The periovulatory period in cattle: progesterone, prostaglandins, oxytocin and ADAMTS proteases

Ano: 2009 | Volume: 6 | Número: 1

Autores: J.E. Fortune, E.L. Willis, P.J. Bridges, C.S. Yang

Palavras-chave: ovary, ovarian follicle, ovulation, cattle, progesterone, prostaglandins, adamts proteases, oxytocin

Resumo Inglês:

Ovulation has long been recognized as one of
the most dramatic reproductive processes. Decades of
research on how the LH/FSH surge leads to ovulation
have made it clear that the surge induces a very complex
cascade of changes. Studies of genetically modified
mice have pointed to progesterone (P4) and its receptor
(PGR) and the prostaglandins (PGs) as critical
components of the ovulatory cascade. In cattle, the
gonadotropin surge also induces oxytocin (OT), which
does not appear to increase in rodent periovulatory
follicles. This review is an attempt to summarize studies
by our laboratory on the temporal patterns, roles,
regulation, and interrelationships among P4/PGR, PGs,
and OT in bovine periovulatory follicles. Most of these
results are based on an experimental model in which the
dominant follicle of the first follicular wave of the
estrous cycle is induced to develop into a preovulatory
follicle by injection of PGF2α on Day 6 of the cycle,
followed 36 h later by an injection of GnRH to induce
the LH/FSH surge. The results suggest that the effects
of the gonadotropin surge on PG production by bovine
granulosa cells are mediated by the gonadotropininduced
increase in intrafollicular P4 and that P4 acts by
binding to its nuclear receptor and increasing the
abundance of mRNA for the enzyme PTGS2 (COX-2).
Our data thus far also support the hypothesis that PGs,
especially PGE2, can stimulate progesterone secretion
by both follicular cell types and suggest a positive
feedback relationship between P4/PGR and the PGs.
Additional results suggest a positive feedback loop
between P4/PGR and OT. The finding that levels of
mRNA for several ADAMTS proteases are regulated by
the LH/FSH surge in vivo and by P4/PGR and/or PGs in
vitro suggests a role for this family of proteases in
remodeling the bovine ovulatory follicle in preparation
for ovulation and the formation of the corpus luteum. It
is important to remember that a process essential for
reproduction, such as ovulation, may involve redundant
mechanisms and that these mechanisms may have
evolved differently from rodents in larger mammalian
species, such as ruminants and humans.