RESUMEN
In order to increase conception rates to AI, an experiment was conducted to determine the effect of clitoral stimulation on pregnancy rate. Seven hundred and thirty-five Zebu-cross heifers were assigned to either of the following treatments: 1) control without clitoral stimulation (n=351) or 2) clitoral stimulation after IA (n=384). The data were analyzed using a linear model procedure. Clitoral stimulation increased pregnancy rates (57 vs 45 % for treated and control groups, respectively; P<0.02). Holstein x Zebu and Brown Swiss x Zebu heifers attained similar rates (P>0.05). There was a significant treatment-by-season interaction (P<0.01), with pregnancy rates being higher using clitoral massage during the rainy season (54.7 and 25.5% for the treated and control group respectively). In this study, manual clitoral stimulation increased conception rates in Zebu cross heifers under tropical conditions.
RESUMEN
One of the main problems in clinical oncology is an acquired cellular drug resistance. Special attention deserves the multidrug resistance phenomenon (MDR) involving tumors which become resistant to a wide spectrum of non-related drugs to which they have never been exposed. Several mechanisms responsible for this phenomenon have been described. Among them is the increased expression of the MDR1 gene which encodes the plasma membrane glycoprotein P-gp. This glycoprotein is an energy-dependant multidrug efflux pump of wide specificity. It seems to have a normal physiological function but in some tumors resistant to chemotherapy its expression is increased. In cell lines the increased expression of P-gp is correlated with a decreased accumulation and retention of drugs inside the cells. In addition to P-gp, at least two other mechanisms of multidrug resistance have been described: a decreased expression and changes in the catalytic activity of topoisomerase II enzyme, and changes in glutathione transferase levels. Through biochemical and molecular methods researchers continue to look for a correlation between non-responding tumors and changes in the known drug-resistance mechanisms. These studies suggest that several factors are involved in the cellular drug resistance observed in human tumors, and probably are interacting between them. In clinical practice, the need of controlling MDR phenomena has led to the creation of alternate therapeutic strategies.