Activation and development of porcine oocytes matured in vitro following injection of inositol 1,4,5-trisphosphate

Abstract

Inositol 1,4,5-trisphosphate (IP3) is considered to be important for activation of mammalian oocytes at the time of fertilization, and activation induces a rise in intracellular Ca 2+ concentration ([Ca 2+] i) by release from the Ca 2+ stores in the oocytes. Therefore, IP3 could act as an artificial activator of porcine oocytes. Activation and development, and rise in [Ca 2+] i in matured oocytes injected with various concentrations of IP3 were investigated in this study. Porcine oocytes were recovered from the ovaries of prepubertal gilts, matured for 46–48 h and cultured in vitro for 7 days in following treatments as non-injected oocytes (NI), injected with carrier buffer, 2.5, 5 and 500 μM of IP3. The result showed that IP3 activated porcine oocytes matured in vitro (NI 3.8%, buffer 7.1%, 2.5 μM IP3 73.5%, 5 μM IP3 76.2%, 500 μM IP3 85.2%). There was a slight but not significant increase in the proportion of oocytes activated as the level of IP3 increased. The rate of development to the cleavage stage increased remarkably when the concentration of IP3 increased (NI 4.9%, buffer 5.7%, 2.5 μM IP3 30.3%, 5 μM IP3 47.1%, 500 μM IP3 78.1%). Blastocyst development was only observed in oocytes that had been injected with a higher concentration of IP3 (5 μM IP3 6.1% and 500 μM IP3 5.3%). Both the peak value and duration of [Ca 2+] i rise also increased as the concentration of IP3 increased. Baseline values (ratio value, R) for [Ca 2+] i ranged from 1.51 to 1.57 and was not affected by the buffer treatment. The peak value of [Ca 2+] i rose significantly with increasing level of IP3 treatment (2.5 μM IP3, 3.54±0.32; 5 μM IP3, 7.50±0.37; 500 μM IP3, 8.54±0.33). Similarly, the duration of the [Ca 2+] i rise increased as the level of IP3 increased (2.5 μM IP3, 43.7±7.00 s; 5 μM IP3, 93.5±9.17 s; 500 μM IP3, 160.6±18.9 s). It was concluded that injected IP3 promotes the development of porcine matured oocytes and that their developmental ability is positively correlated with the rise in [Ca 2+] i induced by IP3.