What question did this study set out to answer?

This research aims to compare the effects of three different drug administration methods on baroreflex sensitivity in conscious rats.

March 1, 1999Brazilian Journal of Medical and Biological Research54 citationsOpen Access

Comparison of three methods for the determination of baroreflex sensitivity in conscious rats

VFVera FarahUniversidade Presbiteriana Mackenzie EMEdson Duarte MoreiraFundação de Amparo à Pesquisa do Estado da Bahia MPMara Dias PiresUniversidade de São Paulo

Key Points

This research aims to compare the effects of three different drug administration methods on baroreflex sensitivity in conscious rats.
Vasoactive drugs were administered using bolus injection, steady-state, and ramp infusion methods.
Heart rate responses were measured and evaluated using mean index, linear regression, and logistic methods.
Experiments were carried out on three consecutive days to ensure consistency.
Bradycardic responses measured by mean index were similar across all administration approaches (-1.5, -2.1, -1.6 bpm/mmHg).
Tachycardic responses assessed by linear regression also showed similarity (-3.9, -2.1, -3.8 bpm/mmHg).
The steady-state method yielded a significantly higher tachycardic mean index (-6.6 bpm/mmHg) compared to other methods.

Abstract

Baroreflex sensitivity was studied in the same group of conscious rats using vasoactive drugs (phenylephrine and sodium nitroprusside) administered by three different approaches: 1) bolus injection, 2) steady-state (blood pressure (BP) changes produced in steps), 3) ramp infusion (30 s, brief infusion). The heart rate (HR) responses were evaluated by the mean index (mean ratio of all HR changes and mean arterial pressure (MAP) changes), by linear regression and by the logistic method (maximum gain of the sigmoid curve by a logistic function). The experiments were performed on three consecutive days. Basal MAP and resting HR were similar on all days of the study. Bradycardic responses evaluated by the mean index (-1.5 +/- 0.2, -2.1 +/- 0.2 and -1.6 +/- 0.2 bpm/mmHg) and linear regression (-1.8 +/- 0.3, -1.4 +/- 0.3 and -1.7 +/- 0.2 bpm/mmHg) were similar for all three approaches used to change blood pressure. The tachycardic responses to decreases of MAP were similar when evaluated by linear regression (-3.9 +/- 0.8, -2.1 +/- 0.7 and -3.8 +/- 0.4 bpm/mmHg). However, the tachycardic mean index (-3.1 +/- 0.4, -6.6 +/- 1 and -3.6 +/- 0.5 bpm/mmHg) was higher when assessed by the steady-state method. The average gain evaluated by logistic function (-3.5 +/- 0.6, -7.6 +/- 1.3 and -3.8 +/- 0.4 bpm/mmHg) was similar to the reflex tachycardic values, but different from the bradycardic values. Since different ways to change BP may alter the afferent baroreceptor function, the MAP changes obtained during short periods of time (up to 30 s: bolus and ramp infusion) are more appropriate to prevent the acute resetting. Assessment of the baroreflex sensitivity by mean index and linear regression permits a separate analysis of gain for reflex bradycardia and reflex tachycardia. Although two values of baroreflex sensitivity cannot be evaluated by a single symmetric logistic function, this method has the advantage of better comparing the baroreflex sensitivity of animals with different basal blood pressures.

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