Biology of Reproduction, Vol 14, 473-477, Copyright © 1976 by Society for the Study of Reproduction

Luteolysis Following Carotid or Ovarian Arterial Injection of Prostaglandin F₂ in Mares

¹ Department of Veterinary Science, University of Wisconsin, Madison, Wisconsin 53706

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 IOA (control); 2) .125 mg PGF₂ ICA, vehicle IOA; 3) vehicle ICA, .125 mg PGF₂ IOA; 4) .250 mg PGF₂ ICA, vehicle IOA; or 5) vehicle ICA, .250 mg PGF₂ IOA. 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 estrus and ovulation, respectively, were shorter (P<0.05) for mares given IOA injection of .125 mg PGF₂ (4.7, 12.8), ICA injection of .250 mg PGF₂ (6.5, 14.8), or IOA injection of .250 mg PGF₂ (2.8, 11.2), than for controls (11.8, 19.5). The intervals for mares given ICA injection of .125 mg PGF₂ (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 PGF₂; however, a significant reduction in progesterone concentration occurred by 24 h after treatment in mares given IOA injection of .125 mg PGF₂. 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 PGF₂ was more effective in causing luteolysis than ICA injection of PGF₂. These data indicate that the principal site of luteolytic action of exogenous PGF₂ in the mare is at the ovarian rather than at the hypothalamic-pituitary level.

Note:
ACKNOWLEDGMENTS Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison and by grant No. 630-0505BC from the Ford Foundation and grant No. 5-TO1-HD00104-10 from the National Institute of Health. Technical assistance was provided by T. Marotz and S. Dolphin. R. H. Douglas is a predoctoral trainee of the Endocrinology-Reproductive Physiology Program, University of Wisconsin, Madison. The PGF₂ was a gift from the Upjohn Company, Kalamazoo, Michigan.

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