ANTISENSE STRATEGY UNRAVELS A DOPAMINE-RECEPTOR DISTINCT FROM THE D2-SUBTYPE, UNCOUPLED WITH ADENYLYL-CYCLASE, INHIBITING PROLACTIN-RELEASEFROM RAT PITUITARY-CELLS

The antisense strategy was used to unravel the functional contribution of the mRNAs encoding dopamine (DA) receptors to the multiple transdu ction mechanisms operated by DA in rat pituitary cells. An antisense o ligonucleotide was designed to recognize seven nucleotides upstream an d 11 nucleotides downstream from the initiation translation codon of t he mRNA that encodes the DA D2 receptor. Addition of the antisense oli gonucleotide for 7 days to primary culture of rat pituitary cells resu lted in a decreased expression of DA D2 receptor as shown by (a) the v irtual disappearance of [H-3]spiroperidol binding sites and (b) the ma rked reduction in the levels of both the long and the short splice var iant of the D2 receptor mRNAs. After this treatment, the DA D2 recepto r agonist bromocriptine lost its capability both to inhibit adenylyl c yclase activity and to reduce prolactin mRNA levels. On the contrary, the inhibition of prolactin release induced by bromocriptine was affec ted minimally by the antisense oligonucleotide treatment. These data i ndicate that (a) translation of the mRNA encoding DA D2 receptors resu lts in receptors that are negatively coupled with adenylyl cyclase and functionally linked to inhibition of prolactin synthesis; and (b) the release of prolactin might be regulated, at least in part, by a DA re ceptor that is encoded by mRNA species distinct from those encoding th e D2 receptor.