Endocrine control of ovarian function in dogs and other carnivores
Animal Reproduction
Endocrine control of ovarian function in dogs and other carnivores
Autor Correspondente: P W Concannon | [email protected]
Palavras-chave: anestrus, canine, carnivore, cat, circannual, corpus luteum, delayed implantation, dog, estrogen, estrus, feline, fsh, lh surge, ovary, pregnancy, progesterone, prolactin, pseudopregnancy
Resumos Cadastrados
Resumo Inglês:
Ovarian function in dogs is minimally but
successfully evolved and adapted for fertility, and
represents a basic model for examining the more
complex evolution of ovarian activity in other
carnivores and mammals in general. Canids are
monoestrous, polytocous, spontaneous ovulators with a
spontaneous luteal function producing progesterone for
the duration of a normal 2-month pregnancy and
unaffected by hysterectomy. They have no acute
luteolytic mechanism in the absence of pregnancy
although PGF is luteolytic and participates in prepartum
luteolysis. The cellular mechanisms of luteal and
follicular tissues appear unlikely to differ meaningfully
from those described in other species, with the
spontaneously prolonged luteal function being similar
to, and in some instances shorter than, the luteal lifespan
of hysterectomized polyestrous species. All or nearly all
female caniform carnivore species have photo-entrained
annual life-cycles and annual or biennial reproduction.
However, the domestic dog, a subspecies of the grey
wolf, is an exception and non-seasonal; but, as an
exception to the exception, the basenji dog like the
dingo, another wolf subspecies, is seasonal, having its
cycle in the autumn. The canine obligate anestrus lasts
2-10 months and is terminated by increased GnRH and
LH pulsatility. The timing is under multiple regulatory
inputs. These include recovery from progesterone
effects at variable times after progesterone declines to
nadir values; increased dopaminergic and/or decreased
opioidergic tones and/or sensitivities, presumably under
the influence of an endogenous circannual cycle
assumed to persists despite the lack of photoresponsiveness;
and, stimulatory pheromonal input from
other females (as well as photoperiod in the case of
Basenji). The only clear adaptations or unique attributes
seen in dogs that are likely beyond what occurred in a
more primitive ancestor are two. One, there is a
pregnancy specific increase in prolactin that as a potent
luteotrophin (as in rodents) acts to enhance progesterone
production during pregnancy, which appears likely to
be the case in all carnivores. And, two, the bitch has a
fertile-mating window as wide as 11 days, and up to
8 days after ovulation. The latter involves the delayed
post-ovulatory maturation of oocytes (also seen in
foxes), prolonged post-maturation oocyte viability, and
a uterine environment hospitable to sperm survival for
up to 7 days during estrus. This relative simplicity
contrasts to more complicated adaptive strategies like
(1) delayed implantation seen in many caniform
carnivores (including many mustelids, ursids, and
phocid and otarid seals); (2) reflex, induced ovulation
(as seen in many feliform carnivores); and (3)
prolongation of post-implantation gestation via
placental secretion of progesterone (some feliform,
some artiodactyls, primates) or gonadotrophin
(primates, equids). Also considered in the review are the
endocrine mechanisms triggering the LH surge and
estrus behavior in dogs, and factors involved in
termination of obligate anestrus.
