The myometrium of the spiny dogfish, squalus acanthias: peptide and
steroid regulation.
Sorbera, Lisa Ann, and Ian P. Callard.
Department of Biology, Boston University, Boston, Massachusetts
02215; and Mount Desert Island Biological Laboratory, Salsbury Cove,
Maine 04672
APStracts 2:0072R, 1995.
The phylogenetic age of endocrine control of viviparous reproduction
may be estimated by examination of elasmobranch models. We have shown
in pregnant Squalus acanthias that Squalus relaxin (sRLX)
significantly decreased the frequency of myometrial contractions in a
dose-dependent, reversible manner in vitro and in vivo, without
altering the intensity or duration of contractions. In contrast,
neurointermediate lobe extract provoked a marked and reversible
enhancement of the duration and intensity of contractions but was
ineffective in altering the frequency of contractions. In steroid
primed animals, untreated and estradiol-17[beta] (E2)-treated animals
exhibited a decrease in the frequency of activity after injection of
sRLX in vivo while pretreatment with progesterone (P4) alone or in
combination with E2, fully suppressed the effects of sRLX. These
results suggest that homologous sRLX slows the frequency of
spontaneous uterine contraction in third trimester sharks (stage C)
in which endogenous P4 is reduced and E2 levels are rising. These
data demonstrate the physiological importance of these hormones and
the antiquity of reproductive tract control mechanisms.
Received 15 August 1994; accepted in final form 13 March 1995.
APS Manuscript Number R450-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 April 1995.