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Biomedical subjects

T Dickerson

Publications and source records attributed to T Dickerson.

10 recordsLinked to original sources
PubMed2006

Gestational, periparturient and preweaning growth traits of Holstein versus Gir x Holstein F1 crossbred dairy calves born to Holstein dams.

The objectives of this study were to assess the gestational, periparturient and preweaning growth traits of Holstein vs Gir x Holstein (G x H F1) cross-bred dairy calves. Holstein cows (n=64) pregnant with Holstein (H x H) calves (bulls, n=16; heifers, n=18) or G x H (bulls, n=8; heifers, n=22) calves were sampled from 60 days of gestation through calving for serum progesterone (P4) and in utero placentome sizes, and at parturition for calving ease scores (CES), calf vigour scores (CVS), and placental characteristics. Post-calving calf measures included birth weight (day 0) and body weight (kg), hip width (HW), body length (BL), wither height (WH), hip height (HH) and heart girth (HG) through 42 days of age. Serum IgG and calf vital function tests (respiration rate (RR), heart rate (HR), rectal temperature (RT) and fecal scores) were recorded on days 1, 3, 7 and 14 of age (a.m. and p.m.). Serum gestational P4 was higher (p < 0.05) for cows with H x H than G x H calves. Placentome measurements in utero were greater (p < 0.01) for H x H calves than for G x H calves, while at parturition placental characteristics did not differ (p > 0.10). Gestation length, CES and CVS also did not differ (p > 0.10) between H x H and G x H calves. Calf RR and HR were higher (p < 0.05) for H x H than G x H calves at both a.m. and p.m., while RT, fecal scores and serum IgG did not differ (p > 0.10) between H x H and G x H calves. Birth weight did not differ (p > 0.10) between H x H and G x H calves within sex. Moreover, bulls did not differ (p > 0.10) in any of the growth measures between H x H and G x H calves, whereas H x H heifers at days 28 and 42 of age were greater (p < 0.05) in all growth traits than G x H heifers. Nevertheless, the relative change in growth measures over time (days 0 to 42) did not differ (p > 0.10) between H x H and G x H calves. While subtle differences in gestational, early growth and vital function characteristics were observed, these data suggest very similar developmental profiles between H x H and G x H calves.

Animals↗
PubMed2005

Administration of 6-methoxybenzoxazolinone (MBOA) does not augment ovulatory responses in St. Croix White ewes superovulated with PMSG.

The objective of this investigation was to examine the effects of 6-methoxy-benzoxazolinone (MBOA), a plant compound that resembles melatonin and alters ovarian function in rodents, in combination with PMSG on superovulatory responses in the cycling ewe. In Experiment I, St. Croix White ewes (n = 44) were synchronized (intra-vaginal progestin sponge) for 14days followed by hCG (750 IU) at 1 day after sponge removal (day 0). Ewes were assigned to one of six treatments administered on day -1: Control (no PMSG or MBOA; n = 7); PMSG (1000 IU i.m.; n = 7); Low MBOA (0.43 mg/kg i.m.; n = 7); High MBOA (1.15 mg/kg i.m.; n = 7); Low MBOA + PMSG (n = 8); High MBOA + PMSG (n = 8). In Experiment II, St. Croix White ewes (n = 24) were synchronized (progestin CIDR) for 14 days followed by hCG on day 1 after CIDR removal (day 0). Ewes were assigned to one of three treatments administered on day -1: Control (n = 8); PMSG (n = 8); Low MBOA+PMSG (n = 8). Laparoscopy was performed on day 9 to assess numbers of corpora lutea (CL) and visible follicles on each ovary. Blood samples were collected on day -13, -1, 0, 1, and days 6 or 7-12 for analysis of serum progesterone (P4) by RIA. Treatment groups receiving PMSG (alone or with MBOA) exhibited greater (P < 0.05) serum concentrations of P4 post-synchrony than Control and MBOA-only groups. Ovulation rate was lower (P < 0.05) for Control and MBOA-only treated ewes than ewes receiving PMSG. Ovulation rate in ewes treated with MBOA alone was similar (P > 0.10) to Controls, and PMSG treatment alone did not differ (P > 0.10) from MBOA + PMSG treatment. Ewes treated with PMSG alone did not differ (P > 0.10) in follicle number from High MBOA + PMSG treated ewes, however, Low MBOA + PMSG treated ewes had greater numbers of follicles at day 9 (P < 0.05) than the PMSG or High MBOA + PMSG groups in Experiment I; although, this was not replicated in Experiment II with numbers of follicles in the Low MBOA + PMSG group being similar (P > 0.10) to PMSG alone. In summary, the addition of MBOA in combination with PMSG as part of a synchronization-superovuation protocol in the ewe did not increase ovulation rate.

Animals↗
PubMed2000

Quadriceps-hamstring EMG activity during functional, closed kinetic chain exercise to fatigue.

It has been hypothesized that the ability of the neuromuscular system to co-contract muscles for joint stabilization may be impaired during the development of fatigue. The purpose of this study was to examine muscle activation of the quadriceps and hamstring muscles during a prolonged closed kinetic chain exercise, the forward lunge. Eight males and two females [mean (SD) age 26.0 (2.3) years, height 177.2 (13.6) cm, body mass 82.8 (17.1) kg] with no prior knee pathology volunteered for this study. Subjects performed repeated forward lunges onto their dominant leg at the cadence of one full lunge cycle every 2 s, until the point of volitional failure. Digital switches were positioned to record foot-strike and knee-strike of the lunge leg at the midpoint of the lunge, as well as heel-strike upon return to stance. During the lunge performance, surface electromyographic (EMG) signals of the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and semitendinosus (ST) muscles of the supporting leg were measured. Heart rate was also monitored every 30 s during the performance. All EMG data were full-wave rectified, partitioned into up and down phases, and integrated over the entire exercise period. The results demonstrated a significant increase in activation of the VL, VM, and BF during performance of the forward lunge to volitional failure (P < 0.05). No significant increase was shown for the ST. Heart rate increased significantly over the course of the lunge. These findings suggest that activation of the VL, VM, and BF muscles occurs as a unit during performance of the forward lunge during both concentric and eccentric lunge phases.

Adult↗
PubMed1994

Bradykinin and angiotensin II: activation of protein kinase C in arterial smooth muscle.

The effects of bradykinin (BK) and angiotensin II (ANG II) were compared in cultured rat mesenteric arterial smooth muscle cells. BK and ANG II activated a phosphoinositide-specific phospholipase C, leading to the rapid release of [3H]inositol phosphates, an increase in intracellular calcium, and formation of sn-1,2-diacylglycerol (DAG). DAG formation was biphasic with a transient peak at 5 s followed by a sustained increase from 60 to 600 s. The BK-mediated increases in inositol triphosphate and DAG were dose dependent with half-maximal increases at concentrations of 5 and 2 nM, respectively. Both hormones were found to activate protein kinase C (PKC) as assessed by phosphorylation of the 68- to 72-kDa intracellular PKC substrate myristoylated alanine-rich C kinase substrate. However, despite similar phosphorylation of this substrate, only ANG II produced a significant increase in membrane-bound PKC activity. The mechanism accounting for the inability of BK to increase membrane-bound PKC activity is unclear. Our studies excluded differential translocation of PKC to the nuclear membrane, production of an inhibitor of membrane-bound PKC activity, and expression of BK and ANG II receptors on different cells as the mechanism. Vascular smooth muscle cells were found to express at least four different PKC isozymes: alpha, delta, zeta, and a faint band for epsilon. All of the isozymes except zeta-PKC were translocated by treatment with the phorbol ester 4 beta-phorbol 12-myristate 13-acetate. However, neither ANG II nor BK produced significant translocation of any measured isozyme; therefore, we could not exclude the possibility that ANG II and BK activate different isozymes of PKC. Both hormones were found to have a similar small and inconsistent effect in stimulating [3H]thymidine incorporation. These observations demonstrate that BK and ANG II have similar biochemical effects on vascular smooth muscle cells and imply that, in selected vessels, the vasodilatory effects of BK mediated by the endothelium may be partially counterbalanced by a vasoconstrictor effect on the underlying vascular smooth muscle cells.

Amino Acid Sequence↗
PubMed1990

Identification of glyoxylate cycle enzymes in chick liver--the effect of vitamin D3: cytochemistry and biochemistry.

Information regarding the presence of the glyoxylate cycle in chick liver was sought. This metabolic pathway has long been thought to be absent from vertebrate tissues. Previous studies in other tissues have shown that, when present, this pathway is sensitive to vitamin-D. Thus, the effect of long-term vitamin-D deficiency and subsequent vitamin-D replacement on liver structure was studied by light microscopy. In addition, specific biochemical assays for the presence of glyoxylate cycle enzymes were performed. Light microscopy of lipid extracted tissues, light microscopic histochemistry, and quantitative histochemistry showed that the hepatocytes from vitamin-D-deficient animals contained primarily lipid. Hepatocytes from normal and vitamin-D-replete livers contained primarily carbohydrate as judged by their staining with periodic acid-Schiff (PAS). Also, malate synthase positive peroxisomes were seen in hepatocytes from normal and vitamin-D-treated chicks. Structures positive for this glyoxylate cycle enzyme were rarely seen in the hepatocytes from vitamin-D-deficient animals. Biochemical analyses showed the presence of the two unique glyoxylate cycle enzymes, isocitrate lyase and malate synthase, in chick hepatocytes. The activity of these enzymes was markedly increased in the vitamin-D-replete livers. In addition, chick hepatocytes demonstrated the capacity to oxidize fatty acid in the presence of cyanide. This activity, which is characteristic of peroxisomal B-oxidation rather than mitochondrial, was stimulated by vitamin-D treatment. Lastly, incubation of chick liver in the presence of a fatty acid substrate (palmitate) led to higher tissue glycogen content. The latter was further increased in liver from vitamin-D-replete animals. These data show the presence of glyoxylate cycle enzymes in a higher vertebrate and indicate that this tissue is endowed with the capacity to convert lipid to carbohydrate.

Animals↗
PubMed1975

Two techniques to make the lymphocytotoxic crossmatch more sensitive: prolonged incubation and the antiglobulin test.

Two techniques capable of increasing the sensitivity of the lymphocytotoxic crossmatch test were compared for sensitivity and practically using the fluorochromasia modification of the cytotoxicity test. Prolonging the incubation period after addition of complement in the standard test resulted in further positive reactions. Modification of the test by addition of antiglobulin reagent increased the reactivity more than prolonged incubation of the standard test. The fluorochromasia adaptation of the antiglobulin test had sensitivity equivalent to the original antiglobulin method. The antiglobulin technique had a number of disadvantages, and neither the prolonged incubation nor the antiglobulin procedure meet the requirements of a busy histocompatibility testing service in view of the time consumed for the first and the complexity of the second.

Coombs Test↗