- Email: [email protected]
Unresponsiveness of forearm hemodynamics to omega-3 polyunsaturated fatty acids and asprin
PROSTAGLANDINS UNRESPONSIVENESS OF FOREARM HEXODYNAMICS TO OMEGA-3 POLYUNSATURATED FATTY ACIDS AND ASPRIN J Ryu, J. Lerner, J.M. Sullivan
Division of Cardiovaecular Diaeaeee, Department of Medicine, University of Tenneeeee, Memphis, TN 38163
Abstract: Prostaglandin synthesis has been reported to change with aspirin ingestion via cyclooxygenase enzyme inhibition and with marine oil supplementation via an increase in the metabolism of 3-series eicosanoids. This study investigated the effects of pharmacological manipulations of prostaglandin metabolism on forearm hemodynamics and blood pressure. The agents studied were omega-3 fatty acids and aspirin. In the omega-3 fatty acid study, two groups of normal volunteers (N=lO/group) supplemented their diets with either marine oil capsules or placebo. Hemodynamic variables (Mercury-in-Silastic forearm plethysmograghy) were measured initially and weekly for 4 weeks. There were no significant differences between the two groups in blood pressure, forearm blood flow, venous capacitance, or forearm vascular resistance. Parallel changes occurred for forearm blood flow and venous capacitance. Six normal volunteers took daily dosages of aspirin, increasing from 162 to 2600 mg. Hemodynamic measurements, ADP-induced platelet aggregation, and serum salicylate levels were obtained daily. Maximum inhibition of platelet aggregation occurred after 162 mg.(serum salicylate = 17.7+/-6.4 mg/l). Though serum salicylate levels rose to 165.0+/- 20.0 mgll, no significant changes occurred in blood pressure or forearm blood flow. Even at aspirin levels 16- fold greater than those required to impair platelet aggregation, the changes in forearm vascular resistance were not found to be significant. These results suggest that under resting conditions in normotensive males, neither pharmacological inhibition nor stimulation of vascular prostaglandin metabolism alters forearm vascular resistance or arterial blood pressure.
introduction The eicosanoids, produced by blood constituents and by vascular endothelial and smooth muscle cells, have a wide range of actions on the cardiovascular system. The cyclooxygenase pathway of eicosanoid metabolism produces thromboxane, a platelet aggregator, and prostacyclin, a vasodilator. Prostacyclin is the major arachadonic acid metabolite in vascular endothelium and may be an important regulator of vascular resistance (VR). Pharmacological agents such as omega-3 fatty acids contained in marine oils and non-steroidal antiinflammatory agents (NSAIA) are known to influence prostacyclin levels. Both these agents have been associated with the prevention of cardiovascular disease. Several studies suggest that aspirin, through its antithrombotic activity reduces myocardial infarctions, strokes, and
MARCH 1990 VOL. 39 NO. 3
339
PROSTAGLANDINS
cardiovascular deaths.(l) Diets containing relatively high levels of marine oils have been demonstrated to lower cholesterol levels, platelet aggregation, thrombotic tendencies, blood viscosity, and BP (2-7). NSAIA, by acetylating cyclooxygenase, prostaglandin
inhibit the formation of both thromboxane
A2 and
I2 (prostacyclin) (8,9); therefore, aspirin is able to decrease platelet aggregation and
decrease vasodilation, thereby potentially increasing VR and BP. Furthermore, studies have shown that a greater amount of aspirin is necessary to inhibit prostaglandin I2 formation than is required to prevent production of thromboxane
A2. At low doses of aspirin, the physiological
effects of prostaglandin
12 are
preserved while platelet aggregation is inhibited.(lO,ll) The proposed mechanism underlying the effects of marine oils is that increases in omega-3 FA’s compete with N-6 fatty acid metabolism, leading to a switch from the 2-series to the 3-series of prostaglandin metabolism. For example, TxA2, a proaggregator, has been noted to decrease while TxA3, which lacks aggregatory activity, increases. that diets rich in marine oils produce increased prostaglandin
Studies have also shown
I3 levels without changing prostaglandin
I2
levels.(l2) This increase in total prostacyclin levels may explain the reported changes in BP with marine oil supplementation. The hemodynamic effects of the changes in prostaglandin levels are not yet understood. Therefore, the purpose of this study was to investigate the effects of pharmacological manipulation of prostaglandin metabolism on VR (forearm hemodynamics).
Subjects
and Methodology:
aa-3Fattvm The Institutional Review Board of the University of Tennessee, Center for Health Sciences approved the protocol for this study. Twenty normal male volunteers participated in the study. They met the predetermined criteria: normotensive, between the ages of 20-39 years, and not taking any medications. The volunteers were within 35% of their ideal body weight as defined by frame size and height (Metropolitan life insurance values). The participants were randomized into two groups. The control group (N=lO) was given six 1000 mg. capsules/day of wheat germ oil (Schii Bio-Food Products). The experimental group (N=lO) was given six 1000 mg. capsules of marine oil (Promega, Parke-Davis Health Products Group), totaling 2100 rng. of eicosapentaenoic acid and 900 mg. of docosahexaenoic per day. The marine oils and the placebo were ingested for 4 weeks as nutritional supplements to the normal diet. Compliance was checked each week by counting the number of capsules remaining in the returned bottle. Three supine blood pressure measurements were obtained in triplicate on three different days before supplementation in order to establish the baseline reading on each of the subjects. Serial BP and plethysmographic readings were measured before administration of placebo or active compound, and once a week thereafter in order to detect any changes on hemodynamics over time. Data Analysis: The experimental group was compared to the control group. A two-tailed analysis of variance with allowances for repeated measures was used to test for significance of changes in BP, forearm blood flow (FBF), venous capacitance (VC), and VR. A p value of 0.05 or less indicated a significant difference. The data was analyzed through a VAX Statistical Analysis Package.
340
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
Aspirin Study Six healthy male volunteers took daily dosages of aspirin increasing from 162 to 2600 mg. over 5 days with day 6 as a recovery day. The dosages were doubled each following day. A baseline plethysmograph ADP-induced platelet aggregation and serum salicylate levels were obtained before administration of aspirin. As dose was increased each day and on the recovery day, a plethysmograph, serum salicylate level, and ADP-induced platelet aggregation were measured. Serum salicylate was measured as described by Trinder (13). performed by the method reported by Born et al.(14). Data Analysis measures.
Forearm
Platelet aggregation studies were
- Data were tested by significance by analysis of variance with allowance for repeated
Hemodynamlcs
Studies:
BP was measured by a Dinamap Vital Signs Monitor at the time of forearm blood flow measurements. Whitney mercury in silastic strain gauge plethysmography was used to measure FBF and VC (15,16,17) The volunteers fasted for 1 hour beforehand and rested for 20 minutes while supine before plethysmography. A mercury filled strain gauge was connected to a Hokanson model EC-4 phethysmograph (18) attached to a Fisher Series 5000 Recordall strip chart recorder. The appropriate length strain gauge was stretched 2% past its resting length, wrapped around the left forearm about 6-7 cm below the elbow, and taped to the arm. A blood pressure cuff was placed on the left upper arm and inflated to 40mmHg to stop venous flow yet still allow arterial flow. FBF (mVmin/lOOg) was calculated from the initial slope obtained from the early phase of radial expansion of the forearm as the veins filled with blood: FBF= initial slo e*K’120. Forearm Vascular Resistance (FVR) was then calculated by using the formula FVR = (MgP / FBF), With maximal distention of the veins, fluid diffuses out of the capillaries and a second slope was obtained. A tangent is drawn from this second slope to an erect perpendicular line drawn at baseline. VC was then calculated from the height of this perpendicular line to where it meets the tangent: VC=heightYYL,, Lo=forearm circumference. VC gives an indication of the veins ability to stretch at a given pressure, 40 mmHg. These hemodynamic rests in between each reading.
measurements were obtained in triplicate with 3 minute
In previous studies, we have shown that this method is able to detect significant changes in FVR between hypertensive and normotensive individuals during rest and reactive hyperemia.l g The reproducibility of this method has been evaluated in 20 normal subjects. MBP varied by 3%, FBF and FVR by 16.5%, and VC by 11.4%.
MARCH 1990 VOL. 39 NO. 3
341
PROSTAGLANDINS
Results:
- 3 Fattv Acid Study:
Qmeaa
Twenty male volunteers joined the study. The placebo group consisted of 9 Caucasians and 1 asian; the marine oil group had 9 Caucasians and 1 black. Adverse effects were not reported by any participants. The average weights for the two groups were not significantly different : Placebo group 168.8 Ibs s marine oil group - 165.7 Ibs. The mean age of 27.2 yr. for the marine oil group differed significantly from the placebo group’s mean age of 24.8 yrs, although the difference was only 2 yrs (P > 0.0180). Table 1 summarizes the results from the hemodynamic
measurements.
Table 1: Marine Oil Results. TimeGnxlg
BP(nn+!c~)
0 placebo
124.8/73.#11
S/7.3
MBP 90.4b3.0
vCfnv1Ocq
FBF
5.45& .27
3.w1.07
B!B 27.1s9.7
active
123.4l73.1f9.4l4.3
89.W.7
5.92rto.94
3.01*0.86
32.1f7.7
1 placebo
122.9/72.ti10.4/6.8
89.2k7.4
5791.47
4.ow1.64
28.ti10.3
active
122.9/73.1~9.4/4.0
90.w.2
6.Olk1.03
3.16-t0.76
31.1ti.8
2
placebo
122.8/71 .910.3/7.8
89.2k7.9
5.3s1.65
2.77kO.48
33.8f7.1
active
123.9/73&l
90.w.2
5.&l
3
placebo
120.1/71 [email protected]/8.4
87.a.7
5.41kl.62
adie
121.7/71.7~9.8/6.0
88.W.8
4
placebo
128.2/73.31t10.4/8.2
91.6f7.6
active
122.5/71.&l
[email protected]
5.Oe1.42
0.814.4
1.115.9
.19
2.eO.81
37.1k11.2
3.3tiO.80
28.7ti.2
5.3w.91
3.om.64
31.3%.8
4.91*1 .17
3.47kO.86
28.7ti.4
3.Oofl.08
33.9kll.3
Mean blood pressure (MBP) did not differ significantly between the two groups. Nor did it change with time (fig.1). At baseline the control group’s MBP was 90.4 +/- 8.0 mmHg, and the experimental group was 89.8 +/- 4.7 mmHg. At the end of the 4 weeks, the control group had a MBP of 91.6 +/- 7.6 mmHg and the experimental group had one of 88.6 +/- 4.7 mmHg. FBF did not differ significantly between the two groups. Over time the placebo group paralleled the changes in the omega-3 fatty acids group (fig.1). With V.C. though there were significant changes over time, the omega-3 fatty acids group did not differ significantly from the controls (fig.1). In the controls, FVR went from 27.6 +I- 9.7 mmHg/ml/min/l00g to 28.7 +I- 8.4 mmHg/ml/min/l00g, and in the omega-3 fatty acids group FVR went from 32.1 +/- 7.7 mmHg/ml/min/l00g to 33.9 +/- 11.3 mmHg/ml/min/l00g by the end of the 4 weeks (fig.1). These FVR changes were also not found to be significantly different.
342
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
MARINE OIL EFFECTS ON FOREARM HEMODYNAMICS Mean Blood Pressure Meank SE.
Venous Capacitance Mean? S.E.
,
Fig.1: Effect of Omega-3 Fatty Acids on Forearm Hemodynamlcs: During the four weeks, the effect of omega-3 fatty acids on mean blood pressure, forearm blood flow, venous capitance, and forearm vascular resistance did not differ significantly from the placebo group.
&Dirin Study; Table 2 summarizes the hemodynamic results.
Table 2: Aspirin Study Results. m
ASAtma/m!)
MBPlmmHQ
FBF~ml/minUOQg)
JVR~mmHa!mVmin/l OOg)
0
0
87.W.9
6.98rt6.0
21.5&l 2.4
1
10.8fo.9
88.8Q.6
5.17Z3.7
24&l
1.9
2
17.7*&l
88.Ok9.1
6.23t3.8
20.3f12.2
3
29.8rt6.4
88.W
6.3W.4
17.7&l 1.3
4
52.7Wl.4
87.2&l 1.1
9.237.3
16.2k13.1
5
90.w9.7
88.7k7.4
5.9w2.7
17.8f6.6
6
165.W20.0
90.0*9.4
6.07Q.O
19.9*12.3
1.4
MARCH 1990 VOL. 39 NO. 3
343
PROSTAGLANDINS
Serum salicylate levels rose from 10.8 to 165.0 mg/L over the 6 day period (fig.2); however, forearm hemodynamics did not change significantly with this increase. MBP did not change significantly from the baseline measurement of 87.0 +/- 5.9 mmHg.(fig.2). FVR was 21.5 +/- 12.4 mmHg/ml/min/l OOg at baseline and 19.9 +/- 12.3 mmHg/ml/min/l00g on day 6 (fig.2). Maximum inhibiton of platelet aggregation took place after ingesting 162 mg.of aspirin at which time serum salicylate was 17.7 +/- 6.4 mg/L.
ASPIRIN EFFECTS ON FOREARM Salicylale Me.” *SE.
Serum
Mean Blood Pressure-Aspirin Mean* S.E.
HEMODYNAMICS
Forearm Blood Flow-Aspirin Ihan *SE.
14,
Forearm Vascular Resistance MM” * S.E.
I
Fig. 2: Effect of Aspirin on Forearm Hemodynamics. Though serum salicylate levels rose with increasing doses, there was no significant differences in mean blood pressure, forearm blood flow, or forearm vascular resistance.
Discussion: Our study shows that supplementing the diet of normotensive males with 3g of omega-3 fatty acids daily for 1 month did not change BP nor decrease vascular resistance. We realize this study is not a
344
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
definitive test of omega-3 fatty acids effects on hemodynamics. Because of the limited sample size and the predominance of normotensive white males as subjects, the hemodynamic effects of marine oils on women, hypertensives, or other ethnic populations are not known. In addition, this study mainly applies to short-term effects. Taking dosages of Sg/day of omega-3 fatty acids, a longer period of marine oil supplementation may be necessary to produce changes in BP, FBF, or FVR. However, von Schacky et al. have shown that prostaglandin I3 urinary metabolite excretion increased at dosages of 10 ml of cod liver oil/day for 4 weeks (20). This amount is less than the 3g of omega-3 fatty acids per day given in this study. Therefore, even though prostaglandin I3 levels were probably increased, a longer duration of intake or a larger dose may be required to effect vascular tone. In contrast to our findings of no change in BP, some studies have reported decreases in BP. Mortenson found systolic BP to decrease with 4gIday of omega-3 fatty acids supplementation for 4 weeks (5). Singer reported decreases in BP with less than 3g/day of omega-3 fatty acids; however, the marine oil came directly from eating a can of mackerel per day as opposed to taking capsules (7). Thus, the effect of dietary omega-3 fatty acid supplementation on BP is still unresolved. Our data addresses the hemodynamic response to aspirin or marine oils under m conditions. However, it is possible that these agents exert their effects on resistance during times of stress, as Singer et al. found that when subjected to psychosocial stress tests (arithmetic calculations and sentence completions), mild essential hypertensive volunteers on mackerel diets did not increase in BP as much as the controls (21). In the aspirin study, it was proposed that as prostacyclin levels were inhibited increasingly with greater doses, BP and VR would have concomitantly increased ff vascular prostaglandin production is important in the regulation of resting vascular tone. Considering the high levels of serum salicylate attained, we would expect that at least by day 5, prostaglandin I2 formation and its vasodilatory activity would be inhibited and BP would have increased. There was no change found in either BP or VR in our study. Jaffe and Weksler have shown that prostacyclin production by endothelial cells after inhibition by aspirin recovers to control values by 35 hrs(22), thus prostaglandin I2 production should have been suppressed adequately during the time of our measurements.
Therefore, we conclude that prostaglandin
I2 production does not play an
important role in the regulation of resting vascular resistance in normal subjects. In summary, in this study of heafthy individuals, BP and FVR did not increase with aspirin ingestion and did not decrease with marine oil supplementation. Therefore, under the conditions in our study, pharmacological inhibition or stimulation of vascular prostaglandin metabolism in normotensive males does not alter resting forearm hemodynamics. We conclude that pharmacological manipulation of prostacyclin levels does not play a major role in regulating resting vascular resistance.
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
References: 1. Cannon PJ: Eicosanoids and the Blood Vessel Wall. Circulation 70523~5281984. 2. Dyerberg J, Bang HO, Stoffersen E: Eicosapentaenoic Atherosclerosis? Lancet2:117-119,1978.
Acid and Prevention of Thrombosis and
3. Dyetberg J, Bang HO: Haemostatic Function and Platelet Polyunsaturated Lancet 2:433-435.1979.
Fatty Acids in Eskimos. The
4. Lorenz Reinhard, et al: Platelet Function, Thrombaxane Formation and Blood Pressure Control During Supplementation of the Western Diet with Cod Liver Oil. Circulation 67:504-511.1978. 5. Mortensen JZ, Schmidt EB, Nielsen AH, Dyerberg J: The Effect of N-6 and N-3 Polyunsaturated Fatty Acids on Hemostasis, Blood Lipids and Blood Pressure. Thromb Haemost 50:543-546,1983. 6. Seiss W, et al: Platelet-Membrane Fatty Acids, Platelet Aggregation, A Mackerel Diet. Lancet 1:441-444,198O. 7. Singer Peter, et al: Lipid and Blood Pressure 49:99-108,1983.
and Thrombaxane
Formation During
- Lowering Effect of Mackerel Diet in Man. Atherosclerosis
8. Smith JB, Willis AL: Aspirin Selectively Inhibits Prostaglandin production in Human Platelets. Nature 231:235-237,1971_ 9. Preston FE, et al: Inhibition of Prostacyclin and Platelet Thromboxane Engl J Med 304:76-79,1981.
A2 After Low-Dose Aspirin.
New
10. Weksler BB, et al: Differential Inhibition by Aspirin of Vascular and Platelet Prostaglandin Synthesis in Atherosclerotic Patients. New Engl J Med308:800-804,1983. 11. Masotti G, et al: Differential Inhibition of Prostacyclin Production and Platelet Aggregation by Aspirin Lancet2:1213-1216,1979. 12. Fischer S, Weber PC: Prostaglandin I3 is Formed In Vivo in Man After Dietary Eicosapentaenoic Nature 30:165-l 68,1984. 13. Trinder P: Biochem J57:301,
Acid
1954.
14. Born GVR: Aggregation of Blood Platelet by Adenosine Diphosphate and Its Reversal. Nature 194:927-929.1962. 15. Katz MA, Janjan N, and Swanson J: Forearm Hemodynamics in Volunteers and in Untreated and Treated Hypertensive Patients. Cerdiovasc Med317-327,1978.
16. Sumner DS: Mercury Strain-Gauge Plethysmography, in Bernstein EF (ed): Noninvasive Diagnostic Techniques in Vascular Disease. St. Louis MO, C.V. Mosby Co, 1978, pp.1 26-147.
346
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
17. Takeshita A, Mark A: Decreased Vasodilator Capacity of Forearm Resistance Vessels in Borderline Hypertension. Hypertension2:610-616,1980. 18. D.E. Hokanson Inc. Principles of Plefhysmography.
Issaquah, WA. USA.
19. Sullivan JM, Prewitt RL, Ratts TE: Sodium Sensitivity in Normotensive Humans. Am J Med Sci295:370-377, 1988.
and Borderline Hypertensive
20. von Schacky C, Fischer S, Weber PC: Long-term Effects of Dietary Marine Omega-3 Fatty Acids Upon Plasma and Cellular Lipids, Platelet Function, and Eicosanoid Formation in Humans. J C/in invest 76:1626-1631,1985. 21. Singer P, et al. Blood Pressure and Lipid Lowering Effect of Mackerel and Herring Diet in Patients with Mild Essential Hypertension. Atherosclerosis 56:223-235,1985. 22.Jaffe EA, Weksler BB: Recovery of Endothelial Cell Prostacyclin Production after lnhibtion by Low Doses of Aspirin. J C/in Invest 63:532-535,i 979.
Editor:
W.E. Lands
MARCH 1990 VOL. 39 NO. 3
Received:10-27-89
Accepted:
l-25-90
347
Division of Cardiovaecular Diaeaeee, Department of Medicine, University of Tenneeeee, Memphis, TN 38163
Abstract: Prostaglandin synthesis has been reported to change with aspirin ingestion via cyclooxygenase enzyme inhibition and with marine oil supplementation via an increase in the metabolism of 3-series eicosanoids. This study investigated the effects of pharmacological manipulations of prostaglandin metabolism on forearm hemodynamics and blood pressure. The agents studied were omega-3 fatty acids and aspirin. In the omega-3 fatty acid study, two groups of normal volunteers (N=lO/group) supplemented their diets with either marine oil capsules or placebo. Hemodynamic variables (Mercury-in-Silastic forearm plethysmograghy) were measured initially and weekly for 4 weeks. There were no significant differences between the two groups in blood pressure, forearm blood flow, venous capacitance, or forearm vascular resistance. Parallel changes occurred for forearm blood flow and venous capacitance. Six normal volunteers took daily dosages of aspirin, increasing from 162 to 2600 mg. Hemodynamic measurements, ADP-induced platelet aggregation, and serum salicylate levels were obtained daily. Maximum inhibition of platelet aggregation occurred after 162 mg.(serum salicylate = 17.7+/-6.4 mg/l). Though serum salicylate levels rose to 165.0+/- 20.0 mgll, no significant changes occurred in blood pressure or forearm blood flow. Even at aspirin levels 16- fold greater than those required to impair platelet aggregation, the changes in forearm vascular resistance were not found to be significant. These results suggest that under resting conditions in normotensive males, neither pharmacological inhibition nor stimulation of vascular prostaglandin metabolism alters forearm vascular resistance or arterial blood pressure.
introduction The eicosanoids, produced by blood constituents and by vascular endothelial and smooth muscle cells, have a wide range of actions on the cardiovascular system. The cyclooxygenase pathway of eicosanoid metabolism produces thromboxane, a platelet aggregator, and prostacyclin, a vasodilator. Prostacyclin is the major arachadonic acid metabolite in vascular endothelium and may be an important regulator of vascular resistance (VR). Pharmacological agents such as omega-3 fatty acids contained in marine oils and non-steroidal antiinflammatory agents (NSAIA) are known to influence prostacyclin levels. Both these agents have been associated with the prevention of cardiovascular disease. Several studies suggest that aspirin, through its antithrombotic activity reduces myocardial infarctions, strokes, and
MARCH 1990 VOL. 39 NO. 3
339
PROSTAGLANDINS
cardiovascular deaths.(l) Diets containing relatively high levels of marine oils have been demonstrated to lower cholesterol levels, platelet aggregation, thrombotic tendencies, blood viscosity, and BP (2-7). NSAIA, by acetylating cyclooxygenase, prostaglandin
inhibit the formation of both thromboxane
A2 and
I2 (prostacyclin) (8,9); therefore, aspirin is able to decrease platelet aggregation and
decrease vasodilation, thereby potentially increasing VR and BP. Furthermore, studies have shown that a greater amount of aspirin is necessary to inhibit prostaglandin I2 formation than is required to prevent production of thromboxane
A2. At low doses of aspirin, the physiological
effects of prostaglandin
12 are
preserved while platelet aggregation is inhibited.(lO,ll) The proposed mechanism underlying the effects of marine oils is that increases in omega-3 FA’s compete with N-6 fatty acid metabolism, leading to a switch from the 2-series to the 3-series of prostaglandin metabolism. For example, TxA2, a proaggregator, has been noted to decrease while TxA3, which lacks aggregatory activity, increases. that diets rich in marine oils produce increased prostaglandin
Studies have also shown
I3 levels without changing prostaglandin
I2
levels.(l2) This increase in total prostacyclin levels may explain the reported changes in BP with marine oil supplementation. The hemodynamic effects of the changes in prostaglandin levels are not yet understood. Therefore, the purpose of this study was to investigate the effects of pharmacological manipulation of prostaglandin metabolism on VR (forearm hemodynamics).
Subjects
and Methodology:
aa-3Fattvm The Institutional Review Board of the University of Tennessee, Center for Health Sciences approved the protocol for this study. Twenty normal male volunteers participated in the study. They met the predetermined criteria: normotensive, between the ages of 20-39 years, and not taking any medications. The volunteers were within 35% of their ideal body weight as defined by frame size and height (Metropolitan life insurance values). The participants were randomized into two groups. The control group (N=lO) was given six 1000 mg. capsules/day of wheat germ oil (Schii Bio-Food Products). The experimental group (N=lO) was given six 1000 mg. capsules of marine oil (Promega, Parke-Davis Health Products Group), totaling 2100 rng. of eicosapentaenoic acid and 900 mg. of docosahexaenoic per day. The marine oils and the placebo were ingested for 4 weeks as nutritional supplements to the normal diet. Compliance was checked each week by counting the number of capsules remaining in the returned bottle. Three supine blood pressure measurements were obtained in triplicate on three different days before supplementation in order to establish the baseline reading on each of the subjects. Serial BP and plethysmographic readings were measured before administration of placebo or active compound, and once a week thereafter in order to detect any changes on hemodynamics over time. Data Analysis: The experimental group was compared to the control group. A two-tailed analysis of variance with allowances for repeated measures was used to test for significance of changes in BP, forearm blood flow (FBF), venous capacitance (VC), and VR. A p value of 0.05 or less indicated a significant difference. The data was analyzed through a VAX Statistical Analysis Package.
340
MARCH 1990 VOL. 39 NO. 3
PROSTAGLANDINS
Aspirin Study Six healthy male volunteers took daily dosages of aspirin increasing from 162 to 2600 mg. over 5 days with day 6 as a recovery day. The dosages were doubled each following day. A baseline plethysmograph ADP-induced platelet aggregation and serum salicylate levels were obtained before administration of aspirin. As dose was increased each day and on the recovery day, a plethysmograph, serum salicylate level, and ADP-induced platelet aggregation were measured. Serum salicylate was measured as described by Trinder (13). performed by the method reported by Born et al.(14). Data Analysis measures.
Forearm
Platelet aggregation studies were
- Data were tested by significance by analysis of variance with allowance for repeated
Hemodynamlcs
Studies:
BP was measured by a Dinamap Vital Signs Monitor at the time of forearm blood flow measurements. Whitney mercury in silastic strain gauge plethysmography was used to measure FBF and VC (15,16,17) The volunteers fasted for 1 hour beforehand and rested for 20 minutes while supine before plethysmography. A mercury filled strain gauge was connected to a Hokanson model EC-4 phethysmograph (18) attached to a Fisher Series 5000 Recordall strip chart recorder. The appropriate length strain gauge was stretched 2% past its resting length, wrapped around the left forearm about 6-7 cm below the elbow, and taped to the arm. A blood pressure cuff was placed on the left upper arm and inflated to 40mmHg to stop venous flow yet still allow arterial flow. FBF (mVmin/lOOg) was calculated from the initial slope obtained from the early phase of radial expansion of the forearm as the veins filled with blood: FBF= initial slo e*K’120. Forearm Vascular Resistance (FVR) was then calculated by using the formula FVR = (MgP / FBF), With maximal distention of the veins, fluid diffuses out of the capillaries and a second slope was obtained. A tangent is drawn from this second slope to an erect perpendicular line drawn at baseline. VC was then calculated from the height of this perpendicular line to where it meets the tangent: VC=heightYYL,, Lo=forearm circumference. VC gives an indication of the veins ability to stretch at a given pressure, 40 mmHg. These hemodynamic rests in between each reading.
measurements were obtained in triplicate with 3 minute
In previous studies, we have shown that this method is able to detect significant changes in FVR between hypertensive and normotensive individuals during rest and reactive hyperemia.l g The reproducibility of this method has been evaluated in 20 normal subjects. MBP varied by 3%, FBF and FVR by 16.5%, and VC by 11.4%.
MARCH 1990 VOL. 39 NO. 3
341
PROSTAGLANDINS
Results:
- 3 Fattv Acid Study:
Qmeaa
Twenty male volunteers joined the study. The placebo group consisted of 9 Caucasians and 1 asian; the marine oil group had 9 Caucasians and 1 black. Adverse effects were not reported by any participants. The average weights for the two groups were not significantly different : Placebo group 168.8 Ibs s marine oil group - 165.7 Ibs. The mean age of 27.2 yr. for the marine oil group differed significantly from the placebo group’s mean age of 24.8 yrs, although the difference was only 2 yrs (P > 0.0180). Table 1 summarizes the results from the hemodynamic
measurements.
Table 1: Marine Oil Results. TimeGnxlg
BP(nn+!c~)
0 placebo
124.8/73.#11
S/7.3
MBP 90.4b3.0
vCfnv1Ocq
FBF
5.45& .27
3.w1.07
B!B 27.1s9.7
active
123.4l73.1f9.4l4.3
89.W.7
5.92rto.94
3.01*0.86
32.1f7.7
1 placebo
122.9/72.ti10.4/6.8
89.2k7.4
5791.47
4.ow1.64
28.ti10.3
active
122.9/73.1~9.4/4.0
90.w.2
6.Olk1.03
3.16-t0.76
31.1ti.8
2
placebo
122.8/71 .910.3/7.8
89.2k7.9
5.3s1.65
2.77kO.48
33.8f7.1
active
123.9/73&l
90.w.2
5.&l
3
placebo
120.1/71 [email protected]/8.4
87.a.7
5.41kl.62
adie
121.7/71.7~9.8/6.0
88.W.8
4
placebo
128.2/73.31t10.4/8.2
91.6f7.6
active
122.5/71.&l
[email protected]
5.Oe1.42
0.814.4
1.115.9
.19
2.eO.81
37.1k11.2
3.3tiO.80
28.7ti.2
5.3w.91
3.om.64
31.3%.8
4.91*1 .17
3.47kO.86
28.7ti.4
3.Oofl.08
33.9kll.3
Mean blood pressure (MBP) did not differ significantly between the two groups. Nor did it change with time (fig.1). At baseline the control group’s MBP was 90.4 +/- 8.0 mmHg, and the experimental group was 89.8 +/- 4.7 mmHg. At the end of the 4 weeks, the control group had a MBP of 91.6 +/- 7.6 mmHg and the experimental group had one of 88.6 +/- 4.7 mmHg. FBF did not differ significantly between the two groups. Over time the placebo group paralleled the changes in the omega-3 fatty acids group (fig.1). With V.C. though there were significant changes over time, the omega-3 fatty acids group did not differ significantly from the controls (fig.1). In the controls, FVR went from 27.6 +I- 9.7 mmHg/ml/min/l00g to 28.7 +I- 8.4 mmHg/ml/min/l00g, and in the omega-3 fatty acids group FVR went from 32.1 +/- 7.7 mmHg/ml/min/l00g to 33.9 +/- 11.3 mmHg/ml/min/l00g by the end of the 4 weeks (fig.1). These FVR changes were also not found to be significantly different.
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PROSTAGLANDINS
MARINE OIL EFFECTS ON FOREARM HEMODYNAMICS Mean Blood Pressure Meank SE.
Venous Capacitance Mean? S.E.
,
Fig.1: Effect of Omega-3 Fatty Acids on Forearm Hemodynamlcs: During the four weeks, the effect of omega-3 fatty acids on mean blood pressure, forearm blood flow, venous capitance, and forearm vascular resistance did not differ significantly from the placebo group.
&Dirin Study; Table 2 summarizes the hemodynamic results.
Table 2: Aspirin Study Results. m
ASAtma/m!)
MBPlmmHQ
FBF~ml/minUOQg)
JVR~mmHa!mVmin/l OOg)
0
0
87.W.9
6.98rt6.0
21.5&l 2.4
1
10.8fo.9
88.8Q.6
5.17Z3.7
24&l
1.9
2
17.7*&l
88.Ok9.1
6.23t3.8
20.3f12.2
3
29.8rt6.4
88.W
6.3W.4
17.7&l 1.3
4
52.7Wl.4
87.2&l 1.1
9.237.3
16.2k13.1
5
90.w9.7
88.7k7.4
5.9w2.7
17.8f6.6
6
165.W20.0
90.0*9.4
6.07Q.O
19.9*12.3
1.4
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PROSTAGLANDINS
Serum salicylate levels rose from 10.8 to 165.0 mg/L over the 6 day period (fig.2); however, forearm hemodynamics did not change significantly with this increase. MBP did not change significantly from the baseline measurement of 87.0 +/- 5.9 mmHg.(fig.2). FVR was 21.5 +/- 12.4 mmHg/ml/min/l OOg at baseline and 19.9 +/- 12.3 mmHg/ml/min/l00g on day 6 (fig.2). Maximum inhibiton of platelet aggregation took place after ingesting 162 mg.of aspirin at which time serum salicylate was 17.7 +/- 6.4 mg/L.
ASPIRIN EFFECTS ON FOREARM Salicylale Me.” *SE.
Serum
Mean Blood Pressure-Aspirin Mean* S.E.
HEMODYNAMICS
Forearm Blood Flow-Aspirin Ihan *SE.
14,
Forearm Vascular Resistance MM” * S.E.
I
Fig. 2: Effect of Aspirin on Forearm Hemodynamics. Though serum salicylate levels rose with increasing doses, there was no significant differences in mean blood pressure, forearm blood flow, or forearm vascular resistance.
Discussion: Our study shows that supplementing the diet of normotensive males with 3g of omega-3 fatty acids daily for 1 month did not change BP nor decrease vascular resistance. We realize this study is not a
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PROSTAGLANDINS
definitive test of omega-3 fatty acids effects on hemodynamics. Because of the limited sample size and the predominance of normotensive white males as subjects, the hemodynamic effects of marine oils on women, hypertensives, or other ethnic populations are not known. In addition, this study mainly applies to short-term effects. Taking dosages of Sg/day of omega-3 fatty acids, a longer period of marine oil supplementation may be necessary to produce changes in BP, FBF, or FVR. However, von Schacky et al. have shown that prostaglandin I3 urinary metabolite excretion increased at dosages of 10 ml of cod liver oil/day for 4 weeks (20). This amount is less than the 3g of omega-3 fatty acids per day given in this study. Therefore, even though prostaglandin I3 levels were probably increased, a longer duration of intake or a larger dose may be required to effect vascular tone. In contrast to our findings of no change in BP, some studies have reported decreases in BP. Mortenson found systolic BP to decrease with 4gIday of omega-3 fatty acids supplementation for 4 weeks (5). Singer reported decreases in BP with less than 3g/day of omega-3 fatty acids; however, the marine oil came directly from eating a can of mackerel per day as opposed to taking capsules (7). Thus, the effect of dietary omega-3 fatty acid supplementation on BP is still unresolved. Our data addresses the hemodynamic response to aspirin or marine oils under m conditions. However, it is possible that these agents exert their effects on resistance during times of stress, as Singer et al. found that when subjected to psychosocial stress tests (arithmetic calculations and sentence completions), mild essential hypertensive volunteers on mackerel diets did not increase in BP as much as the controls (21). In the aspirin study, it was proposed that as prostacyclin levels were inhibited increasingly with greater doses, BP and VR would have concomitantly increased ff vascular prostaglandin production is important in the regulation of resting vascular tone. Considering the high levels of serum salicylate attained, we would expect that at least by day 5, prostaglandin I2 formation and its vasodilatory activity would be inhibited and BP would have increased. There was no change found in either BP or VR in our study. Jaffe and Weksler have shown that prostacyclin production by endothelial cells after inhibition by aspirin recovers to control values by 35 hrs(22), thus prostaglandin I2 production should have been suppressed adequately during the time of our measurements.
Therefore, we conclude that prostaglandin
I2 production does not play an
important role in the regulation of resting vascular resistance in normal subjects. In summary, in this study of heafthy individuals, BP and FVR did not increase with aspirin ingestion and did not decrease with marine oil supplementation. Therefore, under the conditions in our study, pharmacological inhibition or stimulation of vascular prostaglandin metabolism in normotensive males does not alter resting forearm hemodynamics. We conclude that pharmacological manipulation of prostacyclin levels does not play a major role in regulating resting vascular resistance.
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References: 1. Cannon PJ: Eicosanoids and the Blood Vessel Wall. Circulation 70523~5281984. 2. Dyerberg J, Bang HO, Stoffersen E: Eicosapentaenoic Atherosclerosis? Lancet2:117-119,1978.
Acid and Prevention of Thrombosis and
3. Dyetberg J, Bang HO: Haemostatic Function and Platelet Polyunsaturated Lancet 2:433-435.1979.
Fatty Acids in Eskimos. The
4. Lorenz Reinhard, et al: Platelet Function, Thrombaxane Formation and Blood Pressure Control During Supplementation of the Western Diet with Cod Liver Oil. Circulation 67:504-511.1978. 5. Mortensen JZ, Schmidt EB, Nielsen AH, Dyerberg J: The Effect of N-6 and N-3 Polyunsaturated Fatty Acids on Hemostasis, Blood Lipids and Blood Pressure. Thromb Haemost 50:543-546,1983. 6. Seiss W, et al: Platelet-Membrane Fatty Acids, Platelet Aggregation, A Mackerel Diet. Lancet 1:441-444,198O. 7. Singer Peter, et al: Lipid and Blood Pressure 49:99-108,1983.
and Thrombaxane
Formation During
- Lowering Effect of Mackerel Diet in Man. Atherosclerosis
8. Smith JB, Willis AL: Aspirin Selectively Inhibits Prostaglandin production in Human Platelets. Nature 231:235-237,1971_ 9. Preston FE, et al: Inhibition of Prostacyclin and Platelet Thromboxane Engl J Med 304:76-79,1981.
A2 After Low-Dose Aspirin.
New
10. Weksler BB, et al: Differential Inhibition by Aspirin of Vascular and Platelet Prostaglandin Synthesis in Atherosclerotic Patients. New Engl J Med308:800-804,1983. 11. Masotti G, et al: Differential Inhibition of Prostacyclin Production and Platelet Aggregation by Aspirin Lancet2:1213-1216,1979. 12. Fischer S, Weber PC: Prostaglandin I3 is Formed In Vivo in Man After Dietary Eicosapentaenoic Nature 30:165-l 68,1984. 13. Trinder P: Biochem J57:301,
Acid
1954.
14. Born GVR: Aggregation of Blood Platelet by Adenosine Diphosphate and Its Reversal. Nature 194:927-929.1962. 15. Katz MA, Janjan N, and Swanson J: Forearm Hemodynamics in Volunteers and in Untreated and Treated Hypertensive Patients. Cerdiovasc Med317-327,1978.
16. Sumner DS: Mercury Strain-Gauge Plethysmography, in Bernstein EF (ed): Noninvasive Diagnostic Techniques in Vascular Disease. St. Louis MO, C.V. Mosby Co, 1978, pp.1 26-147.
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17. Takeshita A, Mark A: Decreased Vasodilator Capacity of Forearm Resistance Vessels in Borderline Hypertension. Hypertension2:610-616,1980. 18. D.E. Hokanson Inc. Principles of Plefhysmography.
Issaquah, WA. USA.
19. Sullivan JM, Prewitt RL, Ratts TE: Sodium Sensitivity in Normotensive Humans. Am J Med Sci295:370-377, 1988.
and Borderline Hypertensive
20. von Schacky C, Fischer S, Weber PC: Long-term Effects of Dietary Marine Omega-3 Fatty Acids Upon Plasma and Cellular Lipids, Platelet Function, and Eicosanoid Formation in Humans. J C/in invest 76:1626-1631,1985. 21. Singer P, et al. Blood Pressure and Lipid Lowering Effect of Mackerel and Herring Diet in Patients with Mild Essential Hypertension. Atherosclerosis 56:223-235,1985. 22.Jaffe EA, Weksler BB: Recovery of Endothelial Cell Prostacyclin Production after lnhibtion by Low Doses of Aspirin. J C/in Invest 63:532-535,i 979.
Editor:
W.E. Lands
MARCH 1990 VOL. 39 NO. 3
Received:10-27-89
Accepted:
l-25-90
347