Effect of Long-term Hypoxia on Myometrial Contractility in the Pregnant Sheep

<p>Previous research from our laboratory has shown that myometrial contractility is reduced in pregnant sheep exposed to long-term hypoxia (LTH). The studies in this dissertation examined the effect of LTH on various aspects of Ca² regulation, large-conductance, Ca²⁺activated (BK) channels activity and protein expression, and cGMP-depended protein kinase (PKG) activity. Myometrium was collected from near-term pregnant sheep exposed to high altitude-associated LTH and from normoxic pregnant controls. After pretreatment with 10^-8 M oxytocin (OT), circular and longitudinal myometrial strips were treated with nifedipine (L-type Ca²⁺ channel blocker), ruthenium red, ryanodine (blockers of IPssensitive stores), 2-Nitro-4-carboxyphenyI-N,N-diphenyIcarbamate (NCDC; phospholipase C inhibitor), tetraethylammonium (TEA; nonspecific K⁺channel inhibitor), iberiotoxin (IbTX; specific blocker of BK channels), or KT-5823 (PKG inhibitor). Western blots were also conducted for BKa and BKp subunit protein. LTH increased the maximum relaxation response to nifedipine whereas no significant differences were observed in response to ruthenium red or lyanodine. The maximum relaxation response to NCDC was lower in the LTH circular layer. No significant differences in response to TEA were found; however, the maximum tension response to IbTX in the LTH group was significantly increased. Western blot analysis revealed two P1 subunit bands (38 and 48 kDa), but did not show any significant differences between treatment groups or layers. However, the BK P:a subunit ratio (using either the 48 kDa P band only or combined with the 38 kDa P band) showed a significant decrease in the circular layer after exposure to LTH. After treatment with KT-5823, the contractility of LTH tissue significantly decreased in both layers. We conclude that LTH decreases reliance on IPs-associated Ca²⁺ stores and increases dependence upon Ca²⁺ entry through L-type Ca²⁺ channels. The contribution of SR Ca²⁺ is negligible. In addition, BK channel activity is enhanced following LTH, possibly mediated by a decreased P:a subunit ratio. Finally, PKG inhibitory activity may be suppressed in LTH myometrium with a possible switch to stimulatory in the circular muscle. </p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physiology

Year

2008

Author dc:creator

• Arakawa, Timothy Kimo

Contributors dc:contributor

• Charles Ducsay
• Raymond Gilbert
• David Hessinger
• Steven Yellon
• Lubo Zhang

• Physiology
• Fetal Hypoxia -- physiology; Myometrium -- physiology; Parturition -- physiology; Uterine Contraction; Labor -- physiology; Pregnancy, Animal Sheep

Statement dc:rights

• This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Language dc:language

English

Repository record dc:identifier

https://scholarsrepository.llu.edu/etd/1133

OAI identifier oai:identifier

oai:scholarsrepository.llu.edu:etd-2662