The purpose of this study was to describe the course of preterm labor in patients receiving a standard intravenous infusion of the oxytocin antagonist atosiban. An open-labeled, non-randomized study was conducted at 4 sites. Successful tocolysis was defined as delay of delivery larger than 48 hours from starting atosiban and no need for an alternate tocolytic. Atosiban was administered by continuous intravenous infusion at a rate of 300 micrograms per minute until uterine contractions were absent for 6 hours, or up to a maximum infusion time of 12 hours. Sixty-two patients of between 20 and 36 weeks' gestation were enrolled over 6 months. One had rupture of membranes and was excluded. Successful tocolysis was noted in 43 of 61 (70.5%). Four delivered spontaneously within 48 hours and 14 (23.0%) required an alternate tocolytic agent. The chance of successful tocolysis was related to the degree of cervical dilation at the start of therapy. Cessation of uterine contractions was noted in 38 patients (62.3%). A decrease in uterine contraction frequency of 50% or more was noted in 50 of 61 patients (82.0%). Four patients reported side effects (nausea, vomiting, headache, dysguesia, chest pain), but in no case did side effects require discontinuation of the medication. Intravenous administration of atosiban is associated with a delay in delivery comparable to that seen with other tocolytics. If this effect is confirmed in planned placebo-controlled trials, its favorable side effect profile may give it a place in the armamentarium.

Abstract. The Portovelo epithermal vein-system in southwestern Ecuador has produced more than 120 tons of gold and about 250 tons of silver. The veins result from hydrothermal processes close to a Miocene volcano which produced an andesitic to dacitic sequence followed by collapse and post-collapse rhyolitic activity which generated most of the alteration and mineralization. Three main structural segments are defined by NW-trending strike-slip faults, which show later stages of vertical movement. These faults are responsible for development of an extensive N-S dilatational jog within andesitic rocks, which acted as the main host to ore-deposition. A largescale propylitic aureole surrounds a quartz-chloritesericite-adularia core, centered on the rhyolites, within a system of collapse-related ring-structures. A quartzchlorite-sericite-adularia-calcite assemblage is the most common wall-rock alteration close to the veins. The size (4 x 15 km) and vertical range (1400m) of the vein-system is exceptional. Alteration, textures and mineral assemblage, including a quartz-calcite gangue, sulfides, abundant sulfosalts and free gold (electrum), are quite typical of an adularia-sericite epithermal deposit. Spatially, the mineralization is arranged in three zones. In addition, three successive stages can be distinguished. The bulk of economic mineralization was deposited during the second stage, in association with a clear quartz and calcite gangue.Tm-ice and Tm-ctath data of fluid inclusions in the clear quartz indicate a high salinity (--~10.5eq.wt% NaC1). The homogenization temperatures of fluid inclusions in the gangue minerals and in the altered host-rocks vary between 180 ° and 310°C. Quartz 6~s O-values from hydrothermally altered wall-rocks reflect the original isotopic values of the latter. These values show a narrower range in vein quartz (3 018 between + 7.7~o and + 11.5~/oo SMOW). In addition, the 60 18 values of the vein quartz increase systematically with decreasing homogenization temperature. This suggests that quartz was in equilibriumCorrespondence to: F. Van Thournout with a large reservoir of water of constant 1 SO/16 0 composition at decreasing equilibrium temperatures. The estimated isotopic composition of the fluids from which milky quartz and calcite of the main mineralization stage precipitated, lies around -1% SMOW. This value indicates a meteoric rather than a magmatic origin of the ambient fluid. Clear quartz of the second stage seems to have formed from a fluid with a &180 of +3%0 SMOW. This higher value can be due to a more intense water-rock interaction or to mixing of meteoric with magmatic water.

The release of alpha-human chorionic gonadotropin (alpha hCG), gonadotropin human chorionic gonadotropin (hCG) and human chorionic somatomammotropin (hCS) in vitro from placentas of different gestational ages was studied. In addition, the effect of gonadotropin-releasing hormone (GnRH) on these hormonal releases, as related to the gestational age of the placenta cultured and the dose of GnRH, was determined. The basal release of alpha hCG and hCG was greatest at 9-13 wk of gestation (1000-1500 ng/mg and 250-350 ng/mg, respectively). Lowest release rates were at term (28 ng/mg and 20 ng/mg, respectively). Hormonal release declined with extended culture, except from the cultures of 13- and 15-wk placentas, in which the initially high release continued throughout the 8 days of culture. The initial release of hCS was low at 6 wk, increased to maximum rates by 15 wk, and was similar to the initial rate of release at term. Gonadotropin-releasing hormone stimulated the release of alpha hCG and hCG most dramatically in cultures of 16-wk and 17-wk placentas, where as much as a 400- and 250-fold increase, respectively, on Day 6 of culture was observed (p less than 0.0001). In term placenta cultures after 6 days in vitro, a 20-fold stimulation of alpha hCG and a 10-fold increase of hCG was effected by GnRH (p less than 0.001). The largest responses of alpha hCG and hCG to GnRH were observed when estrogen levels were low. Dose-related responses were observed in some placentas, yet in some instances, maximal effects were attained with all doses utilized in these studies (0.2 to 50 micrograms/ml). These data demonstrate that human placentas of different gestational ages have varying hormonogenic capabilities in vitro. The data also establish that synthetic GnRH is capable of stimulating alpha hCG and hCG production, but the degree and pattern of response to GnRH stimulation are related to the gestational age of the placental tissue and its time in culture. The most responsive period to exogenous GnRH stimulation of alpha hCG and hCG release was on Days 5 and 6 of culture, when basal estrogen release was very low. These data support the hypothesis that hCG release might be controlled by a chorionic GnRH stimulation and suggest that local steroid levels may modulate the hCG response to GnRH stimulation.

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