Biomedical subjects

P J Scarpace

Publications and source records attributed to P J Scarpace.

At least 55 records · Page 3Linked to original sources

PubMed1997

Leptin gene expression increases with age independent of increasing adiposity in rats.

Humans and rats tend to gain weight as they age. Leptin is one regulator of food intake and energy expenditure. To determine if the increase in adiposity with age is related to altered leptin gene expression, we assessed adiposity levels, leptin mRNA levels in epididymal and inguinal white adipose tissue (EWAT and IWAT), and uncoupling protein (UCP1) mRNA levels in interscapular brown adipose tissue (IBAT) from F344 x BN rats ages 3, 12, 18, 24, and 30 months (n = 8/age). Levels of adiposity determined by the adiposity index and the Lee index increased between ages 3 and 24 months, with a decrease at age 30 months. There were parallel increases with age in body weight, EWAT, and IWAT depot size up to age 24 months, followed by a nonsignificant decrease at age 30 months. Daily food intake was unchanged with age. In EWAT, leptin mRNA per microgram of RNA was unchanged with age, whereas in IWAT, it increased up to 24 months, then declined at 30 months. Total leptin mRNA levels in both IWAT and EWAT depots increased with age, peaking at age 24 months, and were correlated with adiposity. Serum leptin levels increased with age, also peaking at age 24 months, and were correlated with total leptin mRNA in WAT pads and adiposity. The rate of increase in serum leptin was greater than the increase in adiposity with age, suggesting contributions from both the increase in leptin expression per unit of WAT and the increase in WAT depot size. In addition, UCP1 mRNA levels in IBAT did not change with age. These data suggest that adiposity increases with age and cannot be attributed to increased food intake, impaired leptin gene expression, or decreased UCP1 mRNA level in IBAT. Furthermore, leptin gene expression in IWAT increases with age independent of increasing adiposity.

Adipose Tissue↗

PubMed1996

Thermogenesis in brown adipose tissue with age: post-receptor activation by forskolin.

beta3-Adrenergic-stimulated thermogenesis in brown adipose tissue (BAT) is diminished with age. beta3-Adrenergic receptors are positively coupled to adenylyl cyclase in BAT. To determine whether thermo- genesis, in response to direct activation of adenylyl cyclase, is also impaired with age, we examined whole body oxygen consumption, mitochondrial guanosine diphosphate (GDP) binding and BAT mitochondrial uncoupling protein (UPC) mRNA levels in 4- and 24-month-old F-344 rats following forskolin administration. We also examined the forskolin-induced change in body temperature in 4-month-old rats. In some instances, the results were compared with administration of the specific beta3-adrenergic agonist, CGP-12177. Forskolin (3.5 mg/kg) increased oxygen consumption but decreased body temperature. In subsequent experiments the BAT was unilaterally denervated. In these rats, the forskolin-(1.8 mg/kg) stimulated increase in oxygen consumption was similar in young and old rats. Forskolin increased GDP binding and UCP mRNA levels in both the denervated and innervated BAT pads. The increases were equal or greater in the BAT from senescent rats. These findings, coupled with our previous report of an impaired CGP-12177-stimulated increase in GDP binding in senescent rats, suggests beta3-adrenergic-stimulated, but not post-receptor-stimulated, thermogenesis is diminished with age.

Adipose Tissue, Brown↗

PubMed1996

Myocardial adenylyl cyclase type V and VI mRNA: differential regulation with age.

Myocardial beta-adrenergic signal transduction diminishes with age. This decrease is not due to a decrease in the number of beta-adrenoceptors, but may be a result of an impaired capacity to activate adenylyl cyclase (AC). Forskolin-stimulated AC activity is diminished, and the number of forskolin binding sites is decreased, suggesting that the decrease in signal transduction with age is a result of fewer AC catalytic units. To investigate whether the decrease in AC with age is associated with diminished AC mRNA, we assessed AC type V and type VI mRNA in ventricles from 6-, 11-, and 24-month-old F-344 rats. The predominant mRNA species, type V, increased by 45% between 6 and 11 months of age but decreased to just below the 6-month level by age 24 months. In contrast, type VI mRNA decreased by 44% between 6 and 11 months of age and then increased to the 6-month level at age 24 months. The changes in type V and type VI mRNA did not parallel the decreases in the AC activity or forskolin binding sites with senescence. These data indicate that the steady-state levels of type V and VI AC mRNA are not reliable predictors of the efficacy of forskolin stimulation of AC activity at different ages.

Adenylyl Cyclases↗

PubMed1996

Thermoregulation with age: restoration of beta(3)-adrenergic responsiveness in brown adipose tissue by cold exposure.

The beta(3)-adrenergic-stimulated thermogenic response in brown adipose tissue (BAT) is impaired in senescent rats, whereas cold-induced thermogenesis is not. To determine if cold exposure can restore beta(3)-adrenergic receptor responsiveness in senescent rats, we examined BAT mitochondrial GDP binding in young and old rats, and UCP mRNA levels in young rats following stimulation by the beta(3)-adrenergic agonist CGP-12177 with and without prior cold exposure. F-344 male rats were maintained at thermoneutrality or exposed to 8 degrees C for 48 hr, followed by a 24-hr period of rewarming before administration of 0.75 mg/kg CGP-12177 or vehicle solution. During the rewarming period, GDP binding remained elevated but UCP mRNA levels with a half-life of 11 hr returned to levels observed in the thermoneutral controls. In young rats, both cold exposure and administration of the beta(3)-adrenergic agonist to thermoneutral controls increased GDP binding 2-fold and UCP mRNA levels 4-fold. However, in cold-exposed young rats, there was no further increase with beta(3)-agonist treatment. In senescent control rats, CGP-12177 did not increase GDP binding, but cold exposure did. However, in cold-exposed old rats, the beta(3)-agonist was now able to increase GDP binding. The induction of UCP mRNA by CGP-12177 was also investigated and found to be 25% less in senescent compared with young rats. These observations indicate that cold exposure restores the impaired beta(3)-adrenergic signal transduction in BAT from senescent rats. One possibility is that cold exposure induces the synthesis of one or more components in the beta(3)-adrenergic pathway in senescent rats.

Adipose Tissue, Brown↗

PubMed1996

Effects of age on beta adrenergic subtype activation of adenylyl cyclase in brown adipose tissue.

Thermogenesis in brown adipose tissue (BAT) is believed to be mediated mainly by beta3 adrenergic receptors. We previously demonstrated that the specific beta3 adrenergic agonist CGP-12177 increases whole body oxygen consumption and BAT GDP binding to a greater extent in young than in senescent rats. In contrast, the forskolin-induced increases were maintained with age, suggesting that early events in beta3 adrenergic signal transduction are impaired with age. To investigate whether beta1 or beta3 adrenergic function is decreased with age, we assessed beta1 and beta3 adrenergic receptor mRNA levels and the ability of beta1 and beta3 adrenergic receptors to activate adenylyl cyclase in BAT membranes from 4- and 24-month-old F-344 rats. Both beta1 and beta3 adrenergic receptor mRNA levels decreased by 50% with age. Adenylyl cyclase stimulated by the nonspecific agonist, isoproterenol, and by the specific beta3 agonist, BRL 37344, also declined by 50% with age, whereas glucagon stimulation decreased by more than 70%. The isoproterenol-stimulated adenylyl cyclase activation curves were resolved by two-site regression analysis to determine the contribution of beta1 and beta3 adrenergic receptors. The Vmax for both beta1 and beta3 adrenergic receptors decreased by 50% with age. However, stimulation of adenylyl cyclase by NaF and forskolin was also diminished by the same amount as beta adrenergic stimulation, suggesting that the activation with age may be limited by the amount of adenylyl cyclase catalytic unit rather than by receptor number. These data suggest both beta1 and beta3 adrenergic receptors and adenylyl cyclase catalytic units are deficient with age in rodent BAT.

Adenylyl Cyclases↗

PubMed1994

Relationship between cAMP production and protein secretion in rat submandibular acini: evidence for loss of reserve capacity with age.

We assessed isoproterenol and forskolin-stimulated cAMP production and protein secretion in submandibular salivary glands from young (4-7 mo) and old (25 mo) male F-344 rats. In senescent acini, the maximum amount of cAMP produced was three-fold less and the protein secreted was one-third less in response to the highest dose of isoproterenol (100 microM). Following isoproterenol stimulation, the young acini were more sensitive than the old for protein secretion than for cAMP production. Post-receptor stimulation (by forskolin) of cAMP production and protein secretion were less in the senescent rats. This report demonstrates the validity of an in vitro model for simultaneous assessment of biochemical and functional correlates. Furthermore, the observations suggest that both receptor and post-receptor stimulation of cAMP production and protein secretion diminish with age. Moreover, there is a reserve capacity for cAMP production with respect to protein secretion in the young that is diminished or even absent in the old rats.

Aging↗

PubMed1994

Influence of exercise training and age on uncoupling protein mRNA expression in brown adipose tissue.

The ability to regulate body temperature diminishes with age. Exercise training is known to increase cardiovascular performance, and there is some evidence of a cross-adaptation between exercise and cold tolerance in young rats. The present study was designed to examine the effects of physical training by treadmill running on the capacity for brown adipose tissue (BAT) thermogenesis in young and old rats. To this end, we assessed BAT uncoupling protein (UCP) mRNA expression in sedentary and exercise-trained 5- and 25-mo-old F-344 rats. The amount of UCP mRNA, whether expressed as per unit RNA or per BAT, did not change with either age or training. These data indicate that there is no cross-adaptation by exercise on adaptive thermogenesis in BAT in either young or old rats.

Adipose Tissue, Brown↗

PubMed1994

Alpha-adrenergic receptor-mediated thermogenesis in brown adipose tissue of rat.

1. The present studies were undertaken to characterize the thermogenic response to the alpha 1-adrenergic agonist phenylephrine, to compare this response with the beta-adrenergic response and to assess the role of brown adipose tissue (BAT). 2. Phenylephrine and the beta 3-adrenergic agonist CGP 12177A each caused similar increases in O2 consumption. No synergism was observed when combining the two drugs. Phenylephrine stimulated O2 consumption via an alpha-adrenergic mechanism, as indicated by effective blockade with phenoxybenzamine, but not propranolol. 3. Further evidence for the alpha-adrenergic mechanism of phenylephrine action was seen in studies with BAT membranes. Phenylephrine did not stimulate adenylyl cyclase and did not potentiate beta-adrenergic stimulation of adenylyl cyclase. 4. Skeletal muscle was not a major site of phenylephrine-stimulated O2 consumption, as the response was not inhibited by a concentration of dantrolene which inhibited cold-induced muscle shivering. 5. Phenylephrine caused an increase in the density of available 3H-GDP binding sites in BAT mitochondria, indicating an activation of BAT thermogenesis in vivo. This increase was equal in magnitude to what we have reported previously for CGP-12177A. No changes were observed in the affinity for 3H-GDP. 6. We concluded that phenylephrine stimulates O2 consumption by an alpha-adrenergic mechanism that involves activation of BAT thermogenesis. It remains to be determined whether the activation of BAT occurs by a direct or indirect mechanism.

Adenylyl Cyclases↗

PubMed1994

Alpha 1-adrenergic and arginine vasopressin stimulation of inositide hydrolysis in rat hepatocytes is unaltered in senescence.

Alpha 1-adrenergic receptors in the liver support glucose counterregulation by stimulating glycogenolysis and gluconeogenesis. We have recently reported that senescence is accompanied by reductions both in the density of alpha 1 receptors in liver homogenates and in the affinity of these receptors for agonists (Borst and Scarpace, 1990a). The present studies were undertaken to determine what consequences these reductions may have for agonist-stimulated second messenger production. To this end we measured the density of alpha 1-adrenergic receptors and agonist-stimulated phosphoinositide (PI) hydrolysis in short-term hepatocyte cultures derived from young and senescent rats. Receptor density in hepatocytes was unchanged with age. PI hydrolysis response to epinephrine was alpha 1 in nature, as it was fully blocked by prazosin. The epinephrine response was unchanged with age, both in maximum response and in sensitivity. Similarly, the response to arginine vasopressin (AVP) was also unchanged with age.

Aging↗

PubMed1994

Atypical beta-adrenergic receptors in rat liver: evidence for transient expression during aging.

This study was designed to determine whether functional beta 3-adrenergic receptors exist in the rat liver and whether there are alterations in the beta 3-adrenergic response with age in a manner similar to that which occurs for beta 2-adrenergic receptors. The beta 3 stimulation of adenylyl cyclase activity was assessed using the novel beta 3-specific agonist, CGP-12177A. Adenylyl cyclase activation by CGP-12177A was seen only in the adults. Isoproterenol-stimulated adenylyl cyclase activity was high in the neonates, declined by 45% in the adults, and was high again in the senescent rats. ICI 118551, a beta 2-selective antagonist, attenuated the isoproterenol-stimulated activity by two-thirds but had no effect on the CGP-12177A-stimulated activity. These data demonstrated the presence of the beta 3-adrenergic receptor in the rat liver, although only at the adult stage of development. In addition, these data confirm earlier findings that beta 2-adrenergic activation of adenylyl cyclase is biphasic with age and indicate that the emergence of the beta 3-stimulated activity coincides with the attenuation of beta 2-stimulated activity.

Adenylyl Cyclases↗

PubMed1994

Effects of beta-adrenergic antagonists on salivary secretory function in individuals of different ages.

The purpose of this study was to assess the effects of chronic beta-adrenergic antagonists on parotid and submandibular gland secretions in men and women of different ages. Unstimulated and stimulated saliva flow rates, total protein concentrations, and protein secretion rates were compared from medicated (various beta-antagonists, n = 25) and control (n = 60) subjects. Age-related decreases were found in unstimulated parotid saliva flow rate (p = .011) and protein secretion rate (p = .04), unstimulated submandibular salivary flow rate (p = .005) and protein secretion rate (p = .010), and in stimulated submandibular flow rate (p = .002) and protein secretion rate (p = .006). A drug-related effect was observed only in unstimulated parotid salivary flow (p = .033) and protein secretion rate (p = .04) from medicated subjects. Results from this study indicate that age and beta-adrenergic blockade alter salivary glandular function, but their effects differ with the type of salivary secretion examined.

Adrenergic beta-Antagonists↗

PubMed1994

Influence of exercise training on myocardial beta-adrenergic signal transduction: differential regulation with age.

Exercise training is known to increase cardiovascular performance and decrease heart rate. Because activation of adenylyl cyclase is an important factor in beta-adrenergic signal transduction and in the decline in signal transduction with age, we hypothesized that some of the effects of exercise training may be mediated by changes in postreceptor activation of adenylyl cyclase. To this end, we assessed isoproterenol-, G protein-, and forskolin-mediated activation of adenylyl cyclase as well as G protein immunoreactivity in the myocardium from young and senescent F-344 rats with and without prior exercise training by treadmill running. Isoproterenol, beta-gamma-imidoguanosine 5'-triphosphate, and forskolin stimulation of adenylyl cyclase activity declined by approximately 50% with age. Training increased the stimulation in the senescent rats and decreased the stimulation in the young rats such that the age-related decline in signal transduction was no longer significant. Gs alpha protein immunoreactivity was unchanged by age or training. These data suggest that in young rats exercise training decreases beta-adrenergic signal transduction, whereas in older rats training increases signal transduction, partially offsetting the decline in signal transduction with age.

Adenylyl Cyclases↗

PubMed1994

Thermoregulation with age: role of thermogenesis and uncoupling protein expression in brown adipose tissue.

To investigate whether attenuation of thermogenesis in interscapular brown adipose tissue (IBAT) may account for the loss of thermoregulation with age, we examined two indices of thermogenesis after two types of cold exposure: one in which the senescent rats maintained homeothermy and the other in which the senescent rats became hypothermic. To this end, we assessed body temperature, guanosine 5'-diphosphate (GDP) binding to the IBAT mitochondrial uncoupling protein (UCP) and the induction of UCP mRNA after both 1-hr and 48-hr mild cold exposures at 8 degrees C and after a more severe, 1-hr cold exposure at 4 degrees C in 3- and 24-month-old F-344 rats. Thermoneutrality was determined to occur at an ambient temperature of 26 degrees C in rats of both ages. In the 1-hr mild cold-exposed rats, there was no significant increase in GDP binding to IBAT UCP. However, after 48 hr of mild cold exposure, there was a 3-fold increase in GDP binding and a 5-fold increase in the expression of UCP mRNA despite no hypothermia in either the young or old rats. During the more severe cold exposure, the senescent rats, but not the young rats, became hypothermic. GDP binding to UCP increased 75% following cold exposure and, surprisingly was the same in young and old rats. UCP transcripts did not increase during the 1-hr cold exposure. These data, coupled with our previous findings of diminished beta 3-agonist-stimulated IBAT thermogenesis, suggest that (i) IBAT thermogenesis, at least in the senescent rats, may be mediated by other than beta 3-adrenergic receptors, and (ii) that altered heat dissipation or impaired thermogenesis at some site other than interscapular BAT is responsible for the observed hypothermia.

Adaptation, Physiological↗

PubMed1994

Forskolin binding sites and G-protein immunoreactivity in rat hearts during aging.

Although the number of beta-adrenoceptors is unchanged with age in rat heart, both beta-adrenoceptor and postreceptor activation of adenylyl cyclase decreases with age. Pharmacologic data suggest that it is the amount of adenylyl cyclase enzyme units that limit activation of adenylyl cyclase with senescence, but direct quantitation of either G protein or adenylyl cyclase in rat heart with age is lacking. To quantitate the amount of adenylyl cyclase and G proteins with age directly, we assessed forskolin-stimulated adenylyl cyclase activity, the number of [3H] forskolin binding sites, and stimulatory G protein (Gs alpha) and inhibitory G protein (Gi alpha) immunoreactivity in the ventricles from 6- and 24-month-old F-344 rats. The amount of Gs alpha and Gi alpha was unchanged with age in both crude membranes and partially purified membranes from ventricles. In contrast, there was a 32% decrease in the ability of forskolin to stimulate adenylyl cyclase maximally and a 41% decrease in the number of forskolin binding sites with age. Sensitivity for forskolin activation was unchanged with age, but there was a slight increase in affinity for [3H]forskolin binding. The decrease in the amount of adenylyl cyclase with age correlates with the diminished capacity to activate adenylyl cyclase with age and may account for the reduced beta-adrenergic signal transduction observed in senescent rat heart.

Adenylyl Cyclases↗

PubMed1993

3,5,3'-L-triiodothyronine regulation of beta-adrenergic receptor density and adenylyl cyclase activity in synaptosomal membranes of aged rats.

To determine the effect of aging on T3 up-regulation of beta-adrenergic receptor activity of purified synaptosomal membranes (SPM), beta-adrenergic receptor density (Bmax) and adenylyl cyclase (AC) activity were measured in young (6 months old) and aged (26 months old) male F-344 rats at baseline and after treatment with triiodothyronine (T3), 15 micrograms/100 g, intraperitoneally for 10 days. The Bmax (fmol/mg protein) as measured by 125I-iodocyanopindolol binding was reduced in aged rats (70.8 +/- 4.1) compared to young rats (93.5 +/- 11.2). T3 treatment resulted in a significant increase in Bmax of young rats but not in aged rats (P < 0.05). The AC activity (pmol cAMP/mg) in response to prostaglandin E1 (PGE1) was reduced in aged rats compared to young rats (67.8 +/- 2.9 vs 108.3 +/- 18.6; P < 0.01). The sodium fluoride (NaF) stimulated AC activity was not altered with age. A net isoproterenol stimulated AC activity could not be demonstrated in any age group. T3 treatment did not alter AC activity of SPM. It is concluded that aging is associated with reduced responsiveness to T3-stimulated up-regulation of beta-adrenergic receptor number in synaptosomal membranes.

Adenylyl Cyclases↗

PubMed1993

Desipramine desensitizes beta-adrenergic signal transduction in salivary glands: differential regulation with age.

We previously reported that the tricyclic antidepressant, desipramine desensitizes beta-adrenergic signal transduction in parotid and submandibular salivary glands. To determine the consequences of repeated desipramine administration on beta-adrenergic signal transduction in salivary glands from aged rats and whether the recovery after drug withdrawal is impaired, we assessed the effects of 28-day desipramine administration and the reversibility of this treatment following a 15-day washout period on beta-adrenoceptors and adenylyl cyclase activity in parotid and submandibular glands from F-344 rats of 6, 12 and 24 months of age. beta-Adrenoceptors were also assessed in the cerebral cortex. Desipramine administration down-regulated receptor number and attenuated isoproterenol-stimulated adenylyl cyclase activity in all three ages of rats. However, the reduction in isoproterenol-stimulated adenylyl cyclase activity was greater than the loss of receptor number. Desipramine administration attenuated the efficacy of NaF-stimulated activity with no change in forskolin-stimulated adenylyl cyclase activity. These data suggest that in addition to desensitizing beta-adrenergic-mediated signal transduction, desipramine impaired G-protein-mediated adenylyl cyclase stimulation. The recovery from desipramine desensitization was age dependent. beta-Adrenoceptor density recovered more slowly in the cerebral cortex and the submandibular gland in 24-month-old rats than in 6-month-old rats. In contrast, in 12-month-old rats, there was a receptor up-regulation and adenylyl cyclase supersensitivity. These data indicate that the capacity for receptor modulation is age dependent and suggest that desipramine treatment may down-regulate stimulatory G protein.

Adenylyl Cyclases↗

PubMed1993

Decreased sensitivity to cAMP in the in vitro generation of memory splenic cytotoxic T-lymphocytes from aged mice: role of phosphodiesterase.

The effects of increased intracellular concentration of cyclic AMP (cAMP) on cellular immune function of young and aged mice were examined by using an in vitro anti-influenza cytotoxic T-lymphocyte (CTL) assay. We found that increasing intracellular concentrations of cAMP with either the cAMP analog, N,6O2'-dibutyryl cAMP, or the beta adrenergic agonist, metaproterenol, significantly inhibited the in vitro development of memory CTL activity of young mice. The development of CTL activity of aged mice, however, was less sensitive to the effects of these agents. We found that the S-isomer of cAMPS, a cAMP analog resistant to the effects of PDE, caused equivalent inhibition of CTL activity in the young and aged mice. This suggested that the cause of the decreased cAMP sensitivity in aging was increased PDE activity. In subsequent experiments, we found that the PDE from T-cells of aged mice have higher KM and higher Vmax for cAMP than the PDE from T-cells of young mice. Because beta-agonists probably act as a counter-regulatory hormone at an inflammatory site, the decreased sensitivity to cAMP in aging may be a compensatory response to the age-related decline in immune function.

Aging↗

PubMed1992

Beta-adrenergic receptor activity of cerebral microvessels in experimental diabetes mellitus.

The effect of diabetes mellitus on beta-adrenergic receptor number (B(max)), receptor-cyclase coupling and adenylate cyclase (AC) activity was determined in cerebral microvessels isolated from control and streptozotocin induced diabetic rats after 5 weeks of induction of diabetes. Scatchard analysis of [125I]iodocyanopindolol (ICYP) binding indicated that the B(max) (fmol/mg) in diabetic rat cerebral microvessels (63.8 +/- 4.8) (mean +/- S.E.M.) was not significantly different from the B(max) in control rats (56.5 +/- 6.9). Isoproterenol competition of [125I]ICYP binding sites indicated that the percentage of beta-receptors expressing high affinity binding was 53.9 +/- 0.45% in control rats and 47.5 +/- 2.3% in diabetic rats. The total isoproterenol-stimulated AC activity (pmol cAMP/mg) in diabetic rats (76.7 +/- 6.1) was significantly lower than that in control rats (118.4 +/- 11.2) (P less than 0.01). However, the net isoproterenol-stimulated AC activity (i.e. total minus GTP-stimulated AC activity) was not altered in diabetes. The net sodium fluoride (NaF) stimulated AC activity in diabetic rats (109.5 +/- 11.4) was significantly lower than the control rats (154.3 +/- 16.3) (P less than 0.05). It is concluded that diabetes mellitus in rats is associated with reduced post receptor activation of adenylate cyclase in cerebral microvessels while the beta-adrenergic receptor density, affinity and receptor-cyclase coupling are not significantly altered.

Adenylyl Cyclases↗