Involvement of adenohypophysial dopamine in the regulation of prolactin release during suckling.

Dopamine (DA) was measured in the anterior lobe of the pituitary and median eminence from lactating rats. The effect of pup separation and suckling was studied in order to correlate changes in DA levels with changes in serum PRL. In lactating rats separated from their pups, low levels of circulating PRL were found at 2,4, and 8 h. DA levels in the median eminence showed a decline at 2h; at 4 and 8 h of separation, a significant increase was observed. In the pars distalis, the concentration of DA increased with the length of the nonsuckling interval. Suckling induced a rapid rise in serum PRL levels in rats that were separated from their pups 4 h earlier. Under these conditions, a significant decrease in DA levels in the median eminence and pars distalis was observed as early as 5 min after the onset of suckling; at 30 min, the DA levels were still low. In the situations studied (suckling and pup separation), a negative correlation between serum PRL and DA levels in both the median eminence and pars distalis was always found.