EFFECT OF POSTERIOR PITUITARY LOBECTOMY ON IN-VIVO AND IN-VITRO SECRETION OF PROLACTIN IN LACTATING RATS

The effect of removing the posterior and neurointermediate lobes (PLX) of the pituitary gland of lactating rats was determined on both suckl ing-induced release and transformation of prolactin (PRL), and on regi onalization of PRL release. Sixteen hours, or 1 or 4 d after either PL X or sham surgery, acute (15-min) suckling was applied. Also, regional ization of PRL release was analyzed by incubating the central and peri pheral regions of APs from nonsuckled rats. Plasma PRL was analyzed by radioimmunoanalysis (RIA), whereas anterior pituitary (AP) PRL conten t and in vitro released PRL were determined by polyacrylamide gel elec trophoresis. Plasma PRL increased 25- to 30-fold after suckling in int act and sham, and 10- to 15-fold in 1- and 4-d PLX rats, but no change occurred on either 16-h PLX nonsuckled and suckled rats. Also, PRL tr ansformation occurred in intact, sham, and 4-d PLX suckled rats, but n ot in 16-h sham, or in 16-h and 1-d PLX suckled rats. Finally, the hig her secretion of PRL shown in vitro by the central region of APs from intact and sham was not observed in APs from PLX rats. These results s how that PLX transiently depresses the suckling-regulated PRL transfor mation and release. Likewise, influences from the posterior and/or neu rointermediate lobes may determine regionalization of PRL release.