Absence of uterokinetic effects of prostaglandin F 2 alpha on oxytocin-reactive uterus in the mare.
In most cyclic females, prostaglandin F(2 alpha) (PGF(2 alpha)) triggers a uterine motility response resembling that of oxytocin (OT). To determine if PGF(2 alpha) is a uterokinetic substance in the cycling mare, uterine motility was measured by intrauterine balloon technique in 12 conscious, normally cyclic mares. After 60 min of saline infusion, continuous intravenous (i.v.) infusion with OT (1 i.u./min) was followed by PGF(2 alpha) (200 microg/min) for 60 min each. The experiment was repeated 3 wk later except with PGF(2 alpha) preceding OT. A second group of mares was administered OT (60 i.u.) either i.v., intramuscularly (i.m.), or intrauterinely (i.u.). Plasma samples were studied for progesterone concentration. Control uterine motility for the first group of mares was (mean +/- SEM) 545.83 +/- 45.10 mm(2). Significant (P<0.05) elevation in uterine motility was recorded for OT (1118.60 +/- 70.56 mm(2)) regardless if PGF(2 alpha) preceded OT infusion or vice-versa. No significant difference (P>0.05) was seen in motility after PGF(2 alpha) (423.33 +/- 31.12 mm(2)) infusion. The uterokinetic effect of OT was greatest when OT was administered i.v. (1696.50 +/- 195.46 mm(2)) followed by i.m. (819.82 +/- 39.96 mm(2)), and it was least effective when administered i.u. (607.83 +/- 21.56 mm(2)) as compared to control uterine motility (279.78 +/- 22.33 mm(2)). Skin electrical resistance values rose from 0 to 2000 ohms with PGF(2 alpha) infusion (but not with OT), indicating that PGF(2 alpha) was bioactive. It was concluded that PGF(2 alpha) was not a uterokinetic substance in the cyclic mare.
Sharpe
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KL
Agricultural Experimental Station and College of Veterinary Medicine, The University of Tennessee, P.O. Box 1071, Knoxville, TN 37901, USA.
Eiler
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Hopkins
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FM