The effect of prostaglandin F2α (PGF) infusion
for 3 h into the jugular vein on progesterone
concentrations was studied in 24 Holstein heifers.
Plasma concentrations of PGF were assessed by assay
of 13,14-dihydro-15-keto-PGF (PGFM). The 3 h of
PGF infusion were used to approximate the duration of
the major concentrations of PGFM in a natural pulse.
During infusion of 5, 10, or 15 mg/3 h, the
concentrations of PGFM greatly exceeded the peak of a
natural pulse. Plasma concentrations of progesterone
decreased (P < 0.05) in the three PGF-treated groups by
Hour 1 (Hour 0 = beginning of infusion). Progesterone
increased between Hours 1 and 2, but the increase was
significant (P < 0.03) only in the 5-mg group.
Concentrations decreased more gradually between
Hours 2 and 6 than between Hours 0 and 1 with no
differences among PGF groups. The percentage of CL
area with color-Doppler signals of blood flow were
elevated similarly in the three PGF-treated groups at
Hours 1 to 3 and by Hour 5 decreased to below the
percentage at Hour 0. In a second experiment,
approximating a natural PGFM pulse by intravenous
infusion of PGF at a dose of 0.7 mg/3 h did not affect
plasma progesterone concentrations. Results indicated
that intravenous infusion of PGF for 3 h decreased the
progesterone concentration when the total dose was
equivalent to doses that have been shown to be
completely luteolytic when given as a single systemic
injection. However, intravenous infusion of a dose of
PGF that approximately simulated a natural PGFM
pulse did not effect progesterone concentration.
