Changing adrenergic sensitivity of the caruncular arterial vasculature supplying the bovine placentome.
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 directly 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 beta-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 less than .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 the UA, ICA or CA between mid-pregnant or late pregnant cows. Alpha 1-AR numbers were similar in CA, ICA and UA. However, CA contained threefold greater alpha 2-AR numbers than either the ICA or UA (50.2 +/- 6.1 vs 14.6 +/- 1.6 and 14.8 +/- 2.4 fmol/mg protein, respectively; P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)
Sauer
J J
JJ
Dept. of Anim. Sci., Iowa State University, Ames 50011.
Van Orden
D E
DE
Farley
D B
DB
Ford
S P
SP
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000187:drug effects; D001783:Blood Flow Velocity / Q000187:drug effects / Q000662:veterinary; D002417:Cattle / Q000502:physiology*; D005260:Female; D010920:Placenta / Q000098:blood supply*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology*; D013997:Time Factors
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011433:Propranolol