Protein kinase C mediates angiotensin II-induced contractions and the release of endothelin and prostacyclin in rat aortic rings

Angiotensin II receptor type 1 - An update on structure, expression and pathology

The AT₁ receptor, a major effector of the renin-angiotensin system, has been extensively studied in the context of cardiovascular and renal disease. Moreover, angiotensin receptor blockers, sartans, are among the most frequently prescribed drugs for the treatment of hypertension, chronic heart failure and chronic kidney disease. However, precise molecular insights into the structure of this important drug target have not been available until recently. In this context, seminal studies have now revealed exciting new insights into the structure and biased signaling of the receptor and may thus foster the development of novel therapeutic approaches to enhance the efficacy of pharmacological angiotensin receptor antagonism or to enable therapeutic induction of biased receptor activity. In this review, we will therefore highlight these and other seminal publications to summarize the current understanding of the tertiary structure, ligand binding properties and downstream signal transduction of the AT₁ receptor.

Prostanoids counterbalance the synergism between endothelin-1 and angiotensin II in mesenteric veins of trained rats

Exercise-induced adaptations of the modulating mechanisms that influence the angiotensin (Ang II) responses assume different features depending on the venous bed. In femoral veins, exercise mobilizes vasodilator prostanoids to cooperate with NO in order to maintain reduced Ang II responses. On the other hand, exercise's influence on the Ang II responses in veins that drain blood from the mesenteric region has been poorly described. Therefore, the present study aimed to identify the effects of a single bout of exercise, as well as exercise training, on the Ang II responses in mesenteric veins. The present study also aimed to investigate the involvement of prostanoids, NO and ET-1 in eventual exercise-induced modifications in these veins. To this end, mesenteric veins taken from resting-sedentary, exercised-sedentary, resting-trained and exercised-trained animals were studied in organ baths. In addition, the mRNA expression of prepro-endothelin-1 (ppET-1), as well as that of the ET_A and ET_B receptors, were quantified by real-time PCR in these veins. The results show that, either in absence or in presence of L-NAME, the Ang II responses were not different between groups. In the presence of indomethacin, higher Ang II responses were observed in the resting-trained animals than in the resting-sedentary animals. This difference, however, disappeared when L-NAME, BQ-123 or BQ-788 were added during incubation. In addition, no differences in ppET-1, ET_A or ET_B mRNA expression were observed between groups. Furthermore, in the presence of PD123,319, the Ang II responses in the exercised-sedentary animals were higher than those in the resting-sedentary animals. In conclusion, exercise training mobilizes endothelin-1 (ET-1) to reinforce the Ang II-induced responses mainly through ET_A activation. On the other hand, vasodilator prostanoids are mobilized to act in parallel with NO in order to counterbalance the Ang II responses that have been potentiated by ET-1 in these trained animals.

Sex-Specific Effect of Endothelin in the Blood Pressure Response to Acute Angiotensin II in Growth-Restricted Rats

The renal endothelin system contributes to sex differences in blood pressure with males demonstrating greater endothelin type-A receptor-mediated responses relative to females. Intrauterine growth restriction programs hypertension and enhance renal sensitivity to acute angiotensin II in male growth-restricted rats. Endothelin is reported to work synergistically with angiotensin II. Thus, this study tested the hypothesis that endothelin augments the blood pressure response to acute angiotensin II in male growth-restricted rats. Systemic and renal hemodynamics were determined in response to acute angiotensin II (100 mg/kg per minute for 30 minutes) with and without the endothelin type-A receptor antagonist, Atrasentan (ABT-627; 10 ng/kg per minute for 30 minutes), in rats pretreated with enalapril (250 mg/L for 1 week) to normalize the endogenous renin-angiotensin system. Endothelin type-A receptor blockade reduced angiotensin II-mediated increases in blood pressure in male control and male growth-restricted rats. Endothelin type-A receptor blockade also abolished hyper-responsiveness to acute angiotensin II in male growth-restricted rats. Yet, blood pressure remained significantly elevated above baseline after endothelin type-A receptor blockade, suggesting that factors in addition to endothelin contribute to the basic angiotensin II-induced pressor response in male rats. We also determined sex-specific effects of endothelin on acute angiotensin II-mediated hemodynamic responses. Endothelin type-A receptor blockade did not reduce acute angiotensin II-mediated increases in blood pressure in female control or growth-restricted rats, intact or ovariectomized. Thus, these data suggest that endothelin type-A receptor blockade contributes to hypersensitivity to acute angiotensin II in male growth-restricted rats and further supports the sex-specific effect of endothelin on blood pressure.

Exercise reduces angiotensin II responses in rat femoral veins

The control of blood flow during exercise involves different mechanisms, one of which is the activation of the renin-angiotensin system, which contributes to exercise-induced blood flow redistribution. Moreover, although angiotensin II (Ang II) is considered a potent venoconstrictor agonist, little is known about its effects on the venous bed during exercise. Therefore, the present study aimed to assess the Ang II responses in the femoral vein taken from sedentary and trained rats at rest or subjected to a single bout of exercise immediately before organ bath experiments. Isolated preparations of femoral veins taken from resting-sedentary, exercised-sedentary, resting-trained and exercised-trained animals were studied in an organ bath. In parallel, the mRNA expression of prepro-endothelin-1 (ppET-1), as well as the ETA and ETB receptors, was quantified by real-time PCR in this tissue. The results show that, in the presence of L-NAME, Ang II responses in resting-sedentary animals were higher compared to the other groups. However, this difference disappeared after co-treatment with indomethacin, BQ-123 or BQ-788. Moreover, exercise reduced ppET-1 mRNA expression. These reductions in mRNA expression were more evident in resting-trained animals. In conclusion, either acute or repeated exercise adapts the rat femoral veins, thereby reducing the Ang II responses. This adaptation is masked by the action of locally produced nitric oxide and involves, at least partially, the ETB- mediated release of vasodilator prostanoids. Reductions in endothelin-1 production may also be involved in these exercise-induced modifications of Ang II responses in the femoral vein.

Propofol inhibits phorbol 12, 13-dibutyrate-induced, protein kinase C-mediated contraction of rat aortic smooth muscle

BACKGROUND

Propofol induces dose-dependent vasodilation and hypotension in the clinical situation, and protein kinase C (PKC)-mediated Ca2+ sensitization plays an important role in vascular smooth muscle contraction. This study is designed to examine the effects of propofol on the active phorbol ester (phorbol 12, 13-dibutyrate; PDBu)-induced, PKC-mediated contraction of rat aortic smooth muscle.

METHODS

The PDBu-induced contraction of endothelium-denuded rat aortic rings was measured in the presence or absence of PKC inhibitor, bisindolylmaleimide I, or propofol, using isometric force transducers. The PDBu-induced PKC phosphorylation of endothelium-denuded rat aortic strips was detected in the presence or absence of bisindolylmaleimide I or propofol, using Western blotting.

RESULTS

PDBu, but not the inactive phorbol ester, 4-alpha-phorbol 12-myristate-13-acetate, dose-dependently induced both a slowly developing sustained contraction and PKC phosphorylation of rat aortic smooth muscle, reaching the peak level at the concentration of 10(-6) M. The PDBu (10(-6) M)-induced contraction was dose-dependently inhibited by bisindolylmaleimide I with reductions of 6.8 +/- 1.8% (P > 0.05), 39.8 +/- 8.7% (P < 0.01) and 96.7 +/- 1.4% (P < 0.01) in response to concentrations of 5 x 10(-7) M, 10(-6)x M and 5 x 10(-6) M, respectively, and by propofol with decreases of 5.2 +/- 1. 6% (P > 0.05), 9.4 +/- 1.7% (P < 0.05), 65.3 +/- 9.2% (P < 0.01) and 96.2 +/- 1.6% (P < 0.01) in response to concentrations of 5 x 10(-7) M, 10(-6) M, 5 x 10(-6) M and 10(-5) M, respectively. Both bisindolylmaleimide I and propofol also inhibited the PDBu-induced increase in the density of the phosphorylated PKC bands in a dose-dependent manner, with decreases of 6.3 +/- 2.8% (P > 0.05), 42.9 +/- 3.2% (P < 0.01) and 96.6 +/- 3.4% (P < 0.01) in response to 5 x 10(-7) M, 10(-6) M or 5 x 10(-6) M bisindolylmaleimide I, respectively, and with decreases of 4.2 +/- 2.5% (P > 0.05), 13.5 +/- 1.7% (P < 0.05), 69.5 +/- 3.5% (P < 0.01) and 95.3 +/- 4.3% (P < 0.01) in response to 5 x 10(-7) M, 10(-6) M, 5 x 10(-6) M and 10(-5) M propofol, respectively.

CONCLUSION

Propofol dose-dependently inhibits PDBu-induced, PKC-mediated contraction of rat aortic smooth muscle.

Endothelin-1 Receptor Antagonist BQ123 Prevents Pulmonary Artery Hypertension Induced by Low Ambient Temperature in Broilers

Evidence has indicated that endothelin-1 is related to the pathogenesis of hypertension. To characterize the role of endothelin-1 (ET-1) in the development of pulmonary hypertension syndrome in broilers, the blockade effect of ETA receptor (ET(A)) antagonist, BQ123, on blood pressure in experimental models of pulmonary hypertension was examined. Birds were locally anesthetized and instrumented with venous catheters for pulmonary arterial pressure (PAP) and right ventricular pressure (RVP), followed by packed cell volume (PCV) and Ascites heart index (AHI) measured, after exposed to low ambient temperature for 7 or 14 d. In treated groups, BQ123 (0.4 or 2.0 microg each time, 2 times a day), administered in abdominal cavities for 7 or 14 d during birds kept in low ambient temperature, prevented both PAP and RVP increasing, especially the high dose BQ123 lowered PAP and RVP to normotensive levels as that in control under normal temperature, whereas significant increases (p<0.05) were found in the two parameters of broilers in both untreated and saline treated group under low ambient temperature compared with those of birds in control. Furthermore, there was also a reduction in low ambient temperature-induced right ventricular hypertrophy in the groups administered BQ123. The preventive effect of BQ123 suggests that ET-1 is associated with the development of broilers' pulmonary hypertension, which leads to the development of ascites, and BQ123 can prevent the occurrence of pulmonary hypertension.

Endothelin-A receptors mediate renal hemodynamic effects of exogenous Angiotensin II in humans

To investigate whether endothelin-A receptors mediate hemodynamic changes caused by exogenous Angiotensin II in humans, 7 healthy volunteers on a 250-mmol sodium diet underwent 3 separate p-aminohippurate and inulin-based renal hemodynamic studies. In 2 studies, Angiotensin II (increasing rates of 0.625, 1.25, and 2.5 ng/kg per minute, each for 30 minutes) was infused either alone or combined with endothelin-A blocker, BQ123, 0.4 nmol/kg per minute. A third infusion of BQ123 alone was not followed by any change. Angiotensin II infusion alone produced a progressive decrease in renal blood flow (1080+/-94 mL/minx1.73 m2 to 801+/-52, P<0.001, versus baseline) and glomerular filtration rate (115+/-7 mL/minx1.73 m2 to 97+/-7, P<0.001) with increase in filtration fraction (0.188+/-.017 to 0.220+/-.030, P<0.01). Mean arterial pressure and renal vascular resistance increased markedly (86.8+/-3.1 to 97.5+/-4.4 mm Hg, P<0.001 and 83+/-7 to 133+/-20 mm Hg/min per liter, P<0.001, respectively). With Angiotensin II+BQ 123, mean arterial pressure still rose (86.2+/-3.1 to 91.1+/-4.3, P<0.05 versus both baseline and BQ123 alone) but significantly less than with Angiotensin II alone (P<0.05). Renal blood flow (1077+/-76 to 993+/-79, P<0.001) and glomerular filtration rate (115+/-7 to 105+/-7, P<0.05) also changed to a significantly lesser extent than with Angiotensin II alone (P<0.05 for both), whereas filtration fraction remained unchanged (0.185+/-.015 to 0.186+/-.016). Renal vascular resistance rose only by 17% (82+/-5 to 95+/-9, P<0.001 versus baseline as well as versus BQ123 or Angiotensin II alone). The results show that endothelin through Endothelin-A receptors contributes substantially to the systemic and renal vasoconstriction of low-dose exogenous Angiotensin II in healthy humans.

Placental angiotensin II receptor AT1R in normotensive patients and its correlation between infant birth weight

OBJECTIVE

To evaluate angiotensin II type 1 receptor (AT1R) in the third trimester placenta from normotensive women and the correlation between placental AT1R immunoreactivity and infant birth weight.

PATIENTS AND METHODS

The study was carried out on 18 healthy normotensive patients with singleton uncomplicated pregnancies. Immunohistochemistry was used to examine the localization of AT1R in the human placenta.

RESULTS

Immunohistochemistry using a monoclonal antibody showed that angiotensin II (Ang II) receptor subtype 1 is localized in the decidual cells, syncytiotrophoblast, cytotrophoblast, Hofbauer cells and vascular endothelium. In our study group of patients, we found a significant negative correlation between histological staining in placental tissue and infant birth weight.

CONCLUSION

It seems that the appropriate placental AT1R expression and its normal vascular and endocrine activity plays a very important role in oxygenation and nutrition of the fetus and this ensures proper fetal development and growth.

Endothelin ETA receptor-subtype specific antagonism does not mitigate the acute systemic or renal effects of exogenous angiotensin II in humans

BACKGROUND

Angiotensin II (Ang II) is assumed to play a pathophysiological role in a variety of vascular diseases. Animal studies indicate that these effects are partly attributed to stimulation of endothelin-1 (ET-1) release. The aim of the present study was to investigate whether the acute effects of Ang II on systemic and renal haemodynamics in healthy subjects can be influenced by endothelin ET(A)-receptor blockade.

DESIGN

The study design was balanced, randomized, placebo-controlled, double blind, two-way cross-over, in 10 healthy male subjects.

METHODS

Subjects received stepwise increasing intravenous doses of Ang II (0.65, 1.25, 2.5, 5 ng kg(-1) min(-1) for 15 min per dose level) in the presence or absence of BQ-123 (60 microg min(-1)), a specific ETA-receptor antagonist. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were assessed by the para-aminohippurate and inulin plasma clearance method, respectively. Renal vascular resistance (RVR) was calculated from mean arterial pressure (MAP) and renal plasma flow.

RESULTS

Ang II decreased RPF by 34% and GFR by 9% and increased RVR by 94% and MAP by 27% (ANOVA, P < 0.001 vs. baseline, for all parameters). BQ-123 did not alter these renal and systemic haemodynamic responses to a significant degree. In addition, BQ-123 had no significant haemodynamic effect under baseline conditions.

CONCLUSIONS

Short-term increase of circulating Ang II levels causes systemic and renal pressor effects, which are not mitigated by endothelin ETA-receptor blockade. This suggests that the pressor response to Ang II cannot be accounted for by the acute release of vasoactive ET-1.

Mechanism of action of angiotensin II in human isolated subcutaneous resistance arteries

1. Human isolated subcutaneous arteries were mounted in a myograph and isometric tension measured. In some experiments, intracellular calcium [Ca(2+)]i was also measured using fura-2. 2. Angiotensin II (100 pM - 1 microM) increased [Ca(2+)]i and tone in a concentration-dependent manner. The effects of angiotensin II (100 nM) were inhibited by an AT1-receptor antagonist, candesartan (100 pM). 3. Ryanodine (10 microM), had no effect on angiotensin II-induced responses, but removal of extracellular Ca(2+) abolished angiotensin II-induced rise in [Ca(2+)]i and tone. Inhibition of Ca(2+) entry by Ni(2+) (2 mM), also inhibited angiotensin II responses. The dihydropyridine, L-type calcium channel antagonist, amlodipine (10 microM), only partially attenuated angiotensin II responses. 4. Inhibition of protein kinase C (PKC) by chelerythrine (1 microM), or by overnight exposure to a phorbol ester (PDBu; 500 nM) had no effect on angiotensin II-induced contraction. 5. Genistein (10 microM), a tyrosine kinase inhibitor, inhibited angiotensin II-induced contraction, but did not inhibit the rise in [Ca(2+)]i, suggesting that at this concentration it affected the calcium sensitivity of the contractile apparatus. Genistein did not affect responses to norepinephrine (NE) or high potassium (KPSS). 6. A selective MEK inhibitor, PD98059 (30 microM), inhibited both the angiotensin II-induced contraction and rise in [Ca(2+)]i, but had no effect on responses to NE or KPSS. 7. AT1 activation causes Ca(2+) influx via L-type calcium channels and a dihydropyridine-insensitive route, but does not release Ca(2+) from intracellular sites. Activation of tyrosine kinase(s) and the ERK 1/2 pathway, but not classical or novel PKC, also play a role in angiotensin II-induced contraction in human subcutaneous resistance arteries.

Differential ANG II-induced growth activation pathways in mesenteric artery smooth muscle cells from SHR

Angiotensin II-induced growth signaling mechanisms were investigated in vascular smooth muscle cells (VSMCs) from mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). In WKY, angiotensin II significantly increased protein synthesis ([(3)H]leucine incorporation) but not DNA synthesis ([(3)H]thymidine incorporation). In SHR, angiotensin II increased protein and DNA synthesis. VSMCs from both strains expressed angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors. Losartan (an AT(1) receptor antagonist) but not PD-123319 (an AT(2) receptor antagonist) attenuated angiotensin II-stimulated protein synthesis in WKY VSMCs. In SHR, losartan and PD-123319 partially inhibited angiotensin II-induced VSMC proliferation. The mitogen-activated protein kinase or extracellular signal-regulated protein kinase (ERK) kinase inhibitor PD-98059 blocked VSMC growth responses to angiotensin II in both strains. Angiotensin II increased ERK1/2 activation more in SHR than WKY, an effect inhibited by losartan but not PD-123319. LY-294002 [a phosphatidylinositol-3 (PI3) kinase inhibitor] blocked angiotensin II-stimulated ERK1/2 activation in SHR but not in WKY, whereas bisindolylmaleimide [a protein kinase C (PKC) inhibitor] was ineffective. In conclusion, angiotensin II stimulates VSMC proliferation via AT(1) and AT(2) receptors in SHR. In WKY, angiotensin II induces VSMC hypertrophy via AT(1) receptors. ERK1/2-dependent pathways regulated by intracellular Ca(2+) but not PKC mediate these effects. In SHR VSMCs, PI3 kinase plays a role in augmented angiotensin II-induced ERK1/2 phosphorylation. These angiotensin II-mediated signaling events could contribute to vascular remodeling in SHR.

Endothelin mediates some of the renal actions of acutely administered angiotensin II

Recent studies suggest that endogenous endothelin mediates much of the vasoconstrictor activity and vascular fibrotic damage caused by chronic administration of angiotensin II. The present study uses the mixed endothelin-A and endothelin-B receptor antagonist bosentan and the endothelin-A-selective blocker BQ-123 to study the contribution of endogenous endothelin to the pressor and renal action of acutely administered angiotensin II in conscious, chronically catheterized rats. Exposure to angiotensin II at 0.48 pmol 0.5 ng/100 g body weight per min IV (low dose) and 1.91 pmol 2.0 ng/100 g body weight per min IV (high dose) raised mean arterial blood pressure (18+/-4 mm Hg, P<0.01, and 39+/-4 mm Hg, P<0.005, respectively) while also increasing renal vascular resistance (4.3+/-1 mm Hg/mL per min, P<0.001, and 10+/-1 mm Hg/mL per min, P<0.001, respectively). In the presence of bosentan, pressor and renal vasoconstrictor responses to low-dose angiotensin II were blunted (P<0.02 and P<0.01, respectively), and the results with BQ-123 were similar. In contrast, these parameters were unaffected during high-dose angiotensin II infusion+bosentan, although BQ-123 did selectively reduce the rise in renal vascular resistance, possibly via an endothelin B-mediated nitric oxide effect. In contrast, high-dose angiotensin II caused natriuretic and diuretic effects that were completely prevented by bosentan. These results show that endothelin (via endothelin A) contributes to the pressor and renal vasoconstrictor actions of acutely administered low-dose angiotensin II. Furthermore, our data suggest that the previously described angiotensin II-induced natriuresis and diuresis observed with a high pressor dose of angiotensin II is mediated by endothelin.

Neurovascular interactions between aldose reductase and angiotensin-converting enzyme inhibition in diabetic rats

Increased polyol pathway flux has been linked to nerve complications in diabetic rats, which are attenuated by aldose reductase inhibitors, defective nitric oxide-mediated vasodilation being a particular target. Diabetes also elevates the endothelial angiotensin system, increasing vasa nervorum vasoconstriction. The aim was to assess whether promotion of vasodilation by treatment with the aldose reductase inhibitor, ZD5522 (3',5'-dimethyl-4'-nitromethylsulphonyl-2-(2-tolyl)acetanilide), coupled with reduced vasoconstriction using the angiotensin-converting enzyme inhibitor, lisinopril, interacted positively to improve neurovascular function. After 8 weeks of streptozotocin-induced diabetes, sciatic nerve blood flow and motor conduction velocity were 51% and 21% reduced, respectively. Two weeks of lisinopril treatment dose-dependently corrected the conduction deficit (ED(50) approximately 0.9 mg kg(-1)). Low-dose lisinopril (0.3 mg kg(-1)) or ZD5522 (0.25 mg kg(-1)) had modest corrective (10-20%) effects on nerve conduction and perfusion. However, when combined, blood flow and conduction velocity reached the nondiabetic range. The ZD5522 dose used gave a approximately 45% nerve sorbitol reduction but had no significant effect on fructose content; lisinopril co-treatment did not alter ZD5522 action on polyols. Thus, there was a marked neurovascular synergistic interaction between angiotensin-converting enzyme and aldose reductase inhibition in diabetic rats. This points to a potential therapeutic benefit, which requires evaluation in clinical trials.

Platelets and prostacyclin in arterial bypasses: implications for coronary artery surgery

BACKGROUND

We investigated effects of platelets and prostacyclin formation in human internal mammary (IMA) and radial (RA) arteries.

METHODS

IMA and RA segments were suspended in organ bath with increasing concentrations of platelets. Experiments were applied with and without ketanserin, a 5HT2 receptor antagonist, or U3405, a TXA2 receptor antagonist. The release of prostacyclin (PGI2) was assessed by enzyme immunoassay in vessels without endothelium, before and after contraction with angiotensin (AT) I-II.

RESULTS

In IMA and RA with endothelium, platelets caused contractions, significantly enhanced in arteries without endothelium. Contractions to platelets were higher in RA than in IMA. U3405 reduced the platelet induced contractions in RA but not in IMA. Ketanserin inhibited the platelet induced contractions in IMA and RA. The basal release of PGI2 was more important in IMA than in RA. Addition of AT/I-II significantly reduced the release of PGI2 in IMA but not in RA.

CONCLUSIONS

The RA responds more powerfully to platelets than IMA. Protective system with PGI2 seems to be more powerless in RA than in IMA. This accentuates the importance of antispastic and antiplatelet drugs when arteries are used for coronary artery bypass surgery.

Differential modulation of nitric oxide and prostacyclin release in senescent rat heart stimulated by angiotensin II

To elucidate the mechanism of age-related changes in the cardiovascular function stimulated with angiotensin II, we examined the effects of angiotensin II on the coronary flow, production of nitric oxide (NO) and prostacyclin, and on the cardiac function in the Langendorff-perfused young and aged rats' hearts. Angiotensin II decreased coronary flow, left ventricular dP/dt and heart rate. These effects were more pronounced in aged rats. Pretreatment with a NO synthase inhibitor, N(G)-nitro-L-arginine, significantly increased the angiotensin II-induced vasoconstriction in young rats. Angiotensin II increased the concentration of NO in the coronary effluent in young but not in aged rats. In contrast, angiotensin II stimulated the release of prostacyclin to a much greater extent in aged rats than in young rats. These results suggest that impaired production of NO may contribute to the greater constrictor effect of angiotensin II in the aged rat, although aging modulated the production of prostacyclin in a different manner. This age-related endothelial dysfunction may alter the physiological regulation of coronary flow and cardiac function stimulated with angiotensin II.

Dietary n-3 fatty acids alter angiotensin-induced contraction and 1,2-diacylglycerol fatty acid composition in thoracic aortas from diabetic rats

The effect of diabetes on the incorporation of long-chain n-3 fatty acids into thoracic aorta smooth muscle phospholipids and 1,2-diacylglycerol, and on the contractile response of aortic rings to angiotensin II, was examined in streptozotocin-induced diabetic rats. In diabetic animals fed a diet containing 1% of fatty acids as n-3 fatty acids, smooth muscle membrane levels of 18:2n-6 were elevated in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, whereas 20:4n-6 was depleted. The resultant decreased ratios of 20:3/18:2 and 20:4/20:3 indicate inhibition of delta6- and delta5-desaturase activity in the diabetic state. A diet containing 5% of fatty acids as n-3 fatty acids increased phospholipid levels of eicospentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) several-fold, but with a further reduction in 20:4n-6. Similarly, 1,2-diacylglycerol from rats fed the high n-3 diet was enriched in EPA, DPA and DHA. When incubated with 10(-8) M angiotensin II, the contractile response of intact aortic rings from diabetic animals fed the high n-3 diet was only 60.8+/-9.3% that of controls fed the same diet. However, contractile response was not significantly different from control animals fed the low n-3 diet (55.6+/-7.9%). The results indicate that vascular smooth muscle phospholipid n-6 and n-3 fatty acid metabolism is altered in diabetes, resulting in changes to the fatty acid profile of 1,2-diacylglycerol. Moreover, elevating membrane phospholipid and 1,2-diacylglycerol content of EPA, DPA and DHA partially ameliorates the depressed response to angiotensin II seen in the diabetic state.