The M1 muscarinic receptor antagonist pirenzepine in low doses decreases resting heart rate; this effect declines with age (Poller, U., G. Nedelka, J. Radke, K. Pönicke, and O.-E. Brodde. 1997. J. Am. Coll. Cardiol. 29:187-193). To study possible mechanisms underlying this effect, we assessed (a) in six young (26 yr old) and six older volunteers (61 yr old), pirenzepine effects (0.32 and 0.64 mg intravenous [i.v.] bolus) on isoprenaline-induced heart rate increases; (b) in five heart transplant recipients, pirenzepine effects (0.05-10 mg i.v. bolus) on resting heart rate in the recipient's native and transplanted sinus nodes; and (c) in right atria from 39 patients of different ages (5 d-76 yr) undergoing open heart surgery, M2 muscarinic receptor density (by [3H]N-methyl-scopolamine binding) and adenylyl cyclase activity. (a) Pirenzepine at both doses decreased heart rate in young volunteers significantly more than in older volunteers; (b) pirenzepine (< 1 mg) decreased resting heart rate in the recipient's native but not transplanted sinus node; and (c) M2 receptor density and carbachol-induced inhibition of forskolin-stimulated adenylyl cyclase activity decreased significantly with the age of the patients. We conclude that pirenzepine decreases heart rate via inhibition of presynaptic M1 autoreceptors, thereby releasing endogenous acetylcholine, and that the heart rate-decreasing effect of acetylcholine declines with age because right atrial M2 receptor density and function decrease.

In the human heart, ET(A) and ET(B) receptors coexist; however, only ET(A) receptors are of functional importance. In right atria, ET(A) receptors couple to IP formation and inhibition of adenylyl cyclase; in left ventricles, they couple only to IP formation. In end-stage CHF, the functional responsiveness of the cardiac ET(A)-receptor system is not altered.

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The objective of this study was to determine the effects of cis-9,trans-11 and trans-10,cis-12 CLA on the fatty acid desaturation in a human hepatoma cell line, HepG2. Therefore, experiments were conducted in which HepG2 cells were incubated with various concentrations of those fatty acids and the concentrations of fatty acids in various lipid fractions of HepG2 cells were determined. In the presence of linoleic acid as substrate, cells treated with 25 micromol/L of trans-10,cis-12 CLA had lower ratios of dihomo-gamma-linoleic acid to linoleic acid and of arachidonic acid to linoleic acid in phospholipids than control cells; with alpha-linolenic acid as substrate, they had a lower ratio of eicosapentaenoic acid to alpha-linolenic acid in phospholipids than control cells. Cells treated with cis-9,trans-11 CLA did not differ in these ratios from control cells. Cells treated with trans-10,cis-12 CLA had also a markedly lower ratio of monounsaturated fatty acids (MUFA) to saturated fatty acids (SFA) in lipids than control cells; cells treated with cis-9,trans-11 CLA had a slightly lower MUFA:SFA ratio than control cells. These findings suggest that trans-10,cis-12 CLA suppresses Delta9-, Delta6- and Delta5-desaturation in HepG2 cells; cis-9,trans-11 CLA slightly reduces Delta9-desaturation but does not inhibit Delta6- and Delta5-desaturation. Moreover, HepG2 cells treated with 100 micromol/L of trans-10,cis-12 CLA released larger amounts of 6-keto-prostaglandin F(1alpha) and prostaglandin F(2alpha) than control cells. Treatment of cells with cis-9,trans-11 CLA did not alter the release of these eicosanoids compared with control cells. In conclusion, this study suggests that trans-10,cis-12 CLA has significant effects on the metabolism of essential fatty acids in HepG2 cells, whereas cis-9, trans-11 CLA does not have any effect in this respect.

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, and on contractile force in left ventricular strips of the rat heart. For comparison, eects of prostanoids on InsP-formation and contractile force were determined in rat thoracic aorta, a classical TP-receptor containing tissue. 2 Prostanoid increased InsP-formation and rate of protein synthesis in neonatal as well as adult rat cardiomyocytes; the order of potency was in neonatal (PGF 2a 4PGD 2 5PGE 2 5U 466194PGE 1 ) and adult (PGF 2a 4PGD 2 5PGE 2 4U 46619) rat cardiomyocytes well comparable. Moreover, in electrically driven left ventricular strips PGF 2a caused positive inotropic eects (pD 2 7.5) whereas U 46619 (up to 1 mM) was uneective. 3 In contrast, in rat thoracic aorta U 46619 was about 100 times more potent than PGF 2a in increasing InsP-formation and contractile force. 4 The TP-receptor antagonist SQ 29548 only weakly antagonized prostanoid-induced increases in rate of protein synthesis (pK B about 6) in rat cardiomyocytes but was very potent (pK B about 8 ± 9) in antagonizing prostanoid-induced increases in InsP-formation and contractile force in rat aorta. 5 We conclude that, in cardiomyocytes of neonatal and adult rats, the prostanoid-receptor mediating increases in InsP-formation and rate of protein synthesis is a FP-receptor. Moreover, stimulation of these cardiac FP-receptors can mediate increases in contractile force.

The objective of this study was to determine the effects of cis-9, trans-11 and trans-10, cis-12 CLA on the release of vasoactive eicosanoids and nitric oxide (NO) in human aortic endothelial cells. Experiments were conducted in which cells were incubated with these fatty acids, and the concentrations of various eicosanoids [6-keto prostaglandin (PG) F(1alpha) as a stable product of PGI(2), thromboxane (TX) B(2) as a stable product of TXA(2), and PGE(2)] and NO in the medium were determined. Cells treated with 50 micro mol/L of either cis-9, trans-11 or trans-10, cis-12 CLA released less of all of the eicosanoids and NO than control cells treated with medium alone (P < 0.05). The ratio between the amounts of 6-keto-PGF(1alpha) and that of TXB(2) released did not differ between control cells and cells treated with either CLA isomer. Moreover, cells treated with 50 micro mol/L of cis-9, trans-11 or trans-10, cis-12 CLA had a lower amount of arachidonic acid in their phosphatidylethanolamine fraction and a lower mRNA concentration and activity of secretory phospholipase A(2) than control cells (P < 0.05). These data suggest that eicosanoid formation was impaired by a reduced availability of arachidonic acid for the cyclooxygenase pathway. In conclusion, this study shows that cis-9, trans 11-CLA and trans-10, cis-12 CLA influence the release of various eicosanoids and NO from human aortic endothelial cells. The effects observed in this study might be important because eicosanoids and NO released from endothelial cells are involved in the regulation of vessel tone and platelet aggregation. The results of the present study suggest that both CLA isomers had unfavorable effects on endothelial function.

1 Angiotensin II (AII) and the endothelins (ET) are known to be potent trophic stimuli in various cells including cardiomyocytes. In order to characterize further these eects we studied, in neonatal rat ventricular cardiomyocytes, the eects of several endothelin-receptor antagonists and the AT 1 -receptor antagonist losartan on AII-and endothelin-induced inositol phosphate (IP)-formation (assessed as accumulation of total [ 3 Pretreatment of the cells with 500 ng ml 71 pertussis toxin (PTX) overnight that completely inactivated PTX-sensitive G-proteins did not attenuate but rather enhance ET-1-induced IP-formation. On the other hand, in PTX-pretreated cardiomyocytes ET-1-induced [ 3 H]-phenylalanine incorporation was decreased by 39+5% (n=5). 4 AII (1 nM ± 1 mM) concentration-dependently increased IP-formation (max. increase at 1 mM: 42+7% above basal, n=16) and [3 H]-phenylalanine incorporation (max. increase at 1 mM: 29+2%, n=9). These eects were antagonized by losartan, but they were also antagonized by bosentan and BQ-123. 5 In well-de®ned cultures of cardiomyocytes (not contaminated with non-myocyte cells) AII failed to increase [3 H]-phenylalanine incorporation; addition of non-myocyte cells to the cardiomyocytes restored AII-induced increase in [3 H]-phenylalanine incorporation. 6 We conclude that, in rat neonatal ventricular cardiomyocytes, (a) the ET-1-induced increase in rate of protein synthesis (through ET A -receptor stimulation) involves at least two signalling pathways: one via a PTX-insensitive G-protein coupled to IP-formation, and the other one via a PTX-sensitive G-protein, and (b) the trophic eects of AII are brought about via local ET-1 secretion upon AT 1 -receptor stimulation in neonatal rat ventricular non-myocyte cells.