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Biomedical subjects

M C Lucy

Publications and source records attributed to M C Lucy.

At least 55 records · Page 3Linked to original sources
PubMed2000

Identification of Sp1 as the transcription factor for the alternative promoter P2 of the bovine growth hormone receptor gene.

Growth hormone receptor (GHR) mRNA variants that differ in the 5'-untranslated regions (5'-UTR) have been isolated in various species. These 5'-UTR variants are generated from the use of alternative promoters and/or alternative splicing. The 5'-UTR 1B is one of the GHR 5'-UTR variants isolated in the bovine but its homologues are also present in other species. The 5'-UTR 1B is a predominant GHR 5'-UTR expressed in many tissues. In the present study, we screened a bovine genomic library and isolated a 1.7 kb bovine GHR genomic sequence including exon 1B and its 5' flanking region from which the GHR 5'-UTR 1B is generated. Using primer extension, two major transcription start sites were mapped in the bovine exon 1B. Transient transfection analysis of the 5' flanking region of exon 1B confirmed its promoter activity (termed P2) in both Hep G2 and BHK-21 cells. Furthermore, analysis of deletion promoter-reporter constructs found that the basal activity of P2 resided in the proximal region of P2. DNase I footprinting analysis and electromobility shift assay (EMSA) identified the ubiquitous transcription factor Sp1 as the binding protein to a GC box-containing DNA element within the proximal P2. Deletion of the GC box greatly reduced the activity of P2 in cell lines. The GC box-containing site also appeared to bind Sp1 in the nuclear extracts from diverse bovine tissues. This suggests that interactions of Sp1 with the GC box-containing element in the proximal region of P2 may be part of the mechanism for the expression of the bovine GHR 5'-UTR 1B in diverse tissues.

5' Untranslated Regions↗
PubMed2000

Expression of two variants of growth hormone receptor messenger ribonucleic acid in porcine liver.

Transcription of GH receptor (GHR) mRNA is initiated from multiple promoters. Most GHR mRNA arise from GHR Promoter 1 (GHR P1) and GHR P2, which transcribe GHR 1A and GHR 1B mRNA, respectively. Our objective was to characterize the expression of GHR 1A and GHR 1B mRNA in liver of neonatal intact (1 d of age) and castrated (14, 28, and 42 d of age) male pigs (Exp. 1; n = 6 per age group), intact male pigs treated with recombinant porcine ST (rpST) or control (Exp. 2; 21, 42, and 77 d of age; n = 4 pigs per treatment per age), and pregnant gilts treated with rpST (n = 6) or control (n = 7) (Exp. 3). Tissue samples were collected at slaughter for mRNA analyses. The porcine GHR 1A and GHR 1B cDNA were cloned and were homologous to GHR cDNA isolated from other species. Ribonuclease protection assays were used to measure GHR 1A and GHR 1B mRNA. Liver expressed GHR 1A and GHR 1B mRNA, whereas muscle, uterus, and ovary expressed GHR 1B mRNA. The GHR 1A mRNA in the liver of neonatal intact and castrated male pigs (Exp. 1) was expressed at very low levels on d 1, 14, and 28, and two of six pigs expressed a high level of GHR 1A on d 42. The GHR 1B mRNA, however, was detected at all ages (d 1 through 42), and the amount of GHR 1B increased (P<.05) on d 42. The liver of intact male pigs (Exp. 2) expressed GHR 1B mRNA by 21 d, whereas a high level of GHR 1A mRNA was not detected until d 42 (P<.10). Administration of rpST had no effect on expression of GHR 1A or GHR 1B mRNA in pigs younger than 77 d (Exp. 2), but it tended to decrease (P<.10) GHR 1A mRNA but not GHR 1B mRNA in pregnant gilts (Exp. 3). In conclusion, GHR mRNA in porcine liver was composed of at least two variants (GHR 1A and GHR 1B). The GHR 1B mRNA was the major GHR mRNA in pig liver before 77 d of age. The GHR 1A mRNA increased after 42 d of age and tended to undergo specific down-regulation in response to rpST in pregnant gilts.

Animals↗
PubMed2000

Decreased growth in angus steers with a short TG-microsatellite allele in the P1 promoter of the growth hormone receptor gene.

A polymorphic TG-repeat microsatellite is located 90 base pairs upstream from a major transcription start site in the bovine growth hormone receptor gene. A shorter allele with 11 consecutive TG is common in Bos indicus cattle, whereas longer 16- to 20-TG-repeat alleles predominate in Bos taurus breeds. The purpose of this study was to compare growth and carcass traits between Angus steers that had two of the longer growth hormone receptor alleles with their half-siblings that had one short allele and one of the longer alleles. We genotyped 64 Angus sires with respect to the poly-TG microsatellite and identified six bulls that were heterozygous in that they had one short 11-TG allele and one of the longer alleles. We then grouped 125 steer progeny of these six heterozygous bulls according to their genotypes: only the longer 16- to 20-TG-repeat alleles were found in 73 steer progeny (long/long homozygotes), whereas a short 11-TG allele was paired with one of the longer alleles in 52 progeny (short/long heterozygotes). Contrasts for the long/long homozygotes vs the short/long heterozygotes were significant for weaning weight (17 +/- 4 kg; P < .001) and carcass weight (14 +/- 5 kg; P < .01). Approaching significance (P = .03) was the contrast for USDA marbling score (-.3 +/- .2). No significant differences (P > .05) were detected for contrasts in birth weight (.3 +/- .6 kg), longissimus muscle area (-.2 +/- 1 cm2), or carcass fat depth (-.01 +/- .07 cm). This polymorphism has potential for use in DNA marker-assisted selection programs.

Alleles↗
PubMed2000

Development of an estrus synchronization protocol for beef cattle with short-term feeding of melengestrol acetate: 7-11 synch.

An estrus synchronization protocol (7-11 Synch) was developed to synchronize the first follicular wave and timing of ovulation in postpartum beef cows. In Exp. 1, follicular development and timing of ovulation in response to the following protocol were evaluated. Beef heifers (n = 12) and cows (n = 6), at random stages of the estrous cycle, were fed melengestrol acetate (MGA; .5 mg x animal(-1) x d(-1)) for 7 d and injected with PGF2alpha (PG; 25 mg) on the last day of MGA. A second injection of PG was administered 11 d after cessation of MGA. After the second injection of PG, estrus was synchronized in 6/12 heifers and 3/6 cows. The interval to estrus in heifers and cows was 54 and 64 h, respectively (P > .10). All animals exhibiting estrus ovulated first-wave follicles. Animals that failed to respond to the second injection of PG were in estrus later than 6 d after cessation of MGA and had corpora lutea that were unresponsive to the injection of PG. Based on the variation in interval to estrus following the first PG injection on the last day of MGA feeding in Exp. 1, an injection of GnRH (100 microg) was added to the protocol 4 d after the cessation of MGA to ensure ovulation or luteinization of dominant follicles and synchronization of first-wave follicular development. This revised protocol was termed "7-11 Synch." In Exp. 2, two estrus synchronization protocols were compared. Multiparous beef cows were stratified by breed and postpartum interval and randomly assigned to the 7-11 Synch (n = 44) or Select Synch protocols (GnRH injection followed by PG injection 7 d later; n = 45). Timing of estrus after the last PG injection (0 h) ranged from 42 to 102 h in the 7-11 Synch group and -30 to 114 h in the Select Synch group. Eight cows (18%) in the Select Synch group exhibited estrus 30 h before to 18 h after PG. Synchronized estrus peaked between 42 and 66 h after the last PG injection, and a maximum number of cows were in estrus at 54 h for both treatment groups. Synchrony of estrus from 42 to 66 h was greater (P < .05) in 7-11 Synch (91%: 41/44) than in Select Synch cows (69%: 31/45). Artificial insemination pregnancy rate from 42 to 66 h was greater (P < .05) in the 7-11 Synch group (66%: 29/44) than in the Select Synch group (40%: 18/45). In summary, the 7-11 Synch protocol improved synchrony of estrus without reducing fertility. This protocol has potential future application for fixed-time AI in beef cattle production systems.

Animals↗
PubMed2000

Regulation of ovarian follicular growth by somatotropin and insulin-like growth factors in cattle.

Somatotropin (ST), insulin-like growth factor (IGF)-I, and IGF-II affect animal growth and lactation as well as animal reproduction. Understanding the effects of ST and the IGF on reproduction is important because ST and IGF-I undergo dynamic changes prior to the postpartum breeding period. In addition, administration of recombinant bovine somatotropin (rbST) to lactating cows is a common practice that increases blood concentrations of ST and IGF-I during the breeding period. In vivo, administration of rbST caused greater ovarian follicular development. The effects of rbST may represent direct actions of ST because ST receptors are found within granulosa cells as well as oocytes. Alternatively, the actions of ST may be indirectly mediated by increased IGF-I and (or) nutrient partitioning that occurs after rbST. Both IGF-I and IGF-II are synthesized within the ovary. Ovarian IGF are, therefore, a composite of IGF from both endocrine (liver) and autocrine and paracrine (ovary) sources. The IGF stimulate ovarian function by acting synergistically with gonadotropins to promote growth and steroidogenesis of ovarian cells. Actions of IGF-I and -II are restrained by a series of IGF binding proteins (IGFBP) that either originate from the blood or are synthesized locally within the follicle. Degradation and differential synthesis of IGFBP are important mechanisms regulating IGFBP amounts. The relative amounts of IGFBP may ultimately determine ovarian IGF action. Future studies of ST and IGFs should focus on the hormones, receptors, and binding proteins as well as the metabolic requirements for normal ovarian function in dairy cattle.

Animals↗
PubMed1999

Isolation and characterization of a novel promoter for the bovine growth hormone receptor gene.

The use of alternative promoters represents an important mechanism for the regulation of growth hormone receptor (GHR) gene expression. Two promoters have been isolated previously for the GHR gene: the P1 promoter that drives liver-specific expression, and the P2 promoter that drives ubiquitous expression. In the present study, we isolated a third GHR promoter termed P3. The P3 promoter was GC-rich and TATA-less. The P3 promoter was able to drive the expression of a luciferase reporter gene in cell lines Hep G2, PLC/PRF/5, and BHK-21. In vivo, the P3 promoter initiated transcription from two major sites in exon 1C of the GHR gene in many tissues. In the adult bovine liver, the P3-transcribed GHR mRNA represented only 10% of the total GHR mRNA pool. In non-hepatic tissues such as kidney, skeletal muscle, mammary gland, and uterus, P3-transcribed GHR mRNA represented 30-40% of the total GHR mRNA pool. Within the bovine GHR gene, the P3 promoter was located immediately downstream from the P2 promoter. In transfected cells, the P2 promoter served as an enhancer for the P3 promoter. Existence and co-regulation of two ubiquitous promoters may be a mechanism for achieving a high level of expression of the GHR gene in multiple tissues.

Animals↗
PubMed1999

Plasma GH, IGF-I, and conception rate in cattle treated with low doses of recombinant bovine GH.

Blood and uterine concentrations of GH and insulin-like growth factor (IGF)-I are correlated with improved fertility in cattle. We tested incremental doses of a 14-d sustained release recombinant bovine GH (rbGH) to increase blood GH and IGF-I (Experiments 1 and 2). Conception rate after administration of an optimized rbGH dose was also tested (Experiment 3). In Experiment 1, lactating Holstein cows (n = 18) were randomly assigned to receive 0 (n = 5), 100 (n = 5), 200 (n = 5), or 500 (n = 3) mg sc rbGH. Increasing the doses of rbGH was associated with increased serum concentrations of GH and IGF-I. The 100- and 200-mg doses caused an IGF-I release that was below and above, respectively, the perceived optimum response. Therefore, Experiment 2 was designed to test a rbGH dose (167 mg), which was intermediate to the doses tested in Experiment 1. Lactating and nonlactating postpartum beef cows were treated with 0 (n = 9) or 167 (n = 9) mg rbGH at insemination. Plasma concentrations of GH and IGF-I were greater in rbGH-treated cows than in controls. Lactating cows had initial IGF-I concentrations that were lower than nonlactating cows. The 167-mg dose of rbGH increased plasma IGF-I concentrations in lactating cows to the levels of those of nonlactating cows. In Experiment 3, cows and heifers were administered either 0 or 167 mg rbGH at insemination. The conception rate for rbGH-treated and control cows was 54.4 and 49.5% (n = 617), and 46.0 and 46.3% for heifers (n = 1123), respectively. Herd (P<0.01) and parity (P<0.01) affected conception rate, but conception rates for rbGH and control cattle were similar. In summary, low doses of rbGH increased blood GH and restored blood IGF-I concentrations in lactating cows to those of nonlactating cows, but the conception rate in cows and heifers was not affected by administration of 14-d sustained-release rbGH at insemination.

Animals↗
PubMed1999

A novel phenotype for Lardon dwarfism in miniature Bos indicus cattle suggests that the expression of growth hormone receptor 1A in liver is required for normal growth.

Mutations within the growth hormone receptor (GHR) gene that lead to an inactivated or truncated GHR protein cause abnormal growth and small adult size in a variety of species (Laron dwarfism). We studied a line of miniature Bos indicus cattle that have phenotypic (small mature size) and endocrine (increased blood growth hormone and decreased blood insulin-like growth factor-I concentrations) similarities to Laron dwarfs. Liver mRNA from miniature and control cattle was used to amplify a cDNA within the coding region of the GHR. The miniature cattle had GHR mRNA size (determined by Northern blot) and cDNA sequence that were similar to control cattle and, therefore, were unlike most Laron dwarf genotypes in which the GHR gene is mutated. Amounts of mRNA from liver as well as muscle (superficial neck and longissimus) were analyzed by ribonuclease protection assay for IGF-I, total GHR, GHR 1A (inducible, liver-specific GHR mRNA), and GHR 1B (constitutive GHR mRNA). Four control and five miniature bulls were tested. As expected, liver IGF-I mRNA was decreased in the miniature cattle (approximately 12% of control; P < 0.01). The amount of the total GHR as well as GHR 1A mRNA were also decreased in liver (17% and 19% of control, respectively; P < 0.01). Other GHR mRNA, including GHR 1B mRNA, were similar for miniature and control cattle. In muscle, there was a tendency (P < 0.10) for decreased IGF-I mRNA and increased GHR mRNA in miniature compared with control cattle. In summary, a novel phenotype for Laron dwarfism in Bos indicus cattle was associated with underexpression of GHR 1A mRNA, but not other GHR mRNA variants in liver. In addition to decreased GHR 1A mRNA, the miniature cattle had decreased liver IGF-I mRNA. Full expression of GHR 1A in liver, therefore, may be required for full liver IGF-I expression and normal growth.

Animals↗
PubMed1999

Reduced growth hormone receptor (GHR) messenger ribonucleic acid in liver of periparturient cattle is caused by a specific down-regulation of GHR 1A that is associated with decreased insulin-like growth factor I.

GH receptor (GHR) messenger RNA (mRNA) is transcribed from at least three different promoters within the liver of cattle. The first promoter (P1) is liver specific and alternatively splices exon 1A onto the GHR mRNA (GHR 1A mRNA). The second and third promoters (P2 and P3) have constitutive activity in many tissues and alternatively splice exons 1B and 1C onto the GHR mRNA (GHR 1B and GHR 1C mRNA). The total amount of GHR in the liver partially determines liver insulin-like growth factor I (IGF-I) synthesis in response to GH. Two studies were conducted to characterize the changes in GHR 1A mRNA, alternatively spliced GHR mRNA, and IGF-I mRNA during late pregnancy and early lactation in dairy cattle. Liver RNA was isolated from pregnant Holstein cattle (Bos taurus) on days -14, 0, and 21 relative to parturition (study 1) or days -14, 0, 15, 30, 60, and 90 relative to parturition (study 2). Ribonuclease protection assays were used to quantify total GHR (all GHR variants) as well as liver-specific GHR 1A and alternatively spliced GHR mRNA. Likewise, total IGF-I as well as alternatively spliced IGF-I mRNA (class 1 and class 2 transcripts) were measured. A decrease in total GHR mRNA at parturition (P < 0.01) was associated with a specific decrease in GHR 1A mRNA (P < 0.001). The amount of alternatively spliced GHR mRNA (including GHR 1B and GHR 1C mRNA) did not change at parturition (P > 0.10). Total liver IGF-I mRNA and blood IGF-I concentrations were also decreased at parturition (P < 0.05 and P < 0.01, respectively). However, a decrease in IGF-I mRNA was observed for both class 1 and class 2 IGF-I transcripts (P < 0.01 and P < 0.05, respectively). We conclude that the reduced amount of GHR mRNA during early lactation is caused by a specific down-regulation of GHR 1A mRNA that was associated with decreased liver IGF-I mRNA and decreased blood IGF-I concentrations. These data provide evidence for independent regulation of GHR mRNA by mechanisms that discriminate between GHR P1 (transcribes GHR 1A) and alternative promoters that transcribe constitutive GHR mRNA.

Animals↗
PubMed1999

Effect of anthelmintic treatment on sexual maturation in prepubertal beef heifers.

Heifers treated with ivermectin at weaning have been reported to reach puberty at a younger age and lighter weight than untreated heifers. We tested the hypothesis that heifers administered ivermectin would respond with earlier follicular development and a greater LH response to a 1-mg estradiol-17beta challenge (E2C) than untreated heifers. Fall-born Angus heifers (n = 32) were randomly assigned on 284 +/- 9 d of age (215.5 +/- 20.8 kg) to receive ivermectin (IVR) or albendazole (ALB), IVR + ALB, or to remain as untreated controls (CONT). Each group (n = 8) was housed separately in adjacent pens throughout the trial and managed to gain .8 kg/heifer on a ration containing 13.2% CP, 58.8% TDN, and 49.9% DM. The CONT heifers received an additional 2.27 kg/heifer of corn silage and 1.59 kg/heifer of corn daily to maintain ADG at comparable levels. Individual body weight was recorded weekly, and nematode eggs per gram (EPG) of feces were measured every 21 d. Ultrasonography was performed on alternate days starting 2 wk prior to E2C to characterize follicular wave patterns. Follicles were separated into classes (C1 [3 to 5 mm], C2 [6 to 9 mm], and C3 [10 mm]) and sizes (largest [LF], second [SLF], third [TLF], and fourth largest follicles [FLF]). The sizes of the regressing dominant follicle 1 (DF1) and the progressing dominant follicle 2 (DF2) were also determined. Serum concentrations of LH were determined from hourly jugular blood samples collected 8 to 24 h after injection of E2C. The IVR + ALB treatment group had more C3 follicles than ALB and CONT (P < .07). The IVR-treated heifers had larger TLF than ALB and CONT (P < .04). The IVR- and IVR + ALB-treated heifers had larger FLF and DF2 than ALB and CONT (P < .1). Least squares means for DF2 were 9.5 +/- .5, 8.0 +/- .4, 9.5 +/- .3 and 8.3 +/- .3 mm, for IVR, ALB, IVR + ALB and CONT, respectively (P = .02 for treatment effect). The E2C-induced serum LH concentration did not differ with respect to treatment. We conclude that heifers administered IVR display increased follicular development, supporting our earlier investigations regarding reduced age at puberty in heifers treated with IVR near weaning.

Animals↗
PubMed1999

Suckling reinitiated milk secretion in beef cows after an early postpartum hiatus of milking or suckling.

We determined whether milk secretion in beef cows could be reinitiated by renewed suckling after a hiatus from milking or suckling. Fifty-three Angus x Hereford cows were suckled ad libitum by their own calves for 13 to 18 d postpartum and then assigned to treatments for 4 wk in which cows were 1) neither milked nor suckled (weaned; n = 18), 2) milked 2 x daily (milked; n = 18), or 3) suckled by their own calves (suckled; n = 17). Thereafter, all calves (including earlier weaned calves) suckled their own dams until permanent weaning at 203 d of age, except when their dams were milked once after receiving (i.m.) 40 IU of oxytocin at reinitiation of suckling (0 wk) and again 1 and 5 wk later. Prolactin was increased in milked and suckled cows during 20 min after milking or suckling at the termination of treatments (0 wk). Concentrations of insulin-like growth factor-I were greater for weaned than suckled cows; milked cows had intermediate concentrations. At 0 wk, milk yield was greater for suckled than milked or weaned treatment cows. After 1 wk of renewed suckling, milk secretion of weaned treatment cows increased, and by 5 wk, composition of milk was normal, but yield was still reduced. We concluded that milk secretion was renewed by suckling in early postpartum cows after they were neither suckled nor milked for 4 wk.

Animals↗
PubMed1999

Expression of growth hormone receptor 1A messenger ribonucleic acid in liver of dairy cows during lactation and after administration of recombinant bovine somatotropin.

The mRNA for growth hormone receptor is transcribed from at least three different promoters in cattle. The first promoter (P1) is liver-specific and transcribes growth hormone receptor mRNA containing exon 1A (growth hormone receptor 1A). The second and third promoters (P2 and P3) are active in a variety of tissues and transcribe growth hormone receptor mRNA containing exon 1B and 1C. The objective was to characterize P1 activity by measuring the amount of growth hormone receptor 1A mRNA in liver of dairy cows at different stages of lactation as well as after administration of recombinant bovine somatotropin (rbST). In study 1, liver RNA was isolated from Holstein cows during the dry period (nonlactating, n = 6) and during early (n = 6), mid (n = 6), and late (n = 11) stages of lactation. Six of the late-lactation cows received injections of rbST (25 mg/d) for 7 d prior to collection of liver tissue. In study 2, lactating Holstein cows received either no infusion (control, n = 10) or continuous infusion of rbST (29 mg/d, n = 10) for 63 d. The amount of growth hormone receptor 1A mRNA was decreased in early- and mid-lactation cows compared with late-lactation cows or nonlactating cows (study 1). Administration of rbST increased growth hormone receptor 1A mRNA (studies 1 and 2). The total amount of growth hormone receptor transcribed from alternative promoters (growth hormone receptor P2 and P3) remained unchanged during different stages of lactation or in response to rbST. We conclude that changes in liver growth hormone receptor mRNA in lactating dairy cattle primarily depend on growth hormone receptor P1 activity.

Animals↗
PubMed1999

Role of growth hormone in development and maintenance of follicles and corpora lutea.

Growth hormone (GH) is a pituitary hormone that affects animal growth, metabolism, lactation, and reproduction. Many of the effects of GH are mediated by insulin-like growth factor I (IGF-I) which is synthesized in liver and ovary in response to GH. Insulin-like growth factor I synergizes with gonadotrophins (LH and FSH) to stimulate growth and differentiation of ovarian cells. There are species differences in the effects of GH in reproductive biology. In most species, ovarian follicles and corpora lutea are potential sites for GH action because the GH receptor is found within granulosal cells as well as corpora lutea. However, growth hormone does not control ovarian IGF-I in all species and, in ruminants, endocrine IGF-I from liver may be the principal mediator of GH action. In cattle, administration of GH increases the number of small antral ovarian follicles but does not increase the number of large antral (dominant) follicles. Growth hormone may antagonize some aspects of dominant follicular function because dominant follicles are shorter-lived in GH-treated cattle. The corpora lutea has increased growth and steroidogenesis in response to GH. Growth hormone-induced steroidogenesis in cultured granulosal and luteal cells depends on IGF-I release after GH treatment. Bovine and ovine granulosal cells do not release IGF-I in response to GH in vitro and, therefore, are less responsive to GH. These results demonstrate that GH is required for normal reproductive function in ruminant as well as nonruminant species.

Animal Nutritional Physiological Phenomena↗
PubMed1998

Follicular dominance in cattle is associated with divergent patterns of ovarian gene expression for insulin-like growth factor (IGF)-I, IGF-II, and IGF binding protein-2 in dominant and subordinate follicles.

A decrease in insulin-like growth factor (IGF) binding protein (BP) amount occurs within the follicular fluid of dominant ovarian follicles. At the same time, concentrations of follicular fluid IGF-I do not change. The mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3, in dominant and subordinate follicles were measured to determine if changes in IGF or IGFBP gene expression are associated with follicular dominance. Heifers were ovariectomized during a follicular wave, either during early-dominance (emerging dominant follicle, 9 mm diameter) or mid-dominance (established dominant follicle, 14-16 mm diameter). Follicles were classified as either dominant (DF), subordinate (SF), or not-recruited (NRF; small antral follicles). mRNA was localized by in situ hybridization and measured by image analyses. The IGF-I mRNA (granulosa cells) was greatest in DF and increased in DF, SF, and NRF from early- to mid-dominance. Likewise, IGF-II mRNA (theca cells) was greatest in DF compared with SF or NRF. The IGFBP-2 mRNA (granulosa cells), however, was nearly undetectable in DF, whereas adjacent SF expressed abundant IGFBP-2 mRNA. The NRF were not uniform in their IGFBP-2 expression because only 5 of 13 NRF had IGFBP-2 mRNA. The IGFBP-3 mRNA (granulosa cells) was found only in two NRF, suggesting that local synthesis is not a predominant source of follicular fluid IGFBP-3. These data show that changes in gene expression for IGFBP-2 are opposite to those for IGF-I or IGF-II. Increased IGF-I and IGF-II mRNA and decreased IGFBP-2 mRNA within the DF may be one mechanism leading to follicular dominance. The opposite pattern of IGFBP-2 gene expression in SF and some NRF may lead to follicular atresia.

Animals↗
PubMed1998

Insulin-like growth factor (IGF)-I, IGF-II, IGF-binding protein-2 and pregnancy-associated glycoprotein mRNA in pigs with somatotropin-enhanced fetal growth.

Fetal growth is increased when pregnant gilts are treated with recombinant porcine somatotropin. The mechanism for increased fetal growth was examined by measuring the expression of IGF-I and -II and IGF-binding protein-2 (IGFBP-2) mRNA in liver and reproductive tissues of somatotropin- and saline-treated pregnant gilts. Twenty-four pregnant gilts received daily injections of either saline (control; n=12) or 5 mg recombinant porcine somatotropin (n=12) from day 30 to day 43 of gestation. Gilts were slaughtered on day 44 of gestation and liver, ovary, placenta, placental uterus (uterus with adjacent placental tissue) and non-placental uterus (region of the necrotic tip) were collected. The mRNAs for somatotropin receptor, IGFs -I and -II, IGFBP-2 and pregnancy-associated glycoprotein (a marker of trophoblast tissue) were analyzed by Northern blotting or ribonuclease protection assay. Gilts treated with somatotropin had heavier fetuses and placentas. The concentration of mRNA for the components of the IGF system was tissue-dependent. The uterine IGF-I mRNA concentration was greater in non-placental than in placental uterus. The greatest IGF-II mRNA concentration was observed in placenta, and adjacent uterine tissue expressed IGFBP-2 mRNA intensely. In non-placental uterus, IGFBP-2 mRNA was nearly undetectable. Somatotropin-dependent regulation of IGF-I was only observed in liver, where the greatest somatotropin receptor mRNA concentration was found. In the pregnant uterus, somatotropin failed to change the concentration of IGF or IGFBP-2 mRNA. Pregnancy-associated glycoprotein mRNA concentration was decreased by somatotropin. In summary, increased fetal growth in somatotropin-treated pregnant pigs was not associated with changes in IGF or IGFBP-2 mRNA concentration in reproductive tissues. Other mechanisms, therefore, lead to enhanced fetal growth in somatotropin-treated pregnant pigs.

Animals↗
PubMed1998

Patterns of ovarian growth and development in cattle with a growth hormone receptor deficiency.

Nutritionally induced changes in growth hormone (GH) and IGF-I are associated with decreased ovarian function and may partially explain infertility and anestrus in undernourished cattle. The reproductive importance of GH and IGF-I was tested in cattle with a GH receptor deficiency (GHRD) that have reduced blood IGF-I. Blood was collected daily for plasma, and ovaries were examined daily by ultrasonography for 3 wk during an estrous cycle (estrus = d 0) in GHRD (n = 8) and control (n = 8) cattle. On d 18, blood samples were collected every 10 min for 6 h to measure LH. The GHRD cattle had fewer small antral ovarian follicles (2 to 5 mm, P < .01). After estrous cycle d 5, the first-wave dominant follicle stopped growing in GHRD but continued growing in controls (P < .001). Size of the CL was equivalent for GHRD and controls until d 5, after which CL development slowed in GHRD (P < .01). Likewise, plasma progesterone concentrations were less in GHRD (P < .001). During the luteal phase, GHRD cattle failed to develop follicles greater than 10 mm in diameter (endocrine status x day, P < .05). Size and rate of growth of preovulatory follicles, plasma estradiol, plasma FSH, and plasma LH (d 18 bleed) were similar in GHRD and controls. In conclusion, an important role for GH, GH receptor, and IGF-I in ovarian function was supported because GHRD cattle had distinctly different patterns of ovarian development compared with control cattle.

Animals↗
PubMed1998

Expression of somatotropin receptor messenger ribonucleic acid in bovine tissues.

The somatotropin receptor mRNA is controlled by at least two different gene promoters that generate two variants with different exon 1 sequences (1A and 1B). The location of 1A and 1B somatotropin receptor mRNA within cattle tissues and, hence, the tissue specificity of the 1A and 1B promoters are unknown. In addition, the cDNA sequence of the 1B somatotropin receptor has not been determined. Our objective, therefore, was to sequence a cDNA for the 1B somatotropin receptor and to analyze bovine tissues for expression of 1A and 1B somatotropin receptor mRNA. Twenty adult tissues and six fetal tissues were collected at slaughter from each of four cows and two fetuses. Messenger RNA was analyzed using ribonuclease protection assays. The adult liver expressed both 1A and 1B mRNA. All other adult tissues expressed 1B mRNA but not 1A mRNA. The greatest amount of 1B mRNA was detected in liver and adipose (abdominal and subcutaneous) tissues. Other tissues had approximately one-half to one-tenth of the amount of 1B mRNA in the liver or adipose tissue. Fetal tissues (including fetal liver) expressed 1B mRNA and not 1A mRNA. Based on cDNA sequencing, the protein encoded by the 1A and 1B mRNA was nearly identical. We concluded that 1A somatotropin receptor mRNA is specific to adult bovine liver. Other adult and fetal bovine tissues expressed 1B somatotropin receptor mRNA with a predicted protein sequence that was similar to the 1A somatotropin receptor.

Adipose Tissue↗