Biomedical subjects

G L Williams

Publications and source records attributed to G L Williams.

At least 37 records · Page 2Linked to original sources

PubMed2002

Comparison of three approaches for synchronization of ovulation for timed artificial insemination in Bos indicus-influenced cattle managed on the Texas gulf coast.

Our objectives were to compare the relative efficacies of three protocols designed to synchronize ovulation for timed artificial insemination (AI) of predominantly Brahman-influenced cows and heifers. In Exp. 1, 273 Brahman x Hereford (F1) cows at three locations were stratified by BW, body condition score (BCS), age, and days postpartum and assigned randomly to three treatments: 1) Syncro-Mate-B (SMB), 2) norgestomet-prostaglandin (NP), and 3) Ovsynch. The management goal required that cows have a minimum BCS of 5 and be at least 36 d postpartum (PP) at treatment onset. However, final results included 23 cows (8.4%) whose BCS fell below 5. In Exp. 2, 286 pubertal beef heifers were stratified by BW and BCS and allocated randomly to the three treatments. Heifers were predominantly Brahman crossbred (n = 265; Brahman x Hereford, F1; Santa Cruz) or purebred Brahman-influenced (Santa Gertrudis) with a smaller number (n = 21) of Hereford heifers also included. For both experiments, SMB treatment consisted of a 9-d norgestomet ear implant plus an estradiol valerate/norgestomet injection on d 0. Norgestomet-prostaglandin-treated females were implanted with a SMB implant without the estradiol valerate/norgestomet injection at the time of implant insertion and received 25 mg prostaglandin F2alpha (PGF) i.m. 2 d before implant removal. Ovsynch consisted of 100 microg GnRH i.m. on d 1, 25 mg PGF i.m. on d 8, and a second GnRH injection on d 10. Beginning on d 9, calves were removed for 48 h in Exp. 1. Cattle in SMB and NP groups in both experiments were timed-inseminated 48 to 54 h after implant removal and at 12 to 24 h after the second GnRH injection (Ovsynch). Timed AI conception rates did not differ between the SMB (45.1%) and Ovsynch (42.4%) groups; however, conception rate in the NP group tended (P < 0.12) to be lower overall than in the other groups due to a reduced (P < 0.05) conception rate in cows that were < 60 d PP at treatment onset. Conversely, timed-AI conception was greatest (P < 0.056) in NP (54.7%) compared with SMB (40.4%) and Ovsynch (39.1%) for heifers in Exp. 2. We conclude that in mature, suckled beef cows with Brahman genetic influence, SMB and Ovsynch perform similarly when cow eligibility relies primarily on BCS and minimum days PP. The NP treatment results in lower conception in cows < 60 d PP compared with SMB and Ovsynch. However, in nulliparous Brahman-influenced heifers that are confirmed to be pubertal, NP may be superior to the other two treatments for timed AI.

Age Factors↗

PubMed2002

Serum leptin and its adipose gene expression during pubertal development, the estrous cycle, and different seasons in cattle.

Circulating concentrations of leptin and IGF-I, leptin gene expression, and serum binding of [126I]ovine leptin in cattle during pubertal development, as well as leptin gene expression and circulating concentrations of leptin during the estrous cycle and different calendar seasons, were investigated. Multivariate regression analysis was utilized to evaluate temporal changes in BW, leptin mRNA, and serum concentrations of IGF-I and leptin normalized to the week of puberty (Exp. 1). Body weight accounted for most of the variation associated with the onset of puberty in the full regression model (R2 = 0.99; P < 0.01). However, serum leptin was closely related to changes in BW (r = 0.85; P < 0.02) and in the absence of BW was most predictive of pubertal onset (r2 = 0.73; P < 0.01). Mean concentrations of leptin increased (P < 0.0001) linearly from 16 wk before until the wk of pubertal ovulation in yearling heifers reaching sexual maturation from early spring to midsummer. Leptin mRNA transformed to a percent of the value at puberty increased (P < 0.02) as puberty approached, but serum leptin and leptin mRNA values were not well correlated. We found no evidence of leptin-binding proteins in serum of developing heifers. Combined mean serum concentrations of IGF-I (ng/mL) during periods III and IV (-9 wk to wk of puberty; 216.6 +/- 9) were 21% higher (P < 0.0001) than combined mean concentrations of IGF-I during periods I and II (-19 to wk of puberty; 193 +/- 10). In mature heifers and cows (Exp. 2), serum leptin tended to decrease (P = 0.10) during the late luteal/early follicular phase of the estrous cycle, which corresponded to a reduction (P < 0.03) in adipocyte leptin gene expression. In mature ovariectomized cows, serum concentrations of leptin increased (P < 0.001) by 34% from early winter to the summer solstice and remained unchanged throughout the remainder of the year (Exp. 3). Results from these studies indicate that marked increases in both circulating leptin and leptin gene expression occur in developing heifers during pubertal development and are associated with increases in serum IGF-I and BW. Seasonal effects on circulating leptin observed in mature cows from winter to summer could also plausibly account for a portion of the prepubertal rise in serum leptin observed in heifers.

Adipose Tissue↗

PubMed2001

Selective operative cholangiography and Perioperative endoscopic retrograde cholangiopancreatography (ERCP) during laparoscopic cholecystectomy: a viable option for choledocholithiasis.

BACKGROUND: Most common bile duct (CBD) stones can now be removed by minimally invasive methods using pre- or postoperative endoscopic sphincterotomy. A few centers explore the bile duct laparoscopically, but not every hospital has access to the equipment for magnetic resonance (MR) cholangiopancreatography to diagnose ductal stones. This study shows the results of an alternative management option. METHODS: We did a retrospective review of perioperative endoscopic retrograde cholangiopancreatographies (ERCPs) and sphincterotomies that were performed on patients in whom choledocholithiasis had been revealed on operative cholangiogram. RESULTS: Thirteen patients underwent perioperative ERCP. Nine had successful duct clearance, three had failure to cannulate, and one was converted to an open procedure due to an anatomical problem. The combined median operating time for both procedures was 75 min and hospital stay was 2.5 days. No pancreatitis was reported. CONCLUSION: Selective operative cholangiography and perioperative ERCP during laparoscopic cholecystectomy is a viable option for the simultaneous management of CBD and gallbladder stones. Moreover, it helps to avoid unnecessary normal ERCP.

Adult↗

PubMed2001

Physiological regulation of maternal behavior in heifers: roles of genital stimulation, intracerebral oxytocin release, and ovarian steroids.

We tested the hypotheses that 1) epidural anesthesia at parturition would block both peripheral and central release of oxytocin and eliminate the development of maternal behavior in primiparous heifers and 2) estradiol priming, genital stimulation, and appropriate neonatal stimuli would induce maternal behavior in nulliparous heifers. In experiment 1, primiparous crossbred heifers (n = 13) with cannulas in the third cerebroventricle (IIIV) were assigned randomly to receive epidural treatments of saline (SAL; n = 6) or lidocaine HCl (EPI; n = 7) at the onset of labor induced between Days 270 and 280 of gestation. Epidural anesthesia blocked (P < 0.001) both central and peripheral release of oxytocin and markedly reduced (P < 0.05) or eliminated licking behaviors during a 3-h period following parturition as compared with SAL. Following approximately 1 wk of controlled daily suckling, during which calves were permitted access only to the inguinal region of their dams (three times daily for 10 min each time), a second maternal behavior test was performed. Although licking behavior remained markedly reduced (P < 0.001) in the EPI compared with the SAL groups, all heifers accepted their calf at the udder. In experiments 2-4, neither estradiol priming in ovariectomized heifers nor estradiol plus progesterone in intact heifers resulted in an induction of maternal behaviors following genital stimulation and presentation of a neonate wetted with amniotic fluid. Pelvic sensory deficits apparently block oxytocin release and disturb both short-latency and long-term maternal behaviors but do not result ultimately in rejection of the calf. Combinations of hormonal, sensory, olfactory, and visual cues observed previously to induce maternal behavior in nulliparous ewes do not appear adequate for induction of maternal behavior in nulliparous heifers.

Animals↗

PubMed2000

Leptin gene expression, circulating leptin, and luteinizing hormone pulsatility are acutely responsive to short-term fasting in prepubertal heifers: relationships to circulating insulin and insulin-like growth factor I(1).

In the present study, we tested the hypothesis that short-term fasting would reduce leptin gene expression, circulating leptin, and LH pulsatility in prepubertal heifers in association with a decrease in circulating concentrations of insulin and insulin-like growth factor I (IGF-I). Twelve prepubertal crossbred heifers (mean +/- SD = 315 +/- 5 kg body weight) were assigned randomly to one of two treatments in two replicates: 1) control; normal feed consumption (n = 6) and 2) fasted; 48 h of total feed restriction (n = 6). Blood samples were collected at 15-min intervals for 8 h on Days 0 and 2 of the experiment and twice on Day 1. Subcutaneous fat samples were collected before treatment onset (Day -1) and at the end of the intensive blood sampling on Day 2. Acute feed restriction markedly reduced leptin mRNA in adipose tissue (P < 0.01) and circulating concentrations of leptin (P < 0.05), IGF-I (P < 0.01), and insulin (P = 0.05) as compared with controls on Day 2. Moreover, the treatment x day interaction (P < 0.076) and within-day contrasts (expressed as a percentage of Day 0 values) revealed that the mean frequency of LH pulses in the fasted group was lower (P < 0.06) than in controls on Day 2. Neither mean concentrations of growth hormone (GH) nor GH secretory dynamics were affected by acute feed restriction. Fasting-mediated decreases in leptin gene expression and circulating leptin, in association with reductions in secretion of IGF-I, insulin, and LH, provide a basis for investigating leptin as a hormone signaling energy status to the central reproductive axis in cattle.

Adipose Tissue↗

PubMed1999

Injection of neuropeptide Y into the third cerebroventricle differentially influences pituitary secretion of luteinizing hormone and growth hormone in ovariectomized cows.

Hypothalamic neurons that control the luteinizing hormone (LH) and growth hormone (GH) axes are localized in regions that also express neuropeptide Y (NPY). Increased hypothalamic expression of NPY due to diet restriction has been associated with suppressed secretion of LH and enhanced secretion of GH in numerous species. However, these physiological relationships have not been described in cattle. Thus, two studies were conducted to characterize these relationships using ovariectomized (Experiment 1) or ovariectomized estrogen-implanted (Experiment 2) cows. In Experiment 1, four well-nourished, ovariectomized cows received third cerebroventricular (TCV) injections of 50 and 500 micrograms of NPY in a split-plot design. Venous blood was collected at 10-min intervals from -4 hr (pre-injection control period) to +4 hr (postinjection treatment period) relative to TCV injection. NPY suppressed (P < or = 0.04) tonic secretion of LH irrespective of dose and tended to stimulate (P < or = 0.10) an increase in tonic secretion of GH. In Experiment 2, six ovariectomized cows that were well nourished and implanted with estradiol received TCV injections of 0, 50, or 500 micrograms of NPY in a replicated 3 x 3 Latin Square. Both doses of NPY suppressed (P < 0.06) mean concentration of LH relative to the 0-microgram dose. The 50-microgram dose of NPY tended (P < 0.10) to increase the amplitude of GH pulses. In conclusion, TCV injection of NPY suppressed pituitary secretion of LH and simultaneously tended to increase pituitary secretion of GH.

Animals↗

PubMed1999

Distribution and repeatability of anterior pituitary responses to GnRH and relationship of response classification to the postpartum anovulatory interval of beef cows.

Our objectives were to investigate the phenotypic variation in anterior pituitary responsiveness to GnRH (100 microg, i.v.) of beef cows between d 5 and 8 postpartum, estimate repeatability, and determine the relationship between response classification and duration of the postpartum anovulatory interval (PPI). Brahman x Hereford (F1) cows (n = 137) and primiparous heifers (n = 58) were evaluated. Response classifications (Class) included peak LH (Low, Intermediate, or High; Class I) and time to peak LH (Early, 10 to 30 min or Late, 60 to 120 min; Class II). The independent effects of Class I and II on PPI were determined in 145 of 195 cows through twice-weekly serum samples analyzed for progesterone. For Class I, pituitary responses to GnRH approximated a normal distribution and, by definition, differed (P < .001) in magnitudes of peak LH and area under the curve (AUC). For Class II, 111 and 84 cows exhibited early and late peaks, respectively; mean AUC was greater (P < .05) in cows exhibiting late compared with early peaks. Pretreatment LH (P < .01) and estradiol-17beta (P < .004) influenced responses in one or both response classes. Pluriparous cows had shorter (P < .035) PPI than primiparous cows. Class I did not influence the duration of the PPI; however, in Class II, cows with late peaks exhibited an average PPI that was 8 d shorter (P < .025) than in those with an early peak. To estimate repeatability of pituitary responses, 18 classified cows were subsequently rechallenged with GnRH at d 170 of gestation and at the next postpartum period. Although means for each of these challenges differed (P < .05) throughout in both Classes I and II, the small sample size used to make the estimate failed to yield significant (P > .10) interclass correlations. Nevertheless, overall results provide evidence that variability in individual pituitary responses to GnRH could be targeted as a selection marker to improve reproduction.

Animals↗

PubMed1999

Effects of time of suckling during the solar day on duration of the postpartum anovulatory interval in Brahman x Hereford (F1) cows.

Previously published reports have indicated that postpartum anovulatory intervals can be markedly reduced and rebreeding performance enhanced in Bos taurus cows by eliminating nighttime suckling. We sought to confirm this hypothesis by examining the effects of day, nighttime, and ad libitum suckling on suckling behavior of calves, duration of the postpartum anovulatory interval, and pregnancy rates in 45 fall-calving Brahman x Hereford (F1) cows. Beginning on d 9 to 12 postpartum, calves were removed from lactating cows from 0700 to 1900 (Night-Suckled, n = 15) or from 1900 to 0700 (Day-Suckled, n = 15), or remained with their dams continuously (Ad Libitum-Suckled, n = 15). Cows in each group were maintained with fertile Angus bulls from d 10 postpartum until the first normal luteal phase or 100 d postpartum, whichever occurred first. Cows were observed for estrous behavior twice daily, and jugular blood samples were collected twice weekly for the determination of serum progesterone concentration. Mean number of suckling episodes per 24 h was greater (P < .0001) for the Ad Libitum-Suckled group than either Night- or Day-Suckled groups (5.9+/-.42 vs 3.8+/-.14, and 3.9+/-.32, respectively). Hourly analysis of suckling episodes in the Ad Libitum group indicated that they were not skewed toward a particular period, with suckling occurring at a periodicity of 4 to 6 h. Intervals to the first rise in progesterone > or = 1 ng/mL (32+/-2.5, 32+/-4.5, and 31+/-1.7 d, respectively), first normal luteal phase (38+/-3.1, 38+/-3.8, and 37+/-2.5 d, respectively), and first estrus (43+/-3.5, 40+/-3.9, and 36+/-1.1 d, respectively) did not differ (P > .05) among the three groups. Similarly, cumulative pregnancy rates within 100 d after calving did not differ (P > .05). These results in Bos indicus x Bos taurus (F1) cattle do not support the previous conclusions in Bos taurus that eliminating nighttime suckling reduces the postpartum anovulatory interval.

Anestrus↗

PubMed1998

Microsequencing of bovine cerebrospinal fluid apolipoproteins: identification of bovine apolipoprotein E.

In studies of bovine plasma lipoproteins, apolipoprotein E (apoE) was not found associated with alpha-lipoproteins isolated over a broad range of densities. However, studies of cerebrospinal fluid (CSF) lipoproteins from other mammals have shown that apoE is a major apolipoprotein associated with high density lipoprotein, a fact that prompted us to determine if this were also the case in bovine CSF. CSF samples were obtained from animals with a surgically implanted catheter. Most analyzed samples were obtained from cows at various stages of the postpartum period; however, a few samples also were obtained at term or during pregnancy. Analyses of isolated ultracentrifugal fractions by polyacrylamide gel electrophoresis revealed the presence of two apo, with the expected molecular weights for apoE and apoA-I. By using both matrix-assisted laser desorption mass spectrometry and microsequencing techniques, we demonstrated that these apo are indeed apoE and apoA-I.

Amino Acid Sequence↗

PubMed1998

Gonadotropin-releasing hormone secretion into third-ventricle cerebrospinal fluid of cattle: correspondence with the tonic and surge release of luteinizing hormone and its tonic inhibition by suckling and neuropeptide Y.

Objectives of the current studies were to characterize the pattern of GnRH secretion in the cerebrospinal fluid of the bovine third ventricle, determine its correspondence with the tonic and surge release of LH in ovariectomized cows, and examine the dynamics of GnRH pulse generator activity in response to known modulators of LH release (suckling; neuropeptide Y [NPY]). In ovariectomized cows, both tonic release patterns and estradiol-induced surges of GnRH and LH were highly correlated (0.95; p < 0.01). Collectively, LH pulses at the baseline began coincident with (84%) or within one sampling point after (100%) the onset of a GnRH pulse, and all estradiol-induced LH surges were accompanied by corresponding surges of GnRH. A 500- microg dose of NPY caused immediate cessation of LH pulses and lowered (p < 0.001) plasma concentrations of LH for at least 4 h. This corresponded with declines (p < 0.05) in both GnRH pulse amplitude and frequency, but GnRH pulses were completely inhibited for only 1.5-3 h. In intact, anestrous cows, GnRH pulse frequency did not differ before and 48-54 h after weaning on Day 18 postpartum, but concentrations of GnRH (p < 0.05) and amplitudes of GnRH pulses (4 of 7 cows) increased in association with weaning and heightened secretion of LH. We conclude that the study of GnRH secretory dynamics in third-ventricle CSF provides a reasonable approach for examining the activity and regulation of the hypothalamic pulse generator in adult cattle. However, data generated using this approach must be interpreted in their broadest context. Although strong neurally mediated inhibitors of LH pulsatility (suckling; NPY) had robust effects on one or more GnRH secretory characteristics in CSF, only high doses of NPY briefly abolished GnRH pulses. This implies that the GnRH signal received at the hypophyseal portal vessels under these conditions may differ quantitatively or qualitatively from those in CSF, and theoretically would be undetectable or below a biologically effective threshold when LH pulses are absent.

Animals↗

PubMed1997

Regulatory roles of high-density and low-density lipoproteins in cellular proliferation and secretion of progesterone and insulin-like growth factor I by enriched cultures of bovine small and large luteal cells.

We tested the hypotheses that bovine high-density (HDL) and low-density (LDL) lipoproteins differentially influence cellular proliferation and progesterone and IGF-I production by bovine small and large luteal cells. Unit gravity sedimentation was used to produce enriched cultures of small (> 95% pure) and large (75 to 90% pure) luteal cells from corpora lutea (CL) on d 4 and 10 of the estrous cycle. Addition of LDL, HDL, or both resulted in the maintenance of higher (P < .05) numbers of 3beta-hydroxysteroid dehydrogenase (HSD)-positive small and large cells in culture and produced a marked proliferation of 3beta-HSD-negative small luteal cells compared to control medium. Low-density lipoprotein and HDL each stimulated greater (P < .01) progesterone secretion in enriched large cell cultures on both days of the cycle, and by small luteal cells on d 10, compared to the control. Together, LDL and HDL maximized this response. Lipoproteins markedly stimulated (P < .01) the secretion of IGF-I by bovine large luteal cells, and secretion was greater (P < .05) by cells from d 10 CL compared to d 4 CL. Results suggest that the actions of lipoproteins in bovine luteal cells extend beyond their widely recognized roles in steroidogenesis and include remarkable effects on cellular proliferation and IGF-I secretion. Type of lipoprotein (LDL vs HDL) did not have differential effects on any of the variables measured.

3-Hydroxysteroid Dehydrogenases↗

PubMed1997

Dietary fats varying in their fatty acid composition differentially influence follicular growth in cows fed isoenergetic diets.

The working hypothesis was that dietary fats differing in fatty acid composition would differentially influence ovarian follicular growth. Cows (n = 27) were fed isoenergetic, isonitrogenous, and isofibrous diets containing no added fat (control; CT, n = 7) or diets supplemented with fats containing primarily saturated (SAT, n = 7), polyunsaturated (PU, n = 7), or highly polyunsaturated (HPU, n = 6) fatty acids. Coincident changes in serum lipid metabolites, insulin, and GH and the concentration of IGF-I in large and medium-sized follicles also were examined. Body weights and body condition scores remained similar for all groups throughout the study. Polyunsaturated fat increased (diet x day, P = .06) the number of medium-sized follicles on d 5 through 9 of a synchronized estrous cycle within 3 wk of onset of feeding and maximized (P < .001) this to a fourfold difference at ovariectomy after 7 wk. Fats with predominantly SAT and HPU tended (P < .10) to produce these effects after 7 wk. All fat-supplemented diets increased serum concentrations of total cholesterol (P < .05), GH (P < .05), and follicular fluid IGF-I in large follicles (P < .065) compared to CT but differentially influenced serum concentrations of insulin. Polyunsaturated fat stimulated a marked increase (P < .001) in serum insulin relative to controls within 3 wk, whereas SAT and HPU increased (P < .05) serum insulin only after 6 to 7 wk. We conclude that consumption of PU fatty acids stimulates a greater rate of ovarian follicular growth in cattle compared to CT, AT, and HPU. Future research should investigate the potential role of insulin in mediating PU effects on follicular growth.

Animal Nutritional Physiological Phenomena↗

PubMed1996

Metabolic hormone secretion and FSH-induced superovulatory responses of beef heifers fed dietary fat supplements containing predominantly saturated or polyunsaturated fatty acids.

Ovulatory responses following FSH treatment were examined in beef heifers fed dietary fat supplements expected to produce differential effects on serum insulin concentrations and follicular recruitment patterns. Twenty-one heifers (n = 7/group) exhibiting regular estrous cycles were assigned randomly to either a control diet or to 1 of 2 fat-supplemented diets consisting of soybean oil (polyunsaturated fatty acids) or animal tallow (saturated fatty acids). The diets were formulated to be isoenergetic and isonitrogenous, and were fed until ovariectomy between experimental Days 35 and 45. Experimental Day 1 was defined for each heifer as the first day all of the treatment diet was consumed. After 20 d of diet consumption, estrous cycles were synchronized with prostaglandin F(2alpha) (PGF(2alpha)), and ovarian follicle populations were monitored via transrectal ultrasound for 4 d. Four days after estrus, the dominant follicle was aspirated and heifers were treated with FSH-P to induce superovulation. Ovulation rate was determined at ovariectomy 5 d after the superovulatory estrus (experimental Days 35 to 45). Both soybean oil and animal tallow diets increased (P < 0.05) the number of medium-sized follicles and increased (P < 0.02) serum concentrations of GH relative to the control diet. The soybean oil diet also increased (P < 0.001) serum concentrations of insulin on Days 14, 28, and 5 d after the superovulatory estrus. However, the number of ovulations following FSH treatment did not differ due to diet. Procedures employed in the current study were ineffective in recruiting the increased number of medium-sized follicles into the superovulatory pool.

Journal Article↗

PubMed1996

Roles of maternal vision and olfaction in suckling-mediated inhibition of luteinizing hormone secretion, expression of maternal selectivity, and lactational performance of beef cows.

The roles of maternal vision and olfaction in regulating the suckling-mediated inhibition of LH secretion, expression of maternal selectivity, and lactational performance was examined in anestrous beef cows (n = 57). Pluriparous cows were allotted randomly to one of 10 groups between 17 and 21 days postcalving (Experimental Day 0). Groups 1-8 included cows that were either intact, blind, anosmic, or blind and anosmic, and were control-suckled by either their own or unrelated ("alien") calves every 6 h for 6 days. Groups 9 and 10 served as positive controls and were left intact and weaned, or were anosmic, blind, and weaned. The frequency of LH pulses (pulses/5 h) remained unchanged over the 6-day experiment in sighted and olfactory-intact groups suckling their own calves (1.2 +/- 0.01). In contrast, cows that were olfactory-intact or sighted and suckling alien calves, blind and anosmic and suckling their own or alien calves, or weaned exhibited prompt increases (p < 0.001) in LH pulse frequency to a maximum of 4.6 +/- 0.3 pulses/5 h within 6 days. Mean frequency was greater in these groups (p < 0.05) than in olfactory-intact or sighted groups suckling their own calves. Enforced suckling by an alien calf attenuated (p < 0.001) milk production and calf weight gain, and a greater (p < 0.05) proportion of cows presented with aliens during behavioral tests physically rejected suckling compared to those presented with their own calves. These results confirm that suckling-related events sustain the inhibited pattern of LH secretion in cows only if the offspring are positively identified as their own. Olfaction and vision are equally effective in permitting calf identification, but elimination of both senses prevents calf identification and the negative effects of suckling on LH secretion.

Animals↗

PubMed1995

Steroidogenic activity, insulin-like growth factor-I production, and proliferation of granulosa and theca cells obtained from dominant preovulatory and nonovulatory follicles during the bovine estrous cycle: effects of low-density and high-density lipoproteins.

The role of high- and low-density lipoproteins (HDL and LDL) in regulating steroidogenic activity, cellular viability and proliferation, and insulin-like growth factor-I (IGF-I) production was examined in granulosa and theca cells from dominant preovulatory (DO) and nonovulatory (DNO) bovine follicles. Follicles were obtained from pluriparous nonlactating beef cows at ovariectomy 24 h after administration of a luteolytic dose of prostaglandin F2 alpha (DO) or during the first follicular wave on Days 5-8 of the estrous cycle (DNO). Lipoprotein effects on hormone production (ng/1.5 x 10(5) viable cells) and cell viability were studied in serum-free, defined medium containing LH and FSH (granulosa) or LH only (theca). During late stages (96-144 h) of culture, HDL in the presence of gonadotropins increased (p < 0.001) the production of progesterone by granulosa and theca cells and the production of IGF-I by granulosa cells. LDL did not stimulate granulosa or thecal progesterone synthesis and attenuated HDL-stimulated progesterone production by both cell types. Gonadotropin stimulation of terminal synthetic pathways was either attenuated (granulosa estradiol production) by addition of lipoproteins or maximally stimulated (theca cell androstenedione production) by a combination of LDL and HDL. Both lipoproteins increased (p < 0.05) granulosa cell viability in both follicle types, and a marked proliferation (p < 0.001) of steroidogenically inactive theca cells was observed from DO but not DNO follicles. Proliferation potential appeared to be switched off during the late stages of maturation of DNO follicles and switched on after induced luteal regression and rescue of DO follicles.

Animals↗

PubMed1995

Metabolic and luteal sequelae to heightened dietary fat intake in undernourished, anestrous beef cows induced to ovulate.

Two experiments were conducted to evaluate the effects of dietary fat supplementation and a synthetic progestogen on metabolic hormone patterns and(or) in vitro and in vivo characteristics of induced corpora lutea (CL) in undernourished, post-partum beef cows. Metabolizable energy intake was restricted in all cows in both experiments before calving to achieve a body condition (BC) score of 4 (thin), with cows fed to maintain BW and condition after calving. In Exp. 1, 16 cows were fed isocaloric and isonitrogenous diets after calving with either no added fat (NL, n = 8) or added fat (HL, n = 8; .374 kg of fat/500 kg BW). In Exp. 2, 32 pluriparous cows that had reached targeted body condition were divided randomly at calving into a 2 x 2 factorial treatment arrangement: 1) HL-no implant; HL-CON, 2) HL-norgestomet implant d 14 to 21; HL-NORG, 3) NL-CON and, 4) NL-NORG. Forty-eight-hour calf removal on d 21 and GnRH on d 23 were used to induce CL. The HL diet increased (P < .03) serum growth hormone (GH) concentrations, changed the puerperal pattern of serum insulin from cubic (P < .05) to linear (P < .05), and increased (P < .01) the in vitro production of IGF-I by luteal tissue (Exp. 1). In Exp. 2, both HL diets and NORG treatments (HL-NORG, HL-CON, NL NORG) tended to promote an increased (P < .09) frequency of luteal activity after GnRH, but only HL-CON and NL-NORG enhanced (P < .04) luteal lifespan.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Sensory and behavioural control of gonadotrophin secretion during suckling-mediated anovulation in cows.

A major limiting factor in the resumption of postpartum ovarian cycles in cattle is the inhibitory influence of the suckling calf on central regulatory elements controlling the release of GnRH from the median eminence. This inhibitory influence occurs only as a consequence of specifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally using thermal, electrical or mechanical stimuli, and is not dependent upon sensory ennervation within the udder. Indeed, the identity of the calf, either own or unrelated, appears to define the neuroendocrine events that attend the maintenance of the anovulatory state under controlled experimental conditions. Hence, new hypotheses that focus upon the relationship between physiological correlates of maternal behaviour and hypothalamic regulation of LH secretion are currently being tested. Specific aspects of these relationships remain conjectural, but are postulated to include the regulation of opioid tone, intracerebral oxytocin, and modulation of synthetic or excitatory activity of GnRH secretory neurones. Defining the role of the special senses in transduction of signals from calves that influence these neuronal processes may provide insight for developing practical intervention strategies of the future.

Animals↗

PubMed1994

Ovarian follicular recruitment, granulosa cell steroidogenic potential and growth hormone/insulin-like growth factor-I relationships in suckled beef cows consuming high lipid diets: effects of graded differences in body condition maintained during the puerperium.

The effects of graded differences in body condition score (BCS) on ovarian follicular development, granulosa cell steroidogenic potential, and growth hormone (GH)-insulin-like growth factor-I (IGF-I) relationships were examined during the puerperium in beef cows fed high fat diets. Cows (n = 36) were allocated randomly about 90 d before expected calving to dietary treatments that resulted in BCS of 3 (very thin), 4 (thin), 6 (optimal) and 8 (obese) at parturition. Body weight and BCS were maintained after parturition by adjusting individual intakes of forage throughout the 17-d experiment, and all cows were fed a high lipid supplement (soybean oil; 0.44 kg/500 kg body weight) during this period. Follicular development in BCS 3 and 4 lagged behind that of BCS 6 and 8 throughout most of the study; however, cows in BCS 4 developed numbers of medium and large follicles by day 15 postpartum that were comparable to those of cows in greater BCS. Mean concentrations of total cholesterol (TCH) and total triglycerides (TG) in serum were greater (P < .05) for cows in BCS 8 vs. 3, 4 and 6 through days 12 (TCH) and 16 (TG) postcalving, respectively. High-density lipoprotein cholesterol (HDL-CH), progesterone and estradiol-17 beta concentrations in follicular fluid were not affected by BCS at ovariectomy (day 17 postpartum). Addition of insulin and low-density lipoprotein (LDL) to culture media maximized (P < .05) production of progesterone by granulosa cells, but in vivo BCS treatments had no effect. Serum GH concentrations were elevated (P < .05) in cows in BCS 3 and 4 compared to those in BCS 6 and 8 throughout the puerperium. Serum IGF-I tended (P < .10) to increase during the first few days after parturition, and both serum and follicular fluid IGF-I increased (P < .02 and P < .001, respectively) with increasing BCS. Data indicate that cows calving in BCS < 4, and fed such that weight and BCS do not increase, are unlikely to respond to short-term dietary fat supplementation.

Animals↗