such as phosphatidylcholine and phosphatidylethanolamine increased from 4 to 20 weeks in the myocardium, but there was no difference between the two strains. The cholesterol levels of 4- and 20-week-old SHR were significantly higher than WKY rats. The 1,2-DAG contents of SHR hearts were significantly higher than WKY rats at 4 weeks. An increase in the RNA content was also observed in 4-week-old SHR hearts. However, analysis of the fatty acid composition of 1,2-DAG revealed no difference between the two strains. However, there was no significant difference in the 1,2-DAG content or in its fatty acid composition between SHR and WKY rat hearts at 10 and 20 weeks of age. It is suggested that an increase in the 1,2-DAG content of SHR hearts during the early stages appears related to the initiation of cardiac hypertrophy in SHR hearts before developed hypertension.

1,2-diacylglycerol content in thoracic aorta of spontaneously hypertensive rats

Phosphoinositide metabolism participates in the control of cell calcium homeostasis. Because a notable neutral lipid (1,2-diacylglycerol) is generated from phosphoinositide hydrolysis and is assumed to be a secondary messenger, we determined 1,2-diacylglycerol content and its fatty acid profiles in the thoracic aorta of spontaneously hypertensive rats (SHR) and compared it with those of normotensive Wistar-Kyoto (WKY) rats. After the aorta was exposed to 10(-5) M norepinephrine as a stimulant, 1,2-diacylglycerol content in SHR was significantly higher by 33% than in WKY rats at 4 weeks of age, whereas there was no difference in 1,2-diacylglycerol content between the two strains at 20 weeks of age. Before norepinephrine stimulation, there was no significant difference in 1,2-diacylglycerol level between the two strains at 4 weeks of age. Analysis on a gas chromatograph showed that 1,2-diacylglycerol was composed of similar molecular species of fatty acids in aortas obtained from SHR and WKY rats. On the other hand, the cholesterol content of aortas was higher in SHR than in WKY rats at 20 weeks of age, whereas the difference at 4 weeks was not significant. Phosphatidylcholine, phosphatidylethanolamine, and triglyceride showed no significant difference between the two strains. It is concluded that norepinephrine-induced 1,2-diacylglycerol production increases in the thoracic aorta of SHR before the development of hypertension.

Alteration in 1,2-diacylglycerol level and its fatty acid composition in hearts during the growth of hamsters

We measured the amount of 1,2-diacylglycerol (DAG) and its fatty acid composition in hamster hearts of various ages because 1,2-DAG has been recognized to be one of the intracellular second messengers. The highest level in 1,2-DAG was detected in 30-day-old hamster hearts. The heart weight increased about 2.5 times between 30 and 90 days of age. Hamster hearts at 90 days of age had 72% of the 1,2-DAG content at 30 days of age. The amount of 1,2-DAG at 240 days of age was a little lower than that in 90-day-old and 160-day-old hamsters, whereas there was no significant increase in heart weight and only a little gain in body weight between 90 and 240 days of age. The analysis of the fatty acid composition of 1,2-DAG showed an increase in the percentage of 18:0 accompanied by a change in the percentages of other fatty acids with the growth of hamsters. The largest amount of arachidonic acid expressed as 20:4 (n-6) was found at 30 days of age. On the other hand, triglyceride, cholesterol, and major phospholipid components of hamster hearts increased in accordance with growth. In particular, the increase in triglyceride content was remarkable, indicating that myocardial lipidosis may be induced by aging. These results demonstrate that 1,2-DAG may be involved in the synthesis of protein during heart growth and that the alteration of its fatty acid composition is related to the growth of hamsters.