Intrapulse changes in progesterone and LH concentrations and luteal blood flow during an estradiol-induced pulse of a metabolite of prostaglandin F2alpha in heifers.

Physiologic doses (0.1 mg followed by 0.05 mg 1h later) of estradiol-17beta in sesame-oil vehicle or vehicle alone (n=6/group) were given to heifers on day 14 after ovulation (preluteolysis) to study the effect of estradiol (E2) on circulating 13,14-dihydro-15-keto-PGF2alpha (PGFM) and on PGFM pulses. Blood samples were collected hourly for 10h after the 0.1-mg treatment. The E2 group had an increase (P<0.03) in PGFM concentration by 4h and greater (P<0.0001) prominence of the PGFM pulses. Changes in progesterone and LH concentrations and luteal blood flow within a PGFM pulse were characterized. Within a PGFM pulse in the E2 group, progesterone decreased (P<0.04) between Hours -2 and 0 (ascending portion; Hour 0=peak of pulse) and increased (P<0.04) between Hours 0 and 2 (descending portion). Intrapulse changes in progesterone were not detected in the vehicle group. Concentration of LH in the E2 group increased (P<0.05) between Hours -1 and 1 and in the vehicle group decreased (P<0.03) between Hours -1 and 0 and increased (P<0.06) between Hours 0 and 1. The percentage of luteal area with blood-flow signals increased (P<0.02) between Hours 0 and 1 in the E2 group, and there were no other differences between hours in either group. Results were consistent with reports of changes in progesterone concentration within a PGFM pulse in cattle and demonstrated intrapulse changes in LH concentration and luteal blood flow during an E2-induced PGFM pulse.