Possible direct effect of prolactin on catecholamine synthesis and release in rat adrenal medulla: in vitro studies

It has been recently shown that chronic increase in circulating prolactin (PRL) levels can affect the catecholamine (CA) synthesis and release in the adrenal medulla of female and male rats. However, it is not established if this effect is directly exerted on the adrenomedullary cells. To elucidate this question, we have studied the possible capacity of PRL to modify the in vitro synthesis and release of CA in isolated adrenal medullas of female rats. The study has been performed in animals with hyperprolactinemia induced by pituitary grafts (GRAFT) or with low PRL levels induced by ovariectomy (OVX), and in their respective sham-operated controls (SHAM), in order to establish if the previous plasma levels of this hormone could modify the effects observed in vitro. Basal release of adrenaline (A), noradrenaline (NA) and total CA observed during the first h of tissue incubation was similar in the three groups of animals. However, OVX animals exhibited a decreased release of both CA in the second h of incubation. This low CA release was partially reversed after the exposure of the incubated adrenal medullas of these animals to a medium containing PRL, whereas this hormone was ineffective to modify the CA release in SHAM and GRAFT animals. Moreover, PRL caused a significant decrease in the A production by the adrenal medullas of SHAM animals, since the amount of A released plus the amount of A stored after incubation in presence of PRL was significantly decreased. Finally, the exposure of the adrenomedullary cells from GRAFT rats to PRL was followed by an increase in the contents of both NA and A in the tissues.(ABSTRACT TRUNCATED AT 250 WORDS)