AJP - Renal Physiology, Vol 254, Issue 1 25-F31, Copyright © 1988 by American Physiological Society
Ovine fetal urachus--physiological and hormonal control of its contractile activity
S. J. Lye, C. L. Freitag and J. R. Challis
Department of Obstetrics and Gynaecology, University of Western Ontario, Canada.
We have investigated whether the ovine fetal urachus near term has the
potential to regulate the passage of urine from the bladder into the
allantoic cavity. Experiments were performed primarily on longitudinal
urachal muscle. In Krebs bicarbonate buffer (pH 7.4 bubbled with 95% O2-5%
CO2 at 37 degrees C) the urachus spontaneously developed a prolonged
elevated resting tension (RT, 1.1-1.5 g). Intra-abdominal urachus showed a
greater development of tension than extra-abdominal urachus, which was
associated with the amount of smooth muscle observed in histological
specimens. Isoproterenol (1 microM) produced a significant reversible
reduction in RT (1.36 +/- 0.15 to 0.67 +/- 0.08 g, P less than 0.01, mean
+/- SE). Replacement of normal-O2 buffer (PO2 420.4 +/- 19.5 mmHg) with a
low-O2 buffer (PO2 101.3 +/- 4.7 mmHg), or very low-O2 buffer (PO2 38.2 +/-
2.2 mmHg) while maintaining PCO2 and pH constant, produced a reduction in
RT (from 1.35 +/- 0.21 to 0.52 +/- 0.13 g and from 1.20 +/- 0.17 to 0.46
+/- 0.04 g, respectively; both P less than 0.01). This effect was reversed
when high PO2 was reinstated. Circular muscle showed a similar response
when PO2 was reduced. The urachus showed a significant increase in RT (0.74
+/- 0.08 to 1.71 +/- 0.28 g, P less than 0.01) when prostaglandin F2 alpha
(PGF2 alpha; 10 microM) was added to the low-O2 buffer. These results
demonstrate that the urachus can develop spontaneous contractile activity
and responds to alterations in O2, a beta-agonist, and PGF2 alpha.(ABSTRACT
TRUNCATED AT 250 WORDS)
