Effect of vaginal administration of prostaglandin E2 and/or 17beta-estradiol on luteal function and histological characteristics of the cervix in cyclic pigs.

The overall objective of this study was to examine the effect of vaginal administration of prostaglandin E2 (PGE2) and/or 17beta-estradiol (E2) on luteal function maintenance and histological properties of the porcine cervix. For this purpose, crossbred gilts were divided into three groups (n=5 per group) supplied on days 11-16 of the estrous cycle with suppositories containing: (1) placebo (Group I, Control); (2) 0.4 mg of E2 (Group II); (3) 0.4 mg of E2 and 2 mg of PGE2 (Group III). Blood samples were collected on days 11-19 of the estrous cycle to determine the concentration of progesterone (P4). Additionally, to examine local effects of the hormones applied, segments from the uterine and vaginal parts of the cervix and from the ovaries were collected post-mortem. Prolonged luteal function and extended synthesis of P4 were observed in 2 of 5 gilts receiving PGE2 and E2 simultaneously (Group III). Then, these gilts were subdivided into Group IIIA (n = 2; presence of corpora lutea on the ovaries) and Group IIIB (n = 3; lack of corpora lutea). Increased levels of plasma P4 were observed in Group IIIA on days 15-19 compared to Group IIIB and on days 16-19 compared to Group I and Group II (P < 0.05; P < 0.01; P < 0.001, respectively). In the cervix of gilts in Groups II and III, enlarged blood vessels in the lamina propria of both parts of the cervix were observed. Furthermore, in Group II the epithelium of the uterine part of the cervix was thicker (P < 0.001). Our study confirmed the proposed luteotrophic/antiluteolytic actions of E2 and PGE2 applied intravaginally. These results are significant considering that very low doses of E2 were used when compared to previous attempts. Despite the inadequate response to treatments in some of the gilts, the local effects of these hormones on the histological properties of the porcine cervix suggest that further improvements in the vaginal administration route might help to elaborate new methods for enhancing the luteal function in the pig.