Angiotensin II as a semen extender component increases retention of spermatozoa within the uterus of the heifer

The effects of angiotensin II (Ang II) as a semen extender were studied. In the first experiment, individual ejaculates from 10 bulls were split and extended in egg yolk citrate in the absence or presence of varying concentrations of Ang II (10^-5-10^-10 M) to a final concentration of 35x10⁶ sperm per mL. The percentage of intact acrosomes and percentage motility were determined in all treatments for all bulls at 0 h (immediately post thaw) and after incubation for 4 h at 37°C. Extension of the semen with Ang II did not affect spermatozoal viability at either time studied. In the second experiment, mixed breed virgin heifers were induced into oestrus with intramuscular injections of prostaglandin F(2α) on Days 0 and 3. Animals that stood to be mounted were paired for bilateral intracornual insemination using a 0.5-mL French straw on each side approximately 8 h later. One of the paired heifers received semen containing Ang II (10^-5 M) while the other received control semen. A 1-mL aspirate of vaginal mucus was collected at hourly intervals for 8 h after insemination. Concentration of spermatozoa was determined by haemocytometry. There was a significant reduction in cumulative semen loss into the vagina of heifers inseminated with Ang II extended semen (14.4%) compared with heifers inseminated with control semen (19.7%). This suggests that Ang II, when added to extended semen, may reduce retrograde sperm loss following insemination without affecting sperm viability.