Maturation of cardiovascular control mechanisms in the embryonic emu(Dromiceius novaehollandiae)

Abstract

SUMMARY Our understanding of avian embryonic cardiovascular regulation has been based on studies in chickens. The present study was undertaken to determine if the patterns established in chickens are generally applicable to the emu, a ratite bird species. We studied cardiovascular physiology over the interval from 60% to 90% of the emu's 50-day incubation period. During this period,embryonic emus exhibit a slight fall in resting heart rate (from 171 beats min-1 to 154 beats min-1) and a doubling of mean arterial pressure (from 1.2 kPa to 2.6 kPa). Exposures to 15% or 10%O2 initially decreased heart rate during the first period of emu incubation studied [60% of incubation (60%I)] but increased heart rate in the 90%I group. Arterial pressure responded to hypoxia with an initial depression(-1.6 kPa) at 60%I and 70%I but showed no response during the later periods of incubation (80%I and 90%I). In addition, tonic stimulation of both cholinergic and adrenergic (α and β) receptors was present on heart rate at 70%I, with the cholinergic and β-adrenergic tone increasing in strength by 90%I. Arterial pressure was dependent on a constant β-adrenergic and constant α-adrenergic tone from 60%I to 90%I. A comparison with embryonic white leghorn chickens over a similar window of incubation revealed that emus and white leghorn chickens both possess an adrenergic tone on heart rate and pressure but that only emus possess a cholinergic tone on heart rate. Collectively, these data indicate that the maturation of cardiovascular control systems differs between white leghorn chickens and emus, inviting investigation of additional avian species to determine other patterns.

Temperature-dependent sex determination modulates cardiovascular maturation in embryonic snapping turtles, Chelydra serpentina

“…The β-adrenergic receptor tone we observed in snapping turtle embryos in this study is generally similar to that documented in other egg-laying amniotic vertebrates, although the changes in intensity are species-specific (Crossley et al, 2003a;Crossley and Altimiras, 2005;Lindgren et al, 2011). The American alligator, emu and chicken all exhibit an increase in P m following β-adrenergic receptor blockade, indicating a β-adrenergic depressor tone during the last third of embryogenesis (Eme et al, 2011a;Crossley et al, 2003a;Crossley and Altimiras, 2000). However, the snapping turtle is unique in that the P m response is absent at 90% of embryonic development.…”

“…The decrease in f H for embryonic snapping turtles during this span of incubation is similar to that documented in the emu (Crossley et al, 2003a) and the desert tortoise (Crossley and Burggren, 2009), but it differs from that in the American alligator (Crossley et al, 2003b;Crossley and Altimiras, 2005;Eme et al, 2011a;Eme et al, 2011b), the embryonic chicken Altimiras and Crossley, 2000) and the African brown house snake (Lamprophis fuliginosus) (Crossley and Burggren, 2009). Resting f H differed significantly (~9beatsmin -1 ) in male and female snapping turtles at 90% of incubation.…”

“…Data are presented as means ± s.e.m. agassizii) (Crossley and Burggren, 2009), the American alligator (Alligator mississippiensis) (Crossley et al, 2003b;Crossley and Altimiras, 2005;Eme et al, 2011a), the emu (Dromiceius novaehollandiae) (Crossley et al, 2003a) and the domestic chicken (Gallus gallus) . These findings suggest that an increase in blood pressure during ontogeny is a fundamental requirement for maintaining convective transport in embryos that are increasing in body mass.…”

Atmospheric oxygen level affects growth trajectory, cardiopulmonary allometry and metabolic rate in the American alligator (Alligator mississippiensis)

“…This effect has been demonstrated in internally pipped chicken embryos (Sbong and Dzialowski, 2007), which possess a cardiac shunt via the ductus arteriosus, analogous to the crocodilian cardiac shunt via the left aorta (Ewer, 1950). The similarity of cardiovascular control in embryonic birds and alligators (Crossley et al, 2003a;Crossley et al, 2003b;Crossley et al, 2003c) suggests that hyperoxia may inhibit shunting in alligators. As cardiac shunting can induce hypometabolism in reptiles (Hicks and Wang, 1999;Hicks, 2002), chronic inhibition of shunting due to atmospheric hyperoxia is likely to cause a hypermetabolic state in alligators.…”

The ontogeny of regulatory control of the rainbow trout (Oncorhynchus mykiss) heart and how this is influenced by chronic hypoxia exposure

“…To determine the receptor (adrenergic and cholinergic) tone on heart rate in chronic normoxia, embryos and larvae were serially incubated in autonomic receptor antagonists as described previously (Altimiras et al, 1997;Crossley et al, 2003a). Baseline heart rate was determined following a 30min control period.…”