D2- but not D3-dopamine receptors detected in the anterior pituitary

Using conditions which revealed high affinity binding sites for [3H]ADTN (KD of 1.6 nM), [3H]apomorphine (DK of 3.5 nM) and [3H]dopamine (KD of 1,5 nM) in the calf caudate nucleus, no such high affinity sites could be detected in the calf anterior pituitary gland. In contrast, high affinity binding sites for [3H]-spiperone were found in both the caudate and the anterior pituitary. The apparent absence of high affinity sites for these [3H]-catecholamine ligands (in the 1-10 nM region) and the presence of the [3H]spiperone binding site in the anterior pituitary is compatible with the view that the pituitary [3H]neuroleptic receptor with its low affinity for dopamine, may be the physiological site of dopamine action in the pituitary. THe data, therefore, support the presence of D2- but not D3-dopamine receptor sites in the calf anterior pituitary.