Jeremiah T. Herlihy

Exercise and diet modulate cardiac lipid peroxidation and antioxidant defenses

Free radical metabolism can be altered by several interventions, including dietary restriction (DR) and exercise. Most of the previous work has focused on the liver and skeletal muscle. The following experiments were performed to determine whether long-term DR and chronic exercise affect free radical metabolism and change the status of the antioxidant defenses of the heart. Rats were subjected to DR and/or endurance exercise for 18.5 months and were sacrificed along with their ad lib fed and sedentary controls. Both DR and exercise decreased the malondialdehyde content of cardiac mitochondria, indicating a decrease in lipid peroxidation damage. The antioxidant enzymes in the cytosol, superoxide dismutase, selenium dependent glutathione peroxidase, and glutathione S-transferase were all increased by DR. Catalase activity was unaffected by DR but was increased by exercise. The following results demonstrate that long-term DR and exercise modulate the extent of free radical damage in the heart and enhance the antioxidant defense system.

Long-term food restriction depresses serum thyroid hormone concentrations in the rat.

Long-term food restriction exerts an anti-aging action in rodents. The mechanism underlying its modulation of aging processes is unknown but changes in endocrine systems have been postulated as couplers of food restriction to aging. The effects of long-term food restriction on the serum concentrations of thyroid hormones were examined in 6-month-old, male Fischer 344 rats. For 4.5 months a Food Restricted group was fed 60% of the amount consumed by an Ad Libitum group. Food restriction did not alter the 24-h mean T4 concentration but reduced the 24-h mean T3 concentration from 95 +/- 1 to 87 +/- 3 ng/dl. The Ad Libitum group exhibited diurnal rhythms in both serum T4 and T3 concentrations, with peak values for each hormone at 1000 h. Although food restriction eliminated the 1000 h peak for both thyroid hormones, it abolished the diurnal variation only for T3. The dietary-induced changes in serum T4 and T3 are consistent with a role for these hormones in the anti-aging action of food restriction.

Effect of long-term food restriction on cardiac mechanics

Food restriction (FR) is the only known intervention capable of increasing mammalian life span. It not only increases longevity, but reduces the incidence of a broad spectrum of age-related pathologies, including cardiomyopathy, and retards the physiological decline associated with aging. Previous work from this laboratory has shown that long-term FR affects the contractile machinery of the heart, shifting the cardiac myosin profile from the fast, V1 isoform to the slow, V3 isoform. The aim of the present study was to determine whether FR also induces changes in cardiac mechanics. Isolated, isovolumically beating hearts were examined from four groups of rats: 1) ad libitum-fed rats killed at 10-13 mo of age, 2) FR rats offered only 60% of the calories consumed by ad libitum-fed rats and killed at the same age, 3) young ad libitum-fed rats having the same heart weights as the FR rats, and 4) ad libitum-fed rats subjected to short-term FR, i.e., for the last 3 wk of life, and also killed at 10-13 mo of age. Both short- and long-term FR profoundly and to approximately the same extent affected cardiac mechanics. Hearts from FR rats developed much higher pressures than hearts from the ad libitum-fed rats under conditions of low-calcium perfusate. This difference disappeared, however, when contractility was enhanced by either calcium or isoproterenol. FR prolonged both contraction and relaxation times. Long-term ad libitum-fed rats (adult, 10-13 mo of age) had a lower isoproterenol sensitivity than the young ad libitum-fed rats (10 wk of age). Both short- and long-term FR restored the sensitivity to isoproterenol. In summary, FR profoundly affects many aspects of cardiac mechanics, enhancing some age-related changes (prolongation of the contraction and relaxation times), attenuating another (increasing the isoproterenol sensitivity), and, finally, inducing some unique changes unrelated to age (increased pressure development under low-calcium perfusate).Food restriction (FR) is the only known intervention capable of increasing mammalian life span. It not only increases longevity, but reduces the incidence of a broad spectrum of age-related pathologies, including cardiomyopathy, and retards the physiological decline associated with aging. Previous work from this laboratory has shown that long-term FR affects the contractile machinery of the heart, shifting the cardiac myosin profile from the fast, V1 isoform to the slow, V3 isoform. The aim of the present study was to determine whether FR also induces changes in cardiac mechanics. Isolated, isovolumically beating hearts were examined from four groups of rats: 1) ad libitum-fed rats killed at 10-13 mo of age, 2) FR rats offered only 60% of the calories consumed by ad libitum-fed rats and killed at the same age, 3) young ad libitum-fed rats having the same heart weights as the FR rats, and 4) ad libitum-fed rats subjected to short-term FR, i.e., for the last 3 wk of life, and also killed at 10-13 mo of age. Both short- and long-term FR profoundly and to approximately the same extent affected cardiac mechanics. Hearts from FR rats developed much higher pressures than hearts from the ad libitum-fed rats under conditions of low-calcium perfusate. This difference disappeared, however, when contractility was enhanced by either calcium or isoproterenol. FR prolonged both contraction and relaxation times. Long-term ad libitum-fed rats (adult, 10-13 mo of age) had a lower isoproterenol sensitivity than the young ad libitum-fed rats (10 wk of age). Both short- and long-term FR restored the sensitivity to isoproterenol. In summary, FR profoundly affects many aspects of cardiac mechanics, enhancing some age-related changes (prolongation of the contraction and relaxation times), attenuating another (increasing the isoproterenol sensitivity), and, finally, inducing some unique changes unrelated to age (increased pressure development under low-calcium perfusate).

BK channel β1 subunits regulate airway contraction secondary to M2 muscarinic acetylcholine receptor mediated depolarization

Non‐technical summary  Parasympathetic nerve activation of M3 and M2 muscarinic acetylcholine receptors initiates and modulates calcium release from the sarcoplasmic reticulum to control airway smooth muscle contraction. Here we investigate M2 acetylcholine receptors that also contribute to contraction through depolarization and recruitment of voltage‐dependent calcium channels (VDCCs). We find that the calcium‐ and voltage‐activated potassium channel (BK channel) and its β1 accessory subunit are important proteins that oppose M2‐mediated contraction of airway smooth muscle. BK channels contribute to a negative baseline membrane voltage from which M2‐mediated depolarization only weakly activates VDCCs. The role of BK β1 to oppose M2 signalling is evidenced by a greater than fourfold increase in the contribution of L‐type VDCCs to contraction that otherwise does not occur with M2 receptor antagonist or with β1 containing BK channels. These findings provide a better understanding of how cholinergic second messenger signalling impinges on voltage‐dependent mechanisms and excitation–contraction coupling of smooth muscle.

Effects of ascorbic acid and EDTA on vascular concentration-response to catecholamines

Concentration-response curves are often used as indicators of vascular reactivity and receptor sensitivity. Some investigators use ethylenediaminetetraacetate (EDTA) or ascorbic acid (ASC) to prevent catecholamine oxidation but many others do not. This difference may affect estimates of reactivity. We tested the effect of EDTA or ASC on contractile responses of hamster cremaster arterioles and rat aortic strips to epinephrine (EPI) or norepinephrine (NOR). Comparable contractile responses were elicited by lower EPI or NOR concentrations in the presence than in the absence of EDTA or ASC. Individual responses to EPI or NOR were maintained in the presence of EDTA or ASC, but rapidly declined if neither were present. Rapidly prepared and administered solutions of EPI or NOR elicited similar initial responses in the presence or absence of EDTA or ASC. However, catecholamine solutions prepared without these compounds lose effectiveness within minutes. We conclude that oxidation of EPI and NOR reduces apparent vascular reactivity and that EDTA or ASC prevents or delays the reduction.

Dietary Restriction Modulates the Norepinephrine Content and Uptake of the Heart and Cardiac Synaptosomes

Abstract The present study was designed to examine the effects of long-term dietary restriction on cardiac sympathetic nerves and neurotransmitter. The food intake of male, 6-week-old Fischer 344 rats was reduced to 60% of the intake of control rats fed ad libitum. The body and heart weights of rats diet restricted for 4.5 months were less than those of the ad libitum fed animals, while the heart weight to body weight ratios were higher. The norepinephrine (NE) content of hearts from restricted rats (1073 ± 84 ng/g wet wt) was higher than controls (774 ± 38 ng/g wet wt), although the total amount of NE per heart was unchanged. Similarly, the cardiac synaptosomal P2 fraction from restricted rats possessed a higher NE content (24.1 ± 2.4 ng/mg protein) than the P2 fraction of ad libitum fed controls (13.7 ± 1.3 ng/mg protein). The desmethylimipramine-sensitive norepinephrine uptake of the P2 fraction from restricted rats was significantly higher than that of control rats (9.44 ± 1.33 vs 4.75 ± 0.35 ng/mg protein/hr). The NE uptakes of the two groups were similar when uptake was normalized to endogenous NE levels. These results demonstrate that long-term dietary restriction affects cardiac sympathetic nerve endings and suggest that part of the beneficial action of life-long dietary restriction on the age-related decline in cardiovascular regulation may be related to changes in cardiac sympathetic nerves.

Effects of Aloe vera ingestion in the rat. I. Growth, food and fluid intake and serum chemistry

This study was designed to examine the effects of long‐term (1.5 and 5.5 months) Aloe vera (Aloe barbadensis) ingestion on the growth, food intake and serum chemistry of Fischer 344 male rats. Aloe vera powders, produced by two different methods, were mixed with rat chow at selected concentrations. Process A aloe was prepared from skinned aloe filets by homogenization followed by lyophilization and grinding to a fine powder; Process B aloe was prepared similarly except that the homogenate was charcoal filtered prior to lyophilization. Ingestion of Process A aloe at concentrations greater than 1% was associated with diarrhoea and a decrease in weight gain. Ingestion of 1% Process A and both 1% and 10% Process B aloe had no adverse effect on body weight gain, food intake, gastrointestinal transit time and gross pathology. Serum chemistry was minimally affected. The rats ingesting 10% Process B aloe exhibited a slight, but significant increase in fluid intake. The results indicate that, although high concentrations of aloe should be avoided, ingestion of moderate levels (1%) of aloe from either process causes no apparent adverse effects in the rat.

Effect of Preload on Rat Aortic Smooth Muscle Sensitivity to Vasoactive Agents

Concentration-response curves to potassium chloride, phenylephrine, serotonin and calcium chloride were obtained from rat aortic strips subjected to preloads of 0.75, 1.5 or 3.0 g. The sensitivity of the aortic smooth muscle to potassium chloride, phenylephrine and serotonin increased with increasing preload; whereas the calcium chloride concentration-response curves of K+-depolarized strips were unaffected by preload. These results demonstrate that the sensitivity of rat aortic smooth muscle to many vasoactive agents is a function of preload and also indicate that an alteration in the influx of external Ca2+ is not sufficient to explain the effect of preload on sensitivity.

Effects of Aloe vera ingestion in the rat. II. Hormonal and metabolic characteristics

The aim of this study was to examine the effects of long‐term (1.5 and 5.5 months) Aloe vera (Aloe barbadensis) ingestion on a variety of metabolic parameters of Fischer 344 male rats. Rats were fed Aloe vera powders produced by two different methods and mixed with rat chow at various concentrations. Process A Aloe was prepared from skinned Aloe filets by homogenization followed by lyophilization and included in the rat chow at the 1% level. Process B Aloe was prepared similarly except the homogenate was charcoal filtered prior to lyophilization and mixed with chow at both 1% and 10% levels. Plasma concentrations of parathyroid hormone (PTH) and calcitonin were lower in the older (7 month) Aloe fed than in the control rats of the same age. No statistically significant effects were observed at the younger age (3 month). Aloe feeding did not alter the plasma glucose and insulin levels at any age and had only minor effects on the plasma corticosterone concentrations in the older rats. Serum lipid peroxides were decreased by Aloe feeding, but the malondialdehyde production of cardiac and hepatic mitochondrial and microsomal membranes were unaffected. No alteration in protein turnover was observed in the Aloe fed rats.

Food restriction alters the age-related decline in cardiac β-adrenergic responsiveness

The responsiveness of the heart to beta-adrenergic receptor stimulation declines with age. The aim of this study was to determine whether food restriction (FR), the most effective means of retarding the aging processes, affects the loss of beta-adrenergic responsiveness. Male Fisher 344 rats, fed either ad libitum (Group A) or allowed to eat only 60% of what Group A rats consumed (Group B), were sacrificed at 4, 11 or 22-28 months of age. The hearts were isolated and perfused via the Langendorff method. Ventricular pressure-volume curves were constructed to determine the optimal volume for pressure development and concentration-response curves to isoproterenol were obtained at this optimal volume. Interestingly, the ventricular pressure-volume curve for 4 month Group B lay to the left of all the other groups, suggesting that hearts from younger FR rats possessed higher contractility than the other groups. In the unstimulated heart, aging was associated with a slower relaxation phase of contraction and FR further slowed the relaxation. The maximum response of the heart to isoproterenol declined with age and the decline was unaffected by FR. The concentration-response curves of hearts from older rats were generally shifted to the right of the younger animals, while FR shifted the curves to the left toward greater sensitivity to beta-adrenergic stimulation. The EC50s for isoproterenol increased with age, indicating a decrease in the responsiveness of the heart to beta-adrenergic receptor stimulation. In contrast, FR decreased the isoproterenol EC50, suggesting an enhanced responsiveness. These results demonstrate that FR can retard some aging changes (loss in beta-adrenergic responsiveness), while it enhances others (increase in relaxation times).