Effect of dose of estradiol-17β on prominence of an induced 13,14-dihydro-15-keto-PGF2α (PGFM) pulse and relationship of prominence to progesterone, LH, and luteal blood flow in heifers

Various doses of estradiol-17β (E2) were used in heifers to induce a pulse of 13,14-dihydro-15-keto-prostaglandin F2α (PGFM). The effect of E2 concentration on the prominence of PGFM pulses and the relationship between prominence and intrapulse concentration of progesterone (P4), LH, and luteal blood flow were studied. A single dose of 0 (vehicle), 0.01, 0.05, or 0.1 mg of E2 was given (n = six/group) 14 d after ovulation. Blood samples were collected, and luteal blood flow was evaluated hourly for 10 h after the treatment. The 0.05-mg dose increased and the 0.1-mg dose further increased the prominence of the induced PGFM pulse, compared with the 0.0-mg dose and the 0.01-mg dose. The PGFM pulses were subdivided into three different prominence categories (<50, 50 to 150, and >150 pg/mL at the peak). In the 50 to 150 category, P4 concentration increased (P < 0.05) between −2 h and 0 h (0 h = peak of PGFM pulse). In the >150 category, P4 decreased (P < 0.05) between −1 h and 0 h, LH increased (P < 0.05) at 1 h, and luteal blood flow apparently decreased (P < 0.05) at 2 h of the PGFM pulse. The novel results supported the following hypotheses: (1) an increase in E2 concentration increases the prominence of a PGFM pulse, and (2) greater prominence of a PGFM pulse is associated with a greater transient intrapulse depression of P4 at the peak of the PGFM pulse. In addition, the extent of the effect of prostaglandin F2α on the increase in LH and changes in blood flow within the hours of a PGFM pulse was related positively to the prominence of the PGFM pulse.