INHIBITION OF PROGESTERONE SYNTHESIS IN VITRO BY PROSTAGLANDIN F2

Abstract

Prostaglandins have been shown to be potent stimulants of cl steroid pro- duction in vitro (Pharriss & Wyngarden, 1969; Marsh, 1971; Speroff & Ramwell, 1970), yet prostaglandin F2\g=a\(PGF2\g=a\)given in vivo effectively inhibits progesterone secretion in rats, rabbits, guinea-pigs, sheep and the rhesus monkey (see Pharriss, Tillson & Erickson, 1972, for review). A better under- standing of the possible r\l=o^\leof prostaglandins has been confused by these paradoxical findings. In such studies, it would be of value to have as an experimental model, an in-vitro system in which it is possible to duplicate the inhibitory effects on luteal steroidogenesis seen with the use of PGF2\g=a\adminis- tered in vivo. This communication describes an in-vitro method in which sections of rabbit cl are maintained in a modified organ culture, and in which PGF2\g=a\ exerts an inhibitory effect on steroidogenesis. Mature female New Zealand white rabbits were mated twice with different males. On the 10th day after mating, the animals were anaesthetized with 1-7 to 2-5 ml pentabarbitone intravenously and bilateral ovariectomy was per¬ formed through a midline abdominal incision, the intact ovaries being im¬ mediately transferred to a sterile field. The cl were carefully dissected from the body of the ovary, bisected into sections weighing 5 to 7 mg, and trans¬ ferred to an organ culture dish. Each piece of tissue was placed on a circle of Gelman paper which rested on a metal grid in contact with a nutrient bath. This, in turn, was surrounded by a ring of blotting paper saturated with 5 ml sterile distilled water to maintain humidity. The nutrient medium (pH 7-5) consisted of 90% medium 199 (modified Earle's base, Grand Island Biological Company) and 10% sterile freeze-dried rabbit serum. Materials to be tested were added to the solution. The central well of the culture dish was filled with 1 ml medium to maintain the sample during incubation. The average time from obtaining the tissues to the beginning of incubation was 15 min. The dishes were placed in a container maintained at 37° C in an atmosphere of 95% 02 and 5% C02. At predetermined intervals (usually 1 to 3 hr), the culture dishes were trans¬ ferred to a working hood. The nutrient medium was pipetted into clean sample tubes and frozen at —20° C. The nutrient was replaced by fresh medium and the dishes were then returned to the incubator. When the final medium samples