A Factor(s) from a Rat Trophoblast Cell Line Inhibits Prolactin Secretion in Vitro and in Vivo1

Abstract

The purpose of the present study was to measure the inhibitory action of secretions from trophoblast cells on prolactin (PRL) secretion in cycling and pregnant rats, and to determine whether factor(s) from trophoblast cells act directly on anterior pituitary cells. A rat choriocarcinoma cell line (Rcho)--a line consisting of trophoblast cells, including differentiated giant cells that secrete members of the placental PRL family--was used. When Rcho cells (1 x 10(6) cells) were transplanted under the kidney capsule of cycling rats, tumors developed and the rats went into constant diestrus. Eight days after cell injection, plasma progesterone was significantly increased in treated rats compared to controls, whereas plasma and pituitary PRL and pituitary PRL mRNA levels were significantly decreased. Similar PRL results were seen on Day 9 of pregnancy after injection of Rcho cells on Day 0 or Day 1 of pregnancy. To determine whether secretions from Rcho cells had a direct effect on anterior pituitary cells to inhibit PRL release, anterior pituitary cells were enzymatically dispersed and cultured for 4 days. Conditioned medium was obtained from 9-day Rcho cell cultures and concentrated by ultrafiltration. A fraction containing substances with molecular weights greater than 10,000 suppressed PRL release from the pituitary culture after 3 and 24 h. Conditioned medium containing substances with molecular weights between 1000 and 10,000 had no effect on PRL release, nor did conditioned medium from a placental cell line designated HRP-1. HRP-1 also contains trophoblast cells but does not contain the differentiated giant cells.(ABSTRACT TRUNCATED AT 250 WORDS)