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Nutrient control of cardiac rate in the infant rat: alpha-adrenergic mechanisms
Insights
Nutrient intake significantly impacts heart rate in young rats. Alpha-adrenergic blockade prevents heart rate drops in deprived pups, revealing its role in nutrient-mediated cardiac regulation.
Area of Science:
- Cardiovascular Physiology
- Neonatal Physiology
- Autonomic Nervous System Function
Background:
- Nutrient intake influences beta-adrenergic cardiac activity in young rats.
- The alpha-adrenergic system's role in neonatal cardiac regulation is not fully understood.
Purpose of the Study:
- To investigate the role of the alpha-adrenergic vasoconstrictor system in nutrient regulation of cardiac rate in 2-week-old suckling rats.
- To determine if alpha-adrenergic blockade affects heart rate responses to nutrient availability and deprivation.
Main Methods:
- Experiments involved administering phenoxybenzamine (PBZ), an alpha-adrenergic blocker, to suckling rat pups.
- Heart rates were monitored in well-fed and nutrient-deprived pups before and after PBZ administration.
- Blood pressure and plasma volume changes were assessed during nutrient deprivation and PBZ treatment.
Main Results:
- Alpha-adrenergic blockade with PBZ did not alter heart rates in well-fed pups.
- PBZ prevented the development of bradycardia (slow heart rate) after suckling cessation in deprived pups.
- PBZ dose-dependently reversed the low heart rates of nutrient-deprived pups, indicating a reliance on beta-adrenergic pathways.
Conclusions:
- The alpha-adrenergic vasoconstrictor system is functional by 2 weeks of age in rats.
- Peripheral resistance, modulated by the alpha-adrenergic system, plays a crucial role in nutrient-mediated cardiac rate regulation in suckling rats.
- This system is essential for maintaining appropriate heart rate responses to nutritional status in neonates.
Abstract:
Changes in level of nutrient intake have been shown to exert a major influence on beta-adrenergic cardiac activity in 2 week old suckling rats. A series of experiments demonstrates that the alpha-adrenergic vasoconstrictor system is functional by 2 weeks postnatal age, and that alpha-adrenergic blockade with phenoxybenzomine (PBZ) does not affect the high heart rates of well-fed pups but prevents development of the bradycardia after cessation of suckling and fully reverses the low heart rates of nutrient-deprived pups in a dose-dependent manner. This last effect is dependent upon beta-adrenergic reflex cardiac pathways. After PBZ, milk feeding no longer produces cardiac acceleration in nutrient-deprived pups. Systolic and mean arterial pressure during PBZ administration and estimates of plasma volume change during nutrient deprivation are consistent with the inference that changes in peripheral resistance, mediated by the alpha-adrenergic vasoconstrictor system, accompany nutrient regulation of cardiac rate in the suckling rat.