Luteolysis Following Carotid or Ovarian Arterial Injection of Prostaglandin F2α in Mares

Abstract

On the day of ovulation (Day 0), 20 pony mares were randomly assigned to one of five groups (4 mares/group) which were given intracarotid arterial (ICA) and intraovarian arterial (IOA) injections on Day 7 as follows: 1) vehicle ICA, vehicle lOA (control); 2) .125 mg PGF20 ICA, vehicle IOA; 3) vehicle ICA, .125 mg PGF20 lOA; 4) .250 mg PGF20 ICA, vehicle lOA; or 5) vehicle ICA, .250 mg PGF20 lOA. Peripheral plasma progesterone and LH concentrations were determined for 0 (pretreatment) and .1, .25, .50, .75, 1, 6, 12, 24, 48, 72 and 96 h posttreatment. The intervals (days) from treatment to cstlus and ovulation, respectively, were shorter (P<0.05) for mares given IOA injection of .125 mg PGF20 (4.7, 12.8), ICA injection of .250 mg PGF20 (6.5, 14.8), or IOA injection of .250 mg PGF20 (2.8, 11.2), than for controls (11.8, 19.5). The intervals for mares given ICA injection of .125 mg PGF20 (9.2, 18.5) did not differ from controls. Compared to pretreatment samples (0 h), progesterone concentration did not change significantly throughout the blood sampling period in mares given ICA injection of .125 mg PGF20; however, a significant reduction in progesterone concentration occurred by 24 h after treatment in mares given IOA injection of .125 mg PGF20. Plasma LH concentration (ng/ml) was higher (P<0.05) at 12 h (3.4) than at 0 h for the .250 mg IOA group (0.8), but did not change significantly in the other groups. The correlation between progesterone and LH was significant for mares which were given .125 mg IOA (r=-.65) and .250 mg IOA (r=-.82). The IOA injection of PGF20 was more effective in causing luteolysis than ICA injection of PGF2 �. These data indicate that the principal site of luteolytic action of exogenous PGF20 in the mare is at the ovarian rather than at the hypothalamic-pituitary level.