The classic studies of Ahlquist divided adrenergic agents into two main types, a and β, based on their relative physiologic effects. Those with primarily β-adrenergic activity have been further subdivided by Lands and associates into two major subgroups: β-1 associated with lipolysis and cardiac inotropy, and β-2 with bronchodilation and vasodilation. It is recognized that β-adrenergic agonists and antagonists, although relatively selective in their effects, may overlap with regard to β-1 responses depending on the dose.
In the present study our patient had hypertrophic obstructive cardiomyopathy and severe asthma. The combination of these disease states in a single patient afforded an opportunity to assess the specificity of a β-1 adrenergic antagonist and a β-2 agonist in the management of these conditions.
The results suggest that albuterol is a relatively specific β-2 agonist Its effectiveness in relieving bron-chospasm was equivalent to or greater than that of isoproterenol. The β-1 agonistic properties of albuterol were minimal as evidenced by slight changes in heart rate and no effect on the subvalvular gradient.
Pindolol administration abolished the increase in sub-valvular gradient seen with exercise, thereby confirming its properties as a β-1 antagonist. However, increases in obstructive pulmonary indices were also present demonstrating β-2 antagonistic properties at the doses given. Albuterol could not abolish these obstructive changes when given with pindolol
This study further confirms the overlap among drugs purported to have 0 selectivity. In this patient with coexisting diseases, albuterol was a safe and useful bron-chodilator with relatively selective β-2 agonist properties. The patient has continued to receive albuterol therapy without adverse effect By contrast, pindolol evidenced β-2 antagonistic properties, which precluded its use. Further study in a greater number of patients will be necessary to better define the clinical usefulness of these two cardio-selective β-adrenergic agents.