Scaling of cardiac morphology is interrupted by birth in thedeveloping sheep Ovis aries

Scaling of cardiac morphology is interrupted by birth in the
developing sheep Ovis aries:

Abstract

Scaling of
the heart across development can reveal the degree to which
variation in cardiac morphology depends on body mass. In this
study, we assessed the scaling of heart mass, left and right
ventricular masses, and ventricular mass ratio, as a function of
eviscerated body mass across fetal and postnatal development in
Horro sheep Ovis aries (~50‐fold body mass
range; N = 21). Whole hearts were extracted from
carcasses, cleaned, dissected into chambers and weighed. We found a
biphasic relationship when heart mass was scaled against body mass,
with a conspicuous ‘breakpoint’ around the time of birth, manifest
not by a change in the scaling exponent (slope), but rather a jump
in the elevation. Fetal heart mass (g) increased with eviscerated
body mass (M_b, kg)
according to the power
equation 4.90 M_b^{0.88 ± 0.26
(± 95%CI)}, whereas
postnatal heart mass increased according to
10.0 M_b^{0.88 ± 0.10}.
While the fetal and postnatal scaling exponents are identical
(0.88) and reveal a clear dependence of heart mass on body mass,
only the postnatal exponent is significantly less than 1.0,
indicating the postnatal heart becomes a smaller component of body
mass as the body grows, which is a pattern found frequently with
postnatal cardiac development among mammals. The rapid doubling in
heart mass around the time of birth is independent of any increase
in body mass and is consistent with the normalization of wall
stress in response to abrupt changes in volume loading and pressure
loading at parturition. We discuss variation in scaling patterns of
heart mass across development among mammals, and suggest that the
variation results from a complex interplay between hard‐wired
genetics and epigenetic influences.