In vitro Response of Ovine and Bovine Uterine Arteries to Prostaglandin F2α and Periarterial Sympathetic Nerve Stimulation1

Abstract

Experiments were conducted to study the in vitro responses of bovine and ovine uterine arterial smooth muscle to prostaglandin F2o and periarterial sympathetic nerve stimulation. Five nonpregnant and five pregnant beef heifers and ten nonpregnant and five pregnant unilaterally-ovulating ewes were utilized. Heifers and ewes were necropsied on Days 17 and 15 after detected estrus, respectively. A 3.5 cm segment of the uterine artery supplying each uterine horn was removed immediately proximal to its first bifurcation in the mesometrium. Oxygenated Krebs at 37#{176}C was perfused into the arterial segments mounted in duplicate perfusion chambers at a rate of 17 and 10 mI/mm for arterial segments from heifers and ewes, respectively. Changes in perfusion pressure due to changes in resistance to flow through the arterial segment were recorded in mm Hg. Saline, prostaglandin F2o-tromethamine salt (PGF2co, 1 ng/ml final concentration) and saline, in that order, were each perfused for 30 mm into the perfusion cannulae at a rate of 0.07 mI/mm. Arteries from five nonpregnant ewes also received a perfusion of conceptus brei in uterine flushin�, prepared from Day 15 pregnant ewes, for 30 mm prior to the PGF2a perfusion. During each 30-mm perfusion, periarterial sympathetic nerves were subjected to sequential electrical stimulations (SES) which were applied at 10-mm intervals and the resultant vascular smooth muscle contractions recorded. Baseline perfusion pressure, recorded for each arterial segment following a 30-mm initial equilibration, was higher (P<0.01) for arteries ipsilateral to ovaries bearing corpora lutes (CL) in heifers and ewes. Overall responsiveness to SES of arteries ipsilateral to ovaries bearing CL from both species was greater (P<0.01) than for arteries from the contralateral side only in nonpregnant animals. Arteries from nonpregnant heifers perfused with PGF2o exhibited greater (P<0.01) smooth muscle contractility in response to SES than when arteries were perfused with saline. Similarly, arteries from nonpregnant ewes responded to SES during PGF2s perfusion with increased contractility when compared to arterial responses to SES during saline control perfusions; however, only the increase in responsiveness of arteries contralateral to ovaries bearing CL was significant (P<0.05). Perfusion of arteries from pregnant animals with PGF2s resulted in no change in arterial responsiveness (heifers) or a decrease (P<0.05) in arterial responsiveness (ewes) to SES when compared to responses during respective saline control perfusions before and after PGF2O. Perfusion of conceptus brei in uterine fiushings for 30 minutes, although having no effect on arterial responsiveness to SES alone, caused a pronounced decrease (P<0.01) in responsiveness of arteries to SES during a subsequent perfusion of PGF2s.