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R Nickel

Publications and source records attributed to R Nickel.

7 recordsLinked to original sources
PubMed1992

[Fertility problems in the bitch].

A short review of the oestrous cycle is given, followed by a more detailed look at fertility problems caused by husbandry aspects, anatomical abnormalities, hormonal disturbances and infectious aetiologies. One of the principal causes of fertility problems appears to be mating at an inappropriate time. The ovulation period and therefore the correct time of mating can however, be defined by measuring progesterone levels in peripheral blood three times a week. Vaginoscopy can also be used for this purpose, but is a subjective and less reliable method. Sterility is normally the single symptom of cystic endometrial hyperplasia(-mucometra). This probable major cause of sterility can sometimes be diagnosed with echoscopy but sometimes only during laparotomy. Additionally, hormonal disturbances can precipitate problems such as a persistent (pro-)oestrus, a split heat, or an abnormally long interoestrous interval. Bromocriptine, 15-20 micrograms/kg body-weight, twice daily orally, can be used to induce oestrus if no obvious abnormalities are diagnosed. Attention is paid to fertility problems with an infectious aetiology, such as herpes virus or Brucella canis. A vaginitis or abnormal bacterial growth in the vagina can also influence fertility. Unfortunately, little is known about bacterial growth in the vagina in relation to fertility problems. More research is needed in this field.

Animals↗
PubMed1992

Primary and secondary structure of the pore-forming peptide of pathogenic Entamoeba histolytica.

A pore-forming peptide is implicated in the potent cytolytic activity of pathogenic Entamoeba histolytica. Using NH2-terminal sequence information of this peptide, the corresponding cDNA was isolated. The cDNA-deduced amino acid sequence revealed a putative signal peptide and a mature peptide of 77 amino acids including six cysteine residues. Computer-aided secondary structure analysis predicted that the peptide would be composed of four adjacent alpha-helices, and CD spectroscopy indicated an all alpha-helical conformation. The tertiary structure appears to be stabilized by three disulfide bonds; the pore-forming activity was not sensitive to heat but was lost in the presence of reducing agents. Sequence homology was found to the saposins and to surfactant-associated protein B, both mammalian polypeptides of similar size and secondary structure but of non-lytic function. In particular, the six cysteine residues were found to be conserved, suggesting a common motif for stabilizing a favourable tertiary structure. Compared with previously characterized toxic peptides also containing three disulfide bonds, the amoeba peptide may represent a distinct class of biologically active peptides.

Amino Acid Sequence↗
PubMed1991

Homologous cysteine proteinases of pathogenic and nonpathogenic Entamoeba histolytica. Differences in structure and expression.

A cDNA clone derived from the gene encoding a cysteine proteinase of pathogenic Entamoeba histolytica was isolated using an antiserum to the purified enzyme. This clone was used to identify the homologous clone in a cDNA library from nonpathogenic E. histolytica. Sequence analysis and comparison of the predicted amino acid sequences revealed a sequence divergence of 16%. Southern blot analyses indicated that (i) pathogenic isolates may contain more genes coding for these or related enzymes than nonpathogenic isolates, (ii) the structure and organization of these genes are conserved within each group of amoebae, and (iii) none of the genes is found in both pathogenic and nonpathogenic E. histolytica, underlining the notion that the two groups are genetically distinct. Northern blot analyses suggested that the cysteine proteinase is expressed by pathogenic isolates in substantially higher amounts than by nonpathogenic isolates. Overexpression of this enzyme may be an important factor in the pathogenicity of E. histolytica.

Amino Acid Sequence↗
PubMed1976

Characterization of growth properties and demonstration of the tumor-specific transplantation antigens of Morris hepatomas.

The growth properties of single-tumor-cell suspensions prepared by enzymatic digestion of solid tumors from Morris hepatomas 7777, 5123tc, and 3924a and the presence of tumor-specific transplantation antigen for tumor lines 7777 and 3924a were described. Two of the tumor cell lines (7777 and 3924a) showed consistent i.m. tumor growth following the inoculation of 1 x 10(5) tumor cells, and a similar dose of 5123tc tumor cells resulted in inconsistent tumor growth. Two of the tumor lines (5123tc and 7777) were associated with rapid appearance of lung metastases, whereas with line 3924a metastatic lung lesions rarely developed despite its rapid i.m. tumor growth rate. Tumor resistance to rechallenge with a threshold inoculum of tumor cells was present in approximately 15 to 50% of the animals following amputation of an existing tumor mass. Resistance to a challenge tumor cell inoculum could also be accomplished by immunization with irradiated tumor cells. Tumor-specific resistance was demonstrated to tumor line 3924a in that "immune" animals were able to resist a challenge with 3924a tumor cells but did not resist a challenge with tumor line 9098.

Animals↗
PubMed1976

Effect of anti-alpha1-fetoprotein on alpha1-fetoprotein-producing rat tumors in vivo and in vitro.

Active or passive immunization of rats to alpha1-fetoprotein (AFP) does not consistently inhibit the growth of AFP-producing transplantable hepatomas in vivo, and anti-AFP does not kill these hepatomas in vitro. However, 3 of 14 rats in 1 experiment responded to passive immunization by reversal of tumor growth as evidenced by normalization of elevated AFP serum concentrations, and 1 of 9 rats actively immunized with rat AFP in complete Freund's adjuvant had suppressed growth of transplantable hepatoma 7777.

Animals↗