Decreased prostatic arachidonic acid in human prostatic carcinoma.

OBJECTIVE: To measure prostatic and blood fatty acid composition in a large group of patients undergoing prostatectomy for benign or malignant prostate disease, as there is evidence linking arachidonic acid metabolism and prostate cancer through its role as an eicosanoid precursor, and earlier studies showed lower prostatic arachidonic acid content in a few patients. PATIENTS AND METHODS: Prostatic phospholipid fatty acid composition was determined in prostate tissue from 173 patients undergoing prostate surgery, i.e. radical prostatectomy, cystoprostatectomy or transurethral resection (TURP). Blood fatty acid composition was determined in 99 of these patients and in 85 undergoing prostatic needle biopsy. RESULTS: There was a significantly lower percentage of arachidonic acid in malignant than in benign portions of the prostate (15.2% vs 17%) in all patients assessed. The changes were greatest in those undergoing TURP for known prostate cancer (13.4% vs 17.2%), these patients having the greatest proportion of malignancy in the specimens. There were no consistent changes in blood fatty acid composition. CONCLUSION: This is the first prospective study of arachidonic acids levels involving many consecutive patients undergoing prostate surgery for either benign or malignant disease. The lower prostatic arachidonic acid level is probably a result of the increased use of arachidonic acid for producing prostaglandins and/or leukotrienes. Further understanding of the cause and/or consequence of this finding might lead to a better understanding of prostate cancer.

Increased prostatic lysophosphatidylcholine acyltransferase activity in human prostate cancer: a marker for malignancy.

PURPOSE: Phospholipase A2 and lysophosphatidylcholine acyltransferase (LAT) constitute a deacylation-reacylation cycle that incorporates arachidonic acid into the lipid membrane. In a preliminary report we found increased LAT activity in malignant prostate tissue. We measured LAT activity in prostate tissue from a large number of patients undergoing prostatectomy. MATERIALS AND METHODS: Prostate tissue from 93 patients undergoing radical prostatectomy for prostate carcinoma, 14 undergoing cystoprostatectomy for bladder cancer, 55 undergoing transurethral resection for benign prostatic hyperplasia and 11 with prostate cancer undergoing transurethral resection for relief of obstructive symptoms was analyzed for LAT activity. RESULTS: In radical prostatectomy specimens using oleoyl coenzyme A as substrate mean increase in LAT activity between malignant and benign portions of the same specimen was 0.68 +/- 0.12 nmol./mg. protein per minute (p <0.00001). In all radical prostatectomy specimens analyzed LAT activity was 43% higher in the malignant than benign portions (2.25 +/- 0.15 versus 1.57 +/- 0.11 nmol./mg. protein per minute, p <0.001). In the 10 benign prostate specimens obtained from cystoprostatectomy mean LAT activity was 1.12 +/- 0.18 nmol./mg. protein per minute, which was significantly lower than that of benign portions of radical prostatectomy (p <0.05). LAT activity in benign cystoprostatectomy specimens was significantly higher than that in the 50 benign transurethral resection specimens (0.54 +/- 0.05, p <0.01), possibly due to heat damage in transurethral resection specimens during collection. However, LAT activity in transurethral resection specimens from patients with known prostate cancer was similarly increased. Similar results were obtained using arachidonoyl coenzyme A. CONCLUSIONS: We demonstrated increased LAT activity in malignant tissue from patients with prostate cancer. Thus, the deacylation-acylation remodeling cycle may be enhanced to provide more arachidonic acid to meet the demand for prostaglandin E2 synthesis in malignant tissue.

Gemfibrozil for the secondary prevention of coronary heart disease in men with low levels of high-density lipoprotein cholesterol. Veterans Affairs High-Density Lipoprotein Cholesterol Intervention Trial Study Group.

BACKGROUND: Although it is generally accepted that lowering elevated serum levels of low-density lipoprotein (LDL) cholesterol in patients with coronary heart disease is beneficial, there are few data to guide decisions about therapy for patients whose primary lipid abnormality is a low level of high-density lipoprotein (HDL) cholesterol. METHODS: We conducted a double-blind trial comparing gemfibrozil (1200 mg per day) with placebo in 2531 men with coronary heart disease, an HDL cholesterol level of 40 mg per deciliter (1.0 mmol per liter) or less, and an LDL cholesterol level of 140 mg per deciliter (3.6 mmol per liter) or less. The primary study outcome was nonfatal myocardial infarction or death from coronary causes. RESULTS: The median follow-up was 5.1 years. At one year, the mean HDL cholesterol level was 6 percent higher, the mean triglyceride level was 31 percent lower, and the mean total cholesterol level was 4 percent lower in the gemfibrozil group than in the placebo group. LDL cholesterol levels did not differ significantly between the groups. A primary event occurred in 275 of the 1267 patients assigned to placebo (21.7 percent) and in 219 of the 1264 patients assigned to gemfibrozil (17.3 percent). The overall reduction in the risk of an event was 4.4 percentage points, and the reduction in relative risk was 22 percent (95 percent confidence interval, 7 to 35 percent; P=0.006). We observed a 24 percent reduction in the combined outcome of death from coronary heart disease, nonfatal myocardial infarction, and stroke (P< 0.001). There were no significant differences in the rates of coronary revascularization, hospitalization for unstable angina, death from any cause, and cancer. CONCLUSIONS: Gemfibrozil therapy resulted in a significant reduction in the risk of major cardiovascular events in patients with coronary disease whose primary lipid abnormality was a low HDL cholesterol level. The findings suggest that the rate of coronary events is reduced by raising HDL cholesterol levels and lowering levels of triglycerides without lowering LDL cholesterol levels.

Phenotype differences of resistance to thyroid hormone in two unrelated families with an identical mutation in the thyroid hormone receptor beta gene (R320C).

A new family with resistance to thyroid hormone (RTH) harboring a mutation in the thyroid hormone receptor (TR) beta gene (R320C) is reported. The phenotype of affected members is compared to that of affected members of an unrelated family with an identical mutation in the TR beta gene that occurred independently. In one of the two families higher concentrations of free T4 were required to maintain a normal TSH level in affected subjects and unaffected first degree relatives but not in relatives by marriage. While this finding suggests that genetic background modulated the relative insensitivity to thyroid hormone caused by the mutant TR beta, it is uncertain whether the higher thyroid hormone levels prevented the occurrence of hyperactivity and attention deficit.

Increased phospholipid fatty acid remodeling in human and rat prostatic adenocarcinoma tissues.

PURPOSE: To study the mechanism of diminished arachidonic acid levels in malignant prostatic tissues. MATERIALS AND METHODS: Benign and malignant prostate tissues were obtained from human radical prostatectomy specimens and from rats using Pollard's Lobund/Wistar rat prostate cancer model. Fatty acid composition and a variety of enzyme activities involved in maintaining phospholipid fatty acid composition were compared in malignant and benign prostatic tissues. RESULTS: Decreased arachidonic acid levels, previously reported in human prostate cancer, were present in malignant rat as well as in human tissues. There were 21% and 26% decreases of arachidonic acid levels in the rat and human malignant tissues compared with benign tissues. Fatty acid desaturase activity was undetectable. Fatty acyl-CoA hydrolase and synthetase activities were not altered in the malignant tissues. However, there was a 2-fold increase in phospholipase A2 activity and a 4- to 12-fold increase in fatty acyl-CoA lysophosphatidylcholine acyltransferase activity in malignant rat and human prostatic tissues. CONCLUSIONS: These data indicate that, in malignant prostate tissues, the fatty acid remodeling mechanism is activated through the deacylation-reacylation cycle. This process may be a result of increased use of arachidonic acid for the formation of prostaglandins that may be crucial for the further development and growth of the malignant tissues.

Distribution of lipids in 8,500 men with coronary artery disease. Department of Veterans Affairs HDL Intervention Trial Study Group.

In the present study we measured fasting lipid profiles in over 8,500 community-living men with coronary artery disease (CAD) to determine the distribution of lipid abnormalities in this population: 81% were white and 16% black; mean age 62.9 +/- 8 years; mean total cholesterol 214 +/- 41 mg/dl; low-density lipoprotein (LDL) cholesterol 140 +/- 37 mg/dl; high-density lipoprotein (HDL) cholesterol 39 +/- 11 mg/dl; and triglycerides 190 +/- 142 mg/dl. After adjusting for age, the only significant difference between blacks and whites was a higher HDL cholesterol in blacks (45 vs 38 mg/dl, p < 0.003). With use of cut points established by the National Cholesterol Education Program, 87% of subjects had high LDL cholesterol (> or = 100 mg/dl), 38% had low HDL cholesterol (< 35 mg/dl), and 33% had high triglycerides (> 200 mg/dl). We estimated that 42% of men with CAD would be definite candidates for cholesterol-lowering medication according to the National Cholesterol Education Program guidelines and that 41% of those in whom cholesterol-lowering medication would not be definitely indicated had low levels of HDL cholesterol. We conclude that (1) black men with CAD have substantially higher HDL cholesterol than white men, (2) almost 90% of male patients with CAD are candidates for dietary intervention and > 40% may need medications to lower LDL cholesterol, and (3) 40% of patients without a definite indication for cholesterol-lowering medications have low levels of HDL cholesterol.

Platelet phosphoinositide turnover in streptozotocin-induced diabetes.

Increased platelet aggregation and secretion in response to various agonists has been described in both diabetic humans and animals. Alterations in the platelet membrane fatty acid composition of phospholipids and changes in the prostacyclin and thromboxane formation could only partly explain the altered platelet function in diabetes. In the present study, we have examined the role of phosphoinositide turnover in the diabetic platelet function. We report alterations in 2-[3H] myo-inositol uptake, phosphoinositide turnover, inositol phosphate and diacylglycerol (DAG) formation, phosphoinositide mass, and phospholipase C activity in platelets obtained from streptozotocin (STZ)-induced diabetic rats. There was a significant increase in the 2-[3H] myo-inositol uptake in washed platelets from diabetic rats. Basal incorporation of 2-[3H] myo-inositol into phosphatidylinositol 4,5-bisphosphate (PIP2), phosphatidylinositol 4-phosphate (PIP) or phosphatidylinositol (PI) in platelets obtained from diabetic rats was, however, not affected. Thrombin stimulation of platelets from diabetic rats induced an increase in the hydrolysis of [32P]PIP2 but indicated no change in the hydrolysis of [32P]PIP and [32P]PI as compared to their basal levels. Thrombin-induced formation of [3H]inositol phosphates was significantly increased in both diabetic as well as in control platelets as compared to their basal levels. This formation of [3H]inositol phosphates in diabetic platelets was greater than controls at all time intervals studied. Similarly, there was an increase in the release of DAG after thrombin stimulation in the diabetic platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Modifications of platelet phospholipid fatty acid composition in streptozocin-induced diabetic rats.

Increased thromboxane A2 (TXA2) generation by platelets has been reported both in diabetic patients and streptozocin-induced diabetic rats. This increase is in contrast to the decreased prostacyclin (PGI2) synthesis by endothelial cells in diabetes. An imbalance in the ratio of TXA2/PGI2 has been implicated in increased platelet aggregation and a high incidence of vascular disease in human diabetes. The mechanism for this imbalance, however, remains elusive. In a previous study from our laboratory, we reported unchanged arachidonic acid levels in platelet membrane phospholipids of 3-week diabetic rats, but a decreased arachidonic acid level in platelet membrane phospholipids of 6-week diabetic rats. In the present communication, we report the role of enzymes that are involved in remodeling arachidonic acid levels of platelet membrane phospholipids in both 3- and 6-week diabetic rats. No alterations were observed in the activities of arachidonoyl-CoA synthetase, acyl-CoA: lysophosphatidylcholine acyltransferase, or phospholipase A2 in platelets from both 3- and 6-week diabetic rats. However, both increased uptake and incorporation of [14C]arachidonic acid into platelets were observed in the diabetic platelet-rich plasma. In conclusion, increased TXA2 formation in diabetic platelets is not due to alterations in the activities of enzymes involved in the incorporation into or release of arachidonate from the diabetic platelet membrane phospholipid, but may be due to increased efficiency of uptake, incorporation or possibly redistribution of this fatty acid among phospholipid classes in diabetic platelets.

Decreased incorporation of long-chain fatty acids into erythrocyte phospholipids of STZ-D rats.

We studied the mechanisms for the altered fatty acid composition in erythrocytes (RBCs) derived from streptozocin-induced diabetic (STZ-D) rats. After 3-wk duration of diabetes, blood glucose, plasma triglyceride, and plasma free-fatty acid levels were all significantly increased. In the diabetic platelet-poor plasma (PPP), the most significant increases in free fatty acids were stearate, linoleate, eicosatrienoate (n-6), and docosahexaenoate (n-3). Fatty acid composition of RBC phospholipids was also altered, with significant decreases in arachidonate, docosatetraenoate (n-6), and docosapentaenoate (n-6) and increases in linoleate and docosahexaenoate. Insulin treatment of the diabetic rats resulted in normalization of docosapentaenoate, arachidonate, and linoleate levels in RBC phospholipids but not of docosahexaenoate or docosatetraenoate levels. The incorporation of [5,6,8,9,11,12,14,15-3H]arachidonate into diabetic RBC phospholipids was significantly decreased compared with the corresponding control RBC, regardless of the incubation medium used, which was the PPP derived either from the control or diabetic rats. Therefore, the decreased incorporation of [5,6,8,9,11,12,14,15-3H]arachidonate into diabetic RBC phospholipids was independent of the altered lipid composition of the PPP incubation media. Furthermore, the decreased incorporation was not specific for arachidonate, because the incorporation of other long-chain fatty acids such as [9,10-3H]oleate, [1-14C]palmitate, [2-14C]eicosatrienoate (n-6), and [1-14C]linoleate into RBC phospholipids was also comparably decreased. More important, the decreased fatty acid incorporations were reversed by insulin treatment of the diabetic rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of clenbuterol on skeletal muscle mass, body composition, and recovery from surgical stress in senescent rats.

Aging decreases skeletal muscle mass and strength, which may be exacerbated by age-related diseases. There is a need for therapeutic agents to prevent or restore loss of skeletal muscle in elderly subjects with muscle wasting disorders. Clenbuterol, a beta 2-adrenergic agonist, dramatically increases skeletal muscle mass in young animals and partially prevents or restores muscle loss in experimental models of muscle wasting. However, the protein anabolic and fat catabolic effects of clenbuterol have not been studied in senescent animals. To determine whether this drug has potential for preventing or repairing muscle loss in elderly subjects, we have examined its effects in young and old rats. Clenbuterol was administered by implanted osmotic minipumps to Fischer-344 rats ages 3, 12, and 23 months, at a dose of 1.5 mg/kg/24 h for 3 weeks. The weights of five hindlimb muscles and carcass protein and fat content were determined. Clenbuterol treatment increased the weight of skeletal muscles 22% to 39% in 3-month-old rats, 19% to 35% in 12-month-old rats, and 22% to 25% in 23-month-old animals. Likewise, clenbuterol increased carcass protein content 19% in 3-month-old rats, 16% in 12-month-old rats, and 24% in 23-month-old animals. Conversely, the drug reduced carcass fat content 36% in 3-month-old rats, 32% in 12-month-old rats, and 38% in 23-month-old rats. Therefore, clenbuterol had similar anabolic and catabolic effects in all age groups. In addition, clenbuterol stimulated recovery of skeletal muscle protein lost following pump implantation in senescent rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary fats on fatty acid composition and delta 5 desaturase in normal and diabetic rats.

We have studied the effect of various diets on the phospholipid fatty acid composition and in vitro delta 5 desaturase activity of hepatic microsomes derived either from the normal or streptozotocin-induced diabetic rat. The diets studied were the standard rat chow diet and a basal fat-free diet supplemented either with 20 percent saturated fat, 20 percent unsaturated fat, or 20 percent menhaden oil. Phospholipid fatty acid composition analysis revealed that the normal rat fed the saturated fat or menhaden oil diet had significantly decreased arachidonate levels, consistent with decreased delta 5 desaturase activities and decreased 18:2n-6 intake. On the contrary, the unsaturated fat diet decreased dihomo-gamma-linolenate and increased arachidonate levels, without increased delta 5 desaturase activity. Streptozotocin-induced diabetes resulted in decreased arachidonate and delta 5 desaturase activity. The unsaturated fat diet fed to the diabetic rat also failed to correct this decreased delta 5 desaturase activity. The unsaturated fatty acids in this diet also displaced a substantial amount of n-3 fatty acids in both normal and diabetic microsomes, due to the competition between these two fatty acid families for incorporation into the membrane phospholipids. Conversely, the menhaden oil diet fed to the normal and diabetic rats displaced n-6 fatty acids, reduced delta 5 desaturase activity, and enhanced 22:6n-3 incorporation into diabetic microsomes.

Effects of experimental hypo- and hyperthyroidism on hepatic long-chain fatty acyl-CoA synthetase and hydrolase.

The effects of T3 treatment and thyroidectomy on rat liver microsomal long-chain fatty acyl-CoA (LCFA-CoA) synthetase and LCFA-CoA hydrolase activities were determined. Hyperthyroid rats had a 36-42% decrease in LCFA-CoA synthetase with no change in hydrolase activity. This may contribute to the redirection of fatty acids from esterification to oxidation reactions in hyperthyroidism. Thyroidectomized rats had a 40-44% decrease in synthetase and a 27-42% decrease in LCFA-CoA hydrolase activity. The decrease in both LCFA-CoA synthetase and hydrolase activities in hypothyroidism may indicate that the LCFA-CoA turnover in this futile cycle is decreased in the liver.

Altered fatty acid composition in the plasma, platelets, and aorta of the streptozotocin-induced diabetic rat.

Decreased arachidonate levels have been described in various tissues of the streptozotocin-induced diabetic rat. However, reported arachidonate changes in platelets from diabetic patients have been variable. In this communication, we describe experiments that indicate that in the short-term streptozotocin diabetic rat (2 to 3 weeks), the fatty acid composition of plasma and red blood cell lipids was altered but remained unchanged in platelet and aorta phospholipids. The altered fatty acid composition of the diabetic red blood cells and plasma cholesterol esters and phospholipids was similar to that previously found in the diabetic liver. However, in long-term diabetes (6 weeks), the phospholipid fatty acid composition of the platelet and aorta became significantly altered. Thus, in the 6-week diabetic platelet, there were increases of linoleate, dihomo-gamma-linolenate, docosapentaenoate (C22:5n-3), and docosahexaenoate, and decreases of oleate, arachidonate, and docosatetraenoate. In the aorta, there were increases of linoleate, eicosapentaenoate, and docosahexaenoate, and decreases of arachidonate, docosatetraenoate, and docosapentaenoate (C22:5n-6). Results from these experiments indicate that the fatty acid composition of plasma and red blood cell lipids was altered in short-term diabetes (2 to 3 weeks), but that of platelet and aorta phospholipids was not changed until more prolonged diabetes was present. Insulin treatment of the diabetic rat increased the levels of palmitoleate and oleate and decreased the levels of linoleate in platelet and aorta lipids from insulin-treated diabetic rats, suggesting an overcorrection of diminished delta 9 and delta 6 fatty acid desaturation as compared with the nondiabetic control.(ABSTRACT TRUNCATED AT 250 WORDS)

Red blood cell and plasma fatty acid composition in diabetes mellitus.

Arachidonic acid deficiency and increased linoleic acid levels have been a consistent finding in a variety of tissues in experimental diabetes. To determine if patients with type II non-insulin-dependent diabetes show changes in red blood cell and plasma fatty acid composition, a group of non-insulin-dependent diabetic patients were studied prior to and following treatment with glyburide which substantially improved their diabetic control. Red blood cell and plasma fatty acid composition was compared with that of a group of nondiabetic subjects and to red cell fatty acid composition in normal and streptozotocin diabetic rats. The diabetic patients had no changes in linoleic or arachidonic acid levels prior to treatment and no changes following glyburide therapy. These studies and the available literature suggest to us that either more severe diabetes is required to produce the fatty acid abnormalities described in the diabetic rat or that there is a fundamental species difference in the mechanism of diabetes or in fatty acid metabolism between the human and the rat which allows the human diabetic to more easily maintain normal tissue fatty acid composition.

Comparison of the effect of a protein-free and restricted high protein-low carbohydrate diet on ventricular myosin ATPase activity and isomyosin profile in young rats: evidence that protein-depleted animals are euthyroid.

Young rats fed a protein-deficient diet have elevated total triiodothyronine (T3) levels in spite of decreased skeletal muscle protein turnover. Interpretation of the thyroid status of these animals is complicated by increased T3 binding by serum proteins. Free T3 levels ranging from normal to low and decreased resting oxygen consumption have been reported. To investigate the thyroid status of animals fed a protein-free diet, ventricular myosin ATPase activity and isomyosin profile have been used as an index of thyroid hormone activity. The effect of the protein-free diet has been compared to a restricted high protein-low carbohydrate diet, which causes clear evidence of decreased thyroid hormone effect. After 28 d, calcium-activated myosin ATPase activity was 1.50 +/- 0.05 mumol Pi/(mg protein.min) in animals fed the basal diet, 1.16 +/- 0.03 mumol Pi/(mg protein.min) in animals fed the restricted high protein-low carbohydrate diet and 1.48 +/- 0.04 mumol Pi/(mg protein.min) in animals fed the protein-free diet. In addition, a shift in isomyosin content with the appearance of V2 and V3 isomyosins occurred with the restricted high protein-low carbohydrate diet but not the protein-free diet. The failure of the protein-depleted rats to decrease myosin ATPase activity and alter isomyosin content suggests that they are euthyroid.

Effect of graded doses of tri-iodothyronine on ventricular myosin ATPase activity and isomyosin profile in young and old rats.

Ventricular myosin ATPase activity, V1 isomyosin content and serum T3 (tri-iodothyronine) values decrease with age in male Fischer 344 rats. To determine if the age decrement in ATPase activity and V1 isomyosin content are caused by decreased T3 levels or an age-related decrease in V1 isomyosin induction by T3, 3-, 12- and 24-month-old male Fischer 344 rats were given constant T3 infusions by osmotic minipump. Rats at all ages were given 0.75, 5 and 15 micrograms(/100 g per 24 h) doses of T3, whereas 12- and 24-month-old rats were given an additional 0.4 microgram dose. In control rats, T3 levels decreased from 97 +/- 2.7 at 3 months to 75 +/- 4.7 ng/100 ml at 24 months. Likewise, Ca2+-activated myosin ATPase activity decreased from 1.04 +/- 0.05 to 0.68 +/- 0.05 mumol of Pi/min per mg of protein, and the relative proportion of V1 of isomyosin decreased from 90 +/- 4.0 to 26 +/- 2.0%. The lowest (0.4 microgram) T3 dose, which was sufficient to restore T3 levels in 24-month-old animals to 3-month control values, abolished the age decrement in myosin ATPase activity and markedly increased the proportion of V1 isomyosin present in the ventricle. These findings indicate that the senescent ventricle responds readily to small doses of T3 and strongly suggest that the age decrement in serum T3 levels is sufficient to contribute to the age-related decrease in myosin ATPase activity and V1 isomyosin content. Since these parameters correlate with ventricular contractility, the age decrement in T3 levels may also contribute to the decreased ventricular contractility and cardiac output observed in senescent rats.

Influence of hypo- and hyperthyroidism on rat liver glycerophospholipid metabolism.

The effects of hyper- and hypothyroidism on enzyme activities involved in phospholipid metabolism in the rat liver were studied. Hyperthyroidism significantly decreases activities of both microsomal acyl-CoA:glycero-3-phosphate acyltransferase (GPAT) (34%, p less than 0.01) and microsomal acyl-CoA:1-acylglycero-3-phosphocholine acyltransferase (GPCAT) (28-33%, p less than 0.01). This may contribute to the decreased proportions of certain unsaturated fatty acids found in microsomal phosphoglycerides in hyperthyroidism. Mitochondrial GPAT, phospholipase A2 and cytosol lysophospholipase are unaffected by hyperthyroidism. In contrast, hypothyroidism stimulates mitochondrial GPAT (38%, p less than 0.01) and microsomal GPCAT (14-19%) activities but decreases both mitochondrial phospholipase A2 (36%, p less than 0.01) and cytosol lysophospholipase (56%, p less than 0.01) activities. The increased GPCAT activity may contribute to the increased proportions of certain unsaturated fatty acids found in microsomal phosphoglycerides in hypothyroidism. Triiodothyronine (T3) treatment of the hypothyroid rat (25 micrograms/100 g body weight/day for four days) corrected phospholipase A2 and lysophospholipase activities to the level of the control rat, but failed to correct the increased mitochondrial GPAT activity and not only corrected but lowered GPCAT activity to the level of the hyperthyroid rat.

Effect of thyroid hormone on protein turnover in cultured cardiac myocytes.

Since systemic actions of thyroid hormone increase cardiac work, direct effects of T3 on myocardial protein turnover may be obscured in the intact animal. For this reason, the effects of T3 on synthesis and degradation of cellular protein were measured in replicate cultures of cardiac myocytes obtained from chick embryos. During the first 3 days of exposure, 10(-8) M T3 increased the fractional rate of protein synthesis 10% to 16% and the fractional rate of cell growth 20% to 40% with no change in protein degradation. During the fourth and fifth days of 10(-8) M T3 exposure, fractional synthesis rates in T3 cultures increased 15% to 19% but fractional degradation rates also increased 17% to 29% so that growth rates in T3 cultures fell to control levels. Similar changes in myocardial protein turnover have occurred in response to T3 treatment in intact animals. T3 treatment caused a disproportionately large increase in the rate of myosin heavy chain turnover when compared to total cellular protein and actin. This may be related to the change in amounts of myocardial isomyosins occurring in response to thyroid hormone treatment.

Effects of streptozotocin-induced diabetes on phosphoglyceride metabolism of the rat liver.

We have studied the effect of streptozotocin (SZ)-induced diabetes on fatty acyltransferase and phospholipase enzyme activities involved in the synthesis and degradation of rat liver phosphoglycerides. Neither mitochondrial nor microsomal acyl-CoA:glycerol 3-phosphate acyltransferase (GPAT) activity was altered, although insulin treatment stimulated mitochondrial GPAT activity. However, microsomal acyl-CoA:1-acylglycerol 3-phosphate acyltransferase (1-acyl-GPAT) activity increased (24-33 per cent, p less than 0.01) in the diabetic animals using 3 different acyl-CoA donors: palmitoyl-CoA, oleoyl-CoA and linoleoyl-CoA. SZ-induced diabetes also increased acyl-CoA;1-acylglycerol 3-phosphorylcholine acyltransferase (GPCAT) activity (38-45 per cent, p less than 0.01) with 3 different acyl-CoA donors: oleoyl-CoA, linoleoyl-CoA and arachidonoyl-CoA. 1-acyl-GPAT and GPCAT activity returned to normal with insulin treatment. In contrast to the increased activity of the microsomal fatty acyl-transferases 1-acyl-GPAT and GPCAT, SZ-induced diabetes decreased mitochondrial phospholipase A2 activity and lysophospholipase activity (49-70 per cent, p less than 0.01). Insulin treatment of the diabetic rats corrected the decreased lysophospholipase and stimulated phospholipase A2 activity 35 per cent higher than controls. Since microsomal 1-acyl-GPAT and GPCAT are known to have higher activity toward unsaturated fatty acyl-CoA donors, the increased GPCAT activity coupled with the decreased lysophospholipase activity and the increased 1-acyl-GPAT activity in diabetes would tend to increase the formation of newly synthesized phospholipids containing unsaturated fatty acids. This mechanism plus the decreased fatty acid desaturase (4) may be the factors which alter the fatty acid composition of phosphoglycerides in diabetic rat liver microsomes.

Effects of streptozotocin-induced diabetes on microsomal long-chain fatty acyl-CoA synthetase and hydrolase.

Streptozotocin-induced diabetes significantly decreased rat liver microsomal long-chain fatty acyl-CoA (LCA-CoA) hydrolase. The decrease was observed using either palmitoyl-CoA (35 per cent, p less than 0.01) or oleoyl-CoA (23 per cent, p less than 0.01) as the substrate for the enzyme. Under the same conditions, diabetes did not significantly alter activity of LCA-CoA synthetase. Daily subcutaneous injections of protamine zinc insulin (10-12 units/day) into the diabetic rats returned their blood glucose to normal but only partially corrected the LCA-CoA hydrolase activity and did not effect LCA-CoA synthetase activity. The decreased LCA-CoA hydrolase and the unchanged LCA-CoA synthetase activities in the diabetic rat liver were interpreted as factors that may contribute to elevation of fatty acyl-CoA levels in the diabetic liver.