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Role of Adrenergic Receptors in Mediating Estradiol-17β- Stimulated Increases in Uterine Blood Flow of Cows^{1 ,2,}

Iowa State University, Ames 50011

Abstract

This study was conducted to investigate the association between estradiol-17β (E₂β) and periarterial and β-adrenergic receptors in altering blood flow to the bovine uterus. Three nonpregnant Hereford cows were ovariecto-mized, and an electromagnetic blood flow transducer was placed around the middle uterine artery supplying one uterine horn. A catheter was then placed into a branch of the same artery for infusion of drugs or vehicle. Beginning 3 wk after sugery, uterine blood flow (UBF) of each cow was recorded for 5 min at 20-min intervals throughout a 160-min period three times weeksly for 6 wk. Vehicle (.9% NaCl), phentolamine (PHEN, 1 or 10 µg) or propranolol (PROP, 1 or 10 µg) was infused for 5 min beginning 20 min after the initial UBF measurements, while vehicle or E₂β (1 µg) was infused for 5 min beginning at 40 min. Within a week, the first and third 160-min periods contained the same treatment (vehicle or E₂β), and the second period consisted of vehicle or E₂β plus PHEN or PROP, allowing for direct comparison of periods 1 and 3 with period 2. Twenty minutes after infusion of E₂β, UBF was elevated (26.8 ± 5.4 ml/min; P<.05) over baseline, reaching a maximal increase at 40 min before starting to decline by 120 min. Uterine blood flow increased (39.2 ± 7.6 ml/min; P<.01) during the 5-min infusion of PHEN, and thereafter the magnitude and pattern were similar to those resulting from E₂β treatment. The increase in UBF after E₂β or PHEN was not additive when both were infused during the same treatment period. Propranolol (10 µg) delayed and attenuated (P<.05) the UBF response to E₂β. The response of UBF to E₂β decreased (P<.05) as the length of time from ovariectomy increased. These data suggest a role for and β-adrenergic receptors in the UBF increase elicited by E₂β.

¹ These data were presented, in part, at the 73rd Annu. Meet, of the Amer. Soc. of Anim. Sci. (1981), Raleigh, NC. Journal paper No. J-10678 of the Iowa Agr. and Home Econ. Exp. Sta., Ames; Projects 1994, 2443 and 2444.

² Appreciation is expressed to William McDonald, Kevin Petersburg and Ann Faylor for help with data collection and technical guidance.

³ Dept. of Anim. Sci.

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