AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 6 1526-R1532, Copyright © 1989 by American Physiological Society
Bladder contractions and micturition in fetal sheep: their relation to behavioral states
M. E. Wlodek, G. D. Thorburn and R. Harding
Department of Physiology, Monash University, Melbourne, Australia.
Fetal bladder contractions, indicative of micturition (voiding), and
behavioral states were monitored in unanesthetized fetal sheep in utero
during the last third of gestation. Fetal voids began during low-voltage
electrocortical activity (LV ECoG) at a greater frequency (91.4 +/- 1.0%)
than expected (57.2%) and began during high-voltage electrocortical
activity (HV ECoG) with a lower frequency (8.7 +/- 1.0%) than expected
(42.8%). Fetal voids began significantly sooner after the onset of LV ECoG
(5.84 +/- 0.13 min) than after the onset of HV ECoG (10.88 +/- 0.04 min).
Electroocular and nuchal muscle activities were associated with 96.2 and
66.0% of the voids, respectively, but there was no significant association
between fetal voiding and swallowing episodes. Abolition of spontaneous
voiding, by urine drainage (24 h), caused no significant differences,
relative to a 24-h control period, in the duration or number of episodes of
LV or HV ECoG or percentage of time spent in these states. Also, induction
of voiding by infusing saline into the bladder did not significantly alter
the time to the next change of ECoG state. However, the mean time to the
next void and the mean volume of saline infused into the bladder to induce
voiding tended to be less during LV ECoG than HV ECoG, although not
significantly less. Our data show that most spontaneous voids in the fetus
begin during LV ECoG, suggesting that voiding is regulated by descending
information from the brain. Furthermore, these experiments demonstrate that
fetal bladder contractions and voiding, either spontaneous or induced, do
not influence the normal cycling of fetal ECoG states.
