Effect of prostaglandin F2 alpha and methylxanthines on enzymic release of bull epididymal spermatozoa in vitro.

The in vitro effect of PGF2 alpha and methylxanthines (theophylline and caffeine) on enzymatic release of bull epididymal spermatozoa was investigated. Epididymal spermatozoa were diluted with egg yolk citrate-based diluent to a concentration of 50 x 10(6) spermatozoa per ml. Aliquots were supplemented with PGF2 alpha at levels of 0, 300, 600 and 1200 micrograms/ml, theophylline or caffeine was added at levels of 0, 500 and 1000 micrograms/ml and incubated at 37 degrees C for 4 h. Spermatozoal motility was decreased with increasing level of PGF2 alpha and the activities of transaminases in the extracellular medium showed a continuous increase. Addition of theophylline or caffeine at both dose levels significantly increased the sperm motility; the activities of transaminases either were not significantly changed or were significantly decreased during the 4 h incubation. These results suggest that supplementation of bull spermatozoa with high levels of PGF2 alpha suppressed motility and induced sperm membrane damage and permeability. However, supplementation of bull spermatozoa with methylxanthines enhanced sperm motility and was not harmful to the integrity of the sperm membrane.

Effect of xylazine in heifers under thermoneutral or heat stress conditions.

A study was performed to assess the effect of xylazine HCl (0.1 mg/kg of body weight, IV) in heifers maintained at thermoneutrality (18 C, 42% humidity) or under heat stress (33 C, 63% humidity) conditions. Xylazine caused 50 and 70% decreases in serum insulin concentrations in the thermoneutral and heat-stressed heifers, respectively. Xylazine-induced hypoinsulinemia was associated with hyperglycemia. In the thermoneutral group, serum glucose concentrations increased from a basal concentration of 75 mg/dl to 150 mg/dl after 15 minutes. In the heat stress group, the serum glucose concentration increased from 65 mg/dl to 105 mg/dl. Hyperglycemia peaked at 2 hours and remained high for 6 hours after xylazine administration. Heat-stressed heifers took a longer time (107 minutes) to stand than did heifers under thermoneutral conditions (41 minutes). The time to regain sensation to pain was significantly prolonged in heat-stressed heifers. Xylazine had no effect on body temperature and respiration rate in heifers under the thermoneutral condition, whereas it markedly induced hyperthermia and suppressed respiration rate in the heat-stressed heifers. Furthermore, the pulse rate was slightly decreased in thermoneutral heifers and was markedly decreased in the heat-stressed heifers.