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Biomedical subjects

L A Fitzpatrick

Publications and source records attributed to L A Fitzpatrick.

At least 19 recordsLinked to original sources
PubMed2000

Altered response to thyroid hormones by prostate and breast cancer cells.

Transferrin, an abundant bone marrow constituent, has been shown to be a potent mitogen in vitro in the prostate cancer cell line PC3. T4 (L-thyroxine) and T3 (3',3,5-tri-iodo-L-thyronine) are regulators of cell metabolism. In this study, the effects of nonphysiological concentrations (about two orders of magnitude higher) of T4, T3, T2 (3,5-di-iodo-L-thyronine), RT3 (reverse T3, 3',5', 3-tri-iodo-L-thyronine) and transferrin (about three orders of magnitude lower) were tested on the prostate cancer cell lines PC3, DU145 and LNCaP, and the breast cancer cell line MCF-7. In PC3 cells, increased proliferation by transferrin could be reversed by the addition of T3 or T4. T4 decreased proliferation in all cell lines tested, while transferrin increased proliferation in PC3 cells only. T3 decreased proliferation in PC3, LNCaP and MCF-7 cells but had no effect on DU145 cells. T4 and T3 gave two-state behavior in LNCaP cells. These results were combined to determine the essential iodines which produced the observed proliferative effects. Cell lines responded differently to T4, T3, T2, RT3 and transferrin suggesting a specific interaction among the compounds tested and the different cell lines. Finally, regulation of gene expression was demonstrated using DU145 cells. Upregulation of c-fos mRNA was observed in cultures at early time-points in the presence of T4, transferrin or both. Decreased expression was observed at later time-points with no expression at 4 h. An explanation for these results may be a change in thyroid hormone receptor/ligand affinity. Thus, the interactions between thyroid hormones and cancer cells may be different from those between thyroid hormones and normal cells.

Breast Neoplasms↗
PubMed2000

eNOS gene transfer to vascular smooth muscle cells inhibits cell proliferation via upregulation of p27 and p21 and not apoptosis.

OBJECTIVE: Smooth muscle cell (SMC) proliferation is a critical component of vascular diseases such as atherosclerosis and restenosis. Nitric oxide (NO) donors and gene transfer of endothelial nitric oxide synthase (eNOS) have been shown to inhibit SMC proliferation. NO may cause this effect by delaying cell cycle progression and/or induction of apoptosis. The aim of the current study was to examine the mechanism of eNOS-mediated inhibition of SMC proliferation. In addition, the effect of eNOS expression in vascular SMCs on the expression of the cyclin dependent kinase inhibitors, p27 and p21 was examined. METHODS: SMCs were transduced with an adenoviral vector encoding eNOS (AdeNOS) or beta-galactosidase (Ad beta Gal) at a multiplicity of infection of 100. Non-transduced cells served as additional controls. Transgene expression was sought by NADPH diaphorase staining, immunohistochemistry and Western Blotting. Functionality of the recombinant protein was assessed by measurement of cGMP. Cell cycle analysis was performed by flow cytometry and p27 and p21 expression were studied by western blot analysis. Apoptosis was sought by Annexin V staining and DNA laddering. RESULTS: eNOS expression was detected in transduced SMCs. cGMP levels were increased in eNOS-transduced compared to control cells. Expression of eNOS in SMCs resulted in a delay in cell cycle progression and upregulation of p27 and p21. There was no increase in apoptosis detected in eNOS transduced cells after 24 or 72 h. CONCLUSION: eNOS gene transfer to vascular SMCs inhibits cell proliferation via upregulation of p27 and p21 resulting in a delay in cell cycle progression.

Animals↗
PubMed2000

Comparison of regimens containing oral micronized progesterone or medroxyprogesterone acetate on quality of life in postmenopausal women: a cross-sectional survey.

A cross-sectional survey was conducted to examine quality of life (QOL) related to physiological, somatic, and vasomotor effects of changing progestogen treatment from medroxyprogesterone acetate (MPA) to micronized progesterone in postmenopausal women. Eligible women (n = 176) were currently using hormone replacement therapy (HRT) containing micronized progesterone for 1-6 months and had previously received HRT containing MPA. QOL was assessed via telephone interview using the Greene Climacteric Scale and the Women's Health Questionnaire. When compared with the MPA-containing regimen, women using micronized progesterone-containing HRT experienced significant improvement in vasomotor symptoms, somatic complaints, and anxiety and depressive symptoms. Women reported improved perceptions of their patterns of vaginal bleeding and control of menopausal symptoms while on the micronized progesterone-containing regimen. Approximately 80% of women reported overall satisfaction with the micronized progesterone-containing regimen. A micronized progesterone-containing HRT regimen offers the potential for improved QOL as measured by improvement of menopause-associated symptoms.

Administration, Oral↗
PubMed2000

Effects of transdermal nicotine treatment on structure and function of coronary artery bypass grafts.

Smoking is a major risk factor for failure of coronary artery bypass grafts (CABG). Experiments were designed to determine effects of transdermal nicotine, independent of smoking, on structure and function of CABG. Saphenous veins were placed as CABG in untreated dogs (control) or in dogs treated with transdermal nicotine (one 11-mg or two 22-mg patches/day) for 5 wk. Serum nicotine and plasma nitric oxide were measured. Grafts were removed and prepared for organ chamber studies and histology. Serum nicotine averaged 12.1 and 118.7 ng/ml in the 11 mg/day and 44 mg/day groups, respectively. Plasma nitric oxide was higher in dogs treated with 11 mg/day doses compared with controls. In organ chamber studies, endothelium-dependent relaxations to thrombin and A-23187 and endothelium-independent relaxations to nitric oxide were greatest in grafts from dogs treated with 11 mg/day doses. Intimal thickness of the grafts were similar among groups. However, staining for bone sialoprotein was increased in the media of grafts from the 11 mg/day treatment group. These data suggest that transdermal nicotine in doses comparable and double to those used for conventional smoking cessation treatment in humans does not adversely affect early patency of canine CABG up to 4 wk postoperatively. Transdermal nicotine, however, may increase production of and response to nitric oxide in bypass grafts.

Actins↗
PubMed2000

HMG-CoA reductase inhibitors increase BMD in type 2 diabetes mellitus patients.

Recently, it was reported that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors increased bone mineral density (BMD) in mice. We studied the effect of HMG-CoA reductase inhibitors on BMD of type 2 diabetes mellitus by a retrospective review of medical records. Sixty-nine type 2 diabetic patients were included. The control group (n = 33) did not take HMG-CoA reductase inhibitors. The treatment group (n = 36) was administered either lovastatin, pravastatin, or simvastatin. BMD of the spine, femoral neck, femoral trochanter, and total hip were measured by dual-energy X-ray absorptiometry. There were no significant differences between control and treatment groups in age, sex, body mass index, glycemic control, and serum insulin levels. In the control group, BMD of the spine significantly decreased (from 1.116 +/- 0.165 to 1.081 +/- 0.178 g/cm2) after 14 months. In the treatment group, BMD of the femoral neck significantly increased (from 0.853 +/- 0.139 to 0.878 +/- 0.147 g/cm2) after 15 months. In male subjects treated with HMG-CoA reductase inhibitors, there was a significant increase in BMD of the femoral neck and femoral trochanter (from 0.899 +/- 0.139 to 0.934 +/- 0.139 and from 0.801 +/- 0.145 to 0.833 +/- 0.167 g/cm2, respectively), but in female subjects, only BMD of the femoral neck increased (from 0.819 +/- 0.132 to 0.834 +/- 0.143 g/cm2). Percentage increments of BMD of the femoral neck, femoral wards triangle, femoral trochanter, and total hip in the treatment group were significantly higher than in the control group (2.32% vs. -0.99, 1.77% vs. -1.25%, 1.40% vs. -1.21%, 0.88% vs. -1.03%, respectively). The proportion of subjects who had an increase in BMD of the spine and total hip more than two percentages was significantly larger in the treatment group than in the control group (30.6% vs. 15.2% and 30.6% vs. 9.1%, respectively). The increased increment in BMD of the treatment group was significantly greater than those in the control group after adjustment for age and body mass index (P < 0.05). These results suggest that HMG-CoA reductase inhibitors may increase BMD of the femur in male patients with type 2 diabetes mellitus.

Bone Density↗
PubMed2000

Soy isoflavones: are they useful in menopause?

In October 1999, the US Food and Drug Administration authorized the use on food labels of health claims associated with soy protein and the reduced risk of coronary heart disease. Several studies have indicated that a total daily intake of 25 g of soy protein paired with a low-fat diet resulted in clinically important reductions of total cholesterol and low-density lipoprotein (LDL) cholesterol levels. Soybeans are a rich source of isoflavones, a class of phytoestrogens found predominantly in legumes and beans. Soy isoflavones are heterocyclic phenols with structural similarity to estradiol-17beta and selective estrogen receptor modulators. Actions at the cellular level depend on the target tissue, receptor status of the tissue, and the level of endogenous estrogen. Studies of soy-based diets evaluating the relation between soy consumption and serum lipid concentrations revealed that soy consumption significantly decreased total cholesterol, LDL cholesterol, and triglyceride levels. However, the soy isoflavones do not increase high-density lipoprotein cholesterol or triglyceride levels. The effects of soy protein on other target tissues reflect estrogenlike agonist and antagonist effects. Epidemiological studies suggest a protective effect of soy protein on breast tissue as evidenced by the lower rates of breast cancer in East Asian countries where soy is a predominant part of the diet. Data available from human studies on the effect of isoflavones on osteoporosis are limited, and additional studies are needed to support a role in osteoporosis prevention. Thus far, there is no evidence for a stimulatory effect of isoflavones on the endometrium. A few studies reveal a minimal effect of soy on hot flashes, with soy reducing hot flashes 45% and placebo causing a 30% reduction compared with an approximate 70% reduction in hot flashes with estrogen replacement therapy. Evidence from laboratory studies reveals neither a positive nor a negative effect of soy isoflavones on cognition. To date, no adverse effects of short- or long-term use of soy proteins are known in humans. The only adverse effects known are those reported in animals (infertility in sheep and quails grazing on phytoestrogen-rich pastures). In conclusion, soy isoflavones are biologically active compounds. Current data are insufficient to draw definitive conclusions regarding the use of isoflavones as an alternative to estrogen for hormone replacement in postmenopausal women. Although epidemiological and basic laboratory studies allude to the possible protective effects of soy isoflavones at specific target tissues, randomized, placebo-controlled clinical trials are necessary to address these important issues.

Animals↗
PubMed1999

Treatment with 17beta-oestradiol does not influence age and weight at puberty in Bos indicus heifers.

The working hypothesis was that treatment of heifers with 17beta-oestradiol (E2) during specific periods of prepuberty would reduce the response of the hypothalamic-pituitary axis to E2 negative feedback and induce an earlier onset of puberty. The effects of chronic treatment with exogenous E2 administered at specific maturational phases on the age and weight at puberty were studied in 96 prepubertal Brahman (3/4-7/8 Bos indicus) heifers (187.0 +/- 3.3 days of age, mean +/- SEM), weighing 149.9 +/- 2.5 kg. Heifers were randomly assigned to one of six groups (n = 16 per group). Groups 2-6 received E2 implants (Compudose 200) for 90-day periods starting at 10, 13, 16, 19 and 22 months of age, while animals in group 1 remained untreated. Implants were placed subcutaneously at the base of the ear. Blood was collected for progesterone (P4) determination by radioimmunoassay (RIA) and the animals were weighed at monthly intervals from 6 to 15 months then weekly from 15 to 28 months of age. Puberty was defined by concentrations of P > 1 ng/ml in plasma and identification of a corpus luteum (CL) by transrectal ultrasonography (Aloka 210DX:7.5 MHZ probe). Treatment with exogenous E2 at any of the ages/treatment intervals evaluated in this study did not reduce age or weight at puberty (P > 0.7). The mean age and weight at puberty of control heifers was 735.3 +/- 19.7 days (range: 597-861) and 299.2 +/- 10.2 kg (range: 233-382), respectively, which is greater than the age and weight at puberty of 481 days and 246 kg, that was previously reported for B. indicus heifers [Post, T.B., Reich, M.M., 1980. Puberty in tropical breeds of heifers as monitored by plasmaprogesterone. Proceedings of the Australian Society of Animal Production 13, 61-62.]. The large variation in age and weight at puberty that was observed in the present study among heifers might indicate an individual animal effect to E2 treatment among some of the treated animals. The lengthy interval from birth to puberty observed in this study, as compared to other studies, reflects the effects of other factors such as genotype, environmental or nutritional influences on puberty.

Age Factors↗
PubMed1999

Micronized progesterone: clinical indications and comparison with current treatments.

OBJECTIVE: To integrate and evaluate the pharmacokinetic, endocrine, and clinical effects of micronized progesterone formulations. DESIGN: Published articles concerning the pharmacokinetics of orally administered progesterone and the potential clinical uses of oral micronized progesterone were reviewed. Results concerning their use for secondary amenorrhea, premenopausal bleeding disorders, luteal phase dysfunction, termination of premature labor, hormone replacement therapy, and premenopausal syndrome are summarized. Critical issues to be resolved through ongoing preclinical and clinical research are highlighted. RESULT(S): Because of the enhanced bioavailability of oral micronized progesterone, the compound may be useful for a variety of therapeutic indications. Oral micronized progesterone is available in France, and a formulation recently has been approved in the United States for the treatment of secondary amenorrhea and postmenopausal hormone replacement therapy. A large body of evidence, including the Postmenopausal Estrogen/Progestin Interventions study, suggests that the use of a combination of estrogen and oral micronized progesterone is optimal for long-term hormone replacement therapy. There also are data indicating that oral micronized progesterone could be of potential use for the treatment of premenopausal bleeding disorders, luteal phase disorders, and premature labor. CONCLUSION(S): Oral micronized progesterone has widespread clinical potential, particularly for the treatment of secondary amenorrhea and dysfunctional premenopausal bleeding, and as a component of postmenopausal hormone replacement therapy.

Amenorrhea↗
PubMed1999

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols.

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.

Animal Husbandry↗
PubMed1999

Transplantability and therapeutic effects of bone marrow-derived mesenchymal cells in children with osteogenesis imperfecta.

In principle, transplantation of mesenchymal progenitor cells would attenuate or possibly correct genetic disorders of bone, cartilage and muscle, but clinical support for this concept is lacking. Here we describe the initial results of allogeneic bone marrow transplantation in three children with osteogenesis imperfecta, a genetic disorder in which osteoblasts produce defective type I collagen, leading to osteopenia, multiple fractures, severe bony deformities and considerably shortened stature. Three months after osteoblast engraftment (1.5-2.0% donor cells), representative specimens of trabecular bone showed histologic changes indicative of new dense bone formation. All patients had increases in total body bone mineral content ranging from 21 to 29 grams (median, 28), compared with predicted values of 0 to 4 grams (median, 0) for healthy children with similar changes in weight. These improvements were associated with increases in growth velocity and reduced frequencies of bone fracture. Thus, allogeneic bone marrow transplantation can lead to engraftment of functional mesenchymal progenitor cells, indicating the feasibility of this strategy in the treatment of osteogenesis imperfecta and perhaps other mesenchymal stem cell disorders as well.

Bone Density↗
PubMed1999

Vascular calcification.

Vascular calcification is an active and modifiable process involved in many disease entities, including atherosclerosis, cardiac valve disease and calcific uremic arteriolopathy. It occurs with distinct characteristics at different sites in the vessel wall. The mechanism by which calcification is induced remains uncertain; the roles of bone matrix and extracellular matrix proteins, estrogen and vitamin D are being further defined in animal models and clinical trials. Some risk factors for calcific uremic arteriolopathy and cardiac valve calcification, both disproportionately affecting chronic hemodialysis patients, have been identified in observational studies.

Animals↗
PubMed1999

Estrogen increases Ca2+ efflux from female porcine coronary arterial smooth muscle.

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca2+ concentration ([Ca2+]i). In the present study, we examined the hypothesis that this reduction in [Ca2+]i is mediated in part by enhanced Ca2+ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca2+]i response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17beta-Estradiol (E2beta), but not 17alpha-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC50 = 10 nM) decrease in the [Ca2+]i response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca2+ influx and sarcoplasmic reticulum Ca2+ reuptake were blocked, E2beta still decreased [Ca2+]i. The response was blocked by extracellular lanthanum. These data indicate that E2beta decreases [Ca2+]i in coronary artery smooth muscle by affecting Ca2+ efflux via a receptor-mediated mechanism.

Animals↗
PubMed1999

Gender-related differences in vascular smooth muscle cell proliferation: implications for prevention of atherosclerosis.

Premenopausal women have a significant reduction in coronary artery disease compared to age-matched males. Little is known about the mechanism underlying this cardioprotective effect of estrogen. Contradictory evidence has been published and our lack of basic understanding of hormone interactions and bioavailability of different estrogens prevents definitive interpretation of these data. We demonstrate gender-specific effects in the proliferation of coronary artery vascular smooth muscle cells obtained from a sexually mature animal model. Vascular smooth muscle cells are an integral component of the atherosclerotic plaque, and inhibition of cell proliferation by estrogen may be one mechanism by which estrogen exerts its cardioprotective effect. Various types of estrogen may also have different mechanistic actions on the vascular system. No differences are demonstrated in overall estradiol binding in vascular smooth muscle cells obtained from male or female animals: however, differences in c-jun, c-fos and TIEG gene expression were gender related. Inhibition of vascular smooth muscle cell proliferation may have important implications in the prevention of atherosclerotic disease and these studies may provide evidence for the cardioprotective effect of estrogen.

Animals↗
PubMed1999

Selective estrogen receptor modulators and phytoestrogens: new therapies for the postmenopausal women.

Estrogen deficiency in the postmenopausal woman results in numerous symptomatic and asymptomatic manifestations, including vasomotor symptoms, osteoporosis, heart disease, bladder and vaginal symptoms, and cardiovascular disease. Estrogen replacement therapy is associated with amelioration of these problems but has attendant risks. A newer class of drugs, the selective estrogen receptor modulators, provides both estrogen agonist and antagonist properties, depending on the target tissue. This article discusses the mechanism by which selective estrogen receptor modulators may vary in their end-organ effects and reviews the clinical studies associated with these compounds. Phytoestrogens are widely used in the United States, but little information is available regarding their potential long-term effects.

Aged↗
PubMed1998

Effects of short-term treatment with progesterone superimposed on 11 or 17 days of norgestomet treatment on the interval to oestrus and fertility in Bos indicus heifers.

The aims of this study were to determine: (1) if short-term treatment of Bos indicus heifers with progesterone (P4) while implanted with a s.c. norgestomet implant for 17 days would influence the time interval to oestrus and increase fertility of the synchronised oestrus, and (2) whether the response to treatment with P4 would differ between heifers treated with a norgestomet implant for 17 vs. 11 days when short-term treatment with P4 is applied 3 days prior to implant removal. B. indicus heifers at two separate sites (A and B) were allocated to three groups at each site. Heifers in two groups (NG and NGP4 groups) were given a single s.c. norgestomet implant on the first day of treatment (day 0) while heifers in a third group (NGP4PG group) were implanted on day 6. A single P4 releasing Controlled Internal Drug Release device (CIDR) was inserted on day 14 in heifers in the NGP4 and NGP4PG groups and was removed 23.5 +/- 0.07 h later (day 15). Heifers in the NGP4PG group were administered an analogue of prostaglandin F2 alpha (PGF2 alpha) at the time of CIDR removal to regress corpora lutea. Implants were removed from all heifers on the same day (day 17) and a 400 IU of equine chorionic gonadotrophin (ECG) was administered s.c. Animals were artificially inseminated 11.1 +/- 0.17 h after detection of oestrus, using frozen semen from one bull at site A and one of five bulls at site B. Inseminations were carried out by one of two technicians. Treatment with P4 delayed oestrus and reduced the synchrony of oestrus at site A (hours to oestrus +/- SD: NG group, 39.0 +/- 13.7; NGP4 group, 66.3 +/- 24.4; NGP4PG group, 58.9 +/- 20.5 h; P < 0.05) but not at site B (41.4 +/- 15.2, 42.5 +/- 10.1, 45.4 +/- 10.3 h; P > 0.05). Pregnancy rates 6 weeks after insemination were found to be significantly associated with bull (P < 0.001), treatment group (P = 0.013) and insemination technician (P = 0.033). Pregnancy rates were greater in the heifers in the NGP4 group than heifers in the NG group [50.3% (78/155) vs. 36.4% (60/165); odds ratio = 1.83, 95% CI = 1.14 to 2.96] and similar between heifers in the NGP4 and NGP4PG groups [50.3% (78/155) vs. 51.1% (63/117); odds ratio = 1.06, 95% CI = 0.67 to 1.69]. It was concluded that acute treatment with P4 can improve pregnancy rates in B. indicus heifers treated for 17 days with norgestomet implants. Reducing the duration of norgestomet treatment to 11 days and administration of PGF2 alpha at the time of ending treatment with a CIDR device resulted in no differences in fertility, mean intervals to oestrus or synchrony of oestrus.

Analysis of Variance↗
PubMed1998

Duration of ovulation suppression with subcutaneous silicone implants containing norgestomet in Bos indicus heifers and cows.

The aim of this study is to determine the duration of suppressing oestrus or ovulation in Bos indicus heifers and cows using norgestomet (N) incorporated into a silicone implant. Twelve heifers and 18 cows undergoing oestrous cycles were allocated to one of two treatment groups (6 heifers and 9 cows per group). Animals were treated with a single subcutaneous (s.c.) silicone implant containing 3 mg of N or two identical silicone implants (6 mg of N in two silicone implants) on day 0 of the study. An analogue of prostaglandin F2-alpha was administered intramuscularly, to all animals on days 0 and 6 to induce regression of corpora lutea. Implants were removed from all animals on day 21. Animals were observed for signs of behavioural oestrus while implants were in situ and for 6 d following implant removal. Blood samples were collected on alternate days from day 0 to 20 and again on day 21 and analysed for plasma progesterone (P4). Transrectal ultrasonography was performed on days 0, 6, 10, 14, 18, 21, 24, 26,27, and along with concentration of P4 in plasma was used to confirm ovulation during the treatment period. The cumulative percentages of animals ovulating during the 21 days implants were in situ were 6.7% (3 mg of N in one silicone implant) and 0% (6 mg of N in two silicone implants)Intervals from implant removal to oestrus (mean +/- S.E.M.) did not differ significantly among animals treated with either 3 or 6 mg of N in silicone implants (46.8 +/- 7.0 vs. 55.4 +/- 7.1 h, P = 0.398). Variances in interval from implant removal to oestrus among animals treated with 3 or 6 mg of N in silicone implants were also homogeneous (P = 0.942). The mean diameter of the ovulatory follicle on day 21 was larger in the animals treated with 3 mg of N compared to animals treated with 6 mg of N in two silicone implants ( 13.1 +/- 0.8 vs. 9.7 +/- 0.7 mm, P = 0.005). We conclude that treatment with 3 mg of N in a silicone implant will suppress ovulation in Bos indicus heifers and most cows for 21 d. Six mg of N in two silicone implants will suppress ovulation for 21 d in both cows and heifers.

Animals↗
PubMed1998

Treatment with progesterone and 17 beta-oestradiol to induce emergence of a newly-recruited dominant ovulatory follicle during oestrus synchronisation with long-term use of norgestomet in Brahman heifers.

The aim of this study was to determine the effect on ovarian follicular growth and atresia, of acute treatment with either 100 mg of progesterone (n = 10), 200 mg of progesterone (n = 10), 10 mg of oestradiol + 100 mg of progesterone (n = 10), 10 mg of oestradiol (n = 10) or no treatment (n = 10), given on Day 10 of a 17-day treatment with a norgestomet implant in randomly cycling Bos indicus heifers. The fate of the dominant follicle on Day 10, emergence of the new cohort of follicles and the intervals from implant removal to ovulation were recorded by ultrasonography. Plasma concentrations of Luteinizing hormone (LH), progesterone and oestradiol were determined during the time when the norgestomet implant was in place. All treatments resulted in the emergence of a new cohort of follicles within 5 days of administration. The day of emergence of the ovulatory follicle tended to be delayed after treatment with 100 mg of progesterone (2.7 +/- 0.3 days after treatment), 200 mg of progesterone (3.7 +/- 0.5 days after treatment), 10 mg of oestradiol + 100 mg of progesterone (4.4 +/- 0.2 days after treatment) and 10 mg of oestradiol (4.6 +/- 0.4 days after treatment) compared to control heifers (1.4 +/- 1.4 days after time of treatment). The mean interval from implant removal to onset of oestrus was significantly shorter after treatment with 100 mg of progesterone (38.4 +/- 2.6 h) than after treatment with 200 mg of progesterone (61.5 +/- 3.9 h) but otherwise, the mean interval from implant removal to onset of oestrus did not differ. Oestrus synchrony, measured by the sample standard deviation of oestrus onset, was tighter in all treatment groups compared to untreated control heifers. The mean interval from implant removal to ovulation did not differ significantly between groups. The synchrony of ovulation, measured by the sample standard deviation of the interval from implant removal to ovulation, was significantly tighter after treatment with 100 mg of progesterone, 200 mg of progesterone and 10 mg of oestradiol compared to control heifers. Treatment with 10 mg of oestradiol resulted in ovulation in seven of 10 heifers before implant removal, three of which failed to ovulate after implant removal. Progesterone administered on Day 10 lowered plasma LH concentrations (P < 0.05), whereas treatment with oestradiol caused a surge of LH and ovulation. Progesterone administered with oestradiol prevented the LH surge. A combination treatment of oestradiol and progesterone given on Day 10 of a 17-day norgestomet treatment in a range of follicular states resulted in the consistent emergence of a new cohort of follicles which included the eventual ovulatory follicle.

Animals↗