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The focus of our investigations are periodic fluctuations in the blood pressure (BP) curve in combination with instantaneous heart rate (IHR) changes in chick embryos from the 12th day of incubation (D12) until hatching on day 21 (D21).
The blood pressure was measured by direct punctuation of the allantoic artery in 134 embryos. The IHR was calculated from the beat to beat interval of the blood pressure curve. The peripheral blood supply was recorded with a LASER BLOODFLOW MONITOR (MBF3 Moor Instruments, England) in a second series of experiments. The fertile eggs were continuously turned during incubation at a temperature of 37,5°C and a humidity of 60 %.
The diastolic and systolic blood pressure increased continuously from the beginning of our investigations starting on D12 until hatching. The IHR started to fluctuate around D14 of incubation which increased with the development of the embryo. On D12 of incubation when our measurements started the BP showed a relatively constant period with a PEAK every 20sec in almost all the embryos until about D17/D18 of incubation. Regular and irregular fluctuations started to appear in the further development of the embryo. A second series of measurements was made after having seen these PEAKs in the blood pressure. We detected the peripheral blood supply in the chorioallantoic artery on these 20sec PEAKs by using a laser probe.
From our data it can be concluded that not only IHR also BP fluctuations develop in chick embryos during ontogeny. During the ontogenetic development of the chick embryo rhythmic and arrhythmic IHR and BD changes appear. BP alterations are mostly caused by HR alterations; in addition HR independent rhythmic blood pressure patterns appear. These findings suggest a possible development of a functional autonomic innervation of the peripheral limb of the cardiovascular system prenatally. The distinct 20 sec Peak in nearly all embryos starting to appear on D12 until D17/D18 might be caused by a simple hemodynamic mechanism and most likely do not involve higher nervous control, but the Frank-Starling mechanism should be considered. After D17/ D18 the functional parasympathetic system overtakes this 20 sec rhythm and protects the organism against noxes from outside the egg. The development of fluctuations in the cardiovascular system is an important mechanism to compensate environmental stress especially before the onset of a functional autonomic innervation. The reason is that a non static system is able to react much faster than a static one in the process of keeping an organism in its hemodynamic situation.