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Temporal Associations among Pulses of 13,14-Dihydro-15-keto-PGF_2alpha, Luteal Blood Flow, and Luteolysis in Cattle¹

Eutheria Foundation,³ Cross Plains, Wisconsin 53528 Animal Health and Biomedical Sciences,⁴ University of Wisconsin, Madison, Wisconsin 53706

ABSTRACT

Luteal blood flow was studied in heifers by transrectal color-Doppler ultrasound. Data were normalized to the decrease in plasma progesterone to <1 ng/ml (Day 0 or Hour 0). Blood flow in the corpus luteum (CL) was estimated by the percentage of CL area with color flow signals. Systemic prostaglandin F_2alpha (PGF) treatment (25 mg; n = 4) resulted in a transient increase in CL blood flow during the initial portion of the induced decrease in progesterone. Intrauterine treatment (1 or 2 mg) was done to preclude hypothetical secondary effects of systemic treatment. Heifers were grouped into responders (luteolysis; n = 3) and nonresponders (n = 5). Blood flow increased transiently in both groups; induction of increased blood flow did not assure the occurrence of luteolysis. A transient increase in CL blood flow was not detected in association with spontaneous luteolysis when examinations were done every 12 h (n = 6) or 24 h (n = 10). The role of PGF pulses was studied by examinations every hour during a 12-h window each day during expected spontaneous luteolysis. At least one pulse of 13,14-dihydro-15-keto-PGF_2alpha (PGFM) was identified in each of six heifers during the luteolytic period (Hours –48 to –1). Blood flow increased (P < 0.02) during the 3-h ascending portion of the PGFM pulse, remained elevated for 2 h after the PGFM peak, and then decreased (P < 0.03) to baseline. Results supported the hypothesis that CL blood flow increased and decreased with individual PGFM pulses during spontaneous luteolysis.

blood flow, cattle, corpus luteum function, female reproductive tract, luteolysis, mechanisms of hormone action, ovulatory cycle, prostaglandin F₂, steroid hormones

¹Supported by the Eutheria Foundation projects P1-LS-06, P4-LS-06, P5-LS-06, and B1-RR-06. L.A.S. is supported by a CAPES Scholarship (Brazil) to the University of Florida.

Correspondence: ²O.J. Ginther, Animal Health and Biomedical Sciences, 1656 Linden Dr., University of Wisconsin, Madison, WI 53706. FAX: 608 262 7420; e-mail: ginther{at}svm.vetmed.wisc.edu

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