Comparison between the effects of inhaled isoprenaline and fenoterol on plasma cyclic AMP and heart rate in normal subjects

Antenatal dexamethasone treatment decreases plasma catecholamine levels in preterm infants

Antenatal corticosteroid therapy (ACT) has many beneficial effects on preterm infants. The cellular mechanisms of action of ACT include beta-adrenergic receptor-mediated cAMP generation. This study investigated the effects of ACT on sympathoadrenal mechanisms during immediate postnatal adaptation of preterm infants. Plasma epinephrine, norepinephrine, 3,4-dihydroxyphenylglycol, and cAMP were measured within 12 h after birth in 103 preterm infants (gestational age 24-36 wk), who were divided into two groups (non-ACT and ACT group) according to whether the mother had received dexamethasone treatment. Infants in the ACT group had significantly lower concentrations of plasma catecholamines than infants in the non-ACT group; plasma epinephrine was 38% lower, and plasma norepinephrine was 20-40% lower in the ACT group, depending on gestational age (r = -0.37 in the non-ACT group and r = -0.28 in the ACT group, p < 0.05). Plasma cAMP concentrations were similar in the two groups. Antihypertensive treatment of the mother was associated with low plasma cAMP (p < 0.001), whereas tocolytic treatment was associated with high plasma cAMP (p = 0.001) of the infant. The results indicate that ACT attenuates the birth-related increase in plasma catecholamines. Still, plasma cAMP levels remain high, which suggests enhanced beta-adrenoceptor signaling after ACT.

Pharmacological effects and pharmacokinetics of atipamezole, a novel alpha 2-adrenoceptor antagonist--a randomized, double-blind cross-over study in healthy male volunteers

1. Single doses (10, 30 and 100 mg) of atipamezole (MPV-1248), a new potent and selective imidazole-type alpha 2-adrenoceptor antagonist, and saline placebo were administered as 20 min intravenous infusions to six healthy male volunteers in a randomized double-blind, cross-over phase I study. Later, 100 mg atipamezole was given orally to the same subjects in an open fashion. 2. The i.v. doses resulted in linearly dose-related concentrations of atipamezole in plasma. Pharmacokinetic calculations revealed an elimination half-life of 1.7-2.0 h, an apparent volume of distribution of 3.0-3.5 l kg-1 and a total plasma clearance of 1.1-1.5 l h-1 kg-1. No atipamezole could be detected in plasma after oral dosing. 3. Subjective drug effects were seen mainly after the largest i.v. dose and included increased alertness and nervousness, coldness and sweating of hands and feet, tremor and shivering, motor restlessness, and increased salivation. Salivation was also quantitated using dental cotton rolls, with dose-related increases produced by the i.v. doses. 4. The 100 mg i.v. dose increased plasma noradrenaline concentrations on average by 484 +/- 269 (s.d.)%, and also elevated both systolic and diastolic blood pressure (mean increases 17 +/- 7/14 +/- 2 mm Hg). The 30 mg dose had minor and the 10 mg dose no effects on these variables. Adrenaline and cyclic AMP levels in plasma were increased only after the largest dose. No drug effects were observed after oral dosing. 4. Plasma C-peptide and blood glucose levels were not markedly influenced by the drug, and cortisol secretion was not stimulated. 5. The observed effects are compatible with the presumed alpha 2-adrenoceptor antagonistic action of atipamezole and are in general concordance with the reported results of other alpha 2-adrenoceptor antagonists (yohimbine and idazoxan). 6. Although not orally active, atipamezole may prove to be a useful agent in studies of alpha 2-adrenoceptor function in man.

Hypokalaemia and other non-bronchial effects of inhaled fenoterol and salbutamol: a placebo-controlled dose-response study in healthy volunteers

1. The hypokalaemia-inducing effects of two widely used inhaled antiasthmatic beta 2-adrenoceptor agonists, fenoterol and salbutamol, were compared in six healthy male volunteers. 2. Each drug was administered in three different doses, 400, 600 and 800 micrograms, which were repeated three times with 30 min intervals (total doses 1200, 1800 and 2400 micrograms in 1 h). The treatments were given at 1 week intervals in random order in a single-blind fashion. 3. The concentration of potassium in plasma was dose-dependently reduced by both drugs with peak effects 75-90 min after the first inhalations. The hypokalaemic effect of fenoterol was significantly greater than that of equal doses of salbutamol (average +/- s.d. reductions of 1.13 +/- 0.32 and 0.67 +/- 0.25 mEq l-1, respectively, after the highest doses, P less than 0.05). Concomitantly, decreases were noted in the amplitude of the T-wave on the ECG. 4. The concentration of cyclic AMP in plasma was measured and used as an indicator of systemic beta 2-adrenoceptor agonistic effects of the drugs. Increases in cAMP were a close mirror image of the drugs' effects on potassium in plasma. 5. Plasma renin activity, noradrenaline in plasma and heart rate were also dose-dependently increased by the treatments, whereas blood pressure remained unaltered. 6. While the clinical significance of hypokalaemia induced by inhaled beta 2-adrenoceptor sympathomimetics still is a matter of debate, our results point to possible differences between therapeutically equipotent doses of fenoterol and salbutamol in their propensity to cause hypokalaemia and other acute non-bronchial effects.