Effect of aging on the response of guinea pig trachea to isoprenaline

The use of bronchodilators in the treatment of airway obstruction in elderly patients

Ageing is associated with important anatomical, physiological and psychosocial changes that may have an impact on the management of obstructive airway diseases (asthma and chronic obstructive pulmonary disease (COPD)) and on their optimal therapy. Ageing-related modifications might be responsible for a different effectiveness of bronchodilators in the elderly patients as compared to younger subjects. Furthermore, the physiological involution of organs and the frequent comorbidity, often interfere with pharmacokinetics of bronchodilator drugs used in asthma and COPD. This review will focus on the use of bronchodilators in the elderly, with particular attention to the achievable goals and to rationale, utility and pitfalls in using the inhalation therapy in this age group. beta(2)-agonists, anticholinergics and methylxanthines will be discussed and their side effects in the elderly will be considered.

Ontogeny of beta-adrenergic desensitization in rabbit tracheal smooth muscle

Prolonged or repeated exposure to beta-agonist medications may result in a desensitization of the agonist-mediated response. Under certain conditions, such agonist-induced desensitization may limit the efficacy of administered beta-adrenergic agonists to elicit bronchodilation. Accordingly, the present study was designed to study the mechanism of acute beta-adrenergic desensitization in maturing rabbit tracheal smooth muscle (TSM). Isometric tension was measured in tracheal ring segments isolated from newborn and mature rabbits and half-maximally contracted with Methacholine (Meth) or KCl. TSM segments were serially relaxed with repetitive single doses of isoproterenol (ISO: 0.1, 1.0, 10, or 100 microM) or prostaglandin E2 (PGE2: 0.1 or 10 microM). Serial administration of ISO-elicited dose-dependent desensitization of relaxation in mature and newborn TSM, contracted with either Meth or KCl. In contrast, the relaxant response to PGE2 was retained in the ISO-desensitized tissue. Repeated administration of PGE2 elicited no desensitization of PGE2 responsiveness, but did induce some dose-dependent desensitization of the ISO response in mature TSM. Compared to mature tissues, newborn TSM developed subtotal desensitization to 100 microM ISO and no ISO desensitization in response to PGE2. Thus, these findings demonstrate that (1) beta-adrenoceptor responsiveness undergoes dose-dependent homologous and, to a lesser extent, heterologous desensitization in rabbit TSM; and (2) both beta-adrenergic desensitization mechanisms increase with postnatal maturation.

Effects of ageing on regional differences in the contractile responses to acetylcholine and neurokinin A in rabbit airway

1. Experiments were designed to study the effects of ageing on muscarine and NK2 receptor mechanisms in the three different regions of rabbit airway. 2. The pD2 value of acetylcholine changed with age in three different regions while that of carbamylcholine, which is resistant to acetylcholinesterase, did not. 3. The pD2 values of neurokinin A and the activity of protease, a degradative enzyme, changed with age. However, by the pretreatment with phosphoramidon, a protease inhibitor, the regional difference and age related change of the pD2 value of neurokinin A disappeared. 4. In conclusion, the observations about age related changes and regional differences of pD2 value of acetylcholine and neurokinin A were due to the difference of their degradative enzyme activities.

Peripheral airway hyperresponsiveness in the choline-deficiently fed rat

Rats fed with choline-deficient diets are known as a model of aging and learning impairments due to acetylcholine (ACh) deficiency in the brain which may be associated with a decrease in acetylcholinesterase (AChE; EC 3.1.1.7). To determine the role of AChE in bronchial responsiveness, we examined the contractile response of isolated lung parenchymal strips to ACh in control rats and rats fed with choline-deficient diets. Concentration-response curves to ACh shifted to the lower concentrations and the maximum response to ACh was greater in rats fed with choline-deficient diets than in control rats (P < 0.01). Physostigmine (10(-6) M) mimicked effects of choline-deficient diets on the contractile response to ACh. However, concentration response curves to carbachol and 5-hydroxytryptamine did not differ between control rats and rats fed with choline-deficient diets. Choline-deficient diets significantly decreased the AChE activity from homogenates of lung parenchymal tissues (P < 0.01). These results suggest that a decrease in AChE activity of lung tissues may relate to airway hyperresponsiveness to ACh.

Selective and full beta 1-adrenoceptor agonist action of a catechol derivative of denopamine (T-0509) in the guinea-pig cardiac muscle and trachea: comparison with denopamine, xamoterol and isoprenaline

1. The pharmacological actions of T-0509, a 3-hydroxy derivative of denopamine, were studied in various guinea-pig tissues; these effects were compared with those of isoprenaline, denopamine and xamoterol. 2. The intrinsic activities of the positive inotropic actions of T-0509, denopamine and xamoterol compared with isoprenaline (= 100%) in the papillary muscle were 99%, 83% and 28%, respectively, while their relative potencies (EC50 agonist EC50 isoprenaline) were 0.23, 33 and 1.4, respectively. The intrinsic activities of T-0509, denopamine and xamoterol as positive chronotropic agents in the right atria were 98%, 69% and 48%, respectively, and their equipotent concentrations (isoprenaline = 1) were 0.24, 50 and 4, respectively. 3. The positive chronotropic actions of T-0509 and denopamine were antagonized by bisoprolol (3 x 10(-8) M), but not by ICI 118,551 (3 x 10(-8) M). 4. The intrinsic activity of T-0509 in histamine-contracted tracheae was similar to that of isoprenaline, but its equipotent concentration was 38; the effects of both agents were antagonized by ICI 118,551 (3 x 10(-8) M), but not by bisoprolol (3 x 10(-8) M). Denopamine and xamoterol did not show any agonist activity on guinea-pig trachea. 5. Denopamine and xamoterol antagonized the positive chronotropic (pA2, denopamine: 6.98, xamoterol: 7.75) and tracheal relaxant (pA2, denopamine: 5.39, xamoterol: 6.25) effects of isoprenaline. 6. Isoprenaline, T-0509 and denopamine, but not xamoterol, contracted the guinea-pig aorta in a decreasing order in the presence of propranolol (10(-6) M).7. Based on the above studies, T-0509 appears to be a highly selective betaI-adrenoceptor agonist with full agonist properties, while denopamine and xamoterol appear to be selective, but partial betaI-adrenoceptor agonists.

Alpha 1A-adrenoceptors in rabbit bronchus

In the presence of propranolol, bronchial preparations from rabbits were markedly contracted by norepinephrine and phenylephrine but only slightly by clonidine. The contractile responses to norepinephrine were inhibited by prazosin and by high concentrations of yohimbine. The concentration-response curve of norepinephrine was shifted in parallel by WB4101 and 5-methylurapidil but not by 60-min treatment with chloroethylclonidine. These results suggest strongly that norepinephrine-induced contraction of rabbit bronchus is mediated through alpha 1A-adrenoceptors. Furthermore, cyclooxygenase inhibitors did not influence the response to norepinephrine, so norepinephrine-induced contraction is considered not to be mediated through the release of prostaglandins.

Effects of aging on alpha 2-adrenoceptor mechanisms in isolated guinea-pig tracheal preparations

The effects of aging on alpha 2-adrenoceptor mechanisms in tracheal preparations isolated from 3-, 6-, 10-, 40- and 100-week-old guinea-pigs were studied. The potency of noradrenaline decreased with age. The specific binding of [3H]p-aminoclonidine to microsomal fractions prepared from tracheal smooth muscles from 6- and 40-week-old guinea-pigs was analysed by Scatchard analysis. The capacity of maximum binding sites of [3H]p-aminoclonidine was greater in the preparations from 40-week-old guinea-pigs than in 6-week-old animals, whereas the dissociation constant did not change with age. The amount of prostaglandin F2 alpha released by noradrenaline and the contractile response to prostaglandin F2 alpha decreased with age. These results suggest that an age-related decrease in the potency of noradrenaline is due to the decrease in the amount of excitable prostaglandin F2 alpha released by noradrenaline and in the contractile response to prostaglandin F2 alpha, but not to a change in the total number of alpha 2-adrenoceptors or in the dissociation constant of a drug from alpha 2-adrenoceptors. Extraneuronal uptake also plays a role in the response to noradrenaline in the tracheal preparations from older guinea-pigs.

Effect of ageing on response to nicotine in rabbit bronchial preparation

1. Effect of ageing on the response to nicotine was tested in the bronchial muscle preparations from 5, 13, 100 and 125 week-old rabbits. The pD2 value (potency) of nicotine significantly increased in the preparation from the 125 week-old rabbits. No age-related change was found in the pD2 value of carbamylcholine or pA2 value of atropine. 2. No age-related change in characteristics of nicotine receptors. Choline acetyltransferase activity, the amount of acetylcholine released by nicotine and acetylcholineesterase activity decreased in the preparations from the 125 week-old rabbits. 3. Decrease in the pD2 value of nicotine in the preparation from the older rabbit is due to a decline in choline acetyltransferase activity followed by a reduction in the acetylcholine released, and not to a change in characteristics of nicotine receptors. 4. These results also suggest that enzymes may be influenced more easily with age than drug receptors.