Fetal development of baroreflex sensitivity: the chicken embryo as a case model

The baroreflex is the main short term compensatory mechanism to buffer blood pressure changes and maintain circulatory homeostasis. Its ontogeny and importance during prenatal life is not fully understood so we used broiler chickens to investigate the maturation of the baroreflex in late incubation using a novel method that measured changes in heart rate during spontaneous fluctuations in blood pressure. Our results suggest that a baroreflex is already functional at d17 with no indication of further maturation in terms of sensitivity (gain at 17 d was 52.9±8.3 and at 20 d 69.5±16.2 ms kPa(-1)). The physiological relevance of these values is shown using data surrogation methods. Although the results contrast with the progressive baroreflex maturation indicated by the pharmacological method, we sustain that both methods provide information on baroreflex regulation. While the spontaneous method evaluates truly physiological (but small) pressure changes, the pharmacological method provides a more consistent and repetitive challenge for the reflex that requires a different recruitment of baroreflex effectors.