The Role of Different NO Synthase Isoforms in the Regulatory Effect of Prolactin and Growth Hormone on the State of Chromosomes in Mature Oocytes Aging in vitro

Abstract

The fertility of female mammals depends on the quality of oocytes, which decreases in the process of biological aging. We found an inhibitory effect of two related pituitary hormones (prolactin (PRL) and growth hormone (GH)) on destructive modifications of metaphase chromosomes in the eggs of domestic cow (Bos taurus taurus), aging in vitro. The involvement of different NO synthase (NOS) isoforms in realization of the effect of PRL and GH on age-related changes of MII chromosomes with prolonged cultivation of in vitro matured cow oocytes was studied in the present work. In the absence of hormones NPLA, neuronal NOS (nNOS) inhibitor had no effect on the frequency of chromosomal abnormalities in aging oocytes. At the same time, 1400 W (inducible NOS (iNOS) inhibitor) and L-NAME (efficient endothelial NOS (eNOS and nNOS ) inhibitor) decreased this frequency, while the blocking of all three NO synthase isoforms led to the opposite effect. The inhibitory effect of PRL on destructive chromosome modifications in aging eggs increased in the presence of L-NAME, but was not expressed with the inhibition of nNOS, iNOS, or all NO synthase isoforms simultaneously. Neither NPLA nor L-NAME modulated the inhibitory effect of GH on abnormal chromosome changes in oocytes. On the contrary, the blocking of iNOS, as well as all three NO synthase isoforms, led to an increase in the portion of oocytes with destructive changes of MII chromosomes. At the same time, the level of total activity of NO synthase in oocytes did not depend on the presence of the studied hormones or NOS inhibitors during the prolonged cultivation of oocyte–cumulus complexes. Data obtained suggest that the inhibitory effect of PRL and GH on abnormal changes of metaphase chromosomes in aging cow eggs is associated with a decrease in the activity of endothelial NO synthase, as well as (in the case of PRL) with an increase in the activity of neuronal NO synthase in the cumulus cells surrounding the oocytes.