Beta-adrenergic function in aging. Basic mechanisms and clinical implications

Adrenoceptors and Hypertension

Hypertension is a very prevalent condition associated with high mortality and morbidity, secondary to changes resulting in blood vessels and resultant end-organ damage. Haemodynamic changes, including an initial rise in cardiac output followed by an increase in total peripheral resistance, denote the early changes associated with borderline or stage 1 hypertension, especially in young men. Increased sodium reabsorption leading to kidney damage is another mechanism proposed as one of the initial triggers for essential hypertension. The underlying pathophysiological mechanisms include catecholamine-induced α1- and ß1-adrenoceptor stimulation, and renin-angiotensin-aldosterone system activation leading to endothelial dysfunction which is believed to lead to persistent blood pressure elevation.α1 blockers, α2 agonists, and ß blockers were among the first oral anti-hypertensives. They are no longer first-line therapy after outcome trials did not demonstrate any benefits over and above other agents, despite similar blood pressure reductions. Angiotensin-converting enzyme inhibitors (or angiotensin receptor blockers), calcium channel blockers, and thiazide-like diuretics are now considered the first line of therapy, although adrenoceptor agents still have a role as second- or third-line therapy. The chapter also highlights hypertension in specific medical conditions such as pregnancy, phaeochromocytoma, hyperthyroidism, portal hypertension, pulmonary arterial hypertension, and ocular hypertension, to provide an overview for clinicians and researchers interested in the role of adrenoceptors in the pathophysiology and management of hypertension.

Pharmacotherapies in Older Adults with COPD: Challenges and Opportunities

Older adults have a higher prevalence of chronic obstructive pulmonary disease (COPD), which will likely increase substantially in the coming decades owing to aging populations and increased long-term exposure to risk factors for this disease. COPD in older adults is characterized by low-grade chronic systemic inflammation, known as inflamm-aging. It contributes substantially to age-associated pulmonary changes that are clinically expressed by reduced lung function, poor health status, and limitations in activities of daily living. In addition, inflamm-aging has been associated with the onset of many comorbidities commonly encountered in COPD. Furthermore, physiologic changes that are often seen with aging can influence the optimal treatment of older patients with COPD. Therefore, variables such as pharmacokinetics, pharmacodynamics, polypharmacy, comorbidities, adverse drug responses, drug interactions, method of administration, and social and economic issues that impact nutrition and adherence to therapy must be carefully evaluated when prescribing medication to these patients because each of them alone or together may affect the outcome of treatment. Current COPD medications focus mainly on alleviating COPD-related symptoms, so alternative treatment approaches that target the disease progression are being investigated. Considering the importance of inflamm-aging, new anti-inflammatory molecules are being evaluated, focusing on inhibiting the recruitment and activation of inflammatory cells, blocking mediators of inflammation thought to be important in the recruitment or activation of these inflammatory cells or released by these cells. Potential therapies that may slow the aging processes by acting on cellular senescence, blocking the processes that cause it (senostatics), eliminating senescent cells (senolytics), or targeting the ongoing oxidative stress seen with aging need to be evaluated.

The impact of different forms of exercise on endothelial progenitor cells in healthy populations

Circulating endothelial progenitor cells (EPCs) contribute to vascular healing and neovascularisation, while exercise is an effective means to mobilise EPCs into the circulation.

OBJECTIVES

to systematically examine the acute and chronic effects of different forms of exercise on circulating EPCs in healthy populations.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed.

RESULTS

thirty-one articles met the inclusion criteria including 747 participants aged 19 to 76 years. All included trials used flow cytometry for identification of circulating EPCs. Eight and five different EPC phenotypes were identified in the acute and chronic trials, respectively. In the acute trials, moderate intensity continuous (MICON), maximal, prolonged endurance, resistance and high intensity interval training (HIIT) exercise protocols were utilised. Prolonged endurance and resistance exercise had the most profound effect on circulating EPCs followed by maximal exercise. In the chronic trials, MICON exercise, HIIT, HIIT compared to MICON and MICON compared to exergame (exercise modality based on an interactive video game) were identified. MICON exercise had a positive effect on circulating EPCs in older sedentary individuals which was accompanied by improvements in endothelial function and arterial stiffness. Long-stage HIIT (4 min bouts) appears to be an effective means and superior than MICON exercise in mobilising circulating EPCs. In conclusion, both in acute and chronic trials the degree of exercise-induced EPC mobilisation depends upon the exercise regime applied. In future, more research is warranted to examine the dose-response relationship of different exercise forms on circulating EPCs using standardised methodology and EPC phenotype.

Reduced cardiac response to the adrenergic system is a key limiting factor for physical capacity in old age

Ageing is associated with a progressive reduction in physical capacity reducing quality of life. One key physiological limitation of physical capacity that deteriorates in a progressive age-dependent manner is cardiac reserve. Peak cardiac output falls progressively with advancing age such that in extreme old age there is limited ability to enhance cardiac output beyond basal function as is required to support the increased metabolic needs of physical activity. This loss of dynamic range in cardiac output associates with a progressive reduction in the heart's response to adrenergic stimulation. A combination of decreases in the expression and functioning of beta1 adrenergic receptors partially underlies this change. Changes in end effector proteins also have a role to play in this decline. Alterations in the efficiency of excitation-contraction coupling contribute to the reduced chronotropic, inotropic and lusitropic responses of the aged heart. Moderate to vigorous endurance exercise training however has some potential to counter elements of these changes. Further studies are required to fully elucidate the key pivotal mechanisms involved in the age-related loss of response to adrenergic signalling to allow targeted therapeutic strategies to be developed with the aim of preserving physical capacity in advanced old age.

Isoproterenol-Dependent Activation of TRPM7 Protects Against Neurotoxin-Induced Loss of Neuroblastoma Cells

Neuronal function and their survival depend on the activation of ion channels. Loss of ion channel function is known to induce neurodegenerative diseases such as Parkinson’s that exhibit loss of dopaminergic neurons; however, mechanisms that could limit neuronal loss are not yet fully identified. Our data suggest that neurotoxin-mediated loss of neuroblastoma SH-SY5Y cells is inhibited by the addition of β-adrenergic receptor (β-AR) agonist isoproterenol. The addition of isoproterenol to SHSY-5Y cells showed increased Mg²⁺ influx and cell survival in the presence of neurotoxin especially at higher concentration of isoproterenol. Importantly, isoproterenol potentiated transient receptor potential melastatin-7 (TRPM7) channel activation that leads to an increase in intracellular Mg²⁺ levels. The addition of 2APB, which is a known TRPM7 channel blocker, significantly decreased the TRPM7 function and inhibited isoproterenol-mediated protection against neurotoxins. Moreover, neurotoxins inhibited TRPM7 expression and function, but the restoration of TRPM7 expression increased neuroblastoma cell survival. In contrast, TRPM7 silencing increased cell loss, decreased Mg²⁺ homeostasis, and inhibited mitochondrial function. Moreover, isoproterenol treatment prevented neurotoxin-mediated loss of TRPM7 expression and inhibited Bax expression that induces cell survival. These effects were dependent on the neurotoxin-induced increase in oxidative stress, which inhibits TRPM7 expression and function. Together, our results suggest a positive role for β-AR in activating TRPM7 channels that regulate Mg²⁺ homeostasis and are essential for the survival of SH-SY5Y cells from neurotoxin.

Androgen Effects on the Adrenergic System of the Vascular, Airway, and Cardiac Myocytes and Their Relevance in Pathological Processes

INTRODUCTION

Androgen signaling comprises nongenomic and genomic pathways. Nongenomic actions are not related to the binding of the androgen receptor (AR) and occur rapidly. The genomic effects implicate the binding to a cytosolic AR, leading to protein synthesis. Both events are independent of each other. Genomic effects have been associated with different pathologies such as vascular ischemia, hypertension, asthma, and cardiovascular diseases. Catecholamines play a crucial role in regulating vascular smooth muscle (VSM), airway smooth muscle (ASM), and cardiac muscle (CM) function and tone.

OBJECTIVE

The aim of this review is an updated analysis of the role of androgens in the adrenergic system of vascular, airway, and cardiac myocytes. Body. Testosterone (T) favors vasoconstriction, and its concentration fluctuation during life stages can affect the vascular tone and might contribute to the development of hypertension. In the VSM, T increases α1-adrenergic receptors (α ₁-ARs) and decreases adenylyl cyclase expression, favoring high blood pressure and hypertension. Androgens have also been associated with asthma. During puberty, girls are more susceptible to present asthma symptoms than boys because of the increment in the plasmatic concentrations of T in young men. In the ASM, β ₂-ARs are responsible for the bronchodilator effect, and T augments the expression of β ₂-ARs evoking an increase in the relaxing response to salbutamol. The levels of T are also associated with an increment in atherosclerosis and cardiovascular risk. In the CM, activation of α _1A-ARs and β ₂-ARs increases the ionotropic activity, leading to the development of contraction, and T upregulates the expression of both receptors and improves the myocardial performance.

CONCLUSIONS

Androgens play an essential role in the adrenergic system of vascular, airway, and cardiac myocytes, favoring either a state of health or disease. While the use of androgens as a therapeutic tool for treating asthma symptoms or heart disease is proposed, the vascular system is warmly affected.

Altered expression of hepatic β-adrenergic receptors in aging rats: implications for age-related metabolic dysfunction in liver

Increased β-adrenergic receptor (β-AR)-mediated activation of adenylyl cyclase (AC) in rat liver during aging has been linked to age-related increases in hepatic glucose output and hepatosteatosis. In this study, we investigated the expression of β-ARs, individual receptor subtypes, and G protein-coupled receptor (GPCR) regulatory proteins in livers from aging rats. Radioligand-binding studies demonstrated that β-AR density increased by greater than threefold in hepatocyte membranes from senescent (24-mo-old) compared with young adult (7-mo-old) rats and that this phenomenon was blocked by food restriction, which is known to retard aging processes in rodents. Competition-binding studies revealed a mixed population of β1- and β2-AR subtypes in liver membranes over the adult life span, with a trend for greater β2-AR density with age. Expression of both β-AR subtype mRNAs in rat liver increased with age, whereas β2- but not β1-AR protein levels declined in livers of old animals. Immunoreactive β2- but not β1-ARs were preferentially distributed in pericentral hepatic regions. Levels of GRK2/3 and β-arrestin 2 proteins, which are involved in downregulation of agonist-activated GPCRs, including β-ARs, increased during aging. Insofar as sympathetic tone increases with age, our findings suggest that, despite enhanced agonist-mediated downregulation of hepatic β-ARs preferentially affecting the β2-AR subtype, increased generation of both receptor subtypes during aging augments the pool of plasma membrane-bound β-ARs coupled to AC in hepatocytes. This study thus identifies one or both β-AR subtypes as possible therapeutic targets involved in aberrant hepatic processes of glucose and lipid metabolism during aging.

Renal Physiology and Robotic Urological Surgery

The use of robotic-assisted laparoscopic techniques has transformed the face of urological surgery in the last decade, with demonstrable benefits over both unassisted laparoscopic and traditional open approaches. For example, robotic-assisted partial nephrectomy is associated with lower morbidity, improved convalescence, reduced postoperative pain, shorter length of hospital stay, and a superior cosmetic result when compared to an open procedure. This review discusses the various perioperative influences on the renal physiology of patients undergoing robotic-assisted urological procedures.

Role of β-adrenergic receptors in regulation of hepatic fat accumulation during aging

Excessive fat accumulation in liver (hepatic steatosis) predisposes to hepatic functional and structural impairment and overall metabolic risk. Previous studies noted an association between hepatic steatosis and age in humans and rodents. However, the mechanisms leading to age-associated hepatic fat accumulation remain unknown. Earlier work from our group showed that β-adrenergic receptor (β-AR) levels and β-AR-stimulated adenylyl cyclase activity increase in rat liver during aging. Here we investigated whether age-associated increases in β-AR signaling play a role in augmenting hepatic lipid accumulation. We demonstrate an increase in hepatic lipid content during senescence and a significant correlation between hepatic fat content and stimulation of adenylyl cyclase activity by the β-AR agonist isoproterenol in rat liver. Isoproterenol administration to young and old rodents in vivo increased hepatic lipid accumulation. Furthermore, in vitro overexpression of β1- and β2-AR subtypes in hepatocytes from young rodents increased cellular lipid content, whereas inhibition of β-ARs by receptor subtype-specific inhibitors reduced lipid levels in hepatocytes from senescent animals. Isoproterenol-induced hepatic lipid accumulation in vivo was prevented by the β-AR nonselective blocker propranolol, suggesting a novel therapeutic effect of this class of drugs in hepatic steatosis. Acipimox, which inhibits adipose tissue lipolysis, did not alter isoproterenol-mediated hepatic fat accumulation; thus β-AR responsive hepatic lipid accumulation does not appear to be related primarily to altered lipolysis. These findings suggest that augmented hepatic β-AR signaling during aging may increase lipid accumulation in liver and advocate a possible role for β-adrenergic blockers in preventing or retarding the development of hepatic steatosis.

β-Adrenergic Responsive Induction of Insulin Resistance in Liver of Aging Rats

INTRODUCTION. We previously demonstrated increases in β-adrenergic receptor (β-AR) density in rat liver, in association with increased β-AR-mediated stimulation of glucose output in rat hepatocytes, during senescent aging. We therefore hypothesized that pharmacologic β-adrenergic stimulation might induce insulin resistance and glucose output in liver of aging rats in vivo. METHODS. In this study, pancreatic clamps were performed on young adult (4-month-old) and senescent (24-month-old) Fischer 344 male rats by infusing somatostatin (3 μg/kg/min) at time 0 to inhibit insulin secretion, and then infusing insulin (1 mU/kg/min) to replace basal insulin concentrations. At time 0 rats also received either the β-AR agonist isoproterenol (100 ng/kg/min) or saline (control). After 120 min the insulin infusion rate was increased to 4 mU/kg/min for an additional 120 min. Tritiated glucose was infused throughout the study to measure glucose turnover rates. RESULTS AND CONCLUSION. The results of the pancreatic clamp studies demonstrated that under saline control conditions hepatic glucose production (HGP) was suppressed during hyperinsulinemia in both young and old rats, with a trend toward reduced insulin sensitivity in the older animals. Isoproterenol infusion impaired insulin-induced suppression of HGP in both age groups. The results suggest that β-AR stimulation by isoproterenol increases HGP and acutely induces hepatic insulin resistance in both young and old rats. A similar role for β-adrenergic-mediated hepatic insulin resistance in aging humans would suggest a novel therapeutic target for the treatment or prevention of glucose dysregulation and diabetes developing with advancing age.

Genetic influences of beta-adrenoceptor polymorphisms on arterial functional changes and cardiac remodeling in hypertensive patients

Three subtypes of beta-adrenoceptor, beta1, beta2 and beta3, are involved in the sympathetic nervous system, which plays an important role in the development of hypertension and hypertensive complications. These complications can include left ventricular hypertrophy and arterial stiffness, which are reported risk factors for cardiovascular diseases. We designed clinical trials to clarify the association between hypertensive complications and beta-adrenoceptor single nucleotide polymorphisms in essential hypertension. Using Taqman PCR methods, we detected five polymorphisms of three beta-adrenoceptors: Ser49Gly and Arg389Gly for the beta1-adrenoceptor; Gly16Arg and Glu27Gln for the beta2-adrenoceptor; and Trp64Arg for the beta3-adrenoceptor. We included 300 subjects and measured pulse wave velocity, vasodilator response to hyperemia, left ventricular hypertrophy (by electrocardiogram and echocardiography), and cardiac enlargement (by chest X-ray). We found that pulse wave velocity and nitroglycerin-induced hyperemia were both closely associated with the Ser49Gly polymorphism (p<0.05), and Glu27Gln was found by both electrocardiogram and echocardiography to be significantly associated with left ventricular hypertrophy (p<0.05). These data suggested that two polymorphisms of different beta-adrenoreceptor subtypes are the genetic influences on the development of arterial stiffness and left ventricular hypertrophy in essential hypertension.

Effect of age on vascular beta2-adrenergic receptor desensitization is not mediated by the receptor coupling to Galphai proteins

Beta-adrenergic receptor (beta-AR)-mediated vasorelaxation declines with age. In the vasculature, beta2-AR undergoes protein kinase A-mediated desensitization that causes a switch in the G protein coupled to beta2-AR; Galphai links instead of Galphas. We exposed Fischer 344 rat aortae of increasing age to a desensitizing dose of isoproterenol, and determined its effect on beta2-AR-mediated vasorelaxation. Desensitization decreased beta2-AR-mediated vasorelaxation in young aortae only. Subsequently, we used pertussis toxin to block Galphai to determine whether changes in beta2-AR/G protein coupling occurred. Galphai inhibition did not reverse desensitization or the age-related change, but there appears to be a population of beta2-AR linked to Galphai, as pertussis toxin treatment improved beta2-AR-mediated vasorelaxation in aortae from animals of all ages. These findings suggest aortic beta2-AR in older animals may be maximally desensitized, which would explain impaired vasorelaxation. Our results also imply that protein kinase A-mediated beta2-AR desensitization may not be responsible for the age-related decline.

Cardiovascular drug therapy in the elderly: theoretical and practical considerations

The elderly population is expanding rapidly throughout the world. Hypertension, heart disease and other cardiovascular disorders are prevalent conditions among this age group. Consequently, clinicians will spend a large proportion of their practices managing older adults with cardiovascular disorders. A large proportion of this time will be devoted to using pharmacotherapeutic strategies for the long-term management of chronic conditions. The physiological changes that accompany aging affect cardiovascular function, and the pharmacokinetics and pharmacodynamics of many cardiovascular medications are altered by these physiological changes. The interactions of these changes can have a profound effect on the agents used to treat cardiovascular disorders and may alter their therapeutic outcomes. Several classes of medications are used to treat chronic cardiovascular disorders in older adults. These include the ACE inhibitors and angiotensin II receptor antagonists, calcium channel antagonists, beta-adrenoceptor antagonists (beta-blockers), oral antiarrhythmic agents and warfarin. Drugs such as beta-blockers may aggravate decreased cardiac output and increase peripheral resistance, but are valuable adjuncts in many patients with congestive heart failure. Agents that reduce angiotensin II activity may have several benefits for treating heart failure and hypertension. Successful treatment of cardiovascular disorders in older adults requires the choice of the most appropriate agent, taking into consideration the complex interactions of pharmacokinetics, pharmacodynamics and disease effects.

Age-related changes in vascular adrenergic signaling: clinical and mechanistic implications

A large and growing segment of the general population are age 65 or older, and this percentage will continue to rise. Primary care of this population has, and is becoming a priority for clinicians. Hypertension, orthostatic hypotension, arterial insufficiency, and atherosclerosis are common disorders in the elderly that lead to significant morbidity and mortality. One common factor to these conditions is an age-related decline in beta-adrenergic receptor (beta-AR)-mediated function and subsequent cAMP generation. Presently, there is no single cellular factor that can explain this age-related decline, and thus the primary cause of this homeostatic imbalance is yet to be identified. However, the etiology is clearly associated with an age-related change in the ability of beta-AR receptor to respond to agonist at the cellular level. This article will review what is presently understood regarding the molecular and biochemical basis of age-impaired beta-AR receptor-mediated signaling. A fundamental understanding of why beta-AR-mediated vasorelaxation is impaired with age will provide new insights and innovative strategies for the management of the multiple clinical disorders that effect older people.

Relationships between beta- and alpha2-adrenoceptors and G coupling proteins in the human brain: effects of age and suicide

Interactions between brain alpha2- and beta-adrenoceptors are of interest in physiological (aging) and pathological (major depression) processes involving both receptors. In this study, total beta-adrenoceptors and beta1/2-subtypes were quantitated in postmortem human brains to investigate their relationships with alpha2A-adrenoceptors and specific G proteins during the process of aging and in brains of suicide victims. Analysis of [3H]CGP12177 binding, in the presence of CGP20712A (beta1-antagonist), indicated that the predominant beta-adrenoceptor in the frontal cortex is the beta1-subtype (65-75%). The density of total beta- (r=-0.60, n=44) or beta1-adrenoceptors (r=-0.78, n=22), but not the beta2-subtype, declined with aging (3-80 years). The density of total beta- or beta1-adrenoceptors, but not the beta2-subtype, correlated with the number of alpha2-adrenoceptors quantitated in the same brains with the agonist [3H]UK14304 (r=0.71-0.81) or the antagonist [3H]RX821002 (r=0.61-0.66). Interestingly, the ratios alpha2/beta- or alpha2/beta1-adrenoceptors did not correlate with the age of the subject at death, indicating that the proportion of alpha2/beta-adrenoceptors in brain remains rather constant during the process of aging. The density of beta-adrenoceptors correlated with the immunodensity of G(alpha)s (r=0.55) and Gbeta (r=0.61) proteins, and that of alpha2-adrenoceptors with those of G(alpha)i1/2 (r=0.88) and Gbeta (r=0.65). In brains of suicides, compared to controls, the ratio between alpha2- and beta- or beta1-adrenoceptors (alpha2-full agonist sites/beta-sites) was greater (1.3- to 2.0-fold; P<0.05). The results demonstrate a close interdependence between brain alpha2- and beta-adrenoceptors during aging, and in brains of suicides. The quantitation of the alpha2A/beta-adrenoceptor ratio could represent a relevant neurochemical index in the study of brain pathologies in which both receptors are involved.

An analysis of parotid salivary gland function with desipramine and age in female NIA Fischer 344 rats

Cyclic antidepressants are still a dominating group of psychotherapeutic drugs used in the treatment of depression. Dry mouth is one of their major side effects. In this study we analyzed the effects of the long-term administration of the tricyclic antidepressant desipramine and the reversibility of this treatment following a 15-day washout period on different parameters in parotid gland function in aging rats. We hypothesized that glandular function would be decreased, and recovery delayed with age. Drug treatment affected body weight, glandular weight, DNA synthesis, and the concentration of soluble and structural membrane proteins. Surprisingly, parotid flow rate was increased with desipramine in all ages. While the concentration of secreted proteins was generally decreased with treatment, total proteins secreted were quite stable. SDS/PAGE analysis revealed prominent changes with desipramine. Amylase activity was depressed with treatment, but only low residual cellular enzyme activity was detected in the glandular supernatant. Therefore, a secretory impairment with desipramine was excluded. The content of the antimicrobial proteins peroxidase and lysozyme was increased with desipramine in all age groups. Most parameters measured revealed delayed recovery with age. These data indicate that the tricyclic antidepressant desipramine has profound effects on parotid gland function, accented with age.

Effect of maturation and aging on beta-adrenergic signal transduction in rat kidney and liver

The characteristics of the beta-adrenergic signal transduction system were analyzed in kidney and liver membrane preparations from neonatal (2-3 days), mature (2 months), and old (2 years) rats. When comparing kidneys from adult to neonatal rats, we found a higher beta-receptor density and a higher percentage of beta(1)-receptor subtype, lower immunoreactive G(salpha)-protein, a lower ratio between the high and low molecular weight splice variant of G(salpha), lower immunoreactive G(ialpha)-protein, and lower basal adenylate cyclase activity. When comparing livers from adult to neonatal rats, we found lower beta-receptor density and basal adenylate cyclase activity. Very few differences could be detected when comparing mature to old kidneys or livers. Stimulated adenosine 3',5'-cyclic monophosphate (cAMP) synthesis was tissue- and age-dependent. In liver, G-protein- and beta-receptor-stimulated cAMP synthesis mirrored basal adenylate cyclase activity and was highest in liver from neonatal animals. In contrast, cAMP synthesis was significantly more stimulated in kidneys from mature animals than from neonatal and senescent rats. We conclude that: (i) the stoichiometry of the components within the beta-receptor/G-protein/adenylate cyclase complex is not fixed but is both tissue- and age-dependent; (ii) adenylate cyclase enzyme activity is possibly but not necessarily the rate-limiting step in the beta-receptor-mediated synthesis of cAMP; and (iii) there is in vivo evidence for a preferential co-expression of the large splice variant of the G(s)-protein and beta(2)-receptor subtype. It is speculated that this could have important physiological consequences for the development of the kidney.

An analysis of submandibular salivary gland function with desipramine and age in female NIA Fischer 344 rats

Dry mouth is one of the major side effects of cyclic antidepressants, which are still a dominating group of psychotherapeutic drugs used in the treatment of depression. In this study we analyzed the effects of 28 day tricyclic antidepressant administration and the reversibility of this treatment following a 15 day washout period on different parameters in submandibular gland function in aging rats. We postulated that desipramine would decrease gland function, accented with age, and delay recovery in senescent animals. In contrast to body weight, desipramine had no effect on glandular wet weight. While glandular DNA synthesis was changed with age and treatment, the concentration of total membrane and soluble proteins was not affected. Flow rate was significantly changed with age, but desipramine increased salivary flow in the youngest animals only. Neither age nor treatment influenced salivary protein concentrations, but the total amount of proteins secreted, revealed perturbation with age. SDS- polyacrylamide gel analysis revealed changes in protein expression with treatment and age. Desipramine decreased epidermal growth factor (EGF) levels in all age groups, but increased the secretion of peroxidase and lysozyme. Analysis of total RNA showed a pronounced decrease with age. These data indicate that desipramine has profound effects on submandibular salivary gland function.

Cellular determinants of reduced adaptability of the aging brain: neurotransmitter utilization and cell signaling responses after MDMA lesions

Senescence is accompanied by the loss of neurons and synapses, and the maintenance of function depends on adaptive change at the levels of synaptic activity and cellular responsiveness. In the current study, we administered the neurotoxin MDMA, to young and aged mice and assessed the effects on indices of neuronal activity and cell signaling mediated through adenylyl cyclase. Young mice given MDMA showed 80% depletion of dopamine in the caudate and 30% depletion in the cerebral cortex; measurements of dopamine turnover indicated a compensatory upregulation of the activity of the remaining neurons in the caudate but downregulation in the cerebral cortex. Serotonin levels were comparatively less affected but serotonin turnover was decreased significantly in both regions. At the level of cell signaling, the young mice showed heterologous upregulation of adenylyl cyclase activity and a consequent enhancement of responses mediated through neurotransmitter receptors. In aged mice, MDMA treatment produced the same degree of lesioning but substantially different changes in neuronal activity and cell signaling. In the cerebral cortex, dopamine turnover was increased, and serotonin turnover decreased, effects opposite in direction to those seen in young mice. In the aged group, MDMA elicited heterologous loss of adenylyl cyclase responses instead of displaying the supersensitivity that had been seen in the young group. The aging brain thus displays maladaptation to the loss of monoaminergic input, effects that may augment the functional impairment associated with neurodegenerative disorders or stroke.

Vascular β-adrenoceptor function in hypertension and in ageing

Functional β-adrenoceptors (β-AR) have been identified and characterized in blood vessels under in vivo conditions as well as in vascular smooth muscle cells (SMC) grown in culture. Agonist occupancy of β-AR activates adenylyl cyclase (AC) via the stimulatory guanine nucleotide-binding protein (Gs) and leads to elevations in intracellular adenosine 3',5'-cyclic monophosphate levels (cAMP). Increased cAMP activates the cAMP-dependent protein kinase (PKA), with subsequent phosphorylation of various target proteins. This β-AR pathway interacts with several other intracellular signalling pathways via cross-talk, so that activation by β-AR agonists may also modulate other second messengers and protein kinases. SMC β-AR play an important role in SMC function. In intact blood vessels they mediate SMC relaxation by various intracellular mechanisms, ultimately causing a decrease in intracellular Ca2+ levels. In cultured SMC, activation of the β-AR pathway results in inhibition of cellular proliferation, the development of SMC polyploidy, and SMC apoptosis. Blood vessels from hypertensive animals are characterized by an increase in SMC cell mass, a greater incidence of SMC polyploidy in the aorta, and an impairment in the β-agonist-mediated SMC relaxation. Some of these changes may result from an attenuation of β-AR function due to agonist-induced receptor desensitization caused by the uncoupling of receptors from the Gs-AC system. The phosphorylated β-AR may in turn trigger new signals and activate different intracellular pathways. However, the details of these mechanisms are still unresolved. Since functional β-AR play such a prominent and multi-faceted role in SMC function, it is important to understand how these diverse physiological effects are mediated by this receptor system, and how they contribute to the development of hypertension. With ageing, a decrease in β-AR-Gs-AC coupling is observed, and this is implicated in the reduced responsiveness of SMC. The similarities in SMC β-AR functional changes in hypertension and in ageing suggest that the underlying mechanisms are also analogous.Key words: smooth muscle, β-adrenoceptors, cyclic AMP, protein kinase A, cell proliferation, polyploidy, relaxation, apoptosis, hypertension, ageing.

Glucocorticoid-targeting of the adenylyl cyclase signaling pathway in the cerebellum of young vs. aged rats

Glucocorticoids exacerbate aging-induced cell death, but relatively little is known about other CNS effects in senescence. We examined noradrenergic/adenylyl cyclase signaling in the cerebellum, which is a brain region that is susceptible to deterioration of synaptic function in aging. Aged control rats had increased total cyclase catalytic activity, but showed deficits in basal adenylyl cyclase. Deficits resolved when G-proteins were stimulated with GTP, GTP and fluoride, or GTP and isoproterenol, despite reductions in beta-receptors. In young rats, long-term dexamethasone infusions evoked the same types of changes that had been seen in aging, including induction of cyclase catalytic activity and enhanced G-protein responsiveness. The same dexamethasone regimens given to aged rats failed to cause stimulation of these processes in the cerebellum, but did so in a peripheral tissue (kidney). These data indicate homology between the cellular events involved in noradrenergic signaling during aging and after glucocorticoid administration to young animals; the absence of glucocorticoid effects in the elderly cohort supports a convergent mechanism with aging. Given the high incidence of HPA axis dysregulation in the elderly, and particularly in elderly depression, effects of glucocorticoids on cell signaling may contribute to disrupted function and to altered drug reactivity.

Food restriction alters the age-related decline in cardiac beta-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).

Effect of aging on A1-adenosine receptor-mediated inhibition of norepinephrine release in the rat heart

Adenosine inhibits norepinephrine (NE) release from cardiac adrenergic nerves and reduces the postsynaptic beta-adrenergic mediated actions of NE, leading to decreased myocardial force of contraction. The actions of adenosine are mediated by pre- and postsynaptic adenosine A1 receptors (A1-AdoR). We reported that adenosine inhibition of postsynaptic beta-adrenergic receptor-mediated cyclic adenosine monophosphate (cAMP) production declines with age in male F344 rat hearts. In this study, cardiac synaptosomes, isolated intact adrenergic nerve terminals, were used to examine the effect of age on adenosine inhibition of NE release. Cardiac synaptosomes were prepared from the hearts of 6- and 24-month-old male F344 rats, loaded with [3H]NE, and placed in a superfusion system. [3H]NE release was induced by high [K+] exposure in the presence of varying concentrations of adenosine or the specific A1-AdoR agonist, N6-p-sulfophenyladenosine (SPA). [3H]NE release was significantly reduced in old rats compared with young rats. Inhibition of [3H]NE release by adenosine and SPA was significantly greater in young rats compared with old rats. The A1-AdoR antagonist, 8-(p-sulfophenyl)-theophylline, blocked the actions of adenosine on [3H]NE release, and the specific adenosine A2-receptor agonist, cyclopropylcarboxamidoadenosine, had no effect on [3H]NE release. Our data suggest that presynaptic A1-AdoR-mediated inhibition of NE release in the rat heart declines with age.

Aging and pharmacology

Research on aging and pharmacology in humans has been termed geriatric clinical pharmacology, which is an established subdiscipline within the broad field of clinical pharmacology. This article reviews information relevant to clinical cancer research and the care of older patients with cancer. Accordingly, the current state of knowledge on drug utilization, pharmacokinetics, pharmacodynamics, adverse drug events, drug interactions, polypharmacy, adherence to treatment, and clinical research considerations are reviewed. Although a review of the literature on aging and cancer chemotherapy is not included in this particular presentation, information is very sparse. Thus, there is significant potential for valuable contributions from clinical research through partnerships between geriatric clinical pharmacologists and medical oncologists.

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.

High-risk drugs in the elderly population

Drug therapy in elderly patients is affected by age-related changes in distribution and elimination and is further complicated by the increased sensitivity aged persons have to many of the effects of medications. Medications are often necessary in the elderly population, but care should be made to properly monitor these patients, especially those taking multiple drugs. Nurses, who are at the front lines of health care in all areas of practice, should be aware of drugs that may be high risk for use in the elderly and monitor these patients carefully for signs and symptoms of toxicity.

Fluoxetine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in older patients with depressive illness

The selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor fluoxetine is an effective antidepressant in elderly patients. Its efficacy is similar to that of other frequently used antidepressants, such as the tricyclic antidepressants. However, compared with the tricyclic antidepressants, fluoxetine has a more favourable tolerability profile and is less toxic in overdose. It is associated with fewer anticholinergic, cardiovascular and CNS adverse events, but greater numbers of gastrointestinal adverse events than have been reported for the tricyclic antidepressants. This is important in elderly patients who are more at risk of developing central anticholinergic and cardiovascular effects than are younger patients. Therefore, while its position relative to other selective serotonin reuptake inhibitors requires investigation, fluoxetine represents a major advance over tricyclic antidepressant agents in the treatment of elderly patients with depression, predominantly because of its favourable tolerability profile.

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.

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.

Calcium antagonists in the elderly

The calcium antagonists are associated with a number of advantages over other antihypertensive agents, such as a lack of metabolic, vascular and respiratory adverse events, yet are effective in reducing blood pressure. The currently available calcium antagonists are widely used, and new members, particularly of the dihydropyridine group, continue to emerge. These agents may well be considered for use in the management of hypertension and angina in elderly people. They undergo significant first-pass metabolism and tend to have high values of hepatic clearance with minimal amounts of unchanged drug in the urine. Plasma concentrations tend to be higher in elderly people and for that reason it may be prudent to initiate therapy with lower dosages. With this caveat, adverse effect profiles seem to be qualitatively and quantitatively similar in younger and older people. At equivalent plasma concentrations, the antihypertensive effect appears similar in young and elderly patients, and clinical studies point to comparable efficacy with other drug classes. Calcium antagonists do not have adverse renal, respiratory, cardiovascular, metabolic or peripheral vascular effects and therefore may be useful in patients with relevant concomitant disease.

Influence of aging on fluidity and coupling between beta-receptors and G-proteins in rat lung membranes

We tested the hypothesis that in rat lung membranes, the age-related decline in the percentage of beta-receptors coupled with high affinity to G-proteins, is due to limitation of the diffusion caused by a decrease in membrane fluidity. We measured both parameters simultaneously in a crude membrane preparation from lungs of rat of different age. In contrast to what is found in crude membrane preparations from rat liver and brain, in rat lung fluidity was increased upon aging. We conclude that the age-related alteration in coupling between receptor and G-protein is difficult to explain by alterations of membrane fluidity.

Post-train administration of 9-amino-1,2,3,4-tetrahydroacridine enhances passive avoidance retention and decreases beta-adrenoceptor-linked cyclic AMP formation in middle-aged rats

The possible involvement of beta-adrenoceptor system in the effectiveness of 9-amino-1,2,3,4-tetrahydroacridine (THA) to attenuate retention deficits exhibited by middle-aged rats in a one-trial passive avoidance task has been investigated. THA (2.5 mg.kg-1), injected i.p. after training, induced a significant increase in test step-through latency (STL) in middle-aged rats. Post-training injection of THA reduced basal and isoprenaline stimulated cyclic AMP accumulation in cortex and hippocampus of every group of rats. It is suggested that the effect of THA on memory processes may involve an action on beta-adrenoceptor-linked cyclic AMP accumulation.

Beta-adrenergic responsiveness in cultured aorta smooth muscle cells. Effects of subculture and aging

beta-Adrenoceptor-mediated vasorelaxation is diminished in vessels from a variety of aged species including humans. This phenomenon was studied for the first time in cultured aorta smooth muscle cells (ASMC) from young (4- to 6-month) and old (24- to 26-month) F-344 rats. Cyclic AMP (cAMP) accumulation was assessed following isoproterenol and forskolin stimulations in primary cultures and after 1-4 passages of aorta smooth muscle cells. Isoproterenol and forskolin increased cAMP accumulation 6- and 10-fold, respectively, in primary cultures from young rats. Isoproterenol stimulation was reduced markedly in passaged cells. Forskolin stimulation was unaffected, indicating passage-related phenotypic changes in receptor-mediated stimulation, but not in post-receptor adenylate cyclase activation. The response to isoproterenol was diminished in old animals, but that to forskolin was unaltered. Thus, cultured ASMC from F-344 rats are highly responsive to beta-adrenoceptor stimulation and demonstrate age-related changes, but undergo phenotypic modulation during passage.

Age-related changes in adenosine and beta-adrenoceptor responsiveness of vascular smooth muscle in man

1. Ageing is associated with a decline in beta-adrenergic responsiveness in several tissues. Reduced beta-adrenoceptor mediated smooth muscle relaxation in aged man has been demonstrated using the dorsal hand vein technique. Isoprenaline and adenosine activate adenylate cyclase through separate membrane bound receptors to induce vasodilatation. 2. To determine the specificity of reduced beta-adrenergic responsiveness in smooth muscle of aged man, and possible sites of the defect responsible, venodilatory responses to isoprenaline, a beta-adrenoceptor agonist and adenosine were determined in nine young (age 26 +/- 3 years: mean +/- s.d.) and eight elderly (age 70 +/- 5 years), healthy male volunteers. Veins were partially constricted with the alpha 1-adrenoceptor agonist phenylephrine and increasing doses of adenosine (5 to 1220 micrograms min-1) or isoprenaline (271 ng min-1) were infused. 3. Maximal dilatation induced by isoprenaline was 83 +/- 26% in the young and 51 +/- 34% in the elderly, P = 0.02. Maximal dilatation induced at the highest dose of adenosine (1220 micrograms min-1) was similar in young and elderly: 79 +/- 25% vs 88 +/- 28%, P = 0.26. 4. Adenosine venodilatation was measured before and after infusions of theophylline (6.8 to 135 micrograms min-1) for 30 min in six subjects. Adenosine responsiveness was unchanged following theophylline: 48 +/- 16% to 49 +/- 40%, P = 0.44. 5. The results suggest that the age-associated reduced responsiveness of the beta-adrenergic system in human vascular smooth muscle is not shared by venodilatation mediated by adenosine.

Nitrates in the elderly. Pharmacological considerations

Although a significant proportion of patients receiving nitrates are elderly, surprisingly little published work is available describing the pharmacokinetics and pharmacodynamics of these agents in elderly patients. The lack of pharmacokinetic data is related to the difficulty in assaying nitrates and there are at present no definitive data describing the effect of aging on their bioavailability or elimination. A common finding in old age is of decreased hepatic first-pass metabolism. This would affect isosorbide-2-mononitrate and isosorbide-5-mononitrate less than isosorbide dinitrate and nitroglycerin (glyceryl trinitrate). Venous responsiveness to nitrates does not appear to alter with age, so that pharmacodynamic properties would not be expected to alter. However, decreased baroreflex function causes an increased tendency for posturally related side effects to occur. Mechanisms of tolerance are likely to be unaltered but any possible alteration in quantitative aspects of tolerance has not been studied. Nitrate therapy in the elderly would benefit from systematic investigation. At the moment, therapy needs to be titrated to the individual patient, with care taken to avoid age-related side effects by careful initiation of therapy and appropriate reviews of each patient.