Luteinizing Hormone Secretion and Corpus Luteum Function in Cows Receiving two Levels of Progesterone1

Abstract

The objectives of this experiment were to determine if subnormal levels of progesterone (P4) indicative of luteal insufficiency influence (1) pulsatile release of luteinizing hormone (LH), (2) the interval to the preovulatory surge of LH after removal of P4, and (3) the secretion of P4 during the estrous cycle subsequent to administration of subnormal levels of P4. On Day 5 (Day = 0 day of estrus) of the estrous cycle, cows received P4-releasing intravaginal devices (PRID) to produce normal (2 PRIDs; n = 7) or subnormal (0.5 PRID; n = 6) concentrations of P4. Five cows served as controls. On Day 10, serial blood samples were collected from all cows. Collection of blood samples was again initiated on Day 17 in cows receiving PRIDs. The PRIDs were removed and blood collection continued for 78 h. Daily blood samples were collected from all animals for 42 days subsequent to estrus (estrous cycles 1 and 2, respectively). During estrous cycle 1, mean concentration of P4 was lower (p less than 0.05) and frequency of pulses of LH was higher (p less than 0.05) in cows receiving subnormal P4 than in cows receiving normal P4 and control cows. Plasma concentrations of estradiol (E2) were higher (p less than 0.05) on Days 9-16 of estrous cycle 1 in cows receiving subnormal P4 than in cows receiving normal P4 or in control cows. Concentrations of E2 were greater (p less than 0.05) at 6, 18, and 30 h following removal of PRIDs in cows receiving subnormal P4 than in cows receiving normal P4.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the ovulatory follicle diameter and progesterone concentration on the pregnancy rate of fixed-time inseminated lactating beef cows

“…Unfortunately, the authors of the present study were not able to perform daily ultrasound examination in all cows to ensure that the very large follicles detected were from persistent follicles. Females subjected to low progesterone concentration, in the absence of a corpus luteum, have an increase in LH pulsatility, similar to the LH secretion detected during the follicular phase of the estrous cycle (Kojima et al, 1992;Roberson et al, 1989). The increased frequency of LH pulses apparently impairs the temporal relationship between oocyte and preovulatory follicle maturation (Austin et al, 1999).…”

Utilização prolongada de dispositivo intravaginal contendo progesterona (CIDR®) para indução de folículos persistentes em receptoras de embrião bovino

“…Por outro lado, Bergfeld et al (1995) Baseado na variação da freqüência dos pulsos de LH durante o tratamento com progestágeno, foi especulado que a maior freqüência encontrada em vacas tratadas com progestágenos quando comparadas com aquelas em sua fase luteal, mesmo na presença de concentrações plasmáticas de P 4 similares, como observado por Kojima et al (1992) e Roberson et al (1989), foi devida ao fato da avaliação do padrão dos pulsos de LH, ter sido realizada um dia antes do final do tratamento com progestágeno, sendo que, se o padrão de liberação de LH tivesse sido avaliado no início do tratamento, a freqüência dos pulsos de LH provavelmente teria sido menor do que a encontrada (KINDER et al, 1996).…”

Frequency of luteinizing hormone pulses in cattle influences duration of persistence of dominant ovarian follicles, follicular fluid concentrations of steroids, and activity of insulin-like growth factor binding proteins

“…Persistent follicles secrete greater amounts of 17␤-estradiol (E 2 ) than typical dominant follicles present during the luteal phase of the estrous cycle; concentrations of E 2 in blood, however, are similar to those during the follicular phase of the estrous cycle Roberson et al, 1989;Kojima et al, 1992). Inseminations associated with ovulation from persistent follicles result in lesser pregnancy rates than ovulations from typical dominant follicles (Stock and Fortune, 1993;Savio et al, 1992;Sanchez et al, 1993;Wehrman et al, 1993).…”