Luteolysis, estrus and ovulation, and blood prostaglandin F after intramuscular administration of 15, 30 or 60 mg prostaglanding F2alpha.

During diestrus in three consecutive estrous cycles, each of six heifers was given (im) 30 mg, 15 mg (twice at 6-hr intervals) and 60 mg prostaglandin F2alpha (PGF2alpha) tham salt. Neither the decline in blood progesterone, the increase in blood estradiol, the duration or the peak of the LH surge, the interval to onset of estrus, nor the interval to ovulation was affected significantly by dose of PGF2alpha. Thus, relative to that after 30 mg PGF2alpha im, two injections of 15 mg at 6-hr intervals or 60 mg PGF2alpha did not hasten luteolysis. Thirty mg was an ample in dose of PGF2alpha to cause luteolysis. Regardless of im dose of PGF2alpha, blood PGF peaked at about 6.0 ng/ml within 10 minutes and returned to basal values (less than 1.0 ng/ml) within 90 minutes. In another trial, after a single iv injection of 5 mg PGF2alpha, blood PGF peaked (25 ng/ml) within 5 minutes and returned to basal values within 15 minutes. During a 30-minute infusion (0.5 mg/minute) of PGF2alpha, blood PGF plateaued at 29.5 ng/ml with a metabolic clearance rate of 17.0 liters per minute.