Biomedical subjects

G L Morgan

Publications and source records attributed to G L Morgan.

At least 19 recordsLinked to original sources

PubMed2005

Shock temperature measurement using neutron resonance spectroscopy.

We report a direct measurement of temperature in a shocked metal using Doppler broadening of neutron resonances. The 21.1-eV resonance in 182W was used to measure the temperature in molybdenum shocked to approximately 63 GPa. An explosively launched aluminum flyer produced a planar shock in a molybdenum target that contained a 1-mm thick layer doped with 1.7 at. %(182)W. A single neutron pulse, containing resonant neutrons of less than 1 mus duration, probed the shocked material. Fits to the neutron time-of-flight data were used to determine the temperature of the shocked molybdenum.

Journal Article↗

PubMed2003

Influence of estradiol, progesterone, and nutrition on concentrations of gonadotropins and GnRH receptors, and abundance of mRNA for GnRH receptors and gonadotropin subunits in pituitary glands of beef cows.

Nutritionally induced anovulatory cows (n = 28) were used to determine the effect of steroids on regulation of synthesis and secretion of gonadotropins. Anovulatory cows were ovariectomized and received intravaginal inserts containing estradiol (E2), progesterone (P4), E2 and P4 (E2P4), or a sham intravaginal insert (C) for 7 d. Concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were quantified in serum and E2 and P4 were quantified in plasma. Cows were exsanguinated within 1 to 2 h after removal of intravaginal inserts and pituitary glands were collected and stored at -80 degrees C until messenger ribonucleic acid (mRNA) for gonadotropin-releasing hormone receptor (GnRH-R) and gonadotropin subunits, pituitary content of GnRH-R, and LH and FSH were quantified. Pituitary glands from five proestrous cows were harvested to compare gonadotropin characteristics between ovariectomized, anovulatory cows and intact cows. Plasma concentrations of E2 were greater (P < 0.05) in E2-treated cows than in sham-treated cows. Concentrations of P4 were greater (P < 0.05) in cows treated with P4 than in sham-treated cows. Mean serum concentrations of LH and FSH were not significantly influenced by steroid treatments. However, frequency of LH pulses of ovariectomized, nutritionally induced anovulatory cows was increased (P < 0.05) by treatment with E2 and amplitude of LH pulses was greater (P < 0.05) in cows treated with E2 or P4 than in cows treated with E2P4 or sham-treated. Quantity of mRNA for LHbeta in the pituitary gland was greater when cows were treated with P4. Concentrations of LH in the pituitary gland were not affected by steroid treatments; however, pituitary concentrations of FSH were less (P < 0.1) in E2 cows than in sham-treated cows. The number of GnRH-R was increased (P < 0.05) in cows treated with E2, but P4 treatment did not influence the number of GnRH-R. Abundance of mRNA for GnRH-R, common alpha-subunit, and FSHbeta were not affected by treatments. Pituitary concentrations of LH were greater (P < 0.05) and concentrations of FSH were less (P < 0.05) in proestrous cows than in ovariectomized, anovulatory cows treated with or without steroids. Abundance of mRNA for GnRH-R, common alpha-subunit, LHbeta and FSHbeta were similar for proestrous and anovulatory cows. We conclude that treatment of nutritionally induced anovulatory cows with progesterone and estradiol may cause pulsatile secretion of LH.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Expression patterns of retinoid X receptors, retinaldehyde dehydrogenase, and peroxisome proliferator activated receptor gamma in bovine preattachment embryos.

In cattle, administration of retinol at the time of superovulation has been indirectly associated with enhanced developmental potential of the embryo. Vitamin A and its metabolites influence several developmental processes by interacting with 2 different types of nuclear receptors, retinoic acid receptors and retinoid X receptors (RXRs). Given the limited information available concerning the RXR-mediated retinoid signaling system, particularly in species other than rodents, this study was performed to gain insight into the potential role of retinoid signaling during preattachment embryo development in the cow. Bovine embryos were produced in vitro from oocytes harvested from abattoir ovaries and frozen in liquid nitrogen at the oocyte, 2-, 4-, 8-, and 16- to 20-cell, morula, blastocyst, and hatched blastocyst stages. Reverse transcription polymerase chain reaction (PCR) and whole mount in situ hybridization were utilized to investigate mRNA expression for RXR alpha, RXR beta, RXR gamma, alcohol dehydrogenase I (ADH-I), retinaldehyde dehydrogenase 2 (RALDH2), peroxisome proliferator activated receptor gamma (PPAR gamma), and glyceraldehyde-3-phosphate dehydrogenase. Transcripts for RXR alpha, RXR beta, RALDH2, and PPAR gamma were detected in all stages beginning from the oocyte through to the hatched blastocyst. Whole mount in situ hybridization performed using digoxigenin-labeled antisense probes detected all 4 transcripts in both the inner cell mass and the trophectoderm of hatched blastocysts. PCR products obtained for ADH-I exhibited very low homology to known human and mouse sequences. Immunohistochemistry was performed using polyclonal anti-rabbit antibodies against RXR beta and PPAR gamma to investigate whether these embryonic mRNAs were translated to the mature protein. Strong immunostaining was observed for both RXR beta and PPAR gamma in the trophectoderm and inner cell mass cells of intact and hatched blastocysts. Messenger RNA was not detected at any stage for RXR gamma. Expression of mRNA for RXR alpha, RXR beta, RALDH2, and PPAR gamma suggests that the early embryo may be competent to synthesize retinoic acid and regulate gene expression during preattachment development in vitro.

Alcohol Dehydrogenase↗

PubMed2002

Seasonal effects on estrous behavior and time of ovulation in nonlactating beef cows.

Estrous behavior and time of ovulation relative to the onset of estrus were determined in mature Angus x Hereford cows (n = 17 to 21 each season) during summer, winter, and spring for 2 yr. Estrous behavior was evaluated during the first of two consecutive estrous periods, and time of ovulation was determined during the second estrus. Concentrations of progesterone were quantified in twice weekly blood samples to ensure all cows had normal estrous cycles. The HeatWatch system was used to measure the duration of estrus, number of mounts received per estrus, and duration of the longest interval between mounts received. Commencing 16 h after the onset of the second estrus, transrectal ultrasonography was performed every 4 h until the dominant follicle was no longer present on the ovary, and time of ovulation was defined as 2 h preceding the absence of the dominant follicle. There was a seasonal effect on the duration of estrus; cows were estrus longer in summer (17.6 +/- 0.8 h) than in winter (15.5 +/- 0.8 h; P = 0.07) or spring (13.9 +/- 0.9 h; P < 0.05). Cows were mounted more times per estrus (P < 0.05) in winter (59.0 +/- 5.3) than in summer (43.6 +/- 5.3) or spring (38.2 +/- 5.8). Intervals between mounts of estrous cows were longer (P < 0.05) in summer (4.1 +/- 0.4 h) than in spring or winter (2.7 +/- 0.4 h). During all seasons, cows were mounted more times (P < 0.01) between 0600 to 1200 (3.2 +/- 0.2 mounts received/h of estrus) than during other times of the day (2.1 +/- 0.2 mounts received/h of estrus). Cows ovulated 31.1 +/- 0.6 h after the onset of estrus, and time of ovulation was not influenced by season. We conclude that season influences estrous behavior of beef cows; cows are mounted more times per estrus in winter than in summer or spring. Time of ovulation relative to the onset of estrus is constant during all seasons and averages 31.1 h.

Animals↗

PubMed2002

Influence of exogenous gonadotropin-releasing hormone on ovarian function in beef cows after short- and long-term nutritionally induced anovulation.

The effect of pulsatile infusion of gonadotropin-releasing hormone (GnRH) on follicular function was evaluated in nutritionally induced anovulatory beef cows. After 4 (short; n = 12) or 18 wk (long; n = 12) of anovulation, cows were randomly assigned within anovulatory group to either 2 microg of GnRH treatment or saline (control; i.v.) every hour for 5 d. Ovarian structures were monitored by daily ultrasonography. Growth rate of the largest follicle (P < 0.01) and maximal size of the largest follicle during treatment were greater (P < 0.01) for GnRH vs control cows. At exsanguination after 5 d of GnRH treatment, the size of the second-largest follicle was greater (P < 0.05) in short (i.e., 4 wk) anovulatory cows than in long (i.e., 18 wk) anovulatory cows and the largest follicle tended (P < 0.10) to be larger in long vs short anovulatory cows. Short anovulatory GnRH-treated cows had more small follicles than short anovulatory control cows or long anovulatory GnRH-treated or control cows (anovulation x GnRH; P < 0.10). Follicular fluid (FFL) concentrations of estradiol (P < 0.01) and androstenedione (P < 0.05) were greater in GnRH vs control cows. Concentrations of insulin-like growth factor-I were greater (P < 0.10) in large vs small follicles in cows that were anovulatory for 4 wk, but not in cows that were anovulatory for 18 wk. The amount of insulin-like growth factor-binding protein (IGFBP)-3 in FFL was greater (P < 0.05) in 4- vs 18-wk anovulatory cows. Amounts of IGFBP-2, -4, and -5 were greater (P < 0.001) in FFL of small (< 5 mm) vs large (> or = 5 mm) follicles regardless of treatment. We conclude that pulsatile treatment with GnRH for 5 d stimulates similar growth of the largest follicles in short- and long-term anovulatory beef cows, and that the duration of anovulation is not a major factor that limits follicular growth w hen anovulatory cowsare treated with GnRH. The primary intrafollicular factors associated with increased follicular size were increased concentrations of estradiol, progesterone, and insulin-like growth factor-I,and decreased concentrations of IGFBP-2, -4, and -5. Increased duration of anovulation was associated with decreased concentrations of IGF-I and IGFBP-3 in FFL.

Androstenedione↗

PubMed2001

Expression of retinol-binding protein messenger RNA and retinoic acid receptors in preattachment bovine embryos.

In cattle, retinoic acid (RA) has been indirectly associated with developmental potential of the embryo. RA is transported by retinol-binding protein (RBP) and actions of RA are mediated by several subtypes of nuclear retinoic acid receptors (RAR). Bovine embryos, produced in vitro from oocytes harvested from ovaries collected at a local abattoir, were frozen in liquid nitrogen at the oocyte, 2-, 4-, 8-, 16 to 20-cell, morula, blastocyst, and hatched blastocyst stages. Employing reverse transcription polymerase chain reaction (RT-PCR) we investigated mRNA expression for RBP, RARalpha, RARbeta, RARgamma, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Total RNA was extracted from 25 pooled embryos at each stage and RT-PCR analysis was repeated thrice. GAPDH transcript was detected in all stages. Transcripts for RBP, RARalpha, and RARgamma were also detected in all stages from the oocyte through to the hatched blastocyst. Expression of RARbeta was not detected at any stage. Whole-mount immunohistochemistry was performed with intact and hatched blastocysts using polyclonal antibodies against RARalpha and RARgamma2 to investigate if these embryonic mRNAs were translated to the mature protein. Strong immunostaining was observed for both RARalpha and RARgamma2 in the inner cell mass and trophectoderm of intact and hatched blastocysts. Expression of mRNA for RBP, RARalpha, RARgamma, and of the RARalpha and RARgamma2 receptor proteins in the bovine embryo suggests that RA is likely to directly regulate gene expression during preimplantation development in that species.

Animals↗

PubMed2001

Proteolysis of insulin-like growth factor binding proteins during preovulatory follicular development in cattle.

The present study was conducted to evaluate changes in follicular fluid (FF) insulin-like growth factor binding protein (IGFBP) proteolytic activity and levels of steroids and IGFBP during follicular development in cattle. Estrous cycles of cows were synchronized with two injections of prostaglandin F2alpha (PGF) 11 d apart and follicular growth monitored via daily rectal ultrasonography in order to identify the dominant follicle. All cows were ovariectomized 48 hr after the second injection of PGF. Follicular fluid was collected individually for all follicles > 5 mm and pooled for small (1 to 5 mm) follicles. Follicular fluid estradiol and androstenedione levels were greater (P < 0.05) and progesterone and IGFBP-3 levels not different (P > 0.10) in large dominant than in small (1 to 5 mm) or large (>5 mm) subordinate follicles, whereas IGFBP-2, -4 and -5 levels were less (P < 0.05) in large dominant than in small or large subordinate follicles. To evaluate proteolysis of IGFBPs, FF was incubated with recombinant human (125) I-labeled IGFBP-2, -3, -4, and -5 and proteins separated by 12% SDS-PAGE. Follicular fluid caused little or no proteolysis of (125)I-lableled IGFBP-2 or -3. However, cleavage of (125)I-labeled IGFBP-4 and -5 by FF from large dominant follicles was greater (P < 0.05) than by FF from small or large subordinate follicles indicating that a protease to IGFBP-4 and -5 exists in estrogen dominant follicles. We conclude that lower levels of IGFBP-2 in estrogen dominant follicles of cattle are not due to increased proteolysis, whereas decreases in IGFBP-4 and -5 levels are likely due, in part, to increased protease activity. Changes in IGFBP may alter levels of bioavailable IGFs that stimulate steroidogenesis and mitogenesis in developing bovine follicles.

Androstenedione↗

PubMed2000

Effects of intraovarian infusion of insulin-like growth factor-I on ovarian follicular function in cattle.

The objective of this study was to determine if increased secretion of intraovarian insulin-like growth factor-I (IGF-I), experimentally induced via minipumps, affects follicular function in cattle. Fourteen cycling Holstein cows were divided equally into two groups: Control, osmotic minipumps (containing vehicle) surgically inserted into each ovary, or IGF-I treated, osmotic minipumps as in Controls but pumping 2.0 microg of recombinant human IGF-I per hr for 7 days. All cows were synchronized with prostaglandin F(2alpha) 0.10) between Control and IGF-I-treated cows during Days 2 to 6 of treatment. IGF-I treatment increased (P<0.05) estradiol concentrations in follicular fluid of small follicles, but had no effect (P<0.10) on estradiol concentrations in follicular fluid of large follicles, or on progesterone, androstenedione, or IGF binding protein concentrations in small or large follicles. We conclude that a 7-day infusion of IGF-I directly into the stroma of the ovary altered follicular growth and follicular fluid estradiol concentrations.

Animals↗

PubMed1999

Influence of dose, frequency, and duration of infused gonadotropin-releasing hormone on secretion of luteinizing hormone and follicle-stimulating hormone in nutritionally anestrous beef cows.

Nutritionally induced anovulatory cows were ovariectomized and used to determine the relationships between dose, frequency, and duration of exogenous gonadotropin-releasing hormone (GnRH) pulses and amplitude, frequency, and concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum. In Experiment 1, cows were given pulses of saline (control) or 2 micrograms of GnRH infused i.v. during a 0.1-, 1.25-, 5-, 10-, or 20-min period. Concentrations of LH and FSH during 35 min after GnRH infusion were greater than in control cows (P < 0.01), and FSH concentrations were greater when GnRH infusions were for 10 min or less compared with 20 min. In Experiment 2, the effect of GnRH pulse frequency and dose on LH and FSH concentrations, pulse frequency, and pulse amplitude were determined. Exogenous GnRH (0, 2, or 4 micrograms) was infused in 5 min at frequencies of once every hour or once every 4th hr for 3 d. There was a dose of GnRH x frequency x day effect on LH and FSH concentrations (P < 0.01), indicating that gonadotropes are sensitive to changes in pulse frequency, dose, and time of exposure to GnRH. There were more LH pulses when GnRH was infused every hour, compared with an infusion every 4th hr (P < 0.04). Amplitudes of LH pulses were greater with increased GnRH dose (P < 0.05), and there was a frequency x dose x day effect on FSH pulse amplitude (P < 0.0006). We conclude that LH and FSH secretion in the bovine is differentially regulated by frequency and dose of GnRH infusions.

Anestrus↗

PubMed1997

GnRH antagonist inhibition of luteinizing hormone secretion and ovulation in the pig.

A GnRH antagonist, Ac-D-p-Cl-Phe1,2, D-Trp3, D-Arg6, D-Ala10 GnRHb (Organon), was utilized to determine the effective dosage and duration to inhibit LH secretion in the pig. In a preliminary trial, barrows received either 10, 50, or 250 micrograms/kg BW of the GnRH antagonist. Secretion of LH was inhibited within 30 min for a duration of 12 h with the 100 micrograms/kg dose but persisted for greater than 48 h with the 250 micrograms/kg treatment. A second study determined effectiveness of the antagonist for inhibiting ovulation in cyclic gilts. At first detection of standing estrus, cyclic gilts were treated with either saline (control), 100, or 200 micrograms/kg BW of the GnRH antagonist (GnRH1). A second group of GnRH antagonist gilts received 200 micrograms/kg BW of the GnRH antagonist approximately 8 h prior to standing estrus (GnRH2). The GnRH1-treatment failed to inhibit or delay ovulation. Ovulation was inhibited and estrous cycles lengthened in GnRH2-treated gilts. These preliminary results suggest that ovulation in the gilt can be inhibited if the GnRH antagonist is administered prior to the LH surge.

Animals↗

PubMed1997

Persistence of the dominant follicle during melengestrol acetate administration and its regression by exogenous estrogen treatment in beef cattle.

Experiments were conducted to test the hypothesis that estrogen treatment will regress a persistent dominant follicle developed during melengestrol acetate (MGA) treatment in the absence of a functional corpus luteum (CL) with normal fertility following development and ovulation of a newly recruited follicle. In Exp. 1, nonlactating beef cows (n = 31) were administered .5 mg.cow-1.d-1 of MGA (d 0) for 14 d with 25 mg of prostaglandin F2 alpha (PGF2 alpha) administered on d 6 and 8 to regress the CL. On d 11 of treatment, approximately half the MGA-treated cows received 5 mg of estradiol valerate (EV) i.m. (MGAEV, n = 14) and the remainder were maintained on MGA (n = 17). Ovaries were checked with ultrasound on d 8, 10, 12, and 14 of MGA treatment and every day until ovulation. A persistent dominant follicle developed in 90% of the MGA-treated cows by d 10 of treatment. Most of the MGA-treated cows ovulated the persistent dominant follicle (n = 13/17), whereas EV treatment regressed the persistent dominant follicle (n = 10/14) with the recruitment of a new follicle that ovulated (n = 8/10). Diameter of the ovulatory follicle was larger (P < .05) for the MGA (19.8 +/- .6 mm) than for the control (15.1 +/- .8 mm) and MGAEV (14.8 +/- .7 mm) cows. In Exp. 2, nonlactating, multiparous beef cows (n = 97) and yearling heifers (n = 38) were equally allotted to either a control, MGA alone, or MGA + estradiol-17 beta (MGAE) group with the same dose of MGA as administered in Exp. 1. The 1st d of MGA feeding was the 1st d of treatment. On d 10 of treatment half the MGA-treated animals were injected i.m. with 5 mg of estradiol-17 beta. In controls, behavioral estrus was detected and animals were artificially inseminated (AI) for 5 d (d 10 to 14 of experiment). All controls not exhibiting estrus by d 15 of experiment were injected with 25 mg of PGF2 alpha. The remaining controls and all MGA cows were observed for behavioral estrus and AI commenced for 7 d following withdrawal of MGA (d 15 to 21 of experiment). More (P < .05) controls (90.3%) than MGA (84.8%) or MGAE (63.6%) cows showed estrus within 7 d after MGA withdrawal. The percentage of animals conceiving to the synchronized estrus did not differ (P > .05) among treatments. The data support our hypothesis that a persistent dominant follicle developed and can be regressed with exogenous estrogen treatment followed by the recruitment and ovulation of a new follicle after MGA withdrawal and fertility of that estrus does not seem to be significantly compromised.

Animals↗

PubMed1996

Levels of insulin-like growth factor (IGF) binding proteins, luteinizing hormone and IGF-I receptors, and steroids in dominant follicles during the first follicular wave in cattle exhibiting regular estrous cycles.

Objectives of this study were to determine if concentrations of steroids, insulin-like growth factor -I (IGF-I), and IGF binding proteins (IGFBP) in follicular fluid and numbers of LH and IGF-I receptors change during growth of the dominant follicle. Ovarian follicular development was monitored daily via ultrasound in lactating Holstein cows. Animals underwent bilateral ovariectomy when the dominant follicle was first identified (days 4-6; estrus = day 0; early; n = 5) or when it stopped growing (days 8-12; late; n = 8). All follicles were classified as dominant (DF), large (LG; > = 6 mm in diameter, excluding DF) or small (SM; < 6 mm), follicular fluid was aspirated, and theca and granulosa cells were collected. Levels of IGFBP-2, assessed via ligand blotting, were greater (P < 0.05) in LG and SM follicles compared with DF in early cows. Levels of IGFBP-3 in follicular fluid were unaffected by follicle class. Numbers of specific 125I-hCG/LH binding sites in thecal cells were greater (P < 0.01) in DF compared with LG and SM follicles of both early and late cows. Numbers of specific 125I-hCG/LH binding sites in granulosa cells were similar for follicle sizes in early cows, but, in late cows, were greater (P < 0.01) in DF compared with SM follicles and were severalfold greater (P < 0.01) in late DF compared with early DF. Numbers of receptors for IGF-I in thecal cells were 2-fold greater (P < 0.05) in DP and LG compared with SM in late cows. Numbers of IGF-I receptors in granulosa cells were unaffected by size or growth of follicles, but were severalfold greater than in theca cells. Concentrations of estradiol were severalfold greater (P < 0.01) in DF compared with LG and SM in both early and late cows. Concentrations of androstenedione in early cows were greater (P < 0.05) in DF and SM compared with LG follicles. Concentrations of progesterone and IGF-I did not differ (P > 0.10) among follicle classes, but both were greater (P < 0.10) in late LG compared with early LG follicles. Concentrations of IGF-II in follicular fluid did not differ (P > 0.10) between early and late cows but were greater (P < 0.10) in SM than DF or LG follicles. We conclude that low amounts of IGFBP-2 and increased thecal binding sites for hCG/LH appear to be related to establishment of the dominant follicle during the first follicular wave in cattle exhibiting regular estrous cycles during late lactation.

Androstenedione↗

PubMed1993

Effect of ovarian antral follicle cauterization on the interestrus interval of the gilt.

The objective of the present study was to determine if destruction of ovarian antral follicles by laser-cauterization affects CL lifespan during the estrous cycle of the gilt. Cyclic gilts were randomly assigned to either SHAM, laser (L) or laser-estradiol (L-E2) treatment groups, with the L-E2 group receiving a 5-mg intramuscular (i.m.) injection of estradiol-17beta cypionate at the time of the first surgery. Ovarian antral follicles were laser-cauterized on either Days 12 and 14 (L12) or Days 14 and 17 (L14) of the estrous cycle. In the L12-E2 group, 3 of 4 gilts had extended mean interestrus intervals of more than 22 days compared with 0 of 4, 0 of 6, 0 of 7 and 1 of 5 gilts in the SHAM, L12, L14 and L14-E2 groups, respectively. The L12-E2 gilts had a longer (P<0.05) mean interestrus interval (23.5+/-1.3 days) than the L12 (20.0+/-1.1 days), L14 (20.7+/-1.0 days) and SHAM (20.5+/-1.3 days). The mean interestrus interval of L14-E2 gilts (21.8+/-1.2 days) did not differ from those of the L12-E2 group or the L12, L14 and SHAM group gilts. Six additional gilts were injected with 5 mg estradiol cypionate-17beta to serve as nonsurgical controls for E2 treatment. Gilts (3 of 3) given an E2 injection on Day 12 had extended mean interestrus interval (26.0+/-2.6 days), while 2 of 3 gilts injected with E2 on day 14 had extended mean interestrus intervals (27.7+/-2.1 days). These results indicate that in cyclic gilts destruction of ovarian follicles by laser-cauterization did not affect CL lifespan, and that luteolysis is not dependent on the presence of antral follicles.

Journal Article↗

PubMed1993

Failure of luteolysis and extension of the interoestrous interval in sheep treated with the progesterone antagonist mifepristone (RU 486).

The progesterone antagonist mifepristone (RU 486) was injected i.m. into ewes during the early luteal phase of the oestrous cycle to test the hypothesis that duration of uterine exposure to progesterone from the corpus luteum initiates luteolysis through the proper timing of endometrial oxytocin receptor expression and pulsatile secretion of PGF2 alpha coincident with release of luteal oxytocin. In Expt 1, duration of cycle, the PGF2 alpha metabolite 15-keto-13,14-dihydro-PGF2 alpha (PGFM) and oxytocin concentrations were measured in ewes treated on days 5, 6, 7 and 8 of the oestrous cycle with either 2.5 or 5.0 mg RU 486 kg-1 day-1 (n = 4 per group); control ewes (n = 6) were injected i.m. with 80% ethanol (diluent). In Expt 2, the presence of functional uterine oxytocin receptors was determined indirectly on day 12 of the cycle by measuring the plasma PGFM response to oxytocin challenge (20 iu, i.v.) in diluent-treated ewes (n = 3) and in ewes treated with 2.5 mg RU 486 kg-1 day-1 on days 6, 7 and 8 of the oestrous cycle. Duration of the oestrous cycle of control ewes (16 +/- 1 days) was extended beyond day 24 (day 0 = oestrus) in 10 of 11 ewes treated with RU 486 as determined by daily exposure of ewes to a ram and by measurement of progesterone concentrations in plasma in the two experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Endocrine events associated with endometrial function and conceptus development in cattle.

Regulation and timing of luteolysis during the bovine oestrous cycle is controlled by the initiation and length of progesterone stimulation. Results have demonstrated that early administration of progesterone shortens the interoestrous interval in the ewe and cow, and removal of progesterone stimulation through a progesterone receptor antagonist delays luteolysis in sheep. Current data suggest that down-regulation of progesterone receptors in the uterine epithelium may initiate events involved in the synthesis and release of prostaglandin F2 alpha (PGF2 alpha) for luteolysis. Progesterone is also involved in the stimulation of the uterine secretions that regulate conceptus growth and the release of the bovine trophoblast protein-1 (bTP-1) necessary for inhibiting endometrial PGF2 alpha release. Conceptus secretion of bTP-1, a Type I trophoblast interferon, increases the concentration of the cellular enzyme 2',5'-oligoadenylate synthetase within the endometrium. The biological role of 2',5'-oligoadenylate synthetase in the establishment of pregnancy is discussed.

Animals↗

PubMed1991

Effect of estrogen inhibitors on conceptus estrogen synthesis and development in the gilt.

Two estrogen antagonists (keoxifene and clomiphene) and two aromatase inhibitors (LY56110 and 4-hydroxyandrostenedione, 4-OHA) were utilized to determine the role of conceptus estrogen in trophoblastic elongation and maintenance of pregnancy in the pig. Pregnant gilts were unilaterally hysterectomized on day 10.5, and infused via a uterine arterial catheter with 200 mg of keoxifene or vehicle. The remaining uterine horn was removed based on time estimated for conceptus elongation. In a second study, pregnant gilts were injected daily with 200 mg (i.m.) of clomiphene or vehicle during pregnancy (days 10-16) and hysterectomized on day 30. A third study assessed in vitro aromatase inhibition by 4-OHA and LY56110 using trophoblastic microsomes incubated with [1 beta, 2 beta-3H]-androstenedione for 6 hr. In a fourth study, in vivo inhibition of aromatase activity was determined. For this study pregnant gilts, unilaterally hysterectomized on day 10.5, received either 4-OHA, LY56110, or vehicle. Conceptus development and uterine estrogens were quantified. None of the estrogen antagonists and aromatase inhibitors interferred with conceptus elongation. Uterine protein, calcium and acid phosphatase were similar (P greater than .10) between keoxifene- and vehicle-treated gilts. Embryonic survival of clomiphene- and vehicle-treated gilts was similar (91.5 vs 87.4%). In vitro, 4-OHA and LY56110 had 50% inhibitory concentrations of 0.1 microM and 13 nM. Treatment of gilts with 4-OHA reduced total estrogens in uterine flushings by 57% (P less than .02), whereas treatment with LY56110 did not significantly lower total estrogen content in uterine flushings. Estrogen antagonists were not effective in blocking conceptus elongation and maintenance of pregnancy. Although estrogen synthesis can be inhibited in vitro, dosages of aromatase inhibitors used were not totally effective in vivo.

Acid Phosphatase↗

PubMed1991

Nutritional anestrus in beef cows: effects of body condition and ovariectomy on serum luteinizing hormone and insulin-like growth factor-I.

The objectives of this experiment were to determine if a postcastration increase in concentrations of LH occurs in nutritionally anestrous beef cows and to examine the relationship between body energy reserves and secretion of LH and insulin-like growth factor-I (IGF-I). Nonpregnant, nonlactating, Hereford cows were fed to maintain (M) body weight (BW), body condition score (BCS), and normal estrous cycles (n = 5) or were fed a restricted (R) diet for 26 wk to lose BW and BCS and to become anestrus (n = 10). At 5-7 wk after the initiation of anestrus, R cows were randomly allotted to be ovariectomized (OVX) via flank incision (n = 5) or to remain intact (INT, n = 5). OVX was performed when R cows became anestrous. All M cows were OVX. Serum was collected frequently the day before and during the first 10 days after OVX, and concentrations of progesterone, estradiol, LH and IGF-I were quantified. On Day 10 after OVX, 1 mg of estradiol was injected into 3 cows from each group and serum was collected for 30 h. After OVX, there was a treatment-by-day effect for mean serum LH and IGF-I concentrations. Concentrations of LH increased (p less than 0.01) and concentrations of IGF-I decreased (p less than 0.05) in M-OVX cows when compared with R-OVX and R-INT cows. Concentrations of LH and IGF-I were similar for R-OVX and R-INT cows. The number of LH pulses was similar for M and R cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗

PubMed1991

Survival of bovine embryos transferred to progesterone-treated asynchronous recipients.

Treatment of recipient cows with 100 mg of progesterone daily from Days 1 to 5 of the oestrous cycle increased plasma progesterone compared with vehicle-treated recipients. Embryo transfer to progesterone-treated recipients which showed oestrus 72 h after the donor cows resulted in pregnancy rates at Day 35 similar to those of synchronous (+/- 12 h) recipients (42 vs. 50%). Only 1 of 22 (4.8%) asynchronous (-72 h) vehicle-treated recipients established pregnancy. Similar treatments of cyclic cows with progesterone shortened (P less than 0.01) the interoestrous interval by 3.2 days. When assessed on Day 7 of pregnancy, administration of progesterone to superovulated donor cows on Days 1-4 of pregnancy did not affect early embryo development compared with superovulated cows treated with vehicle alone. Plasma progesterone increased rapidly in superovulated cows compared with cows during the oestrous cycle. The results indicate that administration of progesterone early in the oestrous cycle of the recipient can effectively advance uterine receptivity for the transfer of older asynchronous embryos.

Animals↗