Effect of stimulatory and inhibitory drugs on uterine electrical activity measured noninvasively from the abdominal surface of pregnant rats.
OBJECTIVE
Our purposes were (1) to identify and analyze parameters of uterine electrical activity that change during active term and preterm labor in response to stimulatory (oxytocin) or inhibitory (terbutaline) agents and (2) to correlate the information obtained from abdominal surface measurement of electrical activity with intrauterine pressure and with the electrical activity measured directly from the uterine surface in vivo.


METHODS
Electromyographic activity was acquired simultaneously from the uterine wall and the abdominal surface by means of unipolar electrodes. Electromyographic activity was recorded in the 0.3 to 50-Hz range and digitized at 200 samples per second. Intrauterine pressure was measured via an intrauterine catheter. The effect of cumulative doses of oxytocin and terbutaline on power density spectrum, amplitude, number and duration of electromyographic bursts, and intrauterine pressure was recorded in anesthetized rats during spontaneous active term labor (n = 7) and induced preterm labor (n = 6).


RESULTS
Bursts of electromyographic activity recorded from the abdominal surface mirrored those from the uterine wall, albeit at a lower amplitude. During active term labor, lower concentrations of oxytocin did not significantly affect power-density-spectrum energy, amplitude, or number of bursts per unit time. The duration of electromyographic bursts increased dose dependently. Myometrial contractions were phasic, with return to the baseline between phases. As the concentration of oxytocin increased, the energy, amplitude, and number of bursts per unit time declined while the intrauterine pressure continued to rise until the contraction became tetanic, without return to the baseline. In rats with induced preterm labor, terbutaline inhibited uterine contractility by decreasing the intrauterine pressure. This was accompanied by a progressive decrease in the power density spectrum, amplitude, number, and duration of the uterine wall and abdominal surface electrical bursts.


CONCLUSIONS
First, uterine electromyographic activity measured noninvasively from the abdominal surface reflects changes in uterine electrical activity and intrauterine pressure measured directly and invasively in term and preterm labor, as well as during treatments to stimulate or inhibit labor. Second, this noninvasive method may be useful in monitoring uterine activity in vivo. Third, clinical studies to evaluate this technology in human subjects are warranted.
Buhimschi
C S
CS
Department of Obstetrics and Gynecology, Division of Reproductive Sciences, The University of Texas Medical Branch, Galveston 77555- 1062, USA.
Saade
G R
GR
Buhimschi
I A
IA
Gokdeniz
R
R
Boyle
M B
MB
Garfield
R E
RE
D000005:Abdomen; D000200:Action Potentials; D000818:Animals; D004576:Electromyography; D005260:Female; D005583:Fourier Analysis; D006067:Gonanes; D007743:Labor, Obstetric / Q000502:physiology*; D007752:Obstetric Labor, Premature / Q000139:chemically induced / Q000503:physiopathology*; D010121:Oxytocin / Q000008:administration & dosage / Q000494:pharmacology; D011247:Pregnancy; D011312:Pressure; D051381:Rats; D013726:Terbutaline / Q000494:pharmacology; D015149:Tocolytic Agents / Q000494:pharmacology; D014590:Uterine Contraction / Q000187:drug effects / Q000502:physiology; D014599:Uterus / Q000503:physiopathology*
D006067:Gonanes; D015149:Tocolytic Agents; D010121:Oxytocin; C053238:onapristone; D013726:Terbutaline