Intrinsic Activity of Da Agonists

D2 receptor agonists and partial agonists: relationship between receptor binding measures and functional activity

“…Of these, the correlation between nH and intrinsic activity (Figure 1) is probably the most useful since it is a value which can be determined for any agonist without the requirement that the agonist binds to a high-affinity site. A similar difficulty in using binding data to separate weak partial agonists from antagonists has been previously noted [35]. A relationship between agonist-induced masking of 3H-labelled antagonist binding has previously been reported for the D, dopamine receptor [21].…”

“…The percentage of high-affinity sites recognized by agonists ranged from 0 to 58% of total sites. Using a more complex approach, Lahti et al [35] made essentially the same observation for D2 receptor agonists, namely that intrinsic activity was correlated with KJKH ratios. They used 3H-labelled agonist to label agonist high-affinity state and 3H-labelled antagonist + G T P to label agonist low-affinity states, thereby ensuring that a K H could be determined for all agonists.…”

“…D2 receptors in bovine caudate membranes were labelled with [3H] spiperone; the intrinsic activity measures of the agonists used in this study were taken from a study by Lahti et al [35], who used electrophysiological data to derive values for agonist intrinsic activity and normalized these values relative to that for dopamine. Table 1.…”

“…Displacement of [3H]spiperone was carried out in the presence of 25 nM ketanserin to occlude 5-HT2 receptors The displacement curves for quinpirole, dopamine and R( -)apomorphine (R( -)apo) were best described by a two-site model The curves for all other compounds best tit a single-site model Each binding measure was tested for correlations with agonist intrinsic activity [35] Table 1. Thus, the agonists with high intrinsic activities also had a non-competitive component to their interaction with D2 dopamine receptors.…”

Contrasting effects of bromocriptine on learning of a partially baited radial arm maze task in the presence and absence of restraint stress

“…The other subtypes have also been expressed albeit in lesser quantities (Bouthenet et al 1991;MeadorWoodruff et al 1992). The D 2 receptors are present both post-synaptically and pre-synaptically, and the predominant pre-synaptic receptors are important in the regulation of DA release (Carter and Muller 1991;Lahti et al 1992). The D 2 receptor agonists at lower concentrations are believed to act primarily on these sites to decrease the DA release (Fusa et al 2002).…”