Pulsatile secretion of gonadotrophins, ovarian steroids and ovarian oxytocin during the luteal phase of the oestrous cycle in the cow

Abstract

All hormones were determined in blood samples collected simultaneously from the caudal vena cava and jugular vein at 20-min intervals for 12 h during the early (Day 4) and mid- (approximately Day 11) luteal phases of the oestrous cycle in 7 cows. Mean concentrations of oestradiol, progesterone and oxytocin were greater (P less than 0.01) in the vena cava than in the jugular vein. Pulses of these hormones were also more easily identifiable in the vena cava. The frequency of LH pulses was higher (P less than 0.01) during the early luteal than during the mid-luteal phase (8.0 versus 3.6 pulses/12 h). During both phases, 90-96% of all LH pulses were followed within 60 min by a pulse of oestradiol. Basal concentration and amplitude of oestradiol pulses were greater (P less than 0.05) during the early than during the mid-luteal phase. The frequency of FSH pulses was similar to that of LH during the early luteal phase (8.5 and 8.0 pulses/12 h) but was greater (P less than 0.01) than that of LH during the mid-luteal phase (6.3 versus 3.6 pulses/12 h). Thus, 41% more (P less than 0.01) FSH pulses than LH pulses were observed during the mid-luteal phase. However, the separate FSH pulses were associated with low-amplitude short-duration pulses of LH as clarified by an additional study (in 3 cows) using 5-min sampling intervals: 90-100% of all LH/FSH pulses and separate FSH pulses were secreted either concomitantly with or followed by a pulse of progesterone. However, no separate FSH pulses were associated with a pulse of oestradiol. Basal concentration and amplitude of progesterone were greater (P less than 0.01) during the mid-luteal than during the early luteal phase. The frequency of oxytocin pulses was similar to that of progesterone during the mid-luteal but not during the early luteal phase. During the mid-luteal phase 97% of all oxytocin pulses were associated with a pulse of progesterone. It is concluded that (1) separate FSH pulses are secreted in addition to parallel LH and FSH pulses during the mid-luteal phase; therefore, the frequency of secretion of LH may be modulated to a greater extent by ovarian steroids than is FSH pulse frequency; (2) pulses of progesterone are probably a result of stimulation by pulses of FSH and/or LH whereas pulses of oestradiol are caused by LH pulses; (3) ovarian oxytocin and progesterone are secreted concomitantly during the mid-luteal phase of the oestrous cycle.

Control of Steroidogenesis in Small and Large Bovine Luteal. Cells

“…Interestingly, the pattern of binding of granulosa antibody observed (Alila and Hansel 1984) closely resembled the profile of oxytocin secretion described by Walters et al (1984). The disappearance of granulosa cells during pregnancy coincides with the period when luteal oxytocin concentration is low, suggesting again that granulosa-derived large cells are the source of oxytocin in the bovine CL.…”

Effects of progesterone and oestradiol-17 on oxytocininduced release of prostaglandin F-2 in heifers

“…(McCracken et al, 1984). In the cow, as in the sheep, there is a pulsatile release of oxytocin, presumably from the corpus luteum (Walters et al, 1984), which appears to be responsible for the pulsatile release of PGF-2a at the time of luteolysis (Flint & Sheldrick, 1983;Vighio & Liptrap, 1986). The uterus is responsive to oxytocin stimulation at the end, but not during the middle, of the luteal phase of non-pregnant heifers (Lafrance & Goff, 1985).…”

Changes in pulsatile secretion patterns of LH, FSH, progesterone, androstenedione and oestradiol in cows after superovulation with PMSG

“…The tip of the catheter was located in the vena cava near the bifurcation with the vena ovarica. Correct placing was assessed according to Walters et al (1984) (Dieleman et al, 1983b).…”