The effect of oxytocin on contractile responses and ⁴⁵Ca movements in rat isolated aortic strips

Abstract

1 The effects of oxytocin (Oxt) on contractile responses and transmembrane Ca fluxes were studied in rat isolated aortic strips.2 Oxt (50-1000 mu ml ') induced a dose-dependentcontractile response and spontaneous myogenic activity. 3 The Oxt-induced contractile response was not inhibited by pretreatment of aortic strips with phentolamine plus practolol, atropine, diphenhydramine plus cimetidine or indomethacin, but was significantly reduced by verapamil or deamino-ethyl-Oxt. 4 The dose-response curve for Oxt was shifted upwards and to the left by increasing the Ca concentration of the medium from 1.8 to 4mM. 5 Oxt also shifted upwards the dose-response curve to Ca (I to 5 mM) in aortic strips incubated in K depolarizing Ca-free media. 6 Oxt increased the La3+-resistant 45Ca content without altering 45Ca efflux. 7 The present results suggest that in rat isolated aortic strips Oxt produces a contractile response which, as previously found with other neurotransmitters, can be partly attributed to an increase of Ca influx through receptor-operated channels and to the release of Ca from intracellular stores.

Effects of propafenone on 45Ca movements and contractile responses in vascular smooth muscle

“…After excess of fat and connective tissue were removed, the aortae were cut into helical strips of about 2.0mm width and 20mm in length. Aortic strips and vein segments were mounted vertically under 1 g of tension in organ baths containing 25 ml of KS as previously described (Barrigon & Tamargo, 1986). The tissue bath was maintained at 34°C and bubbled with 95% 02-5% CO2 gas mixture.…”

“…The strips were then placed in scintillation vials and 0.5 ml of Protosol (Dupont) added and the strips digested overnight at 60°C. Radioactivity was assayed in a liquid scintillation counter (LKB Wallac 1211 Rack) as previously described (Barrigon & Tamargo, 1986 At concentrations between 10-7M and 10-4M, propafenone had no effect on base-line tension in aortic strips. However, at this range of concentrations propafenone inhibited the amplitude but not the frequency of the spontaneous myogenic activity in portal veins.…”

Effects of flecainide on isolated vascular smooth muscles of rat

“…The 45Ca uptake was estimated by measurement of the changes in specific activity of the calcium fraction resistant to displacement by lanthanum as previously described by Godfraind (1983) and Barrigon & Tamargo (1986). Aortic rings were equilibrated in KS of the following composition (mM): NaCl 122, KCl 5, NaHCO3 25, CaCl2 1.25, MgSO4 1.2 and glucose 11.5.…”

“…The rings were then placed in scintillation vials and 0.5 ml of Protosol (Dupont) added; the rings were digested overnight at 60°C. Radioactivity was assayed in a liquid scintillation counter (LKB Wallac 1211 Rack) as previously described (Barrigon & Tamargo, 1986). …”

In vitro effects of oxytocin, acepromazine, detomidine, xylazine, butorphanol, terbutaline, isoproterenol, and dantrolene on smooth and skeletal muscles of the equine esophagus

“…16 This effect may be due to an increase in calcium influx through receptor-operated channels and release of intracellular calcium. 17 Oxytocin also causes contraction of the aorta, basilar arteries, and cremaster muscle of rats; carotid arteries of dogs; and urinary bladder of rabbits. [17][18][19][20][21] However, oxytocin also causes vasodilatation in pulmonary vasculature of rats and cerebral arteries in dogs and rats.…”