Spiroperidol binding inhibition

For each response examined, inhibition of isoproterenol-stimulated cAMP accumulation by intact cells ( ) inhibition of basal release of IR-aMSH by intact cells ( J occupancy of specific [3H]-spiroperidol binding sites in a cell-free homogenate (Q) and inhibition of isoproterenol-stimulated adenylate cyclase activity in a cell-free homogenate (M), the effect achieved with the indicated concentration of apomorphine is expressed as a percentage of the maximal effect of apomorphine (33). 

A very intriguing observation noted above was the possibility of presynaptic dopamine agonist activity with SK F 87516 and SK F 85174. The inhibitions of the constrictor response and the 3H -norepinephrine release induced by brief intermittent periarterial sympathetic nerve stimulation of the perfused rabbit ear artery is a convenient in vitro assay for presynaptic dopamine agonist activity (30). In this preparation, both SK F 85174 and SK F 87516 inhibited both stimulation responses with an EC50 of about 100 riM. Another measure of D-2 activity is inhibition of specific spiroperidol binding (20). Comparison of these data (Table I) showed that SK F 85174 is thirty times as potent as dopamine, and thus is a potent D-2 agonist. However, the activity in adenylate cyclase stimulation indicates that this compound may be best described as a D-l/D-2 agonist (19, 20). 

Dopaminergic neurons synapse upon the parenchymal cells of the intermediate lobe (IL) of the rat pituitary gland. Dopamine decreases the capacity of the IL cells to synthesize cyclic AMP and inhibits the release of otMSH and other peptides from this tissue. The presence of a D-2 receptor accounts for both of these phenomena. This D-2 dopamine receptor can be studied in a binding assay using [3H]-spiroperidol, a dopamine... 

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