Synthesis and bronchodilator activity of endo-2-(2-cyclopentyl-2-hydroxy-2-phenyl)acetoxy-7-methyl-7- azabicyclo-[2.2.1]heptane methobromide, a potent and long-acting anticholinergic agent.

The synthesis of the alpha-cyclopentylmandelate ester of quaternized endo-7-methyl-7-azabicyclo[2.2.1]heptan-2-ol (4, RS-11635) is described. The key step of this synthesis consists of the intramolecular trans-diaxial epoxide opening of 4-(N-methylamino)-1,2-epoxycyclohexane (8) to form the endo-azabicyclic structure 9. Evaluation of anticholinergic bronchodilator activity by intravenous administration in methacholine-challenged guinea pigs indicated 4 to be approximately twice as potent as ipratropium bromide (ED50 of 1.1 versus 2 micrograms/kg) and to have a duration of action nearly five times as long (230 versus 50 min). Evaluation of anticholinergic bronchodilator activity by aerosol administration in methacholine-challenged dogs also indicated 4 to be approximately twice as potent as ipratropium bromide and to have a duration of action nearly three times as long.

Ascaris-induced respiratory responses in the conscious rhesus monkey.

Reproducible immediate-type respiratory responses were evoked in conscious monkeys, sensitive to inhaled Ascaris suum, for periods up to 18 months. These responses were characterized by decreases in tidal volume and increases in breathing rate that persisted for about 40 min. Maximum changes were seen 3--5 min after exposure to the aerosolized antigen and were often accompanied by coughing and increased movement of the animals within the plethysmograph used for monitoring their ventilatory changes. Significant inhibition of the Ascaris-induced respiratory changes were seen in animals treated with either isoproterenol or cromolyn sodium. However, the latter agent was not effective in reversing histamine-induced ventilatory changes. The conscious monkey appears to be a suitable animal for evaluating potential antiallergic drugs.

Differences in pulmonary and cardiovascular beta receptors in the guinea pig and rabbit.

An in vivo preparation, in which a body plethysmograph was incorporated, was useful in monitoring the cardiopulmonary effects of pharmacological agents in the guinea pig and rabbit. Isoproterenol, given 30 seconds prior to histamine challenge, reproducibly blocked histamine-induced dynamic compliance decreases and increased heart in the artificially ventilated guinea pig. These effects were used to separate the activity of beta adrenergic blockers on airway and heart muscle. Dose-response data were obtained and ED50 values for pulmonary and cardiovascular blockade were compared. Relative potencies and cardioselectivity ratios for dichloroisoproterenol, practolol, dl-propranolol and d-propranolol were determined. Both practolol and dichloroisoproterenol were cardioselective; dl-propranolol was found to be the most potent. When a similar protocol was tried in the rabbit, isorpoterenol failed to antagonize either histamine or methacholine-induced airway constriction. This finding was supported in subsequent in vitro tests. Isoproterenol and epinephrine were ineffective in blocking methacholine-induced tracheal chain contractions and epinephrine did not significantly enhance adenylate cyclase activity. Our observations suggest rabbit airway smooth muscle is insensitive to beta adrenergic stimulants.

Respiratory and cardiovascular effects of prostaglandins in the conscious guinea pig.

A technique to assess respiratory and cardiovascular effects of prostaglandins (PGs) in conscious guinea pigs was developed. Animals were placed in a plethysmograph and tidal volume, airflow, and heart rate were recorded. In addition, blood pressure and/or pleural pressure were obtained. Some experiments involved the use of a pulmonary calculator that processed the appropriate pulmonary signal and provided on-line readout of dynamic compliance and airway resistance. Aerosolized antagonists were evaluated for their ability to block responses to aerosolized histamine. We found the relative antagonistic potencies of PGE1, PGE2, isoproterenol, and salbutamol to be 5.5, 2.3, 1 and 0.2, respectively. Aerosolized PGE1 and PGE2 but not PGF2alpha given prior to histamine caused decreases in tidal volume, airflow and heart rate. These effects were not seen in animals that were prepared for measurements involving invasive surgical techniques. The aerosolized PGE2 induced tidal volume changes were not prevented by pretreatment with salbutamol, chlorpheniramine, atropine or hexamethonium, though the latter two drugs inhibited the fall in heart rate. We suggest that the bradycardia following aerosolized PGE2 administration may originate from airway irritant receptors. The results validate use of our methods for the assessment of responses to bronchoactive agents under physiological conditions.