BACKGROUNDCardiac aging is characterized by a reduced heart rate response to beta-agonist stimulation with isoproterenol, but whether the ejection fraction and other cardiovascular responses are reduced in humans is largely unknown. In addition, whether reduced beta-agonist responses can be improved with exercise training has not been determined in humans.METHODS AND RESULTSCardiovascular responses to graded isoproterenol infusions (3.5, 7, 14, and 35 ng/kg/min for 14 minutes each) were assessed in 15 older (age, 60-82 years) and 17 young (age, 24-32 years) rigorously screened healthy men. Thirteen older and 11 young subjects completed 6 months of endurance training and were retested. At baseline, the older group had reduced responses to isoproterenol for heart rate (+65% older versus +92% young, p less than 0.001), systolic blood pressure (+9% versus +24%, p less than 0.001), diastolic blood pressure (-12% versus -24%, p less than 0.05), ejection fraction (+12 versus +20 ejection fraction units, p less t...

Differences in cardiovascular responses to isoproterenol in relation to age and exercise training in healthy men.

Cardiac adaptations to chronic exercise

Catecholamines in blood.

Six male non-endurance trained subjects (S) and six marathon runners (M) underwentgraded treadmill exercise (T) andisoproterenol stimulation (I; 2 and 4 Μg·min−1),β-adrenergic receptor density was additionally determined as the amount of3H-Dihydroalprenolol (DHA) specifically bound on intact polymorphonuclear leucocytes. Heart rate,\(\dot V_{{\text{O}}_{\text{2}} }\) uptake, lactate, plasma noradrenaline, and adrenaline were estimated during T. Heart rate, stroke volume, cardiac output, as well as lactate, glucose, free fatty acids (FFA), and glycerol levels in the blood were determined during I. M showed the known training-dependent responses during T, such as lower heart rates, lactate levels, and plasma catecholamines at identical work loads, as well as higher\(\dot V_{{\text{O}}_{\text{2}} {\text{max}}}\) than S. I-induced cardiac output increase was quite similar in both groups. Stroke volume, however, increased significantly in M and stayed constant in S. Lactate decreased (S), glucose increased significantly (M), glycerol increased similarly in both groups, FFA rise was less marked in S. I-induced stroke volume response (I) may be indicative of a more economic regulation of heart work in M than S. Lactate decrease and less marked FFA increase, as observed in S, may be the result of a somewhat higher cardiac energy demand, dependent on less economic heart work. Higher DHA-binding as observed in M, as well as stroke volume response and glucose increase, may be indicators of a training-dependent rise in sensitivity to catecholamines. The unsolved question is, however, to what extentβ-receptor responses in intact blood cells are significant for receptor behavior in other organs.

Plasma catecholamines,β-adrenergic receptors, and isoproterenol sensitivity in endurance trained and non-endurance trained volunteers

Despite recent advances in the medical management of hypertension, chronically elevated blood pressure remains a major health problem in the United States, affecting almost 50 million Americans. It is widely recognized that lifestyle factors contribute to the development and maintenance of elevated blood pressure. This article critically reviews current approaches to the nonpharmacological treatment of high blood pressure and highlights outcome studies of exercise, weight loss and dietary modification, and stress management and relaxation therapies. Methodological issues in the assessment and treatment of hypertension are discussed, along with possible mechanisms by which lifestyle modification may reduce elevated blood pressure.

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Biobehavioral approaches to the treatment of essential hypertension.

Blood pressure and heart rate responses elicited by norepinephrine, epinephrine and histamine were compared before and after duodenal acidification in 27 trained and untrained young healthy men. Before acidification trained subjects showed a lower sensitivity to norepinephrine and histamine and a slightly lower one to epinephrine. In order to explain these phenomena physical training was supposed to affect alpha, respectively beta adrenergic responsivity in a dissimilar manner. This suggestion was confirmed by the isoproterenol studies, too. Duodenal acidification decreased the catecholamine-induced pressor responses. Depressor responses to histamine did not change in the untrained subjects, whereas they increased in the trained group. Thus, during digestion the histamine-induced depressor responses of trained subjects tended to approach that of untrained people.

G. Pavlik

Papers

Sensitivity to catecholamines and histamine in the trained and in the untrained human organism and sensitivity changes during digestion