AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 5 854-R861, Copyright © 1991 by American Physiological Society
Prostaglandins, oviducal function, and parturient behavior in nonmammalian vertebrates
L. J. Guillette Jr, D. H. Dubois and A. Cree
Department of Zoology, University of Florida, Gainesville 32611.
Extensive data show that in mammals and birds, prostaglandins (PGs) are
associated with ovulation, luteal function, oviposition, and parturition,
and that also in mammals they are associated with birth-related behavior
and sexual receptivity. In mammals and birds, the ability of PGs to
stimulate oviducal contractions varies regionally along the oviduct (i.e.,
there is a functional cervix or uterovaginal region that acts to retain
eggs or embryos in utero during shelling or embryonic development).
Furthermore, at least in mammals, there is neural control over oviducal
contractions. In reptiles, PGs stimulate oviducal contractions, and these
contractions may be overridden by neural control. No data are available on
whether PGs stimulate oviducal contractions in amphibians or whether there
is a functional cervix in amphibians or reptiles. We suggest that in
ancestral amphibians with oviparity and external fertilization, eggs moved
rapidly through the oviduct after ovulation and that ovarian and oviducal
PGF served as an endocrine hormone coordinating oviducal contractions and
central nervous system-controlled oviposition behavior. Furthermore, we
hypothesize that there was little or no neural control over oviducal
contractions and no functional cervix. These conditions may still exist in
present-day oviparous amphibians. In contrast, we suggest that modern-day
oviparous reptiles have evolved a functional cervix and neural control over
PG-induced uterine contractions, allowing egg passage to be blocked and
thus the development of egg retention. These characteristics may be viewed
as exaptations for the evolution of viviparity.
