A reproducible method for dissociation and culture of rat luteal cells is described. The concentration of LH required to produce half-maximal stimulation of progesterone secretion was 50 ng/ml. The effects of prostaglandin E2 (PGE2) and prostaglandin F2(PGF2a)on basal and luteinizing hormone (LH) 1344 chorionic gonadotropin (hCG) by corpora lutea in vivo coincident with a decrease in circulating progesterone within 30 min. However, interpretation of these data was confounded by possible effects of PGF2a on blood flow because PGF2a was found to produce a similar effect on luteal accumulation of 15I-labeled prolactin (7).To further examine the interaction between PGF2a and LH on luteal progesterone production, it was deemed important to study the early and direct actions of these agents on luteal cells in vitro. The present studies describe the effect of PGE2 and PGF2c, on LH-dependent progesterone secretion in conjunction with studies on the effect of PGF2. on binding of gonadotropin to isolated luteal cells in culture. In this same model the effect of simultaneous incubation of luteal cells with LH, dibutyryl cyclic AMP [(Bt)2-cAMPJ,' and theophylline in the presence and absence of PGF2a!, in addition to the effect of PGF2 and LH on adenylate cyclase and cAMP accumulation, was examined to provide information on the possible site of action of prostaglandins.MATERIALS AND METHODS Animals. Immature (26-day-old) rats (CD strain, Charles River Laboratories, Wilmington, MA) were given a subcutaneous injection of 50 international units (IU) of pregnant mare serum (Gestyl, Organon) followed, 64 hr later, by a second subcutaneous injection of 25 IU of hCG (A.P.L., Ayerst).Dispersion of Luteal Cells. Ovaries were removed 7 days after hCG injection, and the cells were dispersed in Ca2+-free medium (medium 1) (no. 138, GIBCO, Grand Island, NY) containing 2000 IU of collagenase (Worthington, Freehold, NJ) and 3M00 IU of deoxyribonuclease (Worthington) per g of tissue for 1 hr at 370 under 95% 02/5% CO2. The contents of the flask were filtered through nylon mesh (Nyten, Tetko Inc.) and centrifuged (5 min, 100 X g); the supernatant fraction was discarded and the pellet was washed three times with fresh medium 1. The final cell concentration (106 cells per ml) was made up in minimal essential medium with 25 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonate buffer and Earles's salts (medium 2) (no. 236, GIBCO). Cell numbers were determined with a hemocytometer, and cell viability was tested by the trypan blue dye test (8

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Stimulated by the recent report of Beuhler, Friedlander, and Friedman on the observation of dd fusion under the impact of heavy-water clusters on deuterated solid targets, we undertook a similar study with pure deuterium clusters (D2oo + -D3oo + ) in the same range of incident energy per deuteron (less than 1 keV). We observed no fusion event and our upper limit for the fusion rate is more than 1 order of magnitude below the Brookhaven value. Additional measurements performed with N" + projectiles were not conclusive but showed that beam-contamination problems may be very serious.PACS numbers: 79.20. Rf, 79.90.+b This experimental work was motivated by the recent observation of "cluster-impact fusion" by Beuhler, Friedlander, and Friedman 1 at Brookhaven National Laboratory (BNL). Fusion was claimed to be observed when (D20)" + clusters, with the number n of molecules per cluster ranging from 20 to 1000, accelerated to a total energy of the order of 300 keV, were sent onto a TiD target. The measured maximum fusion rate is more than 10 10 times larger than that expected from isolated deuterons of the same velocity.The cryogenic source of the Lyon accelerator cannot produce water clusters but can deliver deuterium clusters, which allowed us to test the hypothesis that D" + clusters could induce rf(beam)-rf(target) fusion. This paper describes our experimental search for fusion events when 100-150-keV D2oo + -D30o + clusters, carefully mass and energy analyzed after acceleration, bombard deuterated titanium and polyethylene targets. The net result is that we found no evidence for dd fusion.Moreover, we learned that the authors of Ref. 1 also observed fusion when using light-water clusters 2 as projectiles, but with a rate 20 to 50 times smaller. In that case fusion can be due only to rf(target)-rf(target) collisions, which suggests that the oxygen ions of the water projectiles play a major role in the energy deposition process under cluster impact. Minor modifications of our cryogenic cluster-ion source allowed us to produce and accelerate nitrogen clusters (N" + ) depositing about the same amount of energy in the first target layers as with water clusters. Because of the large mass of the projectiles this last experiment was performed with the direct beam. Under these conditions we have not been able to draw conclusions about rf(target)-rf(target) fusion because of the contamination of the incident beam by fast deuterium species.The setup of our experiment is sketched in Fig. 1. After acceleration the incident clusters are selected, first in energy, by a 74° electrostatic analyzer, and then in mass, by a 16° bending magnet, with a mass-energy product of 60 MeVu. The mass resolution (Am/m -3x 10 ~2) is determined by the exit slit of the magnet and an opaque collimator located 44 cm upstream from the target. The distance between the exit slit and the target amounts to 185 cm. The mass selection of the projectiles after acceleration is a major difference between the Lyon and Brookhaven facilities. At BNL the projec...