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Biomedical subjects

H Dobson

Publications and source records attributed to H Dobson.

At least 55 records · Page 3Linked to original sources
PubMed1999

Adoptive transfer of genetically modified human hematopoietic stem cells into preimmune canine fetuses.

To develop a surrogate model system for assaying gene transfer into human hematopoietic stem cells (HSCs) with in vivo repopulating potential, we injected human marrow cells transduced with a reporter retroviral vector in long-term marrow cultures (LTMCs), into the yolk sacs of preimmune canine fetuses. Of eight mid-gestation fetuses injected through the exteriorized uterine wall and under ultrasound guidance, seven were born alive. One puppy died in the neonatal period accidentally. The remaining six puppies are all healthy at 31 months of age. There was no evidence for graft-versus-host disease or any untoward effects of in utero adoptive transfer of transduced human LTMC cells. All puppies were chimeras. Human cells, detected by fluorescence in situ hybridization, were present in blood, declining from 38% to 0.05% between 10 and 44 weeks after birth. Corresponding numbers for marrow were from 20% to 0.05%. Human cells were also detected in assays of hematopoietic cell progenitors and in stimulated blood cultures. All six puppies were positive for the presence of proviral DNA at various time-points after birth. In three dogs, provirus was detected up to 41 weeks after birth in blood or marrow, and in one dog up to 49 weeks in blood. These data support the further development of this large-animal model system for studies of human hematopoiesis.

Adoptive Transfer↗
PubMed1999

Effect of transport on pulsatile and surge secretion of LH in ewes in the breeding season.

The aim of this study was to elucidate the mechanism(s) involved in stress-induced subfertility by examining the effect of 4 h transport on surge and pulsatile LH secretion in intact ewes and ovariectomized ewes treated with steroids to induce an artificial follicular phase (model ewes). Transport caused a greater delay in the onset of the LH surge in nine intact ewes than it did in ten ovariectomized ewes (intact: 41.0 +/- 0.9 h versus 48.3 +/- 0.8 h, P < 0.02; ovariectomized model: 40.8 +/- 0.6 h versus 42.6 +/- 0.5 h, P < 0.02). Disruption of the hypothalamus-pituitary endocrine balance in intact ewes may have reduced gonadotrophin stimulation of follicular oestradiol production which had an additional effect on the LH surge mechanism. In the ovariectomized model ewes, this effect was masked by the exogenous supply of oestradiol. However, in these model ewes, there was a greater suppression of maximum LH surge concentrations (intact controls: 29 +/- 4 ng ml-1 versus intact transported 22 +/- 5 ng ml-1, P < 0.02; ovariectomized model controls: 35 +/- 7 ng ml-1 versus model transported 15 +/- 2 ng ml-1, P < 0.02). Subsequent exposure to progesterone for 12 days resulted in the resumption of a normal LH profile in the next follicular phase, indicating that acute stress leads to a temporary endocrine lesion. In four intact ewes transported in the mid-follicular phase, there was a suppression of LH pulse amplitude (0.9 +/- 0.3 versus 0.3 +/- 0.02 ng ml-1, P < 0.05) but a statistically significant effect on pulse frequency was not observed (2.0 +/- 0.4 versus 1.7 +/- 0.6 pulses per 2 h). In conclusion, activation of the hypothalamus-pituitary-adrenal axis by transport in the follicular phase of intact ewes interrupts surge secretion of LH, possibly by interference with LH pulsatility and, hence, follicular oestradiol production. This disruption of gonadotrophin secretion will have a major impact on fertility.

Analysis of Variance↗
PubMed1999

Effect of transport on pituitary responsiveness to exogenous pulsatile GnRH and oestradiol-induced LH release in intact ewes.

This study examined the effect of transport on GnRH self-priming in vivo as well as the consequential effects on the oestradiol-induced LH surge. The follicular phases of ewes (eight per group) were synchronized with progestin sponges, and 50 micrograms oestradiol benzoate was injected 24 h (time zero) after sponge removal to improve precision in the timing of the LH surge. Beginning 8 h after oestradiol, saline or GnRH (500 ng, i.v.) was given at 2 h intervals with or without 8 h transport beginning 0.5 h before the first GnRH injection (late transport) and effects were compared with those observed during early transport, that is, starting 2.5 h before the first GnRH injection. In all ewes, GnRH alone induced a maximum LH response of 1.9 +/- 0.4 ng ml-1 after the first challenge. The response was enhanced (P < 0.01) after the second and third GnRH injections (7.4 +/- 1.4 ng ml-1 and 7.6 +/- 1.7 ng ml-1, respectively). This self-priming effect after the second GnRH was reduced by late transport (7.4 +/- 1.4 versus 4.2 +/- 0.8 ng ml-1; P < 0.05) but not early transport, that is, transport initiated closer to the time of GnRH administration had greater suppressive effects on LH secretion. Throughout transport, spontaneous LH pulse frequency was lower in treated than it was in control ewes (2.38 +/- 0.53 versus 4.50 +/- 0.53 pulses per 8 h; P < 0.01), with marked effects in the first 4 h of transport (1.0 +/- 0.19 versus 2.63 +/- 0.38 pulses per 4 h; P < 0.02). Spontaneous pulse amplitude also tended to decrease during transport (0.13 +/- 0.02 versus 0.20 +/- 0.03 ng ml-1; P = 0.07). When LH turnover was stimulated by exogenous GnRH, the onset of the LH surge was delayed (controls: 20.5 +/- 2.0 h versus GnRH alone: 25.3 +/- 1.5 h; P < 0.05) and the duration was reduced (8.5 +/- 0.9 versus 6.5 +/- 0.4 h; P < 0.05). Transport tended to delay the LH surge in saline-treated ewes (20.5 +/- 2.0 versus 22.9 +/- 1.9 h; P = 0.08), with a further delay imposed by late transport plus GnRH (27.5 +/- 1.6 h; P < 0.05) but not by early transport plus GnRH (27.8 +/- 2.5 versus 26.4 +/- 2.4 h; P > 0.05), that is, effects mediated by increasing LH turnover were only manifest if transport occurred near the LH surge, when there was insufficient time to replenish stores of releasable LH. In all transported ewes, plasma cortisol increased from 4.5 +/- 1.0 ng ml-1 to 29.2 +/- 5.5 ng ml-1 (P < 0.001) within 15 min of the start of transport and was significantly lower (P < 0.01) by 6.5 h. Plasma progesterone also increased from 0.30 +/- 0.04 to 0.38 +/- 0.04 ng ml-1 (P < 0.05). In conclusion, transport affected the oestradiol-induced LH surge by causing a 50% reduction in the self-priming effect of exogenous GnRH, but hypothalamic effects were also revealed by a two-fold decrease in spontaneous LH pulse frequency in saline-treated ewes.

Analysis of Variance↗
PubMed1999

Effect of transport on pulsatile LH release in ovariectomized ewes with or without prior steroid exposure at different times of year.

The initial aim of the present study was to test whether the stress of transport suppresses LH pulsatile secretion in ewes. In a pilot experiment in the late breeding season, transport resulted in an unexpected response in three out of five transported, ovariectomized ewes pretreated with oestradiol and progesterone. Before transport, seasonal suppression of LH pulses had occurred earlier than anticipated, but LH pulsatility suddenly restarted for the period of transport. This finding was reminiscent of unexplained results obtained in ovariectomized ewes infused centrally with high doses of corticotrophin-releasing hormone after pretreatment with low doses of oestradiol with or without progesterone. Hence, an additional aim of the present study was to examine whether these latter results with corticotrophin-releasing hormone could be reproduced by increasing endogenous corticotrophin-releasing hormone secretion by transport. Subsequent experiments used groups of at least eight ovariectomized ewes at different times of the year with or without prior exposure to steroids to assess whether these unexpected observations were associated with season or the prevailing endocrine milieu. In the mid-breeding season, transport for 4 h in the absence of steroid pretreatment for 8 months reduced LH pulse frequency from 7.5 +/- 0.3 to 6.3 +/- 0.4 pulses per 4 h (P < 0.05) and LH pulse amplitude from 2.6 +/- 0.5 to 1.8 +/- 0.3 ng ml-1 (P < 0.05). Similarly, in the mid-breeding season, 34 h after the cessation of pretreatment with oestradiol and progesterone, transport suppressed LH pulse frequency from 6.1 +/- 0.4 to 5.5 +/- 0.3 pulses per 4 h (P < 0.05) with a tendency of effect on amplitude (6.2 +/- 2.7 to 2.61 +/- 0.6 ng ml-1; P = 0.07; note the large variance in the pretransport data). During mid-anoestrus, evidence of a suppressive effect of transport was only observed on LH pulse amplitude (4.7 +/- 0.6 versus 3.0 +/- 0.5 pulses per 4 h; P < 0.05) in ovariectomized ewes that had not been exposed to ovarian steroids for 4 months. Repetition of the pilot experiment with 12 ewes during the transition into anoestrus resulted in one ewe with LH pulses seasonally suppressed but increased by transport; 11 ewes had a distinct pulsatile LH pattern which was decreased by transport in six ewes. In anoestrus, there was no effect of transport on LH pulse frequency or amplitude in intact ewes, or those ovariectomized 2-3 weeks previously, with or without prior oestradiol and progesterone treatment. However, basal concentrations of cortisol were greater in anoestrus than in the breeding season, and the increment in cortisol during transport was similar in anoestrus and the breeding season but greater during the transition into anoestrus (P < 0.05). Progesterone concentrations increased from 0.31 +/- 0.02 ng ml-1 before transport to 0.48 +/- 0.05 ng ml-1 during the second hour of transport (P < 0.05). In conclusion, transport reduced LH pulse frequency and amplitude in ovariectomized ewes that had not been exposed to exogenous steroids for at least 4 months. In most animals, the previously observed increase in LH pulsatility induced by exogenous CRH was not reproduced by increasing endogenous CRH secretion by transport. However, in four ewes, transport did increase LH pulsatility, but only during the transition into anoestrus in ewes with seasonally suppressed LH profiles after withdrawal of steroid pretreatment.

Animals↗
PubMed1999

Examination of the relative role of FSH and LH in the mechanism of ovulatory follicle selection in sheep.

The GnRH-antagonist suppression-ovarian autotransplant model (n = 18) was used to examine the relative roles of temporal changes in FSH and LH stimulation on follicle development and selection. Follicle development was stimulated by infusion with oFSH for 3 days and treatments applied for 60 h after progestagen sponge withdrawal and before delivery of an ovulatory stimulus. In Expt 1, there was continuous infusion of FSH with or without small amplitude high frequency LH pulses, or withdrawal of FSH with or without pulsatile LH. In Expt 2, there was acute or gradual withdrawal of FSH at sponge withdrawal with pulsatile LH. The patterns of follicle development and basal and pulsatile ovarian hormone secretion were determined. The maintenance of FSH throughout the artificial follicular phase resulted in multiple follicle development and ovulation (3.3 +/- 0.3). Pulsatile LH stimulated steroid secretion (P < 0.001) but had little effect on ovulation rates (3.8 +/- 0.8) when FSH was maintained. However, withdrawal of FSH in the absence of LH resulted in atresia of the ovulatory follicles and anovulation whereas, when FSH was withdrawn in the presence of LH, preovulatory follicle development was maintained in some animals (3/6 and 5/9 in Expts 1 and 2, respectively) and these ewes had lower (P < 0.05) ovulation rates (1-2 ovulations per ewe). When FSH was withdrawn gradually in the presence of pulsatile LH, 9/9 animals ovulated with ovulation rates in the normal range. These results indicate that ovulatory follicles can transfer their gonadotrophic dependence from FSH to LH. It is hypothesized that the ability of a follicle to respond to this switch in gonadotrophic support is central to the mechanism of follicle selection.

Analysis of Variance↗
PubMed1998

Use of ultrasonography to help to predict observed oestrus in dairy cows after the administration of prostaglandin F2 alpha.

A total of 76 cows from seven herds with an ultrasonographically visible corpus luteum at routine herd fertility examinations were treated with prostaglandin F2 alpha. The sizes of the cavities of all the follicles on both ovaries with a diameter greater than 5 mm were measured. The cows were observed for signs of oestrus over the following six days and the time to onset of oestrus was recorded. Milk samples collected when the prostaglandin was administered and at oestrus were assayed for milk progesterone concentration. The herd of origin, lactation number, body condition score, days after calving at the time of examination and the total number of follicles when the prostaglandin was administered were not found to have any correlation with time to oestrus. Seventy-three of the 76 cows had milk progesterone concentrations consistent with active luteal tissue when the prostaglandin was administered, and 33 of them were observed in oestrus and had low milk progesterone concentration within six days. The mean time to the onset of oestrus was significantly and inversely related to the size of the cavity of the smallest follicle with a diameter of more than 5 mm.

Animals↗
PubMed1998

Effect of prolonged exposure to oestradiol on subsequent LH secretion in ewes.

Abnormal follicles can produce oestradiol continuously for up to 20 days and this inhibits the hypothalamic-pituitary axis. The present experimental series was designed to determine the minimum exposure to high or low follicular phase concentrations of oestradiol that were required to exert inhibitory effects on LH surge secretion induced by additional oestradiol administered at the end of continuous exposure to oestradiol. Experiments were also included to establish whether the inhibitory effects of prolonged oestradiol were mediated at the pituitary, and whether the failure of response to the oestradiol challenge could be corrected by exposure to normal luteal phase patterns of progesterone. Treatment of ewes between 2 and 12 days with 1, 2 or 4 oestradiol implants (3 cm) totally blocked the subsequent normal LH surge in response to an oestradiol challenge in 45 of 52 ewes pretreated with oestradiol. In the seven ewes that did have an increase in LH, the response occurred at the expected time but was greatly reduced (14 versus 40 ng ml-1), and occurred only in ewes pretreated with oestradiol implants for 2 or 4 days. We were unable to establish a robust linear time-dose relationship, i.e., when ewes were treated with lower doses of oestradiol (one or two implants) for a reduced time (2, 4 or 8 days), there was random distribution of the 7 of 32 animals that had a reduced LH surge after oestradiol challenge (with four implants or 50 micrograms injection). The present study is the first to show that exposure for only 2-4 days to continuous oestradiol at late follicular phase concentrations can disrupt LH surge release. However, in oestradiol-treated ewes, LH secretion was provoked by high or low doses (0.5 mg or 0.5 microgram) of GnRH, although it was reduced by 50%, and a GnRH self-priming effect was still evident. All of these results suggest that inhibitory effects occur at the pituitary and hypothalamus. It remains to be confirmed whether the major effect is at the pituitary by reducing GnRH receptor or LH synthesis, or at the hypothalamus via inhibition of GnRH secretion.

Analysis of Variance↗
PubMed1998

Ovarian function in ewes made hypogonadal with GnRH antagonist and stimulated with FSH in the presence or absence of low amplitude LH pulses.

This study examined the effect of LH pulses, of similar amplitude and frequency to those found in the luteal phase, on the pattern of hormone secretion and follicle development in GnRH antagonist-suppressed ewes stimulated with exogenous FSH. This experiment was conducted on ewes with ovarian autotransplants in a continuous study. Follicle development was suppressed in 18 ewes by 3 weeks of GnRH antagonist treatment (50 micrograms/kg per 4 days s.c.), and was then stimulated by infusion of ovine (o)FSH (5 micrograms NIADDK-oFSH-16/h i.v.) for 3 days. In addition to FSH, 10 animals received pulses of LH (2.5 micrograms NIADDK-oLH-26 i.v.) every 4 h for the entire period of the FSH infusion. The follicle population was determined by daily ultrasound. Samples of ovarian and jugular venous blood were collected at 4-h intervals over the period of the FSH infusion and there were three periods of intensive blood sampling (15-min intervals for 2.5 h at 24, 48 and 72 h after the start of the FSH infusion) when the steroidogenic capacity of the follicles in all 18 ewes was tested around an LH challenge (2.5 micrograms i.v.). GnRH antagonist treatment resulted in a 57% decrease in FSH concentrations and prevented ovarian follicle development beyond 3 mm in diameter. Infusion of FSH resulted in a 60% increase in FSH concentrations and stimulated the development of large antral follicles and a coincident increase in ovarian androstenedione, inhibin and oestradiol secretion in both experimental groups. In the absence of 4-hourly LH pulses basal steroid secretion was negligible (< 1 ng/min; P < 0.001). Daily LH challenges, however, revealed no difference in the steroidogenic capacity of the follicle population in either experimental group. Similarly, LH pulses had no effect on the growth rate and number of antral follicles stimulated by FSH infusion, or the pattern of ovarian inhibin secretion. In conclusion, these results show that while FSH alone can stimulate the development of ovulatory sized follicles in ewes made hypogonadal with GnRH antagonist, physiological patterns of LH stimulation have no deleterious effects on FSH-stimulated follicle development and are essential for normal steroidogenesis.

Androstenedione↗
PubMed1998

TGF-beta1 binding protein-like modules of fibrillin-1 and -2 mediate integrin-dependent cell adhesion.

Human fibrillin, a major component of the extracellular matrix, exists as two highly homologous forms (fibrillin-1 and -2). Several modules of fibrillin are homologous to TGF-beta1 binding protein. Two of these modules, D25 (the 25th module of fibrillin-1 and -2 D segment) and D12 (the 12th module of fibrillin-2 D segment) contain the cell adhesion motif arginyl-glycyl-aspartyl (RGD). The ability of RGD to mediate adhesion to D25-1 and D12-2 was investigated using bacterially expressed fusion proteins. Human skin fibroblasts and murine L-cells were used in microassays of cell attachment and cell spreading on fibrillin fusion-protein substrata. Dose-dependent experiments and competitive inhibition by soluble RGD-containing peptides demonstrated that D25-1 and D12-2 mediate RGD-dependent cell adhesion. These results provide evidence for a cell adhesion function of fibrillin-2. Inhibition with anti-integrin antibodies showed that alpha(v) and beta3 integrins mediate adhesion to D25-1, while alpha3, alpha(v) and beta1 are involved in adhesion to D12-2. Binding of different receptors may elicit distinct cell signalling supporting the hypothesis that fibrillin-1 and fibrillin-2 have distinct roles.

Amino Acid Sequence↗
PubMed1997

Use of a GnRH antagonist in conjunction with low amplitude, high frequency LH pulses to induce follicular growth without an LH surge and ovulation in ewes.

The present study was undertaken to develop an experimental sheep model which could be used to investigate the abnormal follicle growth that is associated with the absence of the LH surge. On Day 10 of the oestrous cycle, 16 ewes were treated with an analogue of prostaglandin (cloprostenol; PG) and blood sampled every 4 h thereafter to determine the normal timing of the preovulatory LH surge. Three oestrous cycles later, all ewes were simultaneously treated with PG and a gonadotrophin-releasing hormone (GnRH) antagonist ([Ac-DNal1, D4C1Phe2, DTrp3, DArg6, DAla10] GnRH.HOAc; 50 micrograms kg-1 subcutaneously). Group 1 ewes (n = 6) received no further treatment. Group 2 ewes (n = 5) were additionally treated for a total of 7 days, starting at the time of PG injection, with purified ovine luteinising hormone (LH; preparation P 3 R3-5; equivalent to 1.25 micrograms NIH-oLH-S26) administered i.v. over a 2 min period. For the first 24 h, LH was given at 3 h intervals for 12 h, then every 2 h for 12 h, and thereafter hourly for 6 days. Group 3 ewes (n = 5) were treated as Group 2 but at 72 h received an additional antagonist injection (50 micrograms kg-1 subcutaneously). Mean values of LH from 24 to 96 h were significantly lower in untreated controls and Group 1 than in the other two groups (0.58 +/- 0.2 ng ml-1 and 0.55 +/- 0.2 ng ml-1 vs. 1.63 +/- 0.5 and 1.68 +/- 0.6 ng ml-1, respectively; P < 0.01). After treatment with PG alone in the untreated control group, the preovulatory LH surge began in all ewes at 59.9 +/- 2.8 h after PG. All Group 1 ewes also had an LH surge but the period from PG injection to the onset of the surge was 124 +/- 17.3 h (range 96-152 h). Only two of the Group 2 ewes had an LH surge (at 160 and 168 h, respectively) and no surge was detected in Group 3 ewes. In Group 1, mean values of follicle-stimulating hormone (FSH; 0.78 +/- 0.07 ng ml-1) were not affected by treatment with antagonist alone; however, in the two groups receiving exogenous LH pulses there was a marked decrease in FSH concentrations during the period 24-96 h. Progesterone concentrations increased 9 days after PG treatment in five out of six ewes in Group 1. In Group 2, there was evidence of a variable luteinisation response, but in Group 3 progesterone remained less than 0.08 ng ml-1 throughout. Endoscopy 112-115 h after PG confirmed that none of the 16 antagonist-treated ewes had ovulated; an event normally expected approximately 80 h after PG in sheep. The experimental protocol of Group 3 provides the basis for a model which will enable examination of the long-term functional capacity of ovarian follicles which have not been exposed to an LH surge.

Analysis of Variance↗
PubMed1997

Effect of adrenocorticotrophic hormone on gonadotrophin releasing hormone-induced luteinizing hormone secretion in vitro.

An in vitro perifusion study investigated the effect of different forms of adrenocorticotrophic hormone (ACTH) on gonadotrophin releasing hormone (GnRH)-induced luteinizing hormone (LH) secretion, particularly GnRH self-priming, and oestradiol sensitisation of the ovine pituitary. Fragments of pituitaries were obtained from mixed-breed adult nonpregnant female sheep (without corpora lutea, unless otherwise stated). The amount of LH released by different doses of GnRH (2.5 x 10(-10) M (n = 9 chambers), 1 x 10(-10) M (n = 9), or 5 x 10(-11) M (n = 6)) was evaluated by giving two GnRH pulses (5 min each) 2 h apart. In a duplicate set of chambers, ACTH1-24 (5 x 10(-7) M) was included in the perifusate 0.5 h before the first GnRH challenge. Potassium chloride (KCl; 100 mM) was administered 2 h after the second GnRH challenge to assess the viability of the tissue and the size of the releasable LH pool. Results were expressed as percentage of LH secretion. The influence of ACTH1-24 on oestradiol sensitisation was also examined using pituitaries obtained during the luteal phase. Pituitary tissues were perifused throughout with 1 x 10(-9) M or 6 x 10(-11) M oestradiol in the medium. The LH response to the second GnRH challenge (GnRH 2) was significantly greater (p < 0.01) than after the first (GnRH 1) at the highest dose of GnRH (2.5 x 10(-10) M; 2547 +/- 804 vs. 4547 +/- 1013%), but at the lower doses (1 x 10(-10) M or 5 x 10(-11) M), the self-priming effect of GnRH was not evident (3016 +/- 550 vs. 2932 +/- 490% and 841 +/- 205 vs. 711 +/- 87%). Treatment with ACTH1-24 (5 x 10(-7) M) did not affect tonic LH secretion nor the LH response to the first or second GnRH challenge at any of the GnRH doses tested. The LH released in response to KCl was also similar from control and ACTH1-24-treated tissue at all GnRH doses. Both lower doses of GnRH (1 x 10(-10) M or 5 x 10(-11) M) produced the self-priming effect when the pituitary tissue was sensitised with the higher dose of oestradiol (1 x 10(-9) M; 1711 +/- 239 vs. 5085 +/- 1307%, and 1502 +/- 376 vs. 2619 +/- 629%). In the presence of lower concentrations of oestradiol (6 x 10(-11) M), self-priming was observed only after the higher dose of GnRH (1 x 10(-10) M; 1293 +/- 214 vs. 2865 +/- 436%), not the lower dose (5 x 10(-11) M; 985 +/- 203 vs. 1271 +/- 436%). In spite of these differences, ACTH1-24 treatment did not affect LH secretion (neither basal nor potassium-induced). The effect of ACTH1-39 (1 x 10(-8) M or 5 x 10(-7) M; n = 6 chambers per combination) on GnRH-induced LH secretion was examined using the higher (2.5 x 10(-10) M) or lower dose of GnRH (1 x 10(-10) M), with or without oestradiol sensitisation (1 x 10(-9) M). At the lower dose (1 x 10(-8) M), ACTH1-39 influenced neither tonic nor GnRH-induced LH secretion. The LH released by KCl was also similar to the control and ACTH-treated tissue. In contrast, the higher dose of ACTH1-39 (5 x 10(-7) M) increased tonic LH secretion immediately after inclusion in the medium (104 +/- 3 vs. 161 +/- 20%), but suppressed the GnRH self-priming effect after 2.5 x 10(-10) M, i.e., the LH responses to GnRH 1 and 2 were similar (1786 +/- 294 vs. 1553 +/- 373%). However, the LH response to KCl was not significantly different (p > 0.05) between the control and ACTH-treated tissues (2333 +/- 286 vs. 2638 +/- 431%). When the effect of this higher dose of ACTH1-39 on oestradiol-priming was investigated, ACTH increased tonic LH secretion but suppressed the self-priming effect of GnRH (1 x 10(-10) M GnRH; 945 +/- 274 vs. 922 +/- 323%; p > 0.05), and decreased (p < 0.05) the LH released in response to KCl compared to the controls (1803 +/- 409 vs. 4302 +/- 1017%). In summary, in vitro, ACTH1-24 did not affect either tonic LH secretion, the GnRH self-priming effect, or oestradiol sensitisation. The entire ACTH1-39 increased tonic LH secretion, but reduced GnRH self-priming and oestradiol sensitisation. (ABSTRACT TRUNCATED)

Adrenocorticotropic Hormone↗
PubMed1997

Studies on the role of LH in the maturation of the pre-ovulatory follicle in a sheep using a GnRH-antagonist.

A model designed to mimic the action of LH in preovulatory follicle development was evaluated. The model involved treatment of ewes with GnRHa (50 micrograms kg-1 24 h-1; GnRHa) at the time of luteal regression followed by exogenous LH administered as a series of bolus injections of varying frequency and amplitude. Ovarian responses to this regimen were compared to data derived from the same animals during a normal follicular phase. In experiment 1 four ewes with an autotransplanted ovary were treated with GnRHa followed by hourly LH (2.5 micrograms NIH-oLH-S25 i.v.) for 60 h at which time a further bolus of LH (25 micrograms i.v.) was given to mimic the LH surge. Plasma FSH profiles and the pattern and rate of secretion of oestradiol, inhibin, androstenedione and testosterone by the ovary in normal and GnRHa treated ewes were similar, but ovulation did not occur following the induced follicular phase. Experiment 2 examined the ability of a revised LH regimen to induce ovulation in normal intact ewes. Ewes (n = 11) were treated with GnRHa at the time of luteal regression followed by LH injections (1.25 micrograms i.v.) administered every 3 h for 12 h, every 2 h for the next 12 h and every hour for the following 36 h (3,2,1 regimen). After 60 h of LH injections the animals received an 8 h infusion of oLH (25 micrograms min-1) designed to mimic the pre-ovulatory LH surge. This treatment resulted in normal follicular phase patterns of LH and FSH and had no effect on the incidence (100%) or number (1.6 +/- 0.1) of ovulations when compared to a normal cycle (100% and 1.8 +/- 0.2). Experiment 3 examined the pattern of ovarian follicular development and hormone secretion stimulated by the 3,2,1 LH regimen in ewes with autotransplanted ovaries (n = 8). The LH regimen stimulated normal pre-ovulatory follicular development (normal 1.4 +/- 0.2; induced 1.6 +/- 0.2) and a normal pattern of ovarian oestradiol and androstenedione secretion. Pulse analysis showed, however, that baseline steroid secretion was lower in induced animals during the late follicular phase reflecting lower baseline LH at this stage. We conclude that administration of a GnRHa at the time of luteal regression in conjunction with frequent low amplitude pulses of exogenous LH induce follicular and hormonal patterns that closely mimic those observed following normal luteal regression and that this regimen represents a useful model to study the role of LH in the control of follicular selection.

Androstenedione↗
PubMed1997

Endocrine activity of induced persistent follicles in sheep.

This experiment was designed to examine gonadotropin requirements for the induction and maintenance of persistent ovarian follicles in sheep. At the time of prostaglandin (PG) treatment on the tenth day of an induced estrous cycle, 8 ewes (with one ovary autotransplanted to the neck) received an injection of a GnRH antagonist ([Ac-d-Nal1, d-4-C-1-Phe2, d-Trp3, d-Arg6, d-Ala10] GnRH.HOAc; 50 microg/kg s.c.), and continuous hourly injections of exogenous ovine LH (equivalent to 1.25 microg NIH-oLH-S26) began simultaneously with this first antagonist injection (time zero). Antagonist was given three times at 3-day intervals. On Day 6, LH injections were stopped in 4 ewes (group 2) but continued in 4 other ewes (group 1) until the end of the 10-day experiment. Ovarian vein blood was sampled daily every 15 min for a 2-h period around two injections of exogenous LH (this sampling included group 2 after Day 6). Additional jugular and ovarian vein blood samples were collected every 8 h throughout the experiment. Daily ultrasound examination revealed the presence of at least one large follicle (range 4- to 7.5-mm diameter) from Day 3 to Day 10 in all ewes, but no new growing follicles (> 2 mm) were detected for at least 6 days. After Day 2, secretion of estradiol was positively correlated with that of inhibin (r = 0.83, p < 0.001), whereas FSH concentrations were inversely related to inhibin (r = -0.71, p < 0.001) and estradiol (r = -0.81, p < 0.001). In the absence of an LH surge, estradiol and androstenedione secretion (range 5-20 ng steroid/min) was maintained from Day 1 to Day 8 in group 1; but in group 2, secretion decreased abruptly when the LH injections stopped. Thus, continued low-amplitude, high-frequency LH pulses were required to maintain estradiol secretion when concentrations of FSH were < 0.5 ng/ml. However, estradiol and androstenedione secretion decreased (and FSH concentrations increased) between Days 8 and 10 in the ewes that received continued LH injections (group 1), showing that atresia in estrogenic follicles was not due to a lack of gonadotropin availability but to changes within the follicle. For the first 3 days after administration of PG, androstenedione secretion was greater than that of estradiol (p < 0.05), but from Day 4 to 6 the secretion rates were similar (p < 0.1), suggesting that aromatase may be limiting in the first 3 days whereas provision of androstenedione precursors was altered as the follicle persisted. In group 2 on Days 7 and 8 when hourly LH injections had stopped, neither androstenedione nor estradiol secretion increased after one test injection of LH; in contrast, androstenedione but not estradiol secretion increased after a second LH test injection 1 h later, suggesting that secretion of androstenedione is controlled by repeated exposure to LH. In conclusion, persistent estrogenic follicles were produced in the follicular phase in sheep by treatment with a combination of GnRH antagonist and hourly pulses of LH. Secretion of estradiol was dependent on continued hourly LH pulses of approximately 1 ng/ml and the follicles remained estrogenic for 8 days, after which time the ability to secrete estradiol and androstenedione declined even with continued LH injections.

Androstenedione↗
PubMed1997

The anatomy and perfusion of the renal portal system in the red-eared slider (Trachemys scripta elegans).

The anatomy of the renal portal system of the red-eared slider (Trachemys scripta elegans) is described, based on dissection of six double latex-injected specimens (three males, three females). The anatomy of these vessels, which had not previously been described in this species, was found not to differ significantly from the fundamental chelonian pattern. Fluoroscopic radioangiography revealed that venous blood returning from the hindlimbs flowed predominantly to the liver and bypassed the kidneys. Blood from the tail either flowed to the kidneys or bypassed them and flowed directly to the liver. A putative valve is described that governs venous blood flow from the caudal body to or around the kidneys.

Animals↗