Plasma PGFM and progesterone concentrations, luteolysis moment and estrous cycle length in Nelore cows submitted to uterine biopsies / Concentrações plasmáticas de PGFM e progesterona, luteólise e comprimento do ciclo estral em vacas Nelore submetidas à coleta de fragmentos endometriais

In this study, endometrial samples were collected in 14 Nelore cows on days zero (ovulation), five, nine, thirteen and nineteen of the estrous cycle (biopsy group), and in 15 females these collections weren't performed (control group). Biopsies were done on the uterine horn endometrium contralateral to the ovary with corpus luteum. Blood samples were taken at -24, -16, -8, 0 +8, +16 and +24 hours in relation to progesterone drop (<1ng/mL, zero moment) and evaluated for 13, 14-dihydro-15-keto prostaglandin F2-alpha (PGFM) by radioimmunoassay (RIA). Plasma progesterone concentration was determined by RIA every 24 hours. Data were analyzed by ANOVA using the PROC GLM and MIXED of the SAS. The mean value for PGFM during the entire period evaluated was greater in the biopsy group. The mean concentration of PGFM at moment zero was not different between the groups; the mean concentration of PGFM was higher in the biopsy group before and after the drop in progesterone level. The maximum mean concentration observed was not different between the groups; however, the mean minimum concentration was different with high values in the biopsy group. Although the PGFM concentrations were higher in the biopsy group, the biopsy and control groups had similar length of estrous cycle showing that repeated endometrial biopsy on the side contralateral to the ovary with corpus luteum does not affect luteolysis and the length of the estrous cycle.(AU)

No presente estudo, foram coletadas amostras endometriais de 14 vacas Nelore nos dias zero (dia da ovulação), cinco, nove, 13 e 19 do ciclo estral (grupo controle), e em 15 fêmeas essas coletas não foram realizadas (grupo controle). As biópsias foram realizadas no corno uterino contralateral ao ovário contendo o corpo lúteo. Amostras plasmáticas foram coletadas nos momentos -24, -16, -8, 0 +8, +16 e +24 horas em relação à queda de progesterona (<1ng/mL, momento zero) e avaliadas quanto à concentração de 13, 14-di-hidro-15-ceto prostaglandina F2-alpha (PGFM) por radioimunoensaio (RIA). As concentrações plasmáticas de progesterona foram avaliadas a cada 24 horas também por RIA. Os dados foram analisados por ANOVA empregando-se PROC GLM e MIXED do SAS. O valor médio de PGFM durante todo o período avaliado foi maior no grupo biópsia. A concentração média de PGFM no momento zero não diferiu entre os grupos, e foi maior no grupo biópsia antes e após a queda de progesterona. A concentração máxima observada não foi diferente entre os grupos, porém a concentração mínima diferiu com maiores valores observados no grupo biópsia. Embora as concentrações de PGFM fossem maior no grupo biópsia, ambos os grupos apresentaram o mesmo comprimento do ciclo estral, demonstrando que a coleta repetitiva de biópsias endometriais no corno uterino contraletral ao ovário contendo o corpo lúteo não afeta a luteólise e o comprimento do ciclo estral.(AU)

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)

Follicular dynamics and pregnancy rates in Bos taurus x Bos indicus embryo transfer recipients treated to increase plas ma progesterone concentrations

The aim of this study was to evaluate the effects of GnRH, LH, hCG or exogenous progesterone administration on plasma progesterone concentrations and pregnancy rates following embryo transfer in Bos taurus x Bos indicus cross-bred heifers. In Experiment 1, animals with body condition scores  3.5 (1 to 5 scale) were synchronized with two injections of a prostaglandin F2  analog 13 days apart. He ifers detected in estrus (day 0; n = 37) were randomly assigned on day 7 to receive one of five treatments: Control (2 ml saline im; n = 6), GnRH (10  g Buserelin im; n = 8), hCG (1500 IU Chorulon im; n = 8), LH (25 mg pLH im; n = 7) or a CIDR-B device for 13 days (n = 8). Ovarian ultrasonography was performed daily from day 6 until the subsequent estrus. Heifers in the GnRH, hCG and LH groups were evaluated every 12 h between days 7 and 9 to confirm ovulation of the first-wave dominant follicle. Blood samples were collected daily for determination of P4 levels. Estrus detection was performed daily with the aid of androgenized cows. Ovulation rate for the first wave dominant follicle was 100% for heifers treated with GnRH, hCG and LH. Between days 13 and 17, the mean diameter of original CLs, diameter of accessory CLs and P4 concentrations were greater in heifers treated with hCG than in heifers in all other groups (P < 0.05). Duration of the luteal phase (number of days with a P4 concentration  1.0 ng/ml) was similar in hCG (14.3 ± 0.6), LH (13.4 ± 0.6), GnRH (13.4 ± 0.4), CIDR-B (14.5 ± 0.2) and Control (12.8 ± 0.5) groups. In Experiment 2, animals were kept on a grazing regimen at commercial farms in Brazil and were synchronized with one injection of a prostaglandin F2  analog. The same hormonal treatments as in Experiment 1 were given on day 7 after estrus at the time of transfer of frozen/thawed embryos to Bos taurus x Bos indicus recipients (n = 485). Pregnancy rates were higher in GnRH- (53.5%; 53/99) and hCG- (51.0%; 49/96) treated heifers (P < 0.05) than in control heifers (28.6%; 28/98), but were similar to heifers treated with CIDR devices (41.1%; 39/95) and LH (45.4%; 44/97). It was concluded that the improvement in conception rates in hCG treated Bos taurus x Bos indicus cross-bred heifers receiving frozen/thawed embryos were due to both P4-dependent and P4-independent mechanisms.

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.

Follicular dynamics and pregnancy rates in Bos taurus x Bos indicus embryo transfer recipients treated to increase plas ma progesterone concentrations

The aim of this study was to evaluate the effects of GnRH, LH, hCG or exogenous progesterone administration on plasma progesterone concentrations and pregnancy rates following embryo transfer in Bos taurus x Bos indicus cross-bred heifers. In Experiment 1, animals with body condition scores  3.5 (1 to 5 scale) were synchronized with two injections of a prostaglandin F2  analog 13 days apart. He ifers detected in estrus (day 0; n = 37) were randomly assigned on day 7 to receive one of five treatments: Control (2 ml saline im; n = 6), GnRH (10  g Buserelin im; n = 8), hCG (1500 IU Chorulon im; n = 8), LH (25 mg pLH im; n = 7) or a CIDR-B device for 13 days (n = 8). Ovarian ultrasonography was performed daily from day 6 until the subsequent estrus. Heifers in the GnRH, hCG and LH groups were evaluated every 12 h between days 7 and 9 to confirm ovulation of the first-wave dominant follicle. Blood samples were collected daily for determination of P4 levels. Estrus detection was performed daily with the aid of androgenized cows. Ovulation rate for the first wave dominant follicle was 100% for heifers treated with GnRH, hCG and LH. Between days 13 and 17, the mean diameter of original CLs, diameter of accessory CLs and P4 concentrations were greater in heifers treated with hCG than in heifers in all other groups (P < 0.05). Duration of the luteal phase (number of days with a P4 concentration  1.0 ng/ml) was similar in hCG (14.3 ± 0.6), LH (13.4 ± 0.6), GnRH (13.4 ± 0.4), CIDR-B (14.5 ± 0.2) and Control (12.8 ± 0.5) groups. In Experiment 2, animals were kept on a grazing regimen at commercial farms in Brazil and were synchronized with one injection of a prostaglandin F2  analog. The same hormonal treatments as in Experiment 1 were given on day 7 after estrus at the time of transfer of frozen/thawed embryos to Bos taurus x Bos indicus recipients (n = 485). Pregnancy rates were higher in GnRH- (53.5%; 53/99) and hCG- (51.0%; 49/96) treated heifers (P < 0.05) than in control heifers (28.6%; 28/98), but were similar to heifers treated with CIDR devices (41.1%; 39/95) and LH (45.4%; 44/97). It was concluded that the improvement in conception rates in hCG treated Bos taurus x Bos indicus cross-bred heifers receiving frozen/thawed embryos were due to both P4-dependent and P4-independent mechanisms.(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.(AU)

Manipulation of ovarian and uterine function to increase conception rates in cattle

In cattle, embryonic and fetal losses are the major causes of reproductive failure. Losses associated with failure in the process of maternal recognition of pregnancy can amount to as much as 30%. Successful establishment of pregnancy depends on a delicate balance between luteolytic mechanisms inherent to the endometrium at the end of diestrus and antiluteolytic mechanisms, orchestrated by the conceptus to change endometrial function and, ultimately, block luteolysis. Antiluteolytic strategies are pharmacological, mechanical, nutritional and management manipulations of the process of maternal recognition of pregnancy that aim to increase the probability of successful gestations. Objective of the present paper is to review the recent literature on antiluteolytic strategies in cattle. Specifically, we focused on strategies to stimulate production of progesterone, strategies to reduce production of estradiol and other strategies. Future directions for research in this area are proposed.

Manipulation of ovarian and uterine function to increase conception rates in cattle

In cattle, embryonic and fetal losses are the major causes of reproductive failure. Losses associated with failure in the process of maternal recognition of pregnancy can amount to as much as 30%. Successful establishment of pregnancy depends on a delicate balance between luteolytic mechanisms inherent to the endometrium at the end of diestrus and antiluteolytic mechanisms, orchestrated by the conceptus to change endometrial function and, ultimately, block luteolysis. Antiluteolytic strategies are pharmacological, mechanical, nutritional and management manipulations of the process of maternal recognition of pregnancy that aim to increase the probability of successful gestations. Objective of the present paper is to review the recent literature on antiluteolytic strategies in cattle. Specifically, we focused on strategies to stimulate production of progesterone, strategies to reduce production of estradiol and other strategies. Future directions for research in this area are proposed.(AU)

Growth factors and steroidogenesis in the bovine placenta

The control of placental hormone biosynthesiscritical during gestation, since their coordinated action is essential for the normal progress of pregnancy. Hormonal synthesis regulation in placenta is still not elucidated and differs from that observed in other steroidogenic tissues since specific tropic hormones have not yet been identified. Cellular localization of growth factors in the placenta, including VEGF, EG-VEGF and bFGF, ponts that these factors have additional roles in the organ besides their well known modulation on cell proliferation and angiogenesis. In vitro experiments bring new evidence that growth factors play regulatory roles modulating processes related to steroid hormone secretion in the placenta. Importance of local estrogen function has beenhighlighted and a key enzyme for its synthesis is aromatase cytochrome P450. The objective of this review was to describe some aspects of placentalsteroidogenesis, mainly focusing on aromatase cytochrome P450 steroidogenic enzyme expression and growth factors as others potential modulators of hormonal synthesis in the organ.(AU)

Growth factors and steroidogenesis in the bovine placenta

The control of placental hormone biosynthesiscritical during gestation, since their coordinated action is essential for the normal progress of pregnancy. Hormonal synthesis regulation in placenta is still not elucidated and differs from that observed in other steroidogenic tissues since specific tropic hormones have not yet been identified. Cellular localization of growth factors in the placenta, including VEGF, EG-VEGF and bFGF, ponts that these factors have additional roles in the organ besides their well known modulation on cell proliferation and angiogenesis. In vitro experiments bring new evidence that growth factors play regulatory roles modulating processes related to steroid hormone secretion in the placenta. Importance of local estrogen function has beenhighlighted and a key enzyme for its synthesis is aromatase cytochrome P450. The objective of this review was to describe some aspects of placentalsteroidogenesis, mainly focusing on aromatase cytochrome P450 steroidogenic enzyme expression and growth factors as others potential modulators of hormonal synthesis in the organ.