Progesterone effects upon dopamine release from the corpus striatum of female rats. II. Evidence for a membrane site of action and the role of albumin.

In the present experiment we used immobilized progesterone linked to bovine serum albumin (P4-3-BSA) as a probe to examine whether the effects of a direct in vitro infusion of progesterone upon dopamine (DA) release from corpus striatal (CS) tissue fragments from ovariectomized estrogen-treated rats may be attributable to a surface membrane site of action. In Expt. I, a direct in vitro pulsatile infusion of P4-3-BSA resulted in two discrete episodes of stimulated DA release which were not observed in superfusions receiving a continuous infusion of P4-3-BSA or compared to data of control superfusions. In contrast to that of a pulsatile administration, a continuous infusion of P4-3-BSA completely abolished the amphetamine-stimulated response from these tissue preparations with significantly lower DA release rates compared to the pulsatile P4-3-BSA (P less than 0.02) and control (P less than 0.04) conditions. In Expt. II, the addition of tetrodotoxin (TTX, 1 microM) to the superfusion medium abolished the discriminatory response between pulsatile and continuous administration of immobilized progesterone. These results indicate that the action of progesterone on DA release from the CS is mediated primarily through a surface membrane site of an interneuron(s) which can discriminately respond to a specific infusion mode of this steroid.