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Biomedical subjects

T G Dunn

Publications and source records attributed to T G Dunn.

At least 19 recordsLinked to original sources
PubMed1995

Influence of fetal death and fetectomy on gestation and the initiation of parturition in the ewe.

Depressed function of the fetal hypothalamic-pituitary-adrenal axis results in prolonged gestation, and fetal death causes premature parturition. The objective of this experiment was to determine effects of death in utero of a sibling, or its removal, on the duration of gestation and concomitant changes in maternal serum concentrations of oestradiol (E) and progesterone (P). Ovine placental lactogen (oPL) was also determined as an index of placental viability. Blood samples were collected in the morning, beginning 3 days prior to surgery on Day 115 +/- 3 of gestation and continuing daily until 3 days post partum. Surgeries were performed via mid-ventral laparotomy to induce fetal death or to remove the fetus. Fetal death was induced by ligating the umbilicus. Duration of gestation was similar (P > 0.05) in control (C, n = 6) and sham-operated (S, n = 3) ewes (148 +/- 1.0 and 148.6 +/- 0.7 days, respectively). On the day of parturition, concentrations of P, E and oPL were 5.2 +/- 1.9 ng mL-1, 135 +/- 22 pg mL-1 and 153 +/- 54 ng mL-1, respectively, in ewes from combined C and S groups. Total fetectomy (n = 3) resulted in a rapid decrease (P < 0.05) in maternal serum concentrations of P, E, and oPL. Ligation of the umbilicus of both fetus(es) in utero (n = 4) induced fetal death, decreased (P < 0.05) length of gestation to 118.8 +/- 1.8 days and decreased (P < 0.05) serum concentrations of P and oPL prior to parturition and oPL on the day of parturition. In addition, maternal serum concentrations of E failed (P > 0.05) to increase at parturition. Length of gestation and concentrations of P, E and oPL at parturition were not affected (P > 0.05) by removal of one fetus when its sibling was undisturbed (n = 4) compared to control ewes. In contrast, death of one fetus with its sibling undisturbed (n = 5) decreased (P < 0.01) length of gestation (139.2 +/- 2.8 days), but did not affect P, E and oPL (P > 0.05) on all days tested. In conclusion, death of one fetus reduced the duration of gestation, but changes prepartum in maternal serum concentrations of P and oPL were similar to ewes delivering only live fetuses. The increase in maternal concentrations of E that normally occur at parturition was absent in ewes giving birth to only dead fetuses and, therefore, was not a prerequisite to parturition.

Abortion, Veterinary↗
PubMed1993

Extent to which guided-discovery teaching strategies were used by 20 preceptors in family medicine.

BACKGROUND: Learners learn more and are able to categorize problems at higher levels when their teachers use guided-discovery strategies (e.g., questions and advice to investigate relationships between concepts), as opposed to directly telling learners the answers. This study examines the extent to which clinician preceptors of residents use guided-discovery strategies when faced with a diagnostic problem-solving situation. METHOD: Twenty family medicine preceptors from four residencies volunteered in 1991-92 to role-play with a simulated first-year resident on a single standardized case. Judges coded the preceptors' verbal behaviors by type (question, statement, or advice) and by category. The categories were teacher, i.e., behaviors relating to more than the present case (hence exemplifying guided-discovery strategies), and consultant, i.e., behaviors relating to the successful disposition of the case (without overt concern for the education of the resident). RESULTS: Of the preceptors' 846 verbal behaviors, 602 (71%) were coded as teacher behaviors, but only 329 (39%) were teacher behaviors that were of the specific types (high-level advice or questions promoting reflectivity, i.e., mindfulness) described in the literature as being most likely to promote learners' reflectivity and transfer of knowledge and skills from a lower level of abstraction to a higher level. CONCLUSION: The results suggest that the 20 perceptors were aware of the importance of "getting residents to think" and did use teaching strategies known to promote transfer. However, their repertoire of strategies was limited.

Family Practice↗
PubMed1992

Effect of implantation of dexamethasone adjacent to the paraventricular nucleus on messenger ribonucleic acid for corticotropin-releasing hormone and proopiomelanocortin during late gestation in fetal sheep.

Glucocorticoids act upon the hypothalamic paraventricular nucleus (PVN) and anterior pituitary in a classic negative feedback loop to regulate ACTH biosynthesis and secretion. Evidence exists to indicate that glucocorticoid feedback may be attenuated during late gestation in the sheep fetus to allow the preterm rise in fetal plasma cortisol necessary for parturition in this species. The present studies were undertaken to determine the effect of glucocorticoids placed adjacent to the fetal PVN on messenger RNA (mRNA) for CRH in the PVN and mRNA for POMC in the anterior pituitary during late gestation. We performed our studies at two critical stages during late gestation to determine if gestational age related changes occur in the efficacy of negative feedback regulation of expression of CRH and subsequently POMC. Dexamethasone (DEX) implants were placed bilaterally 2 mm lateral to the fetal PVN at 105 to 107 days gestational age (dGA; group I, n = 4) and 121-123 dGA (group II; n = 4). Gestational-age matched, sham implanted fetuses were used as controls (CONT) for both groups (n = 4 per group). Fetuses were recovered at 126-128 (group I) and 136 dGA (group II). Fetal PVN were isolated by micropunching, and the anterior pituitary was separated from neurointermediate and posterior lobes after necropsy. Total RNA was subjected to Northern analysis using specific complementary DNA probes to CRH and POMC, and specific message was normalized to actin mRNA content in each individual sample. Anterior pituitary POMC mRNA was not different in DEX fetuses compared to CONT for either group I (78 +/- 26% of CONT; mean +/- SEM) or group II (84 +/- 17% of CONT). PVN CRH mRNA content was lower in DEX fetuses in group I (28 +/- 14% of CONT; P less than or equal to 0.01) and group II (65 +/- 12% of CONT; P less than or equal to 0.01). The degree to which DEX suppressed mRNA for CRH was greater in group I compared to group II (P less than or equal to 0.05). We conclude that 1) CRH expression in the PVN of fetal sheep is suppressible by glucocorticoids; 2) suppression can occur directly at the level of the PVN and 3) that the efficacy of negative feedback decreases with increasing gestational age. Furthermore, the lack of effect of hypothalamic administration of DEX on anterior pituitary POMC mRNA indicates that basal expression of POMC in fetal sheep may be independent from support from the PVN at this stage of gestation.

Animals↗
PubMed1992

Effects of nutrient deficiencies and excesses on reproductive efficiency of livestock.

Successful reproduction is dependent on a host of macro- and micronutrients and ceases well before an animal expires from deficiency of a particular nutrient. This review focuses on the functional roles phosphorus, vitamin A and beta-carotene, protein, and energy play in reproductive processes. Although it is not known whether deficiencies of these nutrients limit reproduction through common or discrete mechanisms, appropriate quantities of these nutrients are required for optimal reproduction. Mechanisms through which nutritional status is perceived by the hypothalamic-pituitary-gonadal axis remain unclear but seem to impinge on hypothalamic regions that selectively regulate production and release of pituitary trophic hormones. Body condition, or degree of fatness, seems to be the most reliable indicator of well-being of an animal, and, when coupled with changes in BW, provides a useful method to assess reproductive potential.

Animal Nutritional Physiological Phenomena↗
PubMed1990

Luteinizing hormone in nutrient-restricted ovariectomized ewes.

This study was designed to evaluate profiles of serum concentrations of LH, pituitary content of LH and GnRH receptors, and hypothalamic content of GnRH in undernourished, ovariectomized ewes. In earlier studies, pulsatile secretion of LH diminished as duration of undernutrition progressed in prepubertal or adult ovariectomized ewes. Ewes having similar body condition scores (CS) of 5 to 9 (1 = extremely thin, 5 = moderate, 9 = obese) were fed maintenance or low-energy diets (100% and 60% of NRC requirements, respectively). Blood samples for analysis of LH were collected at 15-min intervals for 4 h at initiation of the project and immediately prior to slaughter. Serum concentrations of LH did not differ (P greater than .05) among groups at the initial sampling period. At slaughter, ewes with CS less than or equal to 2 (n = 7) had lost 26.8 kg (42% of initial weight). Ewes with CS greater than or equal to 3 (n = 12) had lost an average of 13.7 kg (18% of initial weight). Concentrations of LH in ewes with final CS greater than or equal to 3 was similar (P greater than .05) to that observed during the initial sampling period. However, release of LH was reduced (P less than .01) in ewes with CS less than or equal to 2 compared with ewes with CS greater than or equal to 3 (2.6 vs 9.5 and 3.2 vs 10.5 ng/ml for basal and mean concentrations, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The learning process in biofeedback: is it feed-forward or feedback?

Twenty participants responded to inquiries about strategies used, and thoughts during, each of three electromyograph biofeedback sessions. The purpose of the study was to learn more about what individuals report doing during biofeedback and, specifically, to determine if individuals construct a response using feedback to sense subtle differences in muscle tension (feedback processes), or select a response from an existing repertoire using feedback primarily for confirmation (feed-forward processes). Protocol analyses found considerable support for feed-forward processes and little support for feedback processes. Such results are important because early reliance on feed-forward processes may result in limited control and limited transfer.

Adult↗
PubMed1986

Fetal growth of beef calves. I. Effect of prepartum dietary crude protein on birth weight, blood metabolites and steroid hormone concentrations.

Fifty-nine crossbred heifers (427 kg) bred to one Hereford sire were randomly assigned at 75 d prepartum to two diets. Heifers were individually fed, and diets were isocaloric but contained either a low (LP = 81% NRC, .56 kg/d) or high (HP = 141% NRC, .98 kg/d) level of crude protein. Jugular vein cannulae were inserted into 16 LP and 16 HP heifers at 10 prepartum. Daily preprandial blood samples that were collected until parturition were analyzed for serum estradiol-17 beta (E2), progesterone (P4), glucose (G) and urea nitrogen (UN). Heifers fed LP gained slower than HP-fed heifers before calving (.73 vs 1.02 kg/d; P less than .01); immediate post-calving weights and condition scores were 418 vs 444 kg (P less than .01) and 5.4 vs 6.1 (P less than .01; LP vs HP, respectively). Calf birth weights (35.3 vs 36.1 kg), average calving difficulty score (1.6 vs 1.6) and percent assisted births (35.5 vs 35.7%) did not differ (P greater than .10; LP vs HP, respectively). Prepartum concentrations of UN (6.2 vs 13.5 mg/dl) and G (52.9 vs 58.2 mg/dl) were lower (P less than .05) and P4 (5.94 vs 4.26 ng/ml) was higher (P approximately equal to .07) in LP heifers. Prepartum concentration profiles were related to calving difficulty score (CD, 1 = no assistance to 3 = hard pull) for E2 (CD1 vs CD2 + CD3, P less than .01; CD2 vs CD3, P approximately equal to .01), P4 (CD1 vs CD2 + CD3, P less than .05), G (CD1 vs CD2 + CD3, P less than .05) and UN (CD2 vs CD3, P less than .05). After calving, all dams were maintained together on pasture and supplemented with alfalfa hay and grain mix until adequate range forage was available to maintain weight gains. Dams that were fed LP prepartum gained faster than HP dams during this period (.49 vs .15 kg/d; P less than .01). Prebreeding weights (443 vs 453 kg; LP vs HP) and condition scores (5.1 vs 5.1) did not differ, nor was the postpartum interval affected (44 vs 40 d; LP vs HP). There was no effect of dietary protein on dystocia or postpartum interval, although there were diet-induced differences in body weight and condition of the dams at calving. Results indicate that differences in prepartum profiles of serum steroid hormones and metabolites may be related to dystocia, in addition to relative fetal oversize.

Animals↗
PubMed1986

Fetal growth of beef calves. II. Effect of sire on prenatal development of the calf and related placental characteristics.

Fifteen Hereford and 47 crossbred heifers were allotted by breed and body weight to be artificially inseminated to one of two Angus sires selected for progeny birth weights (L = low; H = high). Forty-two of the heifers were randomly assigned to be slaughtered at 200, 215, 230, 245 or 260 d of gestation for measurement of fetal and placental characteristics. Twenty heifers were allowed to go to term and five calves from each sire group were randomly assigned to be euthanized and dissected within 24 h after birth. Sire differences in birth weight (BW) and dystocia score (32.9 vs 35.4 kg; 1.8 vs 3.1, L vs H sires, respectively) existed (P less than .01), and there was a sire effect (P less than .01) for fetal calf weights (FW) and eviscerated calf weights (EW). However, there was a sire X calf sex interaction for BW (P less than .05), EW (P less than .01), FW (P less than .01), femur length (P less than .05), heart weight (P less than .05), kidney weight (P less than .01) and pituitary weight (P less than .01). Weight differences suggested these interactions were a result of the relationship of the organ weights to fetal body weights and the interaction effects on calf weights resulted from limitations in the maternal environment which restricted growth of H-sired male calves in utero. Sire X fetal age interaction effects were all nonsignificant (P greater than .10) except for cerebrum weight. This finding indicates that fetus and calf growth rates were parallel for the L and H sires. A sire effect was found for biceps (P less than .01) and liver weights (P less than .01), but not for cerebrum weights (P greater than .10). Increasing weight due to fetal age was attributed to hypertrophy for the cerebrum (P less than .05) and liver (P approximately equal to .01), while the biceps increased (P less than .05) by both hypertrophy and hyperplasia, as determined from deoxyribonucleic acid and protein analyses. All measured fetal organ weights except heart, when expressed as a ratio with EW, decreased (P less than .05) with increasing fetal age. Brain (cerebrum + cerebellum):liver weight ratios were higher (P less than .01) in L-sired calves (.32 vs. .28) than in H-sired calves. Total placentome weight (b' = 91; P less than .01) and placental fluid volume (b' = .32; P less than .01) were highly associated with FW, accounting for 84% of the variation in FW.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Estrous response and pregnancy rates following calf removal in beef cows treated with prostaglandin F(2)alpha.

Five hundred fifty-four suckled beef cows in three herds were allotted within postpartum interval to one of four treatments. All cows received two injections of prostaglandin F(2)alpha (PGF(2)alpha) 11 days apart. Treatment I served as a control. Calves were removed for 48 hr following the first injection of PGF(2)alpha in treatment II. Calves were removed similarly after the second injection of PGF(2)alpha in treatment III and after both injections of PGF(2)alpha in treatment IV. Pregnancy rates at the synchronized service, by 24 days and by 45 days of breeding were not (P>0.05) affected by treatment. Similarly, the treatments had no significant (P>0.05) effect on percentage of animals exhibiting estrus following the first and second injections of PGF(2)alpha.

Journal Article↗
PubMed1984

Uterine and fetal growth following unilateral hysterectomy-ovariectomy in ewes.

The left uterine horn and ovary (UHOX; n = 25) or just the left ovary (UOX; n = 18) were excised from mature ewes to investigate growth capabilities of the uterus and uterine capacity effects on fetal growth in sheep. The remaining right uterine horns were excised from 5 UHOX ewes on day 13 of the second successive estrous cycle following initial surgery and were compared to 11 left uterine horns previously obtained from UHOX ewes during the midluteal phase of the estrous cycle. Uterine and endometrial content of DNA, RNA, protein, and number of myometrial nuclei indicated that removal of the left uterine horns resulted in hypertrophy of the right uterine horns. The conception rate of the remaining 20 UHOX ewes was lower than of the 18 UOX ewes. However, at 140 days of gestation, there appeared to be no uterine capacity effects on fetal growth.

Animals↗
PubMed1984

Negative feedback control of luteinizing hormone secretion in prepubertal beef heifers at 60 and 200 days of age.

Prepubertal beef heifers at 60 and 200 d of age, born in the fall or spring, were assigned randomly to one of three treatment groups: (1) intact = 1; (2) bilateral ovariectomy (OVX); or (3) OVX plus estradiol-17 beta(E2) administered in silastic implants (OVX + E2). Luteinizing hormone (LH) was measured in serum samples collected at 20-min intervals for 4 h from heifers on -1, +7, +21, +35 and +49 d after OVX. Luteinizing hormone concentrations increased in the serum by 7 d after OVX in heifers at both 60 and 200 d of age (P less than .001; time X treatment). Prior to OVX, the LH patterns were characterized by low levels and infrequent episodic pulses. By 49 d after OVX, the mean LH concentrations increased and the pattern changed to one of rhythmic LH pulses with a periodicity of 1 h (P less than .001; time X treatment). Estradiol-treated OVX heifers did not exhibit a postovariectomy rise in serum LH concentrations. Serum E2 concentration 49 d after OVX in OVX heifers was threefold greater than in 1 or OVX heifers, thus demonstrating that E2 exerted negative feedback on pituitary LH secretion in prepubertal heifers. There was no measurable difference in serum E2 concentrations between I and OVX heifers; however, the contrast in the concentration and pattern of serum LH between the two groups was dramatic and suggested gonadal factors in addition to E2 are involved in controlling LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Dynamics of ovarian blood supply to periovulatory follicles of the ewe.

Radioactive microspheres were injected into the ovarian artery ipsilateral to the ovary containing the dominant (preovulatory) or postovulatory follicle of the ewe to estimate the distribution of ovarian blood to those follicles throughout the periovulatory period. The follicle of interest was excised from the ovary at the first sign of estrus (4-h heat checks), or 4, 8, 12, 16, 20, 24, 28 and 32 h later. Blood samples to be analyzed for serum luteinizing hormone (LH) were taken at each observation for estrus. Follicles were partitioned into basal tissue, apical tissue and fluid (preovulatory follicles) constituents. Radioactivity was determined within the residual ovary and in each follicular component. Follicular data were normalized to the ascending limb of the preovulatory surge of serum LH (first detected increase in LH = O h). The supply of ovarian blood to the wall (apex + base) of follicles was elevated after the rise in LH was initially ascertained (0-12 h). The distribution of blood to the follicular wall began to decline from 12 to 16 h, and subsequently continued to decrease (20 h) until after ovulation had occurred (greater than or equal to 24 h after the LH increase). Blood supply was less to the wall of follicles in the 20-h group and to ruptured follicles than that to the wall of follicles collected before the initiation of the surge of LH. There was no evidence that blood supply to either the basal or apical portion of the follicular wall was altered preferentially. Radioactivity was not detectable within follicular fluid.

Animals↗
PubMed1983

Luteal function after ovulation blockade by intrafollicular injection of indomethacin in the ewe.

The dominant follicle of oestrous ewes was injected with saline or indomethacin. Treated follicles were obtained at 2 and 10 days after treatment and examined histologically. Indomethacin-injected follicles were abnormally enlarged and remained unruptured. On Day 2 after treatment, these follicles appeared grossly hyperaemic. The follicular walls of control and indomethacin-treated groups had luteinized. Blood samples for the measurement of serum progesterone were collected from animals with their ovaries left intact. Systemic progesterone and oestrous cycle lengths were unaltered by drug administration. It appears that prostaglandins are essential for ovulation in the ewe. The occurrence of ovulation per se was not a prerequisite of ensuing luteal-phase normality.

Animals↗
PubMed1983

Luteal phase insufficiency in the ewe as a consequence of premature induction of ovulation by intrafollicular injection of gonadotropins.

The largest ovarian follicle of ewes was injected on d 15 of the estrous cycle (2 to 3 d before the anticipated preovulatory surge of gonadotropins) with saline or either luteinizing hormone (LH) or follicle-stimulating hormone (FSH) in saline (5 micrograms). Ovulation was assumed based on the presence of an ovulation stigma at d 5 post-treatment. Control animals expressed estrus 2 to 3 d after treatment with saline, and during the estrous period ovulated from the treated follicle. Gonadotropin-treated animals ovulated from injected follicles prematurely and did not exhibit estrus. The stated observations with respect to time of ovulation were established by visual and hormonal criteria: (1) control follicles appeared to have ruptured within a day or two prior to relaparotomy (corpora hemorrhagica), whereas gonadotropin-treated follicles were in a more advanced stage of luteal development (corpora lutea); and (2) concentrations of systemic sera progesterone rose (P less than .05) in LH- and FSH-treated ewes 2d before such an increase in control animals. Luteal function was assessed by comparing sera concentrations of progesterone throughout the induced and spontaneous (vehicle controls) luteal phases. Premature stimulation of ovulation with either gonadotropin was followed by suppressed luteal function (maximum sera levels of progesterone in gonadotropin-treated animals and controls were slightly greater than 1 ng/ml and nearly 2.5 ng/ml, respectively; P less than .01). No differences in the level of luteal function due to treatment with LH or FSH were observed. The duration of the luteal phases of gonadotropin-treated animals were similar to controls (approximately 17 d).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Serum cortisol and progesterone after administration of adrenocorticotropin and(or) prolactin to sheep.

An experiment was conducted to determine the effect of iv administration of adrenocorticotropin (ACTH) and(or) prolactin on serum cortisol and progesterone concentrations in hypophysectomized, ovariectomized, adult ewes. Twenty-four hours after surgery (d 1), six sheep were used in a crossover design and were assigned randomly to receive iv one of four treatments: (I) 200 IU ACTH in 10 ml .15 M NaCl at 0700 h, (II) 2.5 mg prolactin in 10 ml .15 M NaCl at 0700 h and again at 0730 h, (III) 200 IU ACTH and 2.5 mg prolactin in 10 ml .15 M NaCl at 0700 h followed by 2.5 mg prolactin in 10 ml .15 M NaCl at 0730 h, or (IV) 10 ml .15 M NaCl (vehicle) at 0700 and 0730 h. Blood samples (5 ml) were collected via jugular cannulae at 15-min intervals from 0600 to 0700 h and starting at 0700 h at 5, 10, 15, 30, 35, 40, 45, 60, 75, 90 and 120 min. Samples were then collected at hourly intervals until 1300 h. Twenty-four hours after commencement of first sampling (d 2), treatments were crossed and samples were collected as on d 1. Administration of ACTH alone or in combination with prolactin increased (P less than .01) serum cortisol and progesterone concentrations. Serum cortisol or progesterone concentrations were unaffected (P greater than .05) by administration of prolactin.

Adrenocorticotropic Hormone↗
PubMed1982

Pituitary and ovarian function in postpartum beef cows. I. Effect of suckling on serum and follicular fluid hormones and follicular gonadotropin receptors.

The effect of suckling on serum and follicular fluid hormones and on follicular gonadotropin receptors was studied. Sixteen anestrous postpartum cows were assigned to 1 of 2 groups: suckled (S) or weaned (W). All calves were allowed to suckle ad libitum from parturition to 21 days postpartum when calves from W cows were weaned. All cows were ovariectomized on Day 25 postpartum. W cows had more (P less than 0.01) pulses of LH during the 96-h period from weaning until ovariectomy than S cows (6.3 vs. 1.3 pulses). Serum concentrations of prolactin (Prl), estrone (E1), estradiol-17 beta (E2) and progesterone (P) were not different (P greater than 0.10) between groups. Furthermore, there were n differences (P greater than 0.10) in follicular in contents of luteinizing hormone (LH), E1, E2 and P between the treatment groups. However, follicular fluid content of Prl was greater (P less than 0.05) in the W cows than in the S cows (123 vs. 65.1 ng/cow). The number of follicular LH receptors was greater (P less than 0.05) in the W cows than in the S cows (71.1 vs. 48.3 fmoles/mg protein) although the number of follicular follicle-stimulating hormone (FSH) receptors was not different (P greater than 0.10) between W cows and S cows (1531 vs. 1862 fmoles/mg protein). There were no correlation between serum hormone concentrations and follicular fluid hormone content; however, the numbers of follicular LH receptors and follicular fluid Prl content were highly correlated in the W cows (r = 0.85; P less than 0.05). It is concluded that removal of the suckling stimulus increases pulsatile LH release and the accumulation of Prl in the follicular fluid. These factors, either together or separately, may at least in part be responsible for the increase in follicular LH receptor concentrations that were observed in the W cows.

Animals↗