Chromosome banding in Amphibia. VIII. An unusual XY/XX-sex chromosome system in Gastrotheca riobambae (Anura, Hylidae)

The mitotic and meiotic chromosomes of the marsupial frog Gastrotheca riobambae were analysed with various banding techniques. The karyotype of this species is distinguished by considerable amounts of constitutive heterochromatin and unusual, heteromorphic XY sex chromosomes. The Y chromosome is considerably larger than the X chromosome and almost completely heterochromatic. The analysis of the banding patterns obtained with GC- and AT-base-pair-specific fluorochromes shows that the constitutive heterochromatin in the Y chromosome consists of at least three different structural categories. The only nucleolus organizer region (NOR) of the karyotype is localized in the short arm of the X chromosome. This causes a sex-specific difference in the number of NOR: female animals have two NORs in diploid cells, male animals one. No cytological indications were found for the inactivation of one of the two X chromosomes in the female cells. In male meiosis, the heteromorphic sex chromosomes form a characteristic sex-bivalent by pairing their telomeres in an end-to-end arrangement. The significance of the XY/XX sex chromosomes of G. riobambae for the study of X-linked genes in Amphibia, the evolution of sex chromosomes and their specific DNA sequences, and the significance of the meiotic process of sex chromosomes are discussed.

Gap junctions: their presence and necessity in myometrium during parturition

Thin sections of longitudinal and circular muscle of myometrium obtained from rats during pregnancy, at term, during delivery, and postpartum were quantitatively examined in the electron microscope. Gap junctions (low resistance pathways) were only present during or immediately prior to delivery and immediately postpartum. The absence of gap junctions during gestation may be necessary for maintenance of pregnancy, while their occurrence during parturition may lead to effective termination of pregnancy.

Oxygen consumption changes with stored blood infusions

Stored blood contains microaggregates, often implicated in the pathogenesis of post-traumatic pulmonary insufficiency. This study was an attempt to further elucidate the effect of autologous stored, filtered and non-filtered blood infusions and homologous stored and fresh blood infusions on pulmonary function and hemodynamics. Inconsistent changes in pulmonary hemodynamics and blood oxygenation were noted. The one significant finding was an increase in oxygen consumption, which occurred with unfiltered autologous or homologous blood but not with fresh or filtered blood. Since an increased oxygen consumption results in an oxygen demand which is difficult to meet in the face of multiple other injuries, it is conceivable that this observation implicates massive stored blood transfusion as a major contributing factor in the development of so-called irreversible shock.