Objectives
The goal of this study is to investigate the role of sex and age of the negative chronotropic effect after exposure of 3.5-MHz pulsed ultrasound (US) to the rat heart.
Methods
Forty F344 rats were exposed transthoracically to ultrasonic pulses at a duty factor of ~1.0% at 2.0-MPa peak rarefactional pressure amplitude (PRPA). The transthoracic ultrasonic bursts were delivered consecutively in five 10-s intervals, that is, 10 s of 6-Hz pulse repetition frequency (PRF), 10 s of 5-Hz PRF, 10 s of 4-Hz PRF, 10 s of 5-Hz PRF and 10 s of 6-Hz, for a 50-s total exposure duration. The rats were divided into eight groups (n=5 ea) animals: US young male, Control young male, US young female, Control young female, US old male, Control old male, US old female and Control old female.
Results
Two-way ANOVA for repeated measures was used to compare heart rate, cardiac output, arterial pressure and other hemodynamic values (baseline) before and after ultrasound stimulation. Sex vs. age vs. US interaction was detected for heart rate. Cardiac output showed an age effect and ejection fraction showed age and US effects. The arterial pressure showed a sex effect. A negative chronotropic effect (~30% decrease in heart rate) was observed for young female rats. A hypothesis is that the US effect is weight (menopause)-dependent, because the young (premenopause) female rats weighed ~40–60% less than other groups of rats.
Conclusion
It is likely that the ovarian hormones are responsible for different ultrasound-induced cardiac bioeffects in differents ages and sexes.