Increased production of ovarian thromboxane in gonadotropin-treated immature rats: Relationship to the ovulatory process

Thromboxane (TX) B₂, a stable metabolic product of hydrolysis of TXA₂, was measured by radioimmunoassay in tissue extracts of ovaries of immature rats pretreated with pregnant mare's serum gonadotropin and human chorionic gonadotropin. Ovarian concentrations of TXB₂ increased before, and remained elevated after, the time of ovulation. In a subsequent study, ovulation was inhibited in a dose-dependent fashion by a reported TXA₂ receptor antagonist, AH23848. Nevertheless, inhibition of the preovulatory rise in synthesis of TXB₂ by furegrelate (a thromboxane synthetase inhibitor) did not prevent ovulation. Nor was the blockade of ovulation caused by indomethacin (a cyclooxygenase inhibitor) reversed by a TXA₂ mimetic (U-46619). It does not appear that a preovulatory increase in ovarian thromboxane is an obligatory component of the ovulatory mechanism of gonadotropin-primed immature rats.     

Methotrexate therapy. Nonsurgical management of ectopic pregnancy.

Ectopic pregnancy has become a surgical epidemic over the past two decades. To minimize the morbidity, mortality, and financial burden created by this rapidly growing health problem, nonsurgical alternatives have been investigated, including treatment with methotrexate. We reviewed current literature to evaluate the safety, efficacy, and costs associated with methotrexate treatment of tubal pregnancy. To date, 17 studies have reported on 400 patients with tubal pregnancies treated with parenteral methotrexate; the overall success rate was 92% (95% confidence interval, 89% to 95%). Single-dose parenteral methotrexate has been shown to be safe, effective, and associated with minimal costs when used in carefully selected patients. A prospective, randomized clinical trial comparing medical and surgical management of ectopic pregnancy is needed to assess the risks, benefits, and costs of these two approaches.     

Inhibition of 3-phosphoglycerate dehydrogenase by l-serine

1. l-Serine was shown to be a highly specific inhibitor of 3-phosphoglycerate dehydrogenase. 2. 3-Phosphoglycerate dehydrogenase is cold-labile with respect to its catalytic activity and to sensitivity to serine. 3. l-Serine protects the catalytic site as well as the inhibitor site. 4. Glycerol protects the catalytic site as well as the inhibitor site. 5. Serine acts as a ;classical' non-competitive inhibitor of fresh preparations of 3-phosphoglycerate dehydrogenase. 6. ;Aged' preparations when assayed at pH6.5 show sigmoid inhibition curves at saturating substrate concentrations. 7. A generalized model is advanced to account for the variation of the catalytic activity and the inhibitory effect of l-serine with time and conditions. 8. The possibility that the sigmoid kinetics of inhibition observed are an artifact of isolation is discussed.     

cDNA cloning and expression of oxysterol-binding protein, an oligomer with a potential leucine zipper

Feedback repression of the genes encoding the low density lipoprotein receptor and several enzymes of the cholesterol biosynthetic pathway is mediated by 25-hydroxycholesterol and other oxysterols. In this study, we have cloned a rabbit cDNA encoding an oxysterol-binding protein that may play a role in this regulation. The predicted amino acid sequence revealed a protein of 809 amino acids with two distinctive features: 1) a glycine- and alanine-rich region (63% of 80 residues) at the NH2 terminus, and 2) a 35-residue leucine zipper motif that may mediate the previously observed oligomerization of the protein. When transfected into simian COS cells, the rabbit cDNA produced a protein that exhibited the same affinity and specificity for sterols as the previously purified hamster liver protein. Immunoblotting analysis showed that the rabbit cDNA encodes both the 96- and 101-kilodalton forms of the oxysterol-binding protein that were previously observed. The availability of an expressible cDNA for the oxysterol-binding protein should help elucidate its role in sterol metabolism.     

The effect of high electric fields on the subsequent fermentation performance of cells of Saccharomyces cerevisiae

Summary Suspensions of cells of Saccharomyces cerevisiae were electrostatically sprayed through a charged nozzle into an inert heavy hydrocarbon solvent, collected and used to conduct fermentation of malt extract media. Cell growth and ethanol production were unaffected by voltages up to 25kV.     

Comparison of gamete compatibility between two blue mussel species in sympatry and in allopatry

Recent demonstrations of positive selection on genes controlling gamete compatibility have resulted in a proliferation of hypotheses concerning the sources of selection. We tested a prediction of one prominent hypothesis, selection to avoid hybridization (i.e., reinforcement), by comparing heterospecific gamete compatibility in two Mytilus edulis populations: one population in Cobscook Bay, Maine, in which the close congener, M. trossulus, is abundant (a region of sympatry), and one population in Kittery, Maine, in which M. trossulus is absent (a region of allopatry). Three diagnostic nuclear DNA markers were used to identify mussels to species and to estimate the frequency of both species and their hybrids in the two populations. Controlled crosses were then conducted by combining eggs of M. edulis females with a range of M.edulis and M. trossulus sperm concentrations. Results were not consistent with the reinforcement hypothesis. M. edulis females collected from the region of sympatry were no more incompatible with M. trossulus males than were M. edulis females collected from the region of allopatry. A trend in the opposite direction, toward greater compatibility in sympatry, suggests that introgression of M. trossulus genes that control egg compatibility, such as those encoding receptors for sperm, may influence evolution of gametic isolation in hybridizing populations.