The role of proestrus on fertility and postovulatory uterine function in the cow

Modern protocols to synchronize ovulations for timed artificial insemination and timed embryo transfer that include manipulations in the proestrus period (i.e., between luteolysis and estrus) affect fertility in cattle. Specifically, stimulating pre-ovulatory follicle growth and exposure to estrogens after CL regression increase the proportion of cows pregnant and decrease late embryo mortality. Such effects may be due to both pre-ovulatory actions of estrogens and post-ovulatory actions of progesterone, as concentrations of the later hormone may be changed in response to manipulations conducted during proestrus. In the first portion of this paper we describe strategies used recently to manipulate the proestrus period in protocols for synchronization of ovulation, and to present evidence of their effects on fertility. Manipulations of timing and prominence of sex steroids during the proestrus and early diestrus that affect fertility may act on targets such as the endometrium. This tissue expresses receptors for both estrogens and progesterone and these hormones change endometrial function to support conceptus growth and pregnancy maintenance. However, specific cellular and molecular mechanisms through which fertility is affected via manipulations of the proestrus are poorly understood. In the second portion of this paper we describe a well-defined animal model to study changes in endometrial function induced by manipulations conducted during the proestrus. Such manipulations induced endometrial changes on sex steroid receptors expression, cell proliferation, oxidative metabolism and eicosanoid synthesis in the uterus, but not on glucose transport to uterine lumen . In summary, evidence is accumulating to support a positive role of increasing duration and estrogen availability during the proestrus on fertility to synchronization protocols. Such positive effects may be through changes in endometrial function to stimulate conceptus growth and survival.

The role of proestrus on fertility and postovulatory uterine function in the cow

Modern protocols to synchronize ovulations for timed artificial insemination and timed embryo transfer that include manipulations in the proestrus period (i.e., between luteolysis and estrus) affect fertility in cattle. Specifically, stimulating pre-ovulatory follicle growth and exposure to estrogens after CL regression increase the proportion of cows pregnant and decrease late embryo mortality. Such effects may be due to both pre-ovulatory actions of estrogens and post-ovulatory actions of progesterone, as concentrations of the later hormone may be changed in response to manipulations conducted during proestrus. In the first portion of this paper we describe strategies used recently to manipulate the proestrus period in protocols for synchronization of ovulation, and to present evidence of their effects on fertility. Manipulations of timing and prominence of sex steroids during the proestrus and early diestrus that affect fertility may act on targets such as the endometrium. This tissue expresses receptors for both estrogens and progesterone and these hormones change endometrial function to support conceptus growth and pregnancy maintenance. However, specific cellular and molecular mechanisms through which fertility is affected via manipulations of the proestrus are poorly understood. In the second portion of this paper we describe a well-defined animal model to study changes in endometrial function induced by manipulations conducted during the proestrus. Such manipulations induced endometrial changes on sex steroid receptors expression, cell proliferation, oxidative metabolism and eicosanoid synthesis in the uterus, but not on glucose transport to uterine lumen . In summary, evidence is accumulating to support a positive role of increasing duration and estrogen availability during the proestrus on fertility to synchronization protocols. Such positive effects may be through changes in endometrial function to stimulate conceptus growth and survival. (AU)

Probing the uterine microenvironment through Systems Biology approaches

In cattle, the developing preimplantation conceptus depends solely on its surrounding environment for supplying nutrients and growth stimuli. Also, throughout gestation, it is during the preimplantation stage of gest ation that most conceptus mortality is observed. Thus, one could rationalize that the composition of the uterine environment plays a major role on conceptus survival. However, the biochemical composition of the uterine environment is only just starting to be deciphered and conditions associated with optimal conceptus development are virtually unknown. In this review we attempt to briefly review and discuss issues associated with sampling and analyzing the uterine envir onment. We suggest that modern, holistic approaches such as Systems Biology are necessary to characterize the uterine functions associated with pregnancy success in cattle.

Probing the uterine microenvironment through Systems Biology approaches

In cattle, the developing preimplantation conceptus depends solely on its surrounding environment for supplying nutrients and growth stimuli. Also, throughout gestation, it is during the preimplantation stage of gest ation that most conceptus mortality is observed. Thus, one could rationalize that the composition of the uterine environment plays a major role on conceptus survival. However, the biochemical composition of the uterine environment is only just starting to be deciphered and conditions associated with optimal conceptus development are virtually unknown. In this review we attempt to briefly review and discuss issues associated with sampling and analyzing the uterine envir onment. We suggest that modern, holistic approaches such as Systems Biology are necessary to characterize the uterine functions associated with pregnancy success in cattle.(AU)

Associação entre polimorfismos do gene IGF-IR e características produtivas e reprodutivas em fêmeas bovinas da raça Holandesa / Association between IGF-IR gene polymorphisms and productive and reproductive traits in Holstein cows

Estudou-se a associação entre polimorfismos de conformação de fita simples (SSCP) no gene do receptor do fator-I de crescimento semelhante à insulina (IGF-IR) e idade ao primeiro parto (IPP), intervalo entre partos (IEP), duração da lactação (DL) e produção de leite (PL), em 106 fêmeas puras por cruza da raça Holandesa. A reação em cadeia da polimerase (PCR) com oligonucleotídeos iniciadores específicos gerou um fragmento de 335pb. A freqüência genotípica da população para o polimorfismo foi 82,1% de indivíduos homozigotos para o alelo A e 17,9% de heterozigotos (AB). A freqüência do alelo A foi 0,91 e a do alelo B, 0,09. Não foi encontrada associação entre o polimorfismo estudado e as características IPP, IEP e PL. A característica DL foi positivamente associada (P<0,05) à ausência do alelo B. A lactação dos animais portadores do genótipo AA foi mais longa.(AU)

The association between single-strand conformation polymorphism (SSCP) in the gene of insulin-like growth factor-I receptor (IGF-IR) and age at first calving (AFC), calving interval (CI), lactation length (LL), and milk yield (MY) was studied using 106 graded Holstein females. The polimerase chain reaction (PCR) with specific initiating oligonucleotides, resulted an amplified fragment of 335pb. The population genotypes frequencies were 82.1% and 17.9%, for AA and AB genotypes, respectively. The frequency of A allele was 0.91 and 0.09 of B allele. No association between the identified polymorphism and AFC, CI, and MY was observed. The LL was positively associated (P<0.05) with the absence of B allele. Animals carrying the AA genotype presented a longer lactation period.(AU)