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Ovarian nitric oxide synthase gene expression during peripubertal development
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Nitric oxide (NO) is generated from L-arginine by different isoforms of the enzyme nitric oxide synthase. (NOS) and is known to be involved in mediating several biological functions, some of which are associated with reproduction. Much attention has been given to discerning the role of the NOINOS system regarding hypothalamic-pituitary hormone secretions with less attention devoted to discerning its presence or potential functions in the ovary-Recent data, using NOS inhibitors both in vivo and in vitro, as well as NO donors in vitro, suggests that NO may be involved in ovarian function. However , neither the presence of NOS mRNA nor the potential change in NOS gene expression relating to pre-and postovulatory events have been reported. Because of our interest in ovarian function at the time of puberty, we examined in the present study whether the ovary expresses both the inducible (i) and constitutive (c) forms of NOS and whether either form undergoes changes in the ovary during the phases of peripubertal development. Results indicate that both forms of NOS were expressed in the ovary and that the INOS MRNA transcripts were expressed without being exogenously induced. Importantly, when compared with juvenile levels, INOS, but not CNOS, MRNA increased (p<0.01) during the early proestrous phase of development. By the late proestrous phase, the levels of INOS MRNA declined markedly (p<0.001) and remained low throughout both the first estrous and diestrous phases. Furthermore, Western blot analysis revealed both INOS and CNOS protein expression in each phase of puberty with only INOS showing a significant change during the peripubertal period. Specifically, there was an initial increase in the expression of INOS protein during the late proestrous phase (p < 0. 05) which was accompanied by preovulatory increases in serum estradiol (p<0.01) and LH (p<0.001). The INOS protein levels dramatically increased again to peak on the morning of first estrus (p<0.001), i.e. a few hours after ovulation, an event associated with declining (p<0.05) serum levels of estradiol. These data are the first to demonstrate developmental changes in the expression of ovarian INOS MRNA and protein both before and after first ovulation; hence, suggesting a role for NO in the ovary during pubertal maturation and furthermore, providing compelling evidence at the gene level supporting the hypothesis that the NOINOS system plays a physiological role in ovarian function.
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Jones, Benjamin James (1997). Ovarian nitric oxide synthase gene expression during peripubertal development. Master's thesis, Texas A&M University. Available electronically from
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