La. Sorbera et Ip. Callard, MYOMETRIUM OF THE SPINY DOGFISH SQUALUS-ACANTHIAS - PEPTIDE AND STEROID REGULATION, American journal of physiology. Regulatory, integrative and comparative physiology, 38(2), 1995, pp. 389-397
The phylogenetic age of endocrine control of viviparous reproduction i
n vertebrates 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 alter
ing the intensity or duration of contractions. In contrast, neurointer
mediate lobe extract provoked a marked and reversible enhancement of t
he duration and intensity of contractions but was ineffective in alter
ing the frequency of contractions. In steroid-primed animals, untreate
d and estradiol-17 beta (E(2))-treated animals exhibited a decrease in
the frequency of activity after injection of sRLX in vivo while pretr
eatment with progesterone (P-4) alone or in combination with E(2) full
y suppressed the effects of sRLX. These results suggest that homologou
s sRLX slows the frequency of spontaneous uterine contractions in thir
d-trimester sharks (stage C) in which endogenous P-4 is reduced and E(
2) levels are rising. These data demonstrate the physiological importa
nce of these hormones and the antiquity of reproductive tract control
mechanisms.