The effects of dietary obesity on protein expressions of insulin signaling pathway in rat aorta

The deleterious effects of obesity on insulin response in vasculature may be due to changes in various components of insulin signaling pathway. Therefore, this study was designed to investigate effects of dietary-obesity, removal of palatable diet, and fenofibrate treatment on protein expressions of insulin signaling pathway in rat aorta. Adult male Wistar rats were fed either standard chow or a palatable diet (untreated obese animals) for 15 weeks. Another group of rats were fed the palatable diet for 8 weeks followed by standard chow for further 7 weeks, while a further group were fed the palatable diet for 15 weeks and were dosed with fenofibrate (50 mg/kg/day) for the last 7 weeks. Untreated obese animals had significantly higher body weight than other three groups (p < 0.05 for all). There were no significant differences between IR-β, IRS1 and IRS2, Akt, Shc, and ERK1/2 levels in chow-fed and untreated obese animals, while PI 3-kinase level were significantly (p < 0.0001) decreased in untreated obese animals. Chronic removal of palatable diet completely reversed the levels of PI 3-kinase to the normal while, fenofibrate treatment further reduced PI 3-kinase levels. On the other hand, there was a significant (p < 0.05) increase in eNOS in untreated obese animals compared with chow-fed controls. This effect was reversed by removal of palatable diet and fenofibrate treatment. These data suggest that dietary-obesity selectively inhibits PI 3-kinase while, removal of obesity-inducing diet improves PI 3-kinase levels which may have a role in vascular reactivity.

Lactation modulates diurnal expression profiles of specific leptin receptor isoforms in the rat hypothalamus

We investigated the effects of lactation on diurnal changes in serum leptin and hypothalamic expression of the leptin receptor isoforms, Ob-Ra, -Rb, -Rc, -Re and -Rf in rats. In non-lactating rats, serum leptin concentration was increased at night while hypothalamic mRNA levels of Ob-Rb, -Rc and -Re decreased; by contrast, expression of Ob-Ra and Ob-Rf was unchanged at night. There were significant negative correlations between serum leptin and mRNA expression of Ob-Rb (P<0.001) and Ob-Re (P<0.05), which were independent of time of day. In lactating rats, the nocturnal rise in serum leptin was attenuated. Daytime hypothalamic Ob-Rb mRNA levels were significantly lower than in non-lactating controls, and the normal nocturnal decreases in expression of Ob-Rb, -Rc and -Re were lost. The relationship between serum leptin and Ob-Re expression was not changed by lactation. Lactation had no effect on the expression of Ob-Ra mRNA in the hypothalamus. Decreased daytime Ob-Rb expression could lead to reduced hypothalamic sensitivity to leptin, and thus contribute to increased daytime appetite in lactating rats. Moreover, maintaining high levels of Ob-Re expression could, by increasing hypothalamic leptin-binding protein concentration and reducing local leptin bioavailability, further accentuate hyperphagia. Thus, selective changes in expression of specific isoforms of the leptin receptor may contribute to the hyperphagia of lactation in rats.

Effects of short-term feeding of a highly palatable diet on vascular reactivity in rats

BACKGROUND

Numerous studies have shown that long-term consumption of high-fat, high-energy diet results in obesity, which in turn, leads to cardiovascular disorders. However, there is little or no data on the acute effects of a highly palatable diet on vascular function.

MATERIAL AND METHODS

In this study we aimed to evaluate the changes in metabolic and vascular reactivity in Wistar rats fed a palatable diet for 2 days.

RESULTS

Two-days feeding of rats with a palatable diet did not effect body weight, fat-pad mass or gastrocnemius muscles weights. Nor there were any changes in plasma glucose, insulin or leptin levels. However, compared with chow-fed rats, palatable diet-fed rats had significantly raised plasma free fatty acids and triglycerides levels (for both, P < 0.01). Compared with chow-fed animals, vasorelaxation responses to carbamylcholine and sodium nitroprusside were significantly attenuated in palatable diet-fed rats (for both, P < 0.01). However, there were no differences in histamine-induced vasorelaxation between chow-fed and palatable diet-fed rats.

CONCLUSION

These data indicates that diet-induced endothelium-dependent and -independent vascular dysfunction occurs long before obesity develops.

Dietary obesity in the rat induces endothelial dysfunction without causing insulin resistance: a possible role for triacylglycerols

Impaired arterial vasorelaxation, due primarily to endothelial dysfunction, is associated with obesity. To clarify the relationship with insulin resistance and other metabolic disturbances, we studied endothelial-dependent and -independent vascular responses in rats with dietary-induced obesity. Dietary-obese rats had significantly higher body weights (10-32%; P<0.001) and fat-pad masses (220-280%; P<0.001) than lean controls, together with raised plasma levels of triacylglycerols (15-80%; P<0.001), non-esterified fatty acids (13-38%; P<0.05) and leptin (85-180%; P<0.001). However, measures of insulin sensitivity (including the hyperinsulinaemic-euglycaemic clamp in a parallel experiment) were comparable with those in controls. Contractions induced in mesenteric arteries by noradrenaline (0.5-8 micromol/l) were comparable in lean and obese groups, but vasorelaxation in noradrenaline-preconstricted arteries was markedly reduced in dietary-obese rats of both sexes. Concentration-response curves to endothelium-dependent vasorelaxants (acetylcholine, A23187 and insulin) showed significant reductions in maximal relaxation (20-95% less than in leans; P<0.001) and significant rightward shifts in EC(40) (concentration giving 40% of maximal response) (P<0.01). Relaxation in response to the direct NO donor, sodium nitroprusside, showed a lesser impairment (12%; P<0.01) in dietary-obese rats. Maximal relaxation to acetylcholine was correlated inversely in both sexes with fat-pad mass (r(2)=0.37, P<0.05) and plasma triacylglycerols (r(2)=0.51, P<0.01), and with leptin in males only (r(2)=0.35, P<0.05). Independent determinants of acetylcholine-induced relaxation were fat mass and plasma triacylglycerols; plasma insulin and insulin sensitivity had no effect. Dietary-induced obesity severely impaired arterial relaxation in both sexes, particularly at the endothelial level. This is not attributable to insulin resistance, but may be related to moderate hypertriglyceridaemia.

Diet-induced endothelial dysfunction in the rat is independent of the degree of increase in total body weight

A growing number of studies indicate an association between obesity, insulin resistance, dyslipidaemia and cardiovascular disorders, collectively known as Syndrome X. In this study we have aimed to produce a model of Syndrome X by voluntary feeding of Wistar rats with a highly palatable cafeteria diet, and examined its effects on metabolic changes and vascular reactivity of Wistar rats. At the end of the experiment, the cafeteria-diet fed group was divided into two groups of low weight gain (LWG) and high weight gain (HWG). Both LWG and HWG groups had significantly (P<0.01) higher fat-pad mass than their chow-fed counterparts, while gastrocnemius muscle mass were comparable. All cafeteria-diet fed rats had significantly (P<0.01) raised plasma triacylglycerol (TG) levels whereas plasma non-esterified fatty acids, glucose and insulin levels were similar between chow-fed and cafeteria-diet fed rats. Vasorelaxation responses to acteylcholine, insulin and sodium nitroprusside were significantly (P<0.01) attenuated in cafeteria-diet fed animals; however, there were no differences in contractile responses of the mesenteric arteries to noradrenaline or KCl between the groups. Multiple regression analysis showed a significant (P<0.05) negative association between plasma TG levels and reduction in acetylcholine-induced vasorelaxation. Acetylcholine-induced vasorelaxation was also significantly (P<0.05) associated with the amount of fat-pad mass. These data suggest that diet-induced vascular dysfunction can occur in the absence of insulin resistance, and that plasma TGs may have a detrimental effect on vascular reactivity.

Troglitazone corrects metabolic changes but not vascular dysfunction in dietary-obese rats

Insulin resistance has been attributed to the defect in vascular function associated with obesity, type 2 diabetes and dyslipidaemia. We have investigated vascular effects of chronic (3-week) administration of troglitazone on female Wistar rats with moderate dietary obesity. Compared with lean controls, untreated obese rats had significantly higher body weights, fat pad masses, plasma triglycerides, free fatty acids and leptin levels (for all P < 0.01). These metabolic changes were corrected by troglitazone treatment. In mesenteric arteries, responses to noradrenaline or KCl were similar in all groups. However, in noradrenaline-preconstricted arteries, vasorelaxations to acetylcholine and insulin were significantly (50-60% less than in lean, P < 0.001) attenuated in both untreated and troglitazone-treated obese rats. Relaxations to sodium nitroprusside showed similar but lesser impairment in both untreated and troglitazone-treated obese animals. Our data show that although troglitazone markedly improved obesity-induced metabolic changes, it failed to correct vascular dysfunction associated with obesity in female Wistar rats.

Vasorelaxant effects of oestradiols on guinea pigs: a role for gender differences

Various studies have shown vasorelaxation properties for 17alpha- and 17beta-oestradiol. Here, we studied the effects of gender difference as well as oestrous cycle on oestradiol-induced vasorelaxation in mesenteric arteries from male and female guinea-pigs and in main uterine arteries from female guinea-pigs in vitro. Both 17alpha- and 17beta-oestradiol (0.5-20 micromol L-1) induced concentration-dependent relaxation of both mesenteric and uterine arteries preconstricted with either noradrenaline (NA; 10 micromol L-1) or KCl (125 mmol L-1) from both day-7 and day-15 female guinea-pigs. 17beta-oestradiol was more potent in relaxing arteries precontracted with NA than those pretreated with KCl, while 17alpha-oestradiol was more effective in relaxing those arteries precontracted with KCl. In mesenteric arteries from male animals, 17alpha-oestradiol was significantly (P < 0.001) more potent on arteries precontracted with NA than KCl, an effect opposite to that seen on arteries from female animals. However, both 17alpha- and 17beta-oestradiol were more potent in relaxing arteries from male animals compared with their female counterparts. These data indicate a possible role for gender differences in the vascular effects of oestradiols.

The mechanism of resveratrol-induced vasorelaxation differs in the mesenteric resistance arteries of lean and obese rats

Resveratrol has been shown to induce vasorelaxation. In this study, we investigated the mechanism(s) of resveratrol-induced vasorelaxation in resistance mesenteric arteries from male lean and dietary-induced obese rats. Compared with lean rats, arteries from dietary-obese rats showed significant (P<0.001) endothelial dysfunction, as indicated by a decrease (>20%) in maximal acetylcholine-induced vasorelaxation. Resveratrol (5-35 micromol/l) induced concentration-dependent relaxation of mesenteric arteries preconstricted with noradrenaline (8 micromol/l) or KCl (125 mmol/l) from both lean and dietary-obese rats. There were no significant differences between the two groups, achieving a maximum relaxation of >95% at a concentration of 35 micromol/l. In noradrenaline-preconstricted arteries from lean rats, N(G)-nitro-L-arginine methyl ester (L-NAME; 100 and 300 micromol/l) caused a significant (P<0.01) concentration-dependent rightward shift in reseveratrol activity, with no effect on maximal responses. However, L-NAME (100 and 300 micromol/l) did not alter the effects of reseveratrol on arteries from dietary-obese rats, giving superimposed concentration-responses curves. Indomethacin was also ineffective in altering resveratrol activity in arteries from both lean and dietary-obese rats. In noradrenaline-precontracted arteries from dietary-obese rats, responses to resveratrol were not attenuated by endothelial denudation, indicating an action independent of the endothelium. This study indicates that: (a) the maximal effects of resveratrol on resistance arteries from lean and dietary-obese rats are not effected by endothelial dysfunction, and (b) the effects of resveratrol in lean animals (where endothelial function is not impaired), but not in dietary-obese rats, are mediated via NO.

Resveratrol induces vasorelaxation of mesenteric and uterine arteries from female guinea-pigs

Naturally occurring hydroxystilbenes have been shown to induce vasorelaxation. Here, we studied the mechanism of resveratrol-induced vasorelaxation in different types of blood vessels, namely mesenteric (resistance) and main uterine (conductance) arteries, from female guinea-pigs on day 7 and day 15 of the oestrous cycle. Resveratrol (5-70 micromol/l) induced concentration-dependent relaxation of both mesenteric and uterine arteries preconstricted with either noradrenaline (NA; 10 micromol/l) or KCl (125 mmol/l). Resveratrol was 2-fold more potent in inducing relaxation of mesenteric arteries than of uterine arteries. Its effects on uterine arteries from both day-7 and day-15 guinea-pigs were similar, irrespective of the constrictor used, but it was significantly (P<0.01) more potent in inducing relaxation of mesenteric arteries contracted with NA compared with those constricted with KCl. In day-7 arteries precontracted with NA, N(G)-nitro-L-arginine methyl ester (L-NAME; 10 micromol/l) had no effects on the time course of resveratrol-induced vasorelaxation in either mesenteric or uterine arteries. However, indomethacin (50 micromol/l) significantly (P<0.05) potentiated resveratrol's effect on mesenteric, but not uterine, arteries. Indomethacin had no effect on resveratrol-induced vasorelaxation of arteries contracted with KCl, whereas L-NAME significantly (P<0.05) reduced the effects of resveratrol on uterine, but not on mesenteric, arteries. In day-15 arteries, L-NAME significantly (P<0.01) attenuated the effects of resveratrol on mesenteric arteries contracted with NA. Indomethacin had no effect on resveratrol activity. This study indicates that: (a) the effect of resveratrol on resistance arteries is greater than that on conductance arteries; (b) the effects of resveratrol are not mediated via prostanoids, but NO may play a role; and (c) the stage of the oestrous cycle has no influence on resveratrol-induced vasorelaxation.

Comparable vasorelaxant effects of 17alpha- and 17beta-oestradiol on rat mesenteric resistance arteries: an action independent of the oestrogen receptor

17beta-Oestradiol (17betaE(2)) has vasorelaxant properties that may contribute to its beneficial cardiovascular effects. The mechanism of vasorelaxation remains controversial, but does not appear to involve interaction of 17betaE(2) with its nuclear receptor. The present study examined the effects on resistance arteries of 17betaE(2) and its isomer, 17alpha-oestradiol (17alphaE(2)), which does not bind to the classical oestrogen receptor. In arteries precontracted with either noradrenaline or KCl, 17betaE(2) and 17alphaE(2) caused comparable relaxation in a concentration-dependent manner over the concentration range 0.1-10 micromol/l, with no significant difference in the maximal effect obtained. Pre-incubation of the arteries with 17betaE(2) or 17alphaE(2) for 15 min reduced the magnitude and duration of the force generated with both noradrenaline and KCl to a comparable degree. Vasorelaxation induced by either 17betaE(2) or 17alphaE(2) was not blocked by an inhibitor of NO synthase or by protein synthesis inhibitors, indicating that vasodilatation is not dependent upon either NO generation or protein synthesis. In the absence of extracellular calcium, both oestradiols still relaxed arteries precontracted with NA, suggesting that they inhibit intracellular calcium release. Both 17betaE(2) and 17alphaE(2) therefore have important and comparable vasorelaxant properties that do not require interaction with the nuclear oestrogen receptor. Direct interactions with the cell membrane or with ion-channel proteins may be responsible.

Modulation of force induced by pH in the guinea-pig uterus examined at two stages of the oestrous cycle

Changes in pH have a marked influence on uterine contractility. Changes in uterine pH occur during pregnancy and labour, when marked endocrine changes are occurring. As hormonal status can also influence contractility, this study investigated whether pH-induced modulation of uterine force in influenced by hormonal changes. The effects of altering intracellular and extracellular pH on uterine contractions were studied in guinea-pigs on day 7 (high progesterone) and day 15 (low progesterone) of the oestrous cycle. Resting values of pH were significantly more acidic on day 15 compared with day 7, and more force was produced on day 15. Changing external pH produced similar changes in intracellular pH and force on both days. External acidification was associated with a large increase in force. In contrast, intracellular acidification, at constant external pH, reduced force. In conclusion, the stage of the oestrous cycle has a large effect on resting pH in the myometrium but only small effects on the pH-induced modulation of force, and the link between pH and force is complex.

Differential vasoactive effects of the insulin sensitizers rosiglitazone (BRL 49653) and troglitazone on human small arteries in vitro

BRL 49653 (rosiglitazone) and troglitazone are thiazolidinedione insulin-sensitizing agents, which are undergoing clinical evaluation as treatments for NIDDM. Potential side effects of thiazolidinediones include edema and hemodilution. Although the underlying mechanisms are presently unclear, animal and human studies have demonstrated a vasodilator action of troglitazone, which could in theory cause fluid retention. This in vitro study compared the direct vasodilator effects of troglitazone and BRL 49653 in small arteries (n = 44) from human subcutaneous fat. In arterial rings with a functioning endothelium and preconstricted with norepinephrine (NE; 6 micromol/l), troglitazone (n = 22 vessels), but not BRL 49653 (1-100 micromol/l), caused a concentration-related relaxation (69.4 +/- 5.2% at 100 micromol/l; P < 0.01). In the presence of indomethacin (IM; 10 micromol/l; n = 12), this vasorelaxant effect of troglitazone was abolished (P < 0.01 vs. troglitazone alone) and replaced by enhanced vasoconstriction (58.5 +/- 39.5% over the NE baseline) similar in magnitude to that produced by troglitazone vehicle (ethanol) alone (n = 16; NS vs. ethanol vehicle). By contrast, BRL 49653 (100 micromol/l; n = 22) and an equivalent volume of ethanol alone (n = 12) caused similar degrees of vasoconstriction (18.7 +/- 14.6 and 22.5 +/- 8.0%, respectively; NS). In the presence of IM (10 micromol/l; n = 10), the vasoconstrictor effect of BRL 49653 was enhanced (41.5 +/- 14.4%), although not significantly (NS vs. BRL 49653 alone or ethanol alone). Additional studies in Wistar rat arteries showed a similar vasodilator effect of troglitazone that was not inhibited by L-NAME (100 micromol/l). The alpha-tocopherol moiety alone had no vasorelaxant effect at concentrations up to 300 micromol/l. Thus, in human arterial resistance vessels in vitro, BRL 49653 does not possess the direct, IM-sensitive vasorelaxant action of troglitazone. This vasodilation could, in theory, permit transmission of systemic pressure to the capillary bed.

The role of the sarcolemmal Ca(2+)-ATPase in the pH transients associated with contraction in rat smooth muscle

1. We have investigated the origin of the intracellular acid pH transients that accompany myometrial contraction. Intra- and extracellular pH were measured with SNARF and intracellular Ca2+ concentration ([Ca2+]i) with indo-1. 2. An intracellular acidification accompanied spontaneous contractions and those elicited by KCl depolarization or the addition of the agonists carbachol or prostaglandin F2 alpha. The size of the acidification increased with the magnitude of the contraction. 3. The intracellular acidification was accompanied by an extracellular alkalinization, showing that it results from proton movement across the surface membrane. Furthermore, it was decreased either by addition of Cd2+ (20 nM, an inhibitor of the sarcolemmal Ca(2+)-ATPase) or by elevating [Ca2+]o. 4. Extracellular alkalinization increased the magnitude of the rise of [Ca2+]i and force produced by KCl. 5. An intracellular acidification was also associated with contraction in the portal vein and ureter. 6. We conclude that the sarcolemmal Ca(2+)-ATPase produces a significant intracellular acidification while removing Ca2+. Both the acidification and decrease of [Ca2+]i will promote relaxation. Since Ca2+ and protons have opposite effects on many cellular processes, this dual regulation by these two ions may be of general importance.

External alkalinization decreases intracellular Ca++ and spontaneous contractions in pregnant rat myometrium

OBJECTIVES

As plasma pH rises during pregnancy, the effect of raising external pH on spontaneous contractions in pregnant rat myometrium was investigated to test the hypothesis that elevated external pH depresses contraction.

STUDY DESIGN

Strips of longitudinal myometrium were loaded with SNARF (seminaphthorhodafluor) or Indo-1 for simultaneous intracellular pH or Ca++ and force measurements. Results were obtained from a minimum of five animals in each group, and significant differences were tested for by paired Student t tests.

RESULTS

Raising the external pH significantly reduced spontaneous force and calcium transient in the pregnant uterus. Raising the external pH led to a slow rise in intracellular pH, but this could not account for the functional effect. K+ rubidium 86-labeled efflux rates were unaffected by external pH, suggesting no hyperpolarization. The Ca++ channel agonist Bay K8644 (5 mumol/L) restored contractions abolished by raised external pH.

CONCLUSIONS

Raised external pH reduces spontaneous contractions in the pregnant rat uterus, probably by an external effect on Ca++ entry. This effect may contribute to uterine quiescence before term.

Prostaglandin production by guinea-pig endometrial cells: effects of caffeine and other modulators of intracellular calcium

The glandular epithelial cells were found to be the main source of PGF2 alpha (the uterine luteolytic hormone) in guinea-pig endometrium. There was a selective increase in PGF2 alpha production by these cells in culture at the time of the cycle (i.e. day 15) at which there is increased PGF2 alpha release from the guinea-pig uterus in vivo. TMB-8 (an intracellular calcium antagonist), W-7, trifluoperazine (both calmodulin antagonists), thapsigargin (an inhibitor of intracellular calcium uptake) and berberine (an inhibitor of calcium release) reduced the output of PGF2 alpha from day 7 glandular epithelial cells indicating that intracellular calcium is necessary for PGF2 alpha production by these cells. In contrast to its stimulatory effect on PGF2 alpha output from the guinea-pig uterus superfused in vitro and guinea-pig endometrium in culture, caffeine inhibited the output of PGF2 alpha from guinea-pig glandular epithelial cells in culture. Its effect was not fully shared by theophylline, nor mimicked by forskolin showing that cyclic AMP is not involved. The inhibitory actions of caffeine and those of the compounds which interfere with the action of intracellular calcium were not additive, suggesting that caffeine modulates the action of intracellular calcium in some way. Caffeine reduced the intracellular free calcium concentration in endometrial cells, but it was not particularly effective in this respect on day 7 glandular epithelial cells. Caffeine may therefore modulate the action of intracellular calcium in some other way.

Effects of caffeine and theophylline on prostaglandin production by guinea-pig endometrium

Caffeine and theophylline increased prostaglandin output from day 7 and day 15 guinea-pig endometrium in culture. Ryanodine and forskolin had no effect on endometrial prostaglandin output. These results show that methylxanthines stimulate endometrial prostaglandin synthesis. However, the intracellular mechanisms involved apparently do not entail an increase in the intracellular free concentration by activation of a ryanodine-sensitive receptor or an increase in the cyclic AMP concentration.

Factors controlling prostaglandin production by guinea-pig endometrial cells

The main cell type in the guinea-pig endometrium responsible for prostaglandin (PG) F2 alpha production and some of the intracellular mechanisms responsible for PGF 2 alpha synthesis in this cell type have been investigated. The glandular epithelial cells and not the stromal cells were found to be the main prostaglandin forming cells in the endometrium. A23187 (a calcium ionophore), phospholipase A2 and melittin (an activator of endogenous phospholipase A2) increased PGF 2 alpha output from the glandular epithelial cells, although only the action of melittin was specific to this cell type. Phospholipase A2 also increased the intracellular free calcium concentration in both cell types by an action largely dependent upon the presence of extracellular calcium. Protein synthesis inhibitors (actinomycin D, cycloheximide and puromycin), oestradiol, progesterone and aristolochic acid (an inhibitor of phospholipase A2) reduced PGF 2 alpha output from the glandular epithelial cells, although only the inhibitory action of aristolochic acid was specific. Protein synthesis inhibitors also reduced PGF 2 alpha output from stromal cells, and the outputs of PGE2 and 6 keto-PGF 1 alpha from both cell types. The steroid hormones also reduced PGE2 output from stromal cells. The findings indicate that PGF 2 alpha production by the glandular epithelial cells is dependent upon fresh protein synthesis and the activity of endogenous phospholipase A (which is a calcium-requiring enzyme).

Effect of a selective prostaglandin H synthase-2 inhibitor (NS-398) on prostaglandin production by the guinea-pig uterus

Using guinea-pig uterine tissues, indomethacin (a non-selective inhibitor of prostaglandin H synthase) inhibited prostaglandin (PG) synthesis by homogenates of the endometrium, by cultured endometrium and myometrium, and by cultured epithelial glandular cells and stromal cells derived from the endometrium. NS-398, a selective inhibitor of prostaglandin H synthase-2 (PGHS-2), also inhibited PG synthesis by endometrial homogenates, by cultured endometrium and myometrium, and by cultured epithelial glandular cells and stromal cells. Indomethacin and NS-398 inhibited PG production to similar extents, except for 6-keto-PGF1 alpha production by the myometrium where indomethacin was more effective. In particular, indomethacin and NS-398 produced over 90% inhibition of PGF2 alpha output from the epithelial glandular cells, the main source of PGF2 alpha in the endometrium. These functional studies indicate that prostaglandin H synthase-2 is the predominant PG-forming enzyme in the guinea-pig uterus.

The effect of caffeine on prostaglandin output from the perfused mesenteric vascular bed of the rat

Caffeine significantly (p < 0.05) increased the output of prostacyclin (PGI2) from the perfused rat mesenteric vascular bed. The outputs of PGE2 and PGF2 alpha were also increased by caffeine. This stimulatory response to caffeine did not show rapid desensitization. Ryanodine also increased PG output, suggesting that caffeine may be acting via the stimulation of a ryanodine receptor. The increased production of a vasodilator such as PGI2 from blood vessels following exposure to caffeine may explain why caffeine has a beneficial effect in angina.

The effect of caffeine on prostaglandin output from the guinea-pig uterus

1. Caffeine increased the outputs of prostaglandin F2 alpha (PGF2 alpha), PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus on days 7 and 15 of the oestrous cycle. The effect on PGE2 output depended on the age of the animals and was absent in younger guinea-pigs (< 4 months). Theophylline also stimulated the outputs of PGF2 alpha and 6-keto-PGF1 alpha, but not the output of PGE2, from the day 7 guinea-pig uterus. 2. The stimulatory effects of caffeine on the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus were not prevented by lack of extracellular calcium, ryanodine or ruthenium red (both inhibitors of calcium release via the ryanodine receptor), although the increase in PGF2 alpha output tended to be slower when extracellular calcium was absent. Also, ryanodine flattened and broadened the peak of increased PGF2 alpha release. 3. The calmodulin antagonists, W-7 and trifluoperazine, had no inhibitory effect on the caffeine-stimulated increases in uterine prostaglandin output. In fact, W-7 (but not trifluoperazine) greatly potentiated the action of caffeine on uterine PGF2 alpha output, but had little or no potentiating effect on the action of caffeine on uterine PGE2 and 6-keto-PGF1 alpha outputs. 4. TMB-8, an intracellular calcium antagonist, inhibited the increase in PGF2 alpha output produced by caffeine without preventing the increases in outputs of PGE2 and 6-keto-PGF1 alpha. 5. These studies suggest that caffeine stimulates uterine PGF2 alpha synthesis and release by a mechanism dependent upon intracellular calcium, but this mechanism is not mediated by activation of any of the three well-characterized ryanodine receptors or by calmodulin. Furthermore, the increases in the synthesis and release of PGE2 and 6-keto-PGFI alpha. in the guinea-pig uterus induced by caffeine appear to involve mechanism(s) different from that which stimulates PGF2 alpha production.