Alpha1Adrenergic Receptors in the Porcine Pituitary Neurointermediate Lobe: Detection with [3H]Ketanserin

Publisher Website
Google Scholar
Abstract
[3H]Ketanserin, a serotonin receptor antagonist, labelled high affinity, saturable sites in homogenates of porcine neurointermediate lobe tissue. Cinanserin, a potent and selective serotonin receptor antagonist, inhibited the specific binding of 5 × 10-10M [3H]ketanserin with a high affinity component representing 20% of the total binding. Prazosin, a potent and selective alpha1 adrenergic antagonist, inhibited [3H]ketanserin binding with a high affinity component representing 60% of total binding. The prazosin-specific component was demonstrated to be distinct from the cinanserin-specific component. 10-7M cinanserin was co-incubated with [3H]ketanserin to eliminate the serotonergic component of the binding and allow pharmacological characterization of the remaining prazosin-specific component. The prazosin-specific binding of [3H]ketanserin binding closely resembled the results of experiments using [3H]prazosin to label alpha1 receptors in neurointermediate lobe tissue homogenates. Ketanserin was found to be sevenfold more potent in inhibiting [3H]prazosin binding to alpha1 adrenergic receptors in the neurointermediate lobe tissue than in brain tissue. This observation explains why low concentrations of [3H]ketanserin can selectively label serotonin receptors in the brain but will label both adrenergic and serotonin receptors in the neurointermediate lobe.