Characterisation of pulses of 13,14-dihydro-15-keto-PGF2alpha (PGFM) and relationships between PGFM pulses and luteal blood flow before, during, and after luteolysis in mares

Abstract

Blood collections for characterising 13,14-dihydro-15-keto-PGF2alpha (PGFM) pulses in mares and colour-Doppler examinations for estimating percentage of corpus luteum with blood-flow signals were done hourly for a 24-h session on Day 15 (ovulation = Day 0; n = 13 mares) or during 12-h sessions from Days 12 to 16 (n= 10 mares). Luteolysis was defined as extending from the beginning of a precipitous decrease in progesterone until progesterone was <2 ng mL(-1). Comparisons were made among preluteolysis, luteolysis, and postluteolysis. Greater prostaglandin F2alpha activity (mean PGFM concentration per session) occurred during luteolysis than during preluteolysis and postluteolysis. Statistically-detected PGFM pulses were smaller during preluteolysis with a highly variable interval from the last pulse to the beginning of luteolysis. Either two or three pulses were detected in each 24-h session during luteolysis and postluteolysis, after excluding three of eight sessions with no pulses during postluteolysis. Statistically, 17% of pulses during postluteolysis were prominent outliers. The nadir-to-nadir interval during a pulse (5 h), the peak-to-peak interval between pulses (9 h), and the resulting 4-h gap between pulses were similar during and after luteolysis. The decrease in progesterone encompassed the PGFM pulses, without a detectable fluctuation during a pulse. The percentage of corpus luteum with blood-flow signals did not change during the ascending portion of a PGFM pulse and decreased within 2 or 3 h after the peak, even during preluteolysis. Results indicated that a reported increase in luteal blood flow in heifers during the ascending portion of a PGFM pulse does not occur in mares.

Ovarian and PGF2α responses to stimulation of endogenous PRL pulses during the estrous cycle in mares

“…Assay of plasma concentrations of progesterone (P4) and transrectal ultrasonic evaluation of the CL and percentage of CL with color-Doppler blood flow signals can be used to evaluate the CL in large animals [1,2]. In mares, the average day of transition from preluteolysis to luteolysis is Day 14 (Day 0 ϭ ovulation), based on collection of hourly blood samples [3].…”

“…In mares, the average day of transition from preluteolysis to luteolysis is Day 14 (Day 0 ϭ ovulation), based on collection of hourly blood samples [3]. Secretion of PGF2␣ pulses by the endometrium has a fundamental role in luteolysis in mares [2,3] as in other species [4,5].…”

Dinâmica hormonal durante o processo luteolítico nas espécies equina e bovina; com ênfase sobre o papel da prolactina

“…Uma segunda estratégia protetora seria a eficiente captura de moléculas de PGF2α pelo CL, sendo 10 vezes maior em equinos do que em bovinos (KIMBALL;WYNGARDEN, 1977). Uma terceira estratégia, universal, é a secreção de PGF2α em pulsos, sendo que a indução e finalização da luteólise é feita por dois a quatro pulsos sequenciais de PGF2α tanto em vacas quanto em éguas (GINTHER et al, 2008). Uma ultima estratégia é a forma de transporte da PGF2α do endométrio aos ovários, sendo em bovinos por via unilateral ou local, através do contato da veia uterina com a artéria ovariana (GINTHER, 1981), enquanto que em éguas este transporte é sistêmico, pois não há contato entre vasos uterinos e ovarianos (GINTHER, 1992).…”

“…A maioria dos estudos em animais de produção baseou-se em coletas de sangue pouco frequentes para a detectação e caracterização tanto de pulsos hormonais como da duração de processos reprodutivos específicos, os quais podem ocorrer em poucas horas. Como exemplo, amostras a cada hora são necessárias para identificar tanto pulsos de PGFM em equinos (GINTHER et al, 2008) quanto pulsos de PGFM e LH em bovinos . Amostras diárias não detectaram flutuações de PRL em éguas cíclicas (JOHNSON, 1986).…”

“…Sampling at least every hour is necessary for detecting PGFM pulses in horses (GINTHER at al., 2008) and PGFM and LH pulses in cattle . In gilts during sexual development, blood was sampled every 20 min for 6 h and an episodic pattern was detected for LH but not for PRL.…”