J. Anim Sci.
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J. Anim Sci. 1989. 67:3003-3010.
© 1989 American Society of Animal Science
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Changing Adrenergic Sensitivity of the Caruncular Arterial Vasculature Supplying the Bovine Placentome1,2,

J. J. Sauer3, D. E. Van Orden4, D. B. Farley4 and S. P. Ford3,5,

Iowa State University, Ames 50011 and University of Iowa, Iowa City 52240

Abstract

With the advancement of gestation, blood flow increases preferentially to the caruncular bed of the gravid uterus in association with a decreasing sensitivity of the uterus to the vasoconstrictive effects of circulating catecholamines. This study direcdy compared the sensitivity of the caruncular artery (CA) of the isolated bovine placentome to phenylephrine (PE), a specific {alpha}1-adrenergic receptor (AR) agonist, with that to norepinephrine (NE) and epinephrine (E), both of which are {alpha}1-, {alpha}2- and ß-AR agonists, at two stages of gestation (140 to 170 d, mid-pregnant; 210 to 270 d, late pregnant). The CA of each placentome was perfused with oxygenated Krebs Ringer solution into which PE, NE or E were administered; increases in intra-arterial pressure were recorded. Further, NE content and numbers of {alpha}1- and {alpha}2-AR in the CA, intercaruncular arteries (ICA) and uterine arteries (UA) were quantitated. The CA from mid-pregnant cows exhibited greater (P < .05) contractile responses to NE and E than did the CA from late pregnant cows, whereas responsiveness to PE remained constant. No difference in NE content, {alpha}1-AR or {alpha}2-AR numbers were observed in die UA, ICA or CA between mid-pregnant or late pregnant cows. Alpha1-AR numbers were similar in CA, ICA and UA. However, CA contained threefold greater {alpha}2-AR numbers than eimer the ICA or UA (50.2 ±6.1 vs 14.6 ± 1.6 and 14.8 ± 2.4 fmol/mg protein, respectively; P < .01). Also, CA contained less NE (11.5 ± 2.3 pg/mg tissue wet wt) than the ICA (49.0 ± 5.0; P < .05) or the UA (176.5 ± 21.3; P < .01). These data are consistent with a preferential decrease in sympathetic neuronal control of the CA compared wim the ICA or UA and suggest a decreasing sensitivity of the CA to circulating catecholamines from mid- to late pregnancy.

Footnotes

1 Journal Paper J-13378 of the Iowa Agric. and Home Econ. Exp. Sta., Ames. Proj. 2443 and 2444, and supported in part by United States Public Health Service Grant HD06380.

2 The authors thank Alan Conley, Carole Hertz and Brent Hoehns for their technical expertise and Donna Johnston for typing this manuscript.

3 Dept. of Anim. Sci., Iowa State Univ.

4 Dept. of Obstet. and Gynecol., Univ. of Iowa.

5 Person to whom reprint requests should be addressed.






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Copyright © 1989 by the American Society of Animal Science.