Development of an assay for H2-receptor antagonists using isolated fat cells

Fat cells were isolated by collagenase digestion of adipose tissue from male dogs. The cells were shown to be responsive to both histamine and norepinephrine in producing glycerol, a marker for lipolysis. The histamine-stimulated response was shown to be mediated by H2-receptors because it was inhibited by the H2-receptor antagonists metiamide and cimetidine, but not by H1 blockers such as tripelennamine, or by other agents such as propranolol. Conversely, norepinephrine-stimulated lipolysis was inhibited by propranolol but not by metiamide. The KD estimated for cimetidine and metiamide was approximately 10(-6) M, which compares favorably with that observed in other H2-receptor systems. The relative potency of various histamine H2-receptor agonists in this system was comparable to that seen in other H2-receptor systems. This assay has the advantage of utilizing a homogeneous cell preparation and is not complicated by tachyphylaxis. The dogs which are the source of the adipose tissue can potentially be used for other studies after a suitable recovery period. This system appears useful in screening novel compounds for H2-receptor antagonist or agonist activity.