Effects of prolactin on intracellular stored calcium in the course of bovine oocyte maturation in vitro
1999
Kuzmina, T.I. | Lebedeva, I.Y. | Torner, H. | Alm, H. | Denisenko, V.Y.
At present there are divergent opinions as to the role of prolactin (PRL) in the mechanisms of meiotic regulation in mammals. We investigated the effects of bovine PRL (bPRL) on bovine oocyte maturation in different culture systems and varying levels of intracellular stored calcium [Ca(2+)](is) in the oocytes. Cumulus-oocyte complexes (COC) were incubated in TCM 199 containing either 10% fetal calf serum (FCS) in the absence (System 1) or presence (System 2) of FSH and estradiol, or 6 mg/mL bovine serum albumin (BSA) in the presence of FSH and estradiol (System 3). Levels of [Ca(2+)](is) in oocytes were determined by using the fluorophore chlortetracycline. The addition of 50 ng/mL bPRL to different culture media increased the percentage of oocytes at telophase I and metaphase II stages (Systems 1 and 2) and/or decreased the percentage of oocytes with degenerated chromosomes (Systems 1 and 3). Compared with the control, lower levels of [Ca(2+)](is) were observed in oocytes cultured for 2.5 h in those systems in which bPRL decreased the rate of oocytes with degenerated chromosomes (1.27 +/- 0.11 vs 1.67 +/- 0.09 arbitrary units (AU) in System 1, P < 0.001 and 1.27 +/- 0.12 vs 1.52 +/- 0.04 AU in System 3, P < 0.001). These findings show that the effects of bPRL on bovine oocyte maturation depend on the composition of the culture system and that the decline in the rate of oocytes with with degenerated chromosomes in response to bPRL may be the result of the decrease in [Ca(2+)](is) levels at early stages of oocyte maturation.
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