Age-associated changes of exercise-induced plasma catecholamine responses

Age-associated plasma catecholamine responses were evaluated in 10 young (25 +/- 3 years) and 11 older competition cyclists (66.2 +/- 6 years) during incremental ergometric cycling. Noradrenaline levels were higher in the older subjects at rest, at identical work loads and at exhaustion. Adrenaline levels were similar in both groups at rest, higher in the old test subjects at identical work loads and lower in the old subjects at exhaustion. The noradrenaline-adrenaline ratio changed significantly depending on age from 5.1 +/- 0.5 to 8.7 +/- 2.1 which indicated higher adrenaline-related noradrenaline responses. The observed age-related differences may be caused by a compensatory mechanism which depends both on negatively age-correlated physical fitness, and on the decreased sensitivity of the organism to beta-adrenergic stimulation with age, as well as on an age-dependent change in the clearance of catecholamines from the circulation as described by Esler et al. (1981).     

Effect of aging on the substance P receptor, NK-1, in the spinal cord of rats with peripheral nerve injury

Substance P (SP) levels in the spinal cords of very old rats are less than the levels in younger rats (Bergman et al., 1996). After injury to a peripheral nerve in young rats, immunoreactivity (ir) to the SP receptor, NK-1 (neurokinin-1), increases in the spinal cord ipsilateral to the injury and the increases are correlated with the development of thermal hyperalgesia (Goff et al., 1998). Thus we postulated that aged rats might display an increased sensitivity to thermal stimulation before peripheral nerve injury and that they might respond differently to injury than do younger rats. To test this hypothesis, we used the Bennett and Xie model (1988) of chronic constriction injury (CCI) to the sciatic nerve to induce a neuropathic pain condition. We investigated the effect of age on changes in NK-1 ir in superficial layers of the dorsal horn and on numbers of NK ir cells in deeper laminae at the L4-L5 levels of the spinal cord after CCI. NK-1 receptors were tagged immunohistochemically and their distribution quantified by use of computer-assisted image analysis. NK-1 ir changes were related to alterations in thermal and tactile sensitivity that developed after CCI in young, mature and aged (4-6, 14-16, and 24-26 months) Fischer F344 BNF1 hybrid rats. No differences in thermal or tactile sensitivity of young and aged rats were seen in the absence of nerve injury. After injury, aged rats developed thermal hyperalgesia and tactile allodynia more slowly than did the younger rats. NK-1 receptor ir and numbers of NK-1 ir cells in the dorsal horn increased with time post-injury in all three groups. NK-1 ir increases were correlated with the development of thermal hyperalgesia in those rats that displayed hyperalgesia. However, some rats developed an increased threshold to thermal stimuli (analgesia) and that also was correlated with increases in NK-1 ir. Thus NK-1 ir extent, while correlated with thermal sensitivity in the absence of injury, is not a specific marker for disturbances in one particular sensory modality; rather it increases with peripheral nerve injury per se.     

Effect of aging on the substance P receptor,NK–1, in the spinal cord of rats with peripheral nerve injury

Substance P (SP) levels in the spinal cords of very old rats are less than the levels in younger rats (Bergman et al., 1996). After injury to a peripheral nerve in young rats, immunoreactivity (ir) to the SP receptor, NK–1 (neurokinin-1), increases in the spinal cord ipsilateral to the injury and the increases are correlated with the development of thermal hyperalgesia (Goff et al., 1998). Thus we postulated that aged rats might display an increased sensitivity to thermal stimulation before peripheral nerve injury and that they might respond differently to injury than do younger rats. To test this hypothesis, we used the Bennett and Xie model (1988) of chronic constriction injury (CCI) to the sciatic nerve to induce a neuropathic pain condition. We investigated the effect of age on changes in NK-1 ir in superficial layers of the dorsal horn and on numbers of NK ir cells in deeper laminae at the L4-L5 levels of the spinal cord after CCI. NK-1 receptors were tagged immunohistochemically and their distribution quantified by use of computer-assisted image analysis. NK-1 ir changes were related to alterations in thermal and tactile sensitivity that developed after CCI in young, mature and aged (4-6, 14-16, and 24-26 months) Fischer F344 BNF1 hybrid rats. No differences in thermal or tactile sensitivity of young and aged rats were seen in the absence of nerve injury. After injury, aged rats developed thermal hyperalgesia and tactile allodynia more slowly than did the younger rats. NK-1 receptor ir and numbers of NK-1 ir cells in the dorsal horn increased with time post-injury in all three groups. NK-1 ir increases were correlated with the development of thermal hyperalgesia in those rats that displayed hyperalgesia. However, some rats developed an increased threshold to thermal stimuli (analgesia) and that also was correlated with increases in NK-1 ir. Thus NK-1 ir extent, while correlated with thermal sensitivity in the absence of injury, is not a specific marker for disturbances in one particular sensory modality; rather it increases with peripheral nerve injury per se.     

Expression of the pro-apoptotic gene gadd153/chop is elevated in liver with aging and sensitizes cells to oxidant injury

Aging is generally accompanied by reduced tolerance to oxidative stress and altered responsiveness to proliferative signals. We have shown that hepatocytes derived from aged rats (24-26 months) exhibit greater sensitivity to H(2)O(2) treatment and reduced proliferation following epidermal growth factor (EGF) treatment than cells of young adult rats (5-6 months). Here we examined the effects of aging and calorie restriction (CR) on expression of the oxidative stress-inducible and pro-apoptotic gene gadd153 (chop) in these hepatocytes, and we investigated its influence on sensitivity to oxidants. We show that aging was associated with elevated expression of gadd153, both basally and in response to H(2)O(2) treatment. CR, which attenuates age-associated declines in stress tolerance, prevented the age-related increase in gadd153 expression. EGF treatment also resulted in gadd153 induction in old cells. This effect was absent in young cells and in old cells of CR rats. gadd153 induction by EGF was reactive oxygen species-dependent and correlated with heightened sensitivity to subsequent H(2)O(2) treatment, suggesting that elevated Gadd153 contributes to the greater sensitivity of EGF-pretreated old cells to oxidative stress. Additional support for this hypothesis was provided by experiments with Rat1 fibroblasts in which conditional expression of Gadd153 conferred increased sensitivity to H(2)O(2). We propose a model whereby the diminished ability of old hepatocytes to overcome an EGF-triggered reactive oxygen species load leads to induction of the proapoptotic gene gadd153, which, in turn, sensitizes the cells to oxidant injury. Our findings point to gadd153 expression levels as an important factor in liver aging.     

Changes in plasma oxidative state with age and their influence on contractions elicited by noradrenaline in the rat tail artery.

The present study analyzes the changes in plasma oxidative state with age and their influence on the contractions induced by noradrenaline (NA) in endothelium-denuded segments from the tail artery of 6- (young), 24- (old) and 30- (very old) month-old Sprague Dawley rats. The sensitivity (-log EC50) to NA increased with age, this increase being higher in old than in very old animals. Moreover, the maximum response (Emax) to NA did not change in old rats, whereas decreased in very old animals. We also found a progressive increase in the plasma oxidative state with age, measured as malondialdehyde (MDA) levels, that was accompanied by a decrease in the plasma antioxidative state, measured as glutathione peroxidase activity. In addition, MDA (0.5, 1 and 10 microM) potentiated the NA responses in 6-, 24- and 30-month-old rats, respectively, without affecting Emax. In young animals, catalase (1000 U/ml) or dimethylsulfoxide (7 mM), scavengers of hydrogen peroxide or hydroxyl radicals, respectively, did not modify either the contractions induced by NA in control situation or the potentiation of these responses caused by MDA. However, the superoxide anion scavenger, superoxide dismutase (SOD, 150 U/ml), completely reversed the increase in sensitivity to NA caused by MDA, without affecting NA responses in control situation. These results suggest that the increase in NA sensitivity with age could be due, at least in part, to the enhancement of plasma oxidative state during aging. In addition, in this alteration of the responses to NA caused by MDA, the generation of superoxide anions appears to be involved. This study supports the hypothesis that the enhancement of plasma oxidative state could play an important role in the increase of vascular resistance with age.     

Oxidative stress in the aging rat heart is reversed by dietary supplementation with (R)-(alpha)-lipoic acid.

Oxidative stress has been implicated as a causal factor in the aging process of the heart and other tissues. To determine the extent of age-related myocardial oxidative stress, oxidant production, antioxidant status, and oxidative DNA damage were measured in hearts of young (2 months) and old (28 months) male Fischer 344 rats. Cardiac myocytes isolated from old rats showed a nearly threefold increase in the rate of oxidant production compared to young rats, as measured by the rates of 2,7-dichlorofluorescin diacetate oxidation. Determination of myocardial antioxidant status revealed a significant twofold decline in the levels of ascorbic acid (P = 0.03), but not alpha-tocopherol. A significant age-related increase (P = 0.05) in steady-state levels of oxidative DNA damage was observed, as monitored by 8-oxo-2'-deoxyguanosine levels. To investigate whether dietary supplementation with (R)-alpha-lipoic acid (LA) was effective at reducing oxidative stress, young and old rats were fed an AIN-93M diet with or without 0.2% (w/w) LA for 2 wk before death. Cardiac myocytes from old, LA-supplemented rats exhibited a markedly lower rate of oxidant production that was no longer significantly different from that in cells from unsupplemented, young rats. Lipoic acid supplementation also restored myocardial ascorbic acid levels and reduced oxidative DNA damage. Our data indicate that the aging rat heart is under increased mitochondrial-induced oxidative stress, which is significantly attenuated by lipoic acid supplementation.     

Changes in the concentration of catecholamines in the organs of animals with experimental myocardial infarcts under the influence of malaben]

The content of adrenaline and noradrenaline in the tissues of the heart, adrenal glands, spleen and brain of rats was studied in experimental myocardial infarction. A significant decrease in the catecholamine levels was revealed in the tissues. Malaben promoted normalization of the catecholamine tissue content in myocardial infarction. It is suggested that the said effect of malaben is due to its antihistaminic properties.     

Age related changes in noradrenaline,noradrenaline turnover and adrenaline in brainstem nuclei of wistar kyoto and spontaneously hypertensive rats

Noradrenaline and noradrenaline turnover were determined in regions enriched in catecholamine nuclei of the brainstem (A1, A2, C1, C2 and C3), in the locus coeruleus (A6) and in the nucleus tractus spinalis n. trigemini (Sp5C) of Wistar Kyoto and spontaneously hypertensive rats at four ages from 6 to 40 weeks. Adrenaline levels were also determined but were only consistently detected in the C1 and C2 regions. There was an age-related decline in noradrenaline concentrations in both strains of rats in all brainstem catecholamine nuclei however noradrenaline turnover decreased only in the A2 and C3 regions and this may contribute to the progressive rise in blood pressure with age in spontaneously hypertensive and Wistar Kyoto rats. Adrenaline levels did not alter with age providing evidence of a functional disassociation between adrenaline and noradrenaline neuronal systems. There were several strain-related differences in noradrenaline and adrenaline concentrations in the regions studied, however noradrenaline turnover was reduced only in the A2 and C2 regions (nucleus tractus solitarius) of spontaneously hypertensive rats which is consistent with the sympathoinhibitory role of this nucleus in central blood pressure regulation.     

Anorexic effect of peripheral cholecystokinin (CCK) varies with age and body composition (short communication)

Obesity of middle-aged mammals is followed at old age by anorexia and cachexia leading to sarcopenia. Complex age- and body composition-related alterations in the regulation of energy homeostasis may be assumed in the background. We aimed to test the possible contribution of age- and body composition-related changes of satiety responses to catabolic brain-gut-axis peptide cholecystokinin (CCK) to these alterations in energy balance during aging. Male Wistar rats (6-8 animals/group) aged 2 months (juvenile), 3 months (young adult), 6 or 12 months (early or late middle-aged), and 24 months (old) were injected intraperitoneally with 5 μg CCK-8 prior to re-feeding after 48-h food-deprivation. CCK suppressed re-feeding in young adult (26.8%), early middle-aged (35.5%), and old (31.4%) animals, but not in juvenile or late middle-aged rats (one-way ANOVA). CCK-resistance of 12 months old rats was prevented by life-long calorie-restriction: CCK suppressed their re-feeding by 46.8%. Conversely, in highfat diet-induced obese 6 months old rats CCK failed to suppress re-feeding. In conclusion, age-related changes in satiety responsiveness to CCK may contribute to the age-related obesity of middle-aged as well as to the anorexia of old animals. CCK-responsiveness is also influenced by body composition: calorie-restriction prevents the resistance to CCK, pre-existing obesity enhances it.     

Influence of aging and caloric restriction on activation of Ras/MAPK, calcineurin, and CaMK-IV activities in rat T cells

The signaling cascade mediated by Ras (p21ras) and MAPK (mitogen-activated protein kinase) and calcium/calmodulin regulating enzymes, calcineurin (CaN) and CaMK-IV, are considered to be essential for T-cell growth and function. In the present study, the effect of aging and caloric restriction (CR) on the induction of Ras and MAPK activation by concanavalin A (ConA) was studied. Splenic T cells were isolated from young (4-6 months) and old (22-24 months) rats that had free access to food (control group), and from caloric restricted old (22-24 months) rats that beginning at 6 weeks of age were fed 60%(40% caloric restriction) of the diet consumed by the control rats. We found that the induction of Ras activity in T cells isolated from control old rats was lower (P<0.001) than that in control young rats. However, the levels of Ras activity in T cells isolated from CR old rats were similar to the levels in the age-matched control rats. The induction of MAPK activity in T cells isolated from control old rats and CR old rats was significantly less than in T cells isolated from control young rats, and caloric restriction significantly (P<0.05) reduced the age-related decline in MAPK activation. We also measured the induction of CaN and CaMK-IV activities by ConA in T cells from control young and old and CR old rats. The induction of both CaN and CaMK-IV activity decreased with age. Caloric restriction significantly (P<0.05) reduced the age-related decline in CaN activity, but had no significant effect on CaMK-IV activity. The changes in Ras/MAPK activation and in CaN and CaMK-IV activity with age or with CR were not associated with alterations in their corresponding protein levels. Thus, caloric restriction has a differential effect on the activation of the upstream signaling molecules that are altered with age.     

Hypothalamic luteinizing hormone-releasing hormone (LHRH) and LH secretion in aging female rats

Age-related changes in hypothalamic luteinizing hormone-releasing hormone (LHRH) and luteinizing hormone (LH) secretion were studied in young (6 months), middle-aged (12 months) and old (18 months) female rats. The LHRH levels in the mid-hypothalamic area were higher in intact middle-aged and old females than in young ones. Additionally, there was no age difference in the hypothalamic LHRH levels in male rats. In order to clarify the significance of this age-related increase in female rats, we examined the effects of progesterone treatment in estrogen-primed ovariectomized young and old rats on the LHRH levels in the median eminence (ME) and on plasma LH levels. We found phasic changes in ME-LHRH and plasma LH levels in estrogen-primed rats following progesterone treatment in rats of both ages, but the progesterone-induced change in ME-LHRH levels tended to be delayed in old rats compared with young females. This delay may correspond to the delayed onset, slow and low magnitude of plasma LH increase in old females. The ME-LHRH levels were generally higher in old rats than in young rats. Nevertheless, we found that the increase in plasma LH in response to progesterone treatment in estrogen-primed ovariectomized females was smaller in old rats than young rats. These results suggest that the LHRH secretory mechanism changes with age in female rats. Such alterations may result in the accumulation of LHRH in the mid-hypothalamic area and an increase in ME-LHRH.     

Cardioprotection of the aged rat heart by GSK-3beta inhibitor is attenuated: age-related changes in mitochondrial permeability transition pore modulation

It is well established that inhibition of glycogen synthase kinase (GSK)-3β in the young adult myocardium protects against ischemia-reperfusion (I/R) injury through inhibition of mitochondrial permeability transition pore (mPTP) opening. Here, we investigated age-associated differences in the ability of GSK-3β inhibitor [SB-216763 (SB)] to protect the heart and to modulate mPTP opening during I/R injury. Fischer 344 male rats were assigned from their respective young or old age groups. Animals were subjected to 30 min ischemia following 120 min reperfusion to determine myocardial infarction (MI) size in vivo. Ischemic tissues were collected 10 min after reperfusion for nicotinamide adenine dinucleotide (NAD(+)) measurements and immunoblotting. In parallel experiments, ventricular myocytes isolated from young or old rats were exposed to oxidative stress through generation of reactive oxygen species (ROS), and mPTP opening times were measured by using confocal microscopy. Our results showed that SB decreased MI in young SB-treated rats compared with young untreated I/R animals, whereas SB failed to significantly affect MI in the old animals. SB also significantly increased GSK-3β phosphorylation in young rats, but phosphorylation levels were already highly elevated in old control groups. There were no significant differences observed between SB-treated and untreated old animals. NAD(+) levels were better maintained in young SB-treated animals compared with the young untreated group during I/R, but this relative improvement was not observed in old animals. SB also significantly prolonged the time to mPTP opening induced by ROS in young cardiomyocytes, but not in aged cardiomyocytes. These results demonstrate that this GSK-3β inhibitor fails to protect the aged myocardium in response to I/R injury or prevent mPTP opening following a rise in ROS and suggest that healthy aging alters mPTP regulation by GSK-3β.     

Variability of hemodynamic parameters and resistance to stress damage in rats of different strains

Total power of heart rate variability and baroreflex sensitivity were significantly smaller in the August rats than in the Wistar rats, but adrenal and plasma catecholamine contents were considerably higher in the former ones. 1 hour after stress (30 min in cold water), plasma catecholamine was increased 2-fold in Wistar rats, while in August rats the adrenaline concentration increased only by 58% and the were no changes in noradrenaline content. At the same time, activation of catecholamine metabolism in the adrenal glands was similar in both groups. The oxidative stress induced by hydrogen peroxide depressed the contractile function of isolated heart in the August rats to a smaller extent as compared to Wistar rats, control ones and after the cold-water stress. This effect correlated with more pronounced stability ofantioxidant enzymes in the August rats. It seems that the greater resistance to stress damage in the August rats is mediated by enhanced power of defense mechanisms both at systemic and cellular levels.     

老年大鼠脊髓小胶质细胞分选新方法及功能特征观察*

目的: 建立分离纯化老年大鼠小胶质细胞的改良方法,并初步观察老年大鼠脊髓小胶质细胞的生物学特性。方法: 以年轻SD大鼠(2月龄)为对照组,采用胰酶、胰酶替代物和机械网搓法等不同的制备方法,制备大鼠小胶质细胞的单细胞悬液,通过检测细胞纯度、存活率,观察细胞形态特征,分析细胞的炎性功能特征等,确定老年大鼠(20月龄)小胶质细胞的分离纯化方法,观察老年大鼠脊髓小胶质细胞功能特征。结果: 胰酶消化所得细胞的存活率低(年轻大鼠83%,老年大鼠60%);机械网搓法虽得到的存活率较高(95%),但是细胞获取率最低(年轻大鼠((0.207±0.020)×10⁶,老年大鼠(0.243±0.023)×10⁶);采用胰酶替代物解离、密度梯度离心方法分选出的老年大鼠脊髓小胶质细胞数量多、活性好、存活率高,细胞纯度可达85%以上,我们采用此方法分选纯化不同年龄大鼠脊髓小胶质细胞,与年轻大鼠相比,老年鼠脊髓组织量大,所需消化液多,但消化时间缩短;与年轻大鼠小胶质细胞相比,老年大鼠脊髓小胶质细胞其胞体较大较圆,突起少且粗短,形态上偏向于激活状态,老年大鼠小胶质细胞促炎因子IL-1β表达降低(P＜0.05),而抗炎因子IL-10(P＜0.01)表达升高。结论: 成功建立胰酶替代物解离结合密度梯度离心法从大鼠脊髓组织中分离纯化小胶质细胞,老年大鼠脊髓内小胶质细胞整体表现出抗炎表型。     

Effects of aging on LH and prolactin after LHRL L-dopa, methyl-dopa, and stress in male rat.

Hypothalamic-pituitary control of prolactin and LH secretion was tested in young (4-6 months) and aged (22-30 months) male Long-Evans rats given L-dopa, methyl dopa, LHRH, or stress treatments. Pretreatment serum LH levels were consistently higher in young than in the aged groups. The increase in serum LH after LHRH injection was only about half as much in aged as compared to young control males. Although acute stress caused a prompt increase in serum LH in young male rats, this treatment was without effect in the aged group. Methyl dopa treatment stimulated serum prolactin secretion in both young and old rats. Although L-dopa treatment caused a reduction in serum prolactin in both age groups, the sensitivity, magnitude, and duration of the reduction was smaller in the aged rats.     

Rat-liver superoxide dismutase. Purification and age-related modifications.

Cytoplasmic superoxide dismutase has been purified from livers of young (6 months) and old (27 months) rats. The enzyme purified from old animals shows an age-related reduction in the specific activity, accumulation of antigenically cross-reacting material and increased sensitivity to temperature. No differences were found in the molecular weight, electrophoretic mobility, antigenicity and Ki between enzymes purified from young and old rats. This is the first demonstration of age-related alterations in a purified form of a non-metabolic enzyme, which can be related to reduced activity. The possible role of this reduced activity in age-dependent deterioration of cellular functions is discussed.     

Mechanisms of adaptation to physical exertion and the effect of carbon dioxide excess on their formation

4% CO2 addition to normoxic gas medium increased the activity, mass and functional capacity of the left ventricular myocardium, enhanced the stability of acetylcholine (AC) and noradrenaline (NA) storage in the myocardial tissues and stimulated myocardial response to these mediators during physical training of rats (swimming for 2 months). When the duration of the training period was prolonged to 3 months, CO2 had a decreasing effect on the myocardial activity, AC concentration and storage stability, as well as on the myocardial response to AC. The possibility of reducing signal and increasing metabolic CO2 effects during physical training is considered. The importance of intensified heart regulation by sympathetic and parasympathetic mechanisms during adaptation and the role of mechanism dissociation with the decrease in the degree of adaptation are discussed.     

Growth factor-mediated reversal of senescent dysfunction of ischemia-induced cardioprotection

Based on the role of tumor necrosis factor-alpha (TNF-alpha) in ischemic preconditioning (IPC) and the age-associated loss of both TNF-alpha-induced platelet-derived growth factor-AB (PDGF-AB)-mediated cardioprotection and IPC-mediated cardioprotection, we hypothesized that targeting of PDGF-AB-based pathways would restore cardioprotection by IPC in the aging heart. To study this, IPC was induced in 4- and 24-mo-old F344 rats. Sections of young hearts isolated 1 day post-IPC revealed increased TNF-alpha compared with controls. In old rats, TNF-alpha was higher at baseline than IPC young rats and was not significantly altered after IPC. Treatment of old rats with PDGF-AB with vascular endothelial growth factor and angiopoietin-2 (a combination termed PVA), but not PDGF-AB alone, at the time of IPC decreased TNF-alpha. In addition, when compared with young hearts, IPC induced greater apoptosis in the old hearts, which was decreased with PVA treatment but was markedly increased with PDGF-AB. To test the significance of these findings, additional rats underwent permanent coronary ligation 1 day post-IPC. IPC was cardioprotective in young rats [14 days postmyocardial infarction (MI), fractional shortening 29 +/- 6% vs. control MI 17 +/- 4%, P < 0.05; Masson's trichrome stain MI size: 13 +/- 2% vs. control MI 17 +/- 4% left ventricular area (LVA); P < 0.05]. In old rats, however, IPC reduced the post-MI 14-day survival (33% vs. controls 67%; P < 0.05). Treatment of IPC-aging rats with PVA, but not PDGF-AB-alone, reversed IPC-induced mortality (PVA-IPC-MI survival, 88%; PDGF-AB-IPC-MI, 14%) and reduced myocardial injury (fractional shortening: PVA-IPC, 31 +/- 1% vs. control MI, 21 +/- 6%, P < 0.05; MI size: PVA-IPC, 12 +/- 2% vs. control MI, 18 +/- 3% LVA, P < 0.05) and thus demonstrated that PDGF-AB-based pathways can reverse the senescent impairment in IPC-mediated cardioprotection.     

Myocardial NOS activity and connexin-43 expression in untreated and omega-3 fatty acids-treated spontaneously hypertensive and hereditary hypertriglyceridemic rats

The purpose of this study is to investigate myocardial nitric oxide synthase (NOS) activity and connexin-43 (Cx43) expression in young and old spontaneously hypertensive rats (SHR), adult hereditary hypertriglyceridemic (HTG) rats, and age-matched healthy rats without and with omega-3 PUFA supplementation for 2 months. Results showed that comparing to healthy rats the myocardial NOS activity was significantly increased in young SHR (8.2 ± 1.16 vs. 1.37 ± 0.67 pmol/min/mg) as well as old SHR (3.21 ± 0.75 vs. 2.22 ± 0.56 pmol/min/mg) and to much lesser extent in HTG rats, i.e., 1.87 ± 0.42 vs. 1.34 ± 0.1 pmol/min/mg. In parallel, there was a significant decline of total and phosphorylated forms of Cx43 in both groups of SHR while not in HTG rat hearts in which phosphorylated form of Cx43 was increased. Elevated NOS activity was suppressed (P < 0.05) in young and old SHR supplemented with omega-3 PUFA and it was associated with up-regulation of Cx43. In contrast to SHR, elevation of NOS activity in HTG rat hearts was not affected by treatment with omega-3 PUFA. However, increase of phosphorylated form of Cx43 was suppressed. In conclusion, there is an inverse relationship between myocardial NOS activity and Cx43 expression in SHR while not HTG rat hearts and omega-3 PUFA modulate both NOS activity and Cx43 expression. Whether over-expression of inducible NOS might account for down-regulation of myocardial Cx43 and whether its up-regulation is associated with an increase of endothelial NOS should be explored in further study.