Canine-chilled sperm: study of a semen extender made with low-density lipoproteins from hen egg yolk supplemented with glutamine.

The objective of this study was to evaluate the effects of a combination of 6% low-density lipoproteins (LDL) and 20 mm glutamine in comparison with other extenders used for the refrigeration of canine semen: Tris egg yolk (EY) 20% and 6% LDL. The percentages of mobile spermatozoa after 4 days storage in a domestic refrigerator at +4 °C were 53.1%, 44.2% and 52.2% for the 6% LDL + 20 mm glutamine, 20% EY and 6% LDL extenders respectively for 100% of the dogs. After 7 days of storage, these percentages fell to 37.8%, 26.4% and 33.6% in the same extenders for 50% of the dogs. In vitro fertility tests were performed with all of the extenders following the mobility results. These tests were conducted on the day of sampling (D0), and 48 and 96 h after sampling. The results of the hypo-osmotic swelling test were 82.6%, 81.2% and 85.7% on D0, 75.2%, 74.1% and 78.5% on D2, and 70.8%, 71% and 76.1% on D4 for the 6% LDL + 20 mm glutamine, 20% EY and 6% LDL extenders, respectively. For the FITC/pisum sativum agglutinin (PSA) test, the results were 81.5%, 70.2% and 84.8% on D0, 78.9%, 62.3% and 84.2% on D2, and 72.7%, 59.6% and 73.7% on D4 for the 6% LDL + 20 mm glutamine, 20% EY and 6% LDL extenders, respectively. The acridine orange test was positive; in nearly 100% of cases, none of the spermatozoa had been denatured on D0, D2 and D4. The 6% LDL + 20 mm glutamine and the 6% LDL extenders are capable of preserving spermatozoa that have been stored in a domestic refrigerator at +4°C for at least 4 days. This means that the spermatozoa retain good cytoplasmic membrane integrity, had not capacitated and contained intact DNA in comparison with spermatozoa preserved in the egg yolk extender. The duration of storage is a very important consideration when faced with the problem of sending semen over ever-greater distances.

Isoform variable action among thyroid hormone receptor mutants provides insight into pituitary resistance to thyroid hormone.

Resistance to thyroid hormone (RTH) is due to mutations in the beta-isoform of the thyroid hormone receptor (TR-beta). The mutant TR interferes with the action of normal TR to cause the clinical syndrome. Selective pituitary resistance to thyroid hormone (PRTH) results in inappropriate TSH secretion and peripheral sensitivity to elevated thyroid hormone levels. Association of the PRTH phenotype with in vitro behavior of the mutant TR has proved elusive. Alternative exon utilization results in two TR-beta isoforms, TR-beta 1 and TR-beta 2, which differ only in their amino termini. Although the TR-beta 1 isoform is ubiquitous, the TR-beta 2 isoform is found predominantly in the anterior pituitary and brain. To date, in vitro evaluation of RTH mutations has focused on the TR-beta 1 isoform. Site-directed mutagenesis was used to create several PRTH (R338L, R338W, V349M, R429Q, I431T) and generalized RTH (delta 337T, P453H) mutations in both TR-beta isoforms. The ability of mutant TRs to act as dominant negative inhibitors of wild type TR-beta function on positive and negative thyroid hormone response elements (pTREs and nTREs, respectively) was evaluated in transient transfection assays. PRTH mutants had no significant dominant negative activity as TR-beta 1 isoforms on pTREs found in peripheral tissues or on nTREs found on genes regulating TSH synthesis. PRTH mutants, in contrast, had strong dominant negative activity on these same nTREs as TR-beta 2 isoforms. Cotransfected retinoid X receptor-alpha was required for negative T3 regulation via the TR-beta 1 isoform but was not necessary for negative regulation via the TR-beta 2 isoform in CV-1 cells. The differing need for retinoid X receptor cotransfection demonstrates two distinct negative T3-regulatory pathways, one mediated by the TR-beta 1 and the other mediated by TR-beta 2. The selective effect of PRTH mutations on the TR-beta 2 isoform found in the hypothalamus and pituitary vs. the TR-beta 1 isoform found in peripheral tissues suggests a molecular mechanism for the PRTH disorder.

Cross-resistances to antiviral drugs of IUdR-resistant HSV1 in rabbit keratitis and in vitro.

The emergence of cross-resistance to various antiviral drugs was investigated both in vivo and in vitro for herpes simplex virus type 1 (HSV1) resistant to idoxuridine (IUdR 0.24%) obtained by seven successive passages (from P0 to P7) in rabbit keratitis treated by IUdR. The viral population obtained at the seventh IUdR passage (P7) showed an activity of the thymidine kinase (TK) reduced to 5.6% of the parental strain (PO); moreover, most of the clones of P7 showed an altered TK phenotype determined by the [125I]iododeoxycytidine (IDC) procedure. In rabbit keratitis, IUdR-resistant viral population P7 showed cross-resistance to bromovinyl desoxyuridine (BVDU) (0.5%) and to acyclovir (ACV) (3%). Under trifluorothymidine (1%) treatment, P7 showed an intermediate sensitivity. HSV1 at P7 remained sensitive to adenine arabinoside (Ara A) (3%) and to dihydroxy-propoxymethylguanine used at high concentration (3%). The in vitro sensitivity determination to various antiviral drugs was investigated by dye-uptake assay for the initial viral population PO and for HSV1 collected under IUdR treatment at the third (P3) and the seventh (P7) passages. Cross-resistance to TK-dependent drugs, such as IDC, BVDU, and ACV were found at P7. P7 remained sensitive to Ara A and to phosphonoformic acids antiviral drugs known not to be dependent on viral TK.

Emergence of cross-resistant herpes simplex virus following topical drug therapy in rabbit keratitis.

The acquisition of drug resistance in vivo was investigated by 7 serial passages (from P0 to P7) of herpes simplex virus (HSV-1) in rabbit cornea treated with either IUdR (idoxuridine), IDC (idoxycytidine), ACV (acyclovir), TFT (trifluridine), or Ara A (adenine arabinoside). Therapeutic failure was acquired gradually: at P3 for IUdR, at P4 for ACV and at P5 for TFT. At P7, viral thymidine kinase (TK) activity was reduced to 5.6% of the parental strain for IUdR, to 7.5% for ACV and to 4.6% for TFT treatment. No signs of clinical unresponsiveness occurred with IDC or Ara A. The in vitro determination of antiviral drug sensitivity performed by the dye-uptake assay on HSV isolates at each passage showed a correlation between the increase in the 50% effective dose (ED50) and the increase of ulcer area grade at each passage under antiviral drug (p less than 0.1). Both IUdR- and TFT-resistant HSV1 developed cross-resistances to TK dependent drugs. However ACV-resistant HSV1 did not show cross-resistance to other antiviral TK dependent drugs. The acquisition of the cross-resistances is discussed, and the practical implications in case of therapeutic failures are suggested.