Temperature gradients in female reproductive tissues and their potential significance

Ano: 2009 | Volume: 6 | Número: 1

Autores: R.H.F. Hunter

Palavras-chave: fallopian tube, spermatozoa, thermotaxis, graafian follicle, endothermic reaction, oocyte, zygote, gene expression, cloning

Resumo Inglês:

This review challenges the long-standing
dogma that deep-body temperature should be regarded
as uniform. Not only may this not be so, but small
gradients in temperature in and across reproductive
tissues might have assumed functional importance
during the evolution of eutherian mammals.
Temperature gradients within the Fallopian tubes of
estrous animals are interpreted in a context of preovulatory
storage of viable spermatozoa and their periovulatory
activation and release from the functional
reservoir in the caudal isthmus. Proposals concerning
the response of potentially-fertilizing spermatozoa to
increasing temperature along the isthmus of the
Fallopian tube are recalled, and application of the term
thermotaxis to this phase of sperm migration is assessed
critically. Classical findings on the temperature of
Graafian follicles in rabbits and women are highlighted,
and more recent work on temperatures in pig preovulatory
follicles is considered in detail. Although an
experimental approach involving anaesthesia and infrared
sensing is open to criticism, the finding that preovulatory
follicles are cooler than ovarian stroma cannot
be discounted as artifact. Instead, evidence for
endothermic reactions that act to lower temperature
within pre-ovulatory follicles is presented together with
a description of relevant counter-current vascular
physiology that enables maintenance of a cooler
follicular temperature. As to future experimental work,
the possibility is raised that temperatures may not be
uniform across the cytoplasm of maturing oocytes nor at
different stages of the cell cycle in very young embryos.
These proposals lead to speculation that temperature
may be exploited at a molecular level to modulate
unfolding gene expression in zygotes and early cleavage
stage embryos. Modern micro-imaging technology
needs to be applied to such concepts.