Meeting Abstract
143.5 Monday, Jan. 7 Development of the cardiac and peripheral limbs of the baroreflex in embryonic chickens HEDRICK, MS*; CROSSLEY II, DA ; University of North Texas; University of North Texas michael.hedrick@unt.edu
The baroreflex is the primary short-term compensatory mechanism to buffer arterial pressure (Pa) changes and maintain cardiovascular homeostasis. Compensatory adjustments in mechanisms include both parasympathetic and sympathetic efferent activity acting on the heart (cardiac limb) as well as sympathetic efferents that modify vascular resistance and perfusion. Although the afferent and efferent limbs of the baroreflex are well-characterized in adult vertebrates, the developmental onset of function in most vertebrates is poorly characterized. Moreover, measurement of the baroreflex in fetal animals is normally limited to the cardiac limb of the reflex in response to changes in Pa. We sought to measure both cardiac and peripheral limbs of the baroreflex using fetal chickens as a model to examine the onset and development of the baroreflex. Fetal chickens were instrumented with chorioallantoic membrane (CAM) arterial catheters to measure Pa and heart rate (fH), Doppler flow probes to measure peripheral blood flow (femoral artery) and miniature bipolar electrodes to measure whole vagal (parasympathetic) nerve activity and peroneal (sympathetic) nerve activity. These measurements were made in day 18/19 (of 21 day development) in white leghorn embryos. Pa was altered using the Oxford method with drugs injected into the CAM artery to increase (Phenylephrine; Phe) or decrease (sodium nitroprusside; SNP) Pa. Injection of SNP resulted in reductions in Pa and vagal afferent activity and increased fH. Nerve activity in the peroneal nerve was associated with increases in Pa and fH, indicating an intact sympathetic limb of the baroreflex at day 18/19 of development. These are the first data to characterize the peripheral limbs of the baroreflex in a developing chicken and show that afferent and efferent components of the baroreflex are functional by day 18/19.
