Search Results

You are looking at 1 - 10 of 10 items for

  • Author: M. B. Brown x
Clear All Modify Search
Free access

B. W. Brown and M. A. Driancourt

Summary. Radioactive microspheres (15 μm diameter) were used to measure capillary blood flow rates in the ovaries and ovarian follicles (Qf) in high fecund Romanov and low fecund Préalpes-du-Sud ewes at the preovulatory stage of the oestrous cycle. Additionally, assessments of the percentage of arterial blood passing through ovarian arterio-venous anastomoses were obtained.

The mean ± s.e.m. Qf per unit volume of theca ((ml/min) × 104/mm3) for non-atretic follicles in Romanov ewes was significantly greater (P < 0·05) than that in Préalpes ewes (365·8 ± 42·4, n = 19, compared with 241·3 ± 30·1, n = 14). For each breed, the mean Qf value for non-atretic follicles was 8–10 times greater than that for atretic follicles.

In Romanov ewes, total Qf ((ml/min) × 104) and Qf per unit volume of theca was greatest in small-sized follicles (3· 1–5·0 mm) while in Préalpes ewes, maximum flow was attained in larger-sized follicles (5·1–7·0 mm). The elevated Qf in small-sized follicles in Romanov ewes may be conducive to more follicles achieving maturation at a smaller diameter in this breed than occurs in the Préalpes ewes.

The absence of flow through ovarian arterio-venous anastomoses in the Romanov, but not in the Préalpes, ewes suggests different mechanisms for controlling the distribution of the total ovarian blood supply in the 2 breeds.

Keywords: follicles; blood flow; sheep; prolificacy

Free access

B. W. Brown, M. J. Emery and P. E. Mattner

Summary. Changes in the mean velocity of ovarian arterial blood flow during the oestrous cycle were monitored in 5 ewes by the use of Doppler ultrasonic transducers chronically implanted around the ovarian arteries. In arteries supplying ovaries with a corpus luteum (CL), the velocity was minimal from Day −1 to Day 2 inclusive (Day 0 = day of oestrus), increased steadily until Day 13 (−4) and then declined precipitously. In contralateral arteries supplying ovaries without a CL, the velocity remained at a consistently low level throughout the oestrous cycle.

In each ewe, arterial blood velocity to the ovary with a CL and progesterone levels in peripheral plasma were highly correlated; within-individual correlations falling between r = 0·830 (P < 0·001, n = 15) and r = 0·936 (P < 0·001, n = 15). The changes in the velocity of the arterial supply to the ovulatory ovary and the plasma progesterone levels during the luteal stage of the cycle followed a similar pattern to that for weight of luteal tissue in similar ewes.

Free access

C. R. Brown, N. Clarke, M. Aiken and B. D. Bavister

Summary. Hamster zonae pellucidae were obtained from follicular oocytes, superovulated eggs, and eggs fertilized in vivo or in vitro. Zonae were labelled with N-succinimidyl-3(4-hydroxy,5-[125I]iodophenyl)propionate, and compared on single-and two-dimensional SDS-PAGE. Single-dimensional electrophoresis showed considerable differences between zona categories in the amount of label that they incorporated; follicular zonae incorporated the least label and zonae from eggs fertilized in vivo the most. On two-dimensional electrophoresis, polypeptides from 3 of the 4 zona categories migrated into 4 major groups: two of these groups each with M r 150 000–250 000 were within the M r range of ZP1, and two others, at M r 90 000 and 55 000, appeared to be analogous to ZP2 and ZP3, respectively. The fourth zona category (zonae from eggs fertilized in vivo) showed a changed polypeptide profile as well as incorporating the most label; one of the polypeptides, M r 150 000–250 000, was undetectable, but a train of M r 70 000–90 000 polypeptides and a discrete polypeptide at M r 20 000 were new. Since this changed profile did not occur in zonae from superovulated eggs, or in zonae from eggs fertilized in vitro, a synergism between oviducal factors and factors from the spermatozoon or egg, or both, towards the zona in vivo is indicated.

Keywords: fertilization; zona pellucida; electrophoresis; hamster

Free access

M. J. Hötzel, C. M. Markey, S. W. Walkden-Brown, M. A. Blackberry and G. B. Martin

The effects of nutrition on the testis were investigated in groups of five mature Merino rams that were fed either a sub-maintenance (low) diet or a supra-maintenance (high) diet for 69 days. Testosterone, oestradiol and inhibin were measured in blood plasma sampled simultaneously from jugular and testicular veins after an i.v. injection of 200 ng ovine LH kg−1. Plasma concentrations of testosterone, inhibin and oestradiol were higher in testicular than in jugular vein plasma for both diets (P < 0.01). After the LH injection, jugular plasma testosterone increased more rapidly (P < 0.01) in rams fed the high diet than in rams fed the low diet. This was not seen in the testicular vein. Oestradiol concentrations were higher in rams on the high diet than in those on the low diet, in both the testicular (P < 0.0001) and the jugular vein (P < 0.02). Diet did not affect inhibin concentrations. Testes were surgically removed and processed for light microscopy. Testicular mass and seminiferous tubule length and diameter were higher with the high diet than the low diet (P < 0.01). The number of Sertoli cell nuclei per testis was also affected (high diet: 120 ±6×108; low diet: 77 ± 7 × 108; P < 0.001), whereas the proportion of testis occupied by Sertoli cell nuclei was not affected. The number of Leydig cells per testis was not affected by diet, but Leydig cells occupied a greater volume of testis in rams on the high diet than in those on the low diet (P < 0.001). The effects of nutrition on Leydig and Sertoli cells are consistent with changes in the endocrine and exocrine functions of the testis. The finding that Sertoli cell population was altered in adult rams may be explained by the GnRH-independent effects of nutrition.

Free access

B. Malpaux, J. E. Robinson, M. B. Brown and F. J. Karsch

Summary. Three groups of ovariectomized Suffolk ewes bearing s.c. Silastic implants of oestradiol were subjected to a 90-day priming treatment of an inhibitory long photoperiod (16 h light/day; 16L:8D). On Day 0 of the experiment, they were moved to stimulatory photoperiods. One control group was transferred to 12L:12D and a second control group was transferred to 8L:16D; both groups remained in those photoperiods to determine the timing of reproductive induction and refractoriness. The experimental group was transferred to 12L:12D on Day 0 and then to 8L:16D on Day 55 to determine whether the further reduction in daylength could delay the development of refractoriness. Reproductive neuroendocrine condition was monitored by serum concentrations of LH and FSH. Both gonadotrophins remained elevated for a longer period of time in the experimental group receiving the second reduction in daylength than in either control group, indicating that the second photoperiodic drop delayed the onset of photorefractoriness. Measurement of 24-h patterns of circulating melatonin suggests that the prolonged stimulation of reproductive neuroendocrine activity in the experimental group resulted from a lengthening of the nocturnal melatonin rise. These findings indicate that refractoriness to an inductive photoperiod can be temporarily overcome by exposure to a shorter daylength, and that the change in duration of the nocturnal increase in melatonin secretion is important in photoperiodic signalling. Thus, in natural conditions, the decreasing autumnal daylength, and the resulting expansion of the nocturnal elevation in melatonin secretion, may be utilized to produce a breeding season of normal duration.

Keywords: seasonal reproduction; photorefractoriness; melatonin; oestradiol negative feedback; photoperiodic history; sheep

Free access

B. W. Brown, P. E. Mattner, P. A. Carroll, R. M. Hoskinson and R. D. G. Rigby

Groups of Merino ewe lambs were immunized against GnRH either soon after birth (prepubertal) or around puberty (peripubertal) with a prototype commercial preparation and were studied over the following 2 years to determine the long-term effects on reproductive development, function and hormone concentrations. At least 60% of the GnRH-immunized ewes in either treatment group did not experience oestrus and possessed small uteri and small ovaries that lacked follicular development. Growth rates of immunized and control ewes were similar throughout the study. Compared with the increase in plasma LH and FSH concentrations with age in control ewes, the concentrations of these hormones in immunized animals were lower and remained relatively constant from 46 to 90 weeks of age. Plasma FSH concentrations were particularly suppressed in immunized ewes and were significantly (P < 0.05) lower than the control values of 61 and 90 weeks of age. LH release after injection of 1 μg GnRH at 90 weeks of age was either absent or suppressed in immunized ewes compared with controls. The findings suggest that the lack of GnRH stimulation and consequent deprivation of gonadotrophins, early in the life of ewes, may result in some degree of permanent impairment of hypothalamic and/or pituitary function.

Free access

Hannah M Brown, Kylie R Dunning, Melanie Sutton-McDowall, Robert B Gilchrist, Jeremy G Thompson and Darryl L Russell

In vitro maturation (IVM) offers significant benefits for human infertility treatment and animal breeding, but this potential is yet to be fully realised due to reduced oocyte developmental competence in comparison with in vivo matured oocytes. Cumulus cells occupy an essential position in determining oocyte developmental competence. Here we have examined the areas of deficient gene expression, as determined within microarrays primarily from cumulus cells of mouse COCs, but also other species, between in vivo matured and in vitro matured oocytes. By retrospectively analysing the literature, directed by focussing on downregulated genes, we provide an insight as to why the in vitro cumulus cells fail to support full oocyte potential and dissect molecular pathways that have important roles in oocyte competence. We conclude that the roles of epidermal growth factor signalling, the expanded extracellular matrix, cumulus cell metabolism and the immune system are critical deficiencies in cumulus cells of IVM COCs.

Free access

J. L. Brown, D. E. Wildt, J. R. Raath, V. de Vos, J. G. Howard, D. L. Janssen, S. B. Citino and M. Bush

Summary. Pituitary, gonadal and adrenal activity were compared in free-living, adult African buffalo bulls during the breeding and nonbreeding seasons. Frequent blood samples were collected for 2 h from anaesthetized bulls treated intravenously with saline, gonadotrophin-releasing hormone (GnRH, 200 μg), human chorionic gonadotrophin (hCG, 10 000 i.u.) or adrenocorticotrophic hormone (ACTH, 1·5 mg). Electroejaculates also were collected from anaesthetized bulls during the breeding and nonbreeding seasons. Pretreatment testosterone concentrations among bulls varied more during the breeding (0·17–23·0 ng/ml) than the nonbreeding (0·15–2·21 ng/ml) season. The variation within the breeding season was attributed to 8 of 25 bulls producing higher (P < 0·05) serum testosterone (High-T; 16·28 ± 2·03 ng/ml) and testicular LH receptor (1·53 ± 0·22 fmol/mg testis) concentrations compared with their seasonal counterparts (Low-T; 0·95 ± 0·26 ng/ml; 0·38 ± 0·04 fmol/mg) or with all bulls during the nonbreeding season (0·90 ± 0·27 ng/ml; 0·31 ± 0·04 fmol/mg). The magnitude of GnRH- and hCG-induced increases in serum testosterone was similar (P > 0·05) between Low-T bulls and bulls during the nonbreeding season. In the High-T animals treated with GnRH or hCG, serum testosterone did not increase, suggesting that secretion was already maximal. Peak serum LH concentrations after GnRH were greater (P < 0·05) in bulls during the nonbreeding than the breeding season; FSH responses were similar (P > 0·05). ACTH treatment did not increase serum cortisol concentrations above the 2-fold increase measured in bulls treated with saline, hCG and GnRH (P > 0·05). Ejaculate volume, sperm motility and the proportion of morphologically normal spermatozoa were greater (P < 0·05) during the breeding than in the nonbreeding season, but the total number of spermatozoa/ejaculate was similar (P > 0·05). We suggest that season effects endocrine function and seminal quality in free-living, male African buffalo. During the breeding season some, but not all, adult bulls produce high circulating concentrations of testosterone associated with increased testicular LH receptor binding. These findings suggest that this species may experience selective gonadal suppression, perhaps related to differences in social status.

Keywords: buffalo; LH; FSH; testosterone; testis; gonadotrophin receptors; seasonality; spermatozoa

Free access

J. L. Brown, D. E. Wildt, J. R. Raath, V. de Vos, D. L. Janssen, S. B. Citino, J. G. Howard and M. Bush

Summary. Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April–May) and nonbreeding (September–October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 μg/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut. These data indicate that: (i) seminal quality in free-ranging impala undergoes seasonal changes coincident with alterations in testicular steroidogenic activity, and (ii) the increased testosterone secretion observed during rut is associated with increased testicular sensitivity to LH (via increased gonadotrophin receptors) rather than to increased circulating gonadotrophin concentrations or pituitary responsiveness to GnRH.

Keywords: impala; LH; FSH; testosterone; testis; receptors

Free access

B. W. Brown, P. E. Mattner, P. A. Carroll, E. J. Holland, D. R. Paull, R. M. Hoskinson and R. D. G. Rigby

Groups of Merino ram lambs were immunized against GnRH either soon after birth (prepubertal) or around puberty (peripubertal) with a prototype commercial preparation and studied over the following 2 years to determine the long-term effects of such immunization on reproductive development, function and hormone concentrations. The treatment was equally effective in suppressing reproductive function and hormones when given at either time. Growth rates of immunized and controls rams were similar throughout the study. Prepubertal immunization delayed testicular growth until the rams were at least 27 weeks of age and some rams had subnormally sized testes even at 115 weeks of age. After peripubertal immunization, the mass of the testes declined and remained regressed until the rams were from 51 to 90 weeks old. There was a significant correlation between total testicular mass at 115 weeks of age and duration (weeks) of suppression of testicular growth (prepubertal, r= −0.7375; peripubertal, r= −0.7132, P < 0.001). Prepubertal immunization markedly delayed separation of the penis from the prepuce. The immunized rams did not display sexual activity until their total testicular mass reached at least 70 g. In control and immunized rams with testicular mass > 100 g, the semen did not differ in the percentage of spermatozoa that were unstained (live), of normal morphology, or showed progressive movement. Compared with the increase in plasma LH and FSH concentrations with age in control rams, the concentrations of these hormones in the immunized animals were lower and remained relatively constant from 46 to 90 weeks of age. Plasma FSH concentration was particularly suppressed in immunized rams and was significantly (P< 0.05) lower than the control values at 61 and 90 weeks of age. LH release after injection of 1 μg GnRH at 90 weeks of age was either absent or markedly suppressed in immunized rams compared with that for controls.