Abstract
We examined the effect of prostaglandin (PG) E2 on the secretory function of equine corpus luteum (CL), according to the application site: intra-CL injection vs. an intrauterine (intra-U) administration. Moreover, the effect of intra-CL injection vs. intra-U administration of both luteotropic factors: PGE2 and human chorionic gonadotropin (hCG) as a positive control, on CL function was additionally compared. Mares were assigned to the groups (n = 6 per group): (1) an intra-CL saline injection (control); (2) an intra-CL injection of PGE2 (5 mg/ml); (3) an intra-CL injection of hCG (1,500 IU/ml); (4) an intra-U saline administration (control); (5) an intra-U administration of PGE2 (5 mg/5 ml); (6) an intra-U administration of hCG (1,500 IU/5 ml). Progesterone (P4) and PGE2 concentrations were measured in blood plasma samples collected at −2, −1, and 0 (pre-treatment), and at 1, 2, 3, 4, 6, 8, 10, 12, and 24 h after treatments. Moreover, effects of different doses of PGE2 application on the concentration of total PGF2α (PGF2α and its main metabolite 13,14-dihydro-15-keto-prostaglandin F2α– PGFM) was determined. The time point of PGE2, hCG, or saline administration was defined as hour “0” of the experiment. An intra-CL injection of PGE2 increased P4 and PGE2 concentrations between 3 and 4 h or at 3 and 12 h, respectively (p < 0.05). While intra-U administration of PGE2 elevated P4 concentrations between 8 and 24 h, PGE2 was upregulated at 1 h and between 3 and 4 h (p < 0.05). An intra-CL injection of hCG increased P4 concentrations at 1, 6, and 12 h (p < 0.05), while its intra-U administration enhanced P4 and PGE2 concentrations between 1 and 12 h or at 3 h and between 6 and 10 h, respectively (p < 0.05). An application of PGE2, dependently on the dose, supports equine CL function, regardless of the application site, consequently leading to differences in both P4 and PGE2 concentrations in blood plasma.
Highlights
Corpus luteum (CL) is critical for reproductive cyclicity and pregnancy maintenance, which depends on the supportive action of progesterone (P4) secreted by this transient endocrine gland [1–3]
Only one intra-U administration of PGE2 at the dose of 5 mg/5 ml increased the total amount of P4 concentrations in blood plasma, compared with the control group (p < 0.05; Table 1)
An increase in P4 concentrations in blood plasma was observed at 2 h and between 4 h and 6 h after intra-U administration of PGE2 at the dose of 1 mg/5 ml, compared with the control group (p < 0.05; Figure 2A), while intra-U administration of PGE2 at the dose of 20 mg/5 ml decreased its concentrations at 6 h compared with the pre-treatment time, and at 8 h, compared with the control group (p < 0.05; Figure 2A)
Summary
Corpus luteum (CL) is critical for reproductive cyclicity and pregnancy maintenance, which depends on the supportive action of progesterone (P4) secreted by this transient endocrine gland [1–3]. The lifespan of CL is controlled by numerous regulatory factors with luteotropic and luteolytic effects [4] such as cytokines, growth factors, P4, 17β-estradiol (E2), luteinizing hormone (LH), prostaglandin (PG) E2, and PGF2α, respectively [5–7]. Some of these factors are widely applied in veterinary practice for estrus synchronization. Application of PGE2 or LH analogs (human chorionic gonadotropin; hCG and equine chorionic gonadotropin; eCG) are key areas of veterinarian interests in the control of equine reproduction. The interesting issues in the veterinary practice are different models of drug administration have been investigated in farm animals [5, 8, 9]
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