Ecological approach of macrolide-lincosamides-streptogramin producing Actinomyces from Cuban soils

We report in this study the frequency of Streptomyces strains to produce macrolide-lincosamide-streptogramin (MLS) antibiotics isolated from Cuban soils. The screening assay is based on the induction of MLS-resistance phenotype in a clinical isolated strain of Staphylococcus aureus S-18. Our results suggest that of 800 Streptomyces strains isolated from different soil samples, 6% were positives in the screening test used. The ferralitic red soil from Pinar del Río (north) provided the major percentage (3.6%) of MLS producing strains. The other soil samples tested belonging to Guira de Melena and Bauta in Havana, Matanzas City, Topes De Collantes (Villa Clara), and Soroa Mountains (Pinar del Rio) hill reached very low percentages.     

The androgenic effect of norethisterone and 5alpha-norethisterone on the contractile response of the rat vas deferens to methoxamine and serotonin.

Norethisterone (NET) and its metabolite 5alpha-norethisterone (5alpha-NET) are competitors for the androgen receptor. The sensitivity of the rat vas deferens to the contractile action of methoxamine and serotonin is regulated by hormonal and anatomical factors. The aim of this study was to evaluate the ability of NET and 5alpha-NET to induce the androgen-regulated contractile response to methoxamine and serotonin in the epididymal and prostatic portions of rat vas deferens. Adult male rats either intact, castrated or steroid-treated castrated were used. The contractility was recorded isometrically, and non-cumulative concentration-response curves to either methoxamine or serotonin were obtained. NET and 5alpha-NET partially restored the sensitivity to methoxamine and serotonin in the epididymal portion of castrated rats. The maximal responses to both agonists were significantly higher than those observed in castrated rats, and significantly lower than the responses observed in either intact or androgen-treated castrated rats. The prostatic portion was less responsive to both agonists than the epididymal portion, in all groups but castrated rats, as castration induced sensitivity to both agonists. NET and 5alpha-NET displayed a partial though similar androgenic activity in the rat vas deferens. These results contrast with previous reports where a decrease of androgenic effect due to the 5alpha-reduction of NET has been found.     

Mechanisms of hormonal and antihormonal action of contraceptive progestins at the molecular level

19-Nor synthetic progestins undergo extensive metabolism at the target cells. The resulting metabolic conversion products interact with putative steroid receptors within the cells, and through those interactions, they may exert either agonistic, synergistic and antagonistic hormonal effects. Studies conducted in our laboratories have disclosed that norethisterone (NET) and D-(l) norgestrel (LNG), two widely used contraceptive progestins, are biotransformed to several A-ring reduced (dihydro and tetrahydro) derivatives. The resulting metabolites 5-dihydro NET (5-NET) and 5-dihydro LNG bind with relative high affinity to the progesterone and androgen receptors. To gain insight into the underlying molecular events mediating the mode of action of NET and its neutral metabolites, we have examined the expression of their biological effects at target organs by using the rabbit uteroglobin gene model and the ß-glucuronidase activity of the mouse kidney. The results of a series of experiments seem to indicate that the enzyme-mediated formation of the 5 (trans A/B ring junction) NET derivative results in a significant diminution of its progestational and androgenic potencies. Furthermore, 5-NET acquire a potent anti-progestational/ contragestational effect as assessed in the female rabbit. These results demonstrated that 5-reduction of 19-nor progestins exerts a paradoxical effect, at least in terms of their hormone-like effects. The overall data are in line with the concept that metabolism of synthetic progestins at hormone-sensitive organs modulates their mechanisms of action.     

Detection of sugar residues in lizard tooth germs (Liolaemus gravenhorsti) using lectin histochemistry

The appearance, cellular distribution, and changes of sugar residues during tooth development in adults of the polyphyodont, Liolaemus gravenhorsti, were investigated by using horseradish–peroxidase–conjugate lectins (lectin–HRP). With Con A (Canavalia ensiformis), the ameloblasts (late bell stage) show granular supranuclear positivity and also at the Golgi zone and on their tomes process. Reactivity also appears at the apical surface of the odontoblasts and odontoblastic process. With WGA (Triticum vulgaris), the tooth germs (late bell stage) show cytoplasmatic granular positivity in the ameloblast cells, Golgi regions, and in a lesser extent of the cytoplasm. Also, the apical surface and the odontoblastic process react. WGA reaction is depressed following sialidase treatment. The significance in tooth germs of α-D -mannose, α-D -glucose as well as β-D -N-acetylglucosamine and sialic acid is difficult to ascertain. These oligosaccharides may have some significance in odontogenesis. In fact, Con A-HRP- and WGA-HRP-binding components in ameloblasts and odontoblasts may be functionally related to molecules that are thought to contribute to odontogenesis in lizards. © 1994 Wiley-Liss, Inc.     

Ultrastructural aspects of dental tissues and their behavior in xenoplastic association (lizard quail)

Ultrastructural characteristics of tooth buds of the polyphyodont adult lizards Liolaemus tenuis and Liolaemus gravenhorsti have been elucidated. Xenoplastic combinations of lizard whole tooth buds and neural crest cells from embryos of the quail Coturnix coturnix japonica have been cultured in vitro. Mesenchymal cells (preodontoblasts) of lizard teeth early develop filopodia that contact the basal lamina. Fragments of quail neural crest isolated by dissection were recombined with isolated lizard tooth buds and cultured for 84 hours in dishes kept in an incubator at 37.8 degrees C in air. Some identifiable quail cells in these recombinants developed a cytoplasmic extension like that of an odontoblastic process. These results suggest that lizard tooth rudiments already determined for tooth development produce some non-species specific transmissible constituents which are capable of inducing quail cranial neural crest cells to express certain dental characteristics (odontoblastogenesis) not expressed in their normal development in vivo.     

In vitro differentiation of tooth buds from embryos and adult lizards (L. gravenhorsti): An ultrastructural comparison

It is well established that the capacity for teeth to differentiate “in vitro” depends upon: (a) the age of the embryonic rudiments at the time of excision and (b) the number of cells within each tissue type which are capable of differentiating into organ culture. This paper studies ultrastructural aspects of tooth buds grown in vitro from lizard embryos and compares these characteristics with those observed in dental germs grown in situ in older lizard embryos. Moreover, we report the self-differentiation in vitro dental tissues from adult lizard and compare this phenomenon with the main features of a morphogenetic field. Our results suggest that approximately in the first third of gestation in L. gravenhorsti the dental buds has already acquired the capacity for self-differentiation in vitro. The ultrastuctural observations show that there are no significant differences between odontoblasts and ameloblasts in situ and in vitro. The tooth from “adult lizards,” isolated by combined microsurgical and enzymatic procedure and cultured in semisolid-liquid medium were also able to differentiate teeth. This phenomenon implies that self-differentiation is not rigidly determined, and that in these animals the tooth tissues represents a continuous morphogenetic field throughout the animal's life. This property is intrinsic, resides in the isolated tooth tissues, and is relatively independent of external factors. In addition, these studies indicate that the chick chorio–allantoic membrane and the semisolid-liquid culture medium supply the majority of the factors required for development of these tissues.