Progesterone and conceptus elongation in cattle: a direct effect on the embryo or an indirect effect via the endometrium?

Abstract

The steroid hormone progesterone (P 4 ) plays a key role in the reproductive events associated with pregnancy establishment and maintenance. High concentrations of circulating P 4 in the immediate post-conception period have been associated with an advancement of conceptus elongation, an associated increase in interferon-t production and higher pregnancy rates in cattle. Using in vitro and in vivo models and w8500 bovine oocytes across six experiments, the aim of this study was to establish the route through which P 4 affects bovine embryo development in vitro and in vivo. mRNA for P 4 receptors was present at all stages of embryo development raising the possibility of a direct effect of P 4 on the embryo. Exposure to P 4 in vitro in the absence or presence of oviduct epithelial cells did not affect the proportion of embryos developing to the blastocyst stage, blastocyst cell number or the relative abundance of selected transcripts in the blastocyst. Furthermore, exposure to P 4 in vitro did not affect post-hatching elongation of the embryo following transfer to synchronized recipients and recovery on Day 14. By contrast, transfer of in vitro derived blastocysts to a uterine environment previously primed by elevated P 4 resulted in a fourfold increase in conceptus length on Day 14. These data provide clear evidence to support the hypothesis that P 4 -induced changes in the uterine environment are responsible for the advancement in conceptus elongation reported previously in cattle and that, interestingly, the embryo does not need to be present during the period of high P 4 in order to exhibit advanced elongation.

Physiological and practical effects of progesterone on reproduction in dairy cattle

“…Nevertheless, embryos that were transferred into recipients that had received prior P4 exposure (days 3 to 6 increased P4) had longer embryos on day 14 and embryo area was much greater (Clemente et al, 2009). The authors concluded that 'P4-induced changes in the uterine environment are responsible for the advancement in conceptus elongation reported previously in cattle and that, interestingly, the embryo does not need to be present during the period of high P4 in order to exhibit advanced elongation ' (Clemente et al, 2009). These results are consistent with the studies of (Larson et al, 2011) that also failed to find a direct effect of P4 during either days 1 to 3 or days 4 to 7 of culture on percentage of embryos that developed to the morula or blastocyst stage; although small differences in glucose metabolism were observed.…”

“…An elegant series of experiments found no effect of P4 supplementation after fertilization, in vitro, on blastocyst yield, in the presence or absence of bovine oviductal epithelial cells (Clemente et al, 2009). In a surprising twist, these researchers treated recipient cows with an intravaginal P4-releasing device (PRID) starting on day 3 after estrus with in vitro produced blastocysts transferred on day 7.…”

“…Early embryos express different types and concentrations of P4 receptors (Clemente et al, 2009) raising the possibility that P4 may be acting directly on the embryo to improve embryo development. An elegant series of experiments found no effect of P4 supplementation after fertilization, in vitro, on blastocyst yield, in the presence or absence of bovine oviductal epithelial cells (Clemente et al, 2009).…”

“…Thus, the rise in P4 concentrations in treated cows occurred before the transfer of embryos. Nevertheless, embryos that were transferred into recipients that had received prior P4 exposure (days 3 to 6 increased P4) had longer embryos on day 14 and embryo area was much greater (Clemente et al, 2009). The authors concluded that 'P4-induced changes in the uterine environment are responsible for the advancement in conceptus elongation reported previously in cattle and that, interestingly, the embryo does not need to be present during the period of high P4 in order to exhibit advanced elongation ' (Clemente et al, 2009).…”

“…A particularly intriguing recent study reported that one of the major hormonal differences found in cows with genetics for high fertility was 34% greater circulating P4 concentrations than cows with poor genetic merit for fertility (Cummins et al, 2012). Many recent studies have attempted to unravel the mechanisms involved in the complex relationship between circulating P4 concentrations and levels of fertility in lactating dairy cows.Early embryos express different types and concentrations of P4 receptors (Clemente et al, 2009) raising the possibility that P4 may be acting directly on the embryo to improve embryo development. An elegant series of experiments found no effect of P4 supplementation after fertilization, in vitro, on blastocyst yield, in the presence or absence of bovine oviductal epithelial cells (Clemente et al, 2009).…”