Biomedical subjects

M G Hunter

Publications and source records attributed to M G Hunter.

At least 73 records · Page 4Linked to original sources

PubMed1994

Effects of progesterone pretreatment on the oxytocin receptor concentration and the response to oxytocin during the simulated early luteal phase in the ovariectomized ewe.

A steroid-treated ovariectomized ewe model was used to investigate the role of progesterone pretreatment in the control of functional oxytocin receptor concentrations during the early luteal phase. Ovariectomized ewes (n = 28) were injected with oestradiol for 2 days (final injection = day 0) with or without progesterone pretreatment (progestagen sponge for 10 days). Ewes were then given high or low concentrations of progesterone combined with high, low or zero concentrations of oestradiol in a pattern known to simulate the early luteal phase profile (n = 4 per group). Ewes were given 1 microgram oxytocin (i.v.) on day 4 and plasma was collected to assay 13,14-dihydro-15-keto PGF2 alpha. The concentration of progesterone and oestradiol administered had no effect on the concentration of 13,14-dihydro-15-keto PGF2 alpha following oxytocin administration (P > 0.05). However, the group that was not pretreated exhibited a small but significant 13,14-dihydro-15-keto PGF2 alpha response in comparison with the equivalent pretreated group (P < 0.05). In a subsequent study, ewes were divided into groups pretreated and not pretreated with progesterone; both groups were given oestrous concentrations of oestradiol and high concentrations of progesterone and oestradiol together. On day 0, 2, 3 or 4, ewes from each group (n = 3, 3, 4 and 4, respectively) were given 1 microgram of oxytocin i.v., and the endometrium was collected to measure the binding of oxytocin receptors. Oxytocin caused a significant (P < 0.05) increase in the concentration of 13,14-dihydro-15-keto PGF2 alpha in all ewes on day 0 but not on days 2, 3 or 4. Oxytocin receptor concentrations were maximal on day 0 and basal by day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Suckling-induced inhibition of luteinizing hormone secretion and follicular development in the early postpartum sow.

The endocrine basis of lactational anestrus, the causes of reproductive dysfunction after early weaning, and the relationships among LH, FSH, and prolactin (PRL) secretion and follicular development were evaluated in sows weaned 6 h after farrowing (zero-weaned, n = 8) and in normally lactating sows (n = 9). An irregular, high-frequency episodic-type pattern of LH secretion was present in the early postpartum period, irrespective of treatment, and in a proportion of sows this pattern was associated with a marked elevation of baseline LH concentrations. This pattern of LH secretion was maintained in the zero-weaned sows but LH secretion was inhibited in lactating sows, resulting in a difference (p < 0.05) in mean plasma LH between groups 72-78 h postpartum. There were no differences in FSH between groups in any period of sampling. Variable but elevated plasma PRL was observed in suckled sows but declined (p < 0.05) to basal levels within 12 h of zero-weaning. Follicular development measured at laparotomy or slaughter 96 h postpartum was greater (p < 0.05) in zero-weaned than in control sows. The development of lactational anestrus in the sow therefore requires suckling-induced inhibition of LH secretion by 78 h postpartum. This inhibition of LH release does not appear to be causally related to short-term changes in PRL secretion.

Animals↗

PubMed1993

Comparison of follicular heterogeneity and ovarian characteristics in Meishan and large-white hybrid pigs.

Comparisons were made between characteristics of pre-ovulatory follicles recovered from prolific Chinese Meishan gilts (n = 12) and from European Large-White hybrid gilts (n = 13) in the late follicular phase preceding their fifth oestrous cycle, to determine whether there is an ovarian basis for the enhanced prolificacy in the Meishan. A total of 177 follicles per breed was classified as pre-ovulatory, based on follicular fluid oestradiol concentrations. Results obtained demonstrated high variability in all follicular characteristics in both breeds and no decrease in heterogeneity was evident in the Meishan. The Meishan follicles tended to be smaller (P < 0.06) and had less follicular fluid (P < 0.005), but total oestradiol content per follicle was similar (P < 0.1) with the result that the concentration of oestradiol in follicular fluid tended to be higher (P < 0.06) in Meishan than Large-White hybrid pigs. There were no differences between breeds in terms of testosterone concentrations in follicular fluid, hCG binding to granulosa cells or total DNA content of granulosa cells. Concentrations of inhibin in follicular fluid were similar in both breeds (P > 0.1) which resulted in a trend towards less total inhibin content in Meishan than Large-White hybrid follicles (P = 0.065). Corpora lutea were recovered from both breeds (n = 12 per breed) on days 27-31 of pregnancy after mating at first, second and third oestrus:corpora lutea were smaller (P < 0.001) and contained less progesterone per corpus luteum in the Meishan (P < 0.05) than in Large White hybrid pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Comparisons of endocrinology and behavioural events during the periovulatory period in Meishan and large-white hybrid gilts.

Attainment of puberty, cycle lengths, ovulation rate and endocrinology during the periovulatory period were studied in Meishan (MS) and European Large-White hybrid (LW) gilts. The mean age at onset of puberty of 115 days in MS (n = 20) gilts was younger (P < 0.001) than the 235 days in LW (n = 23). In the MS population studied, ovulation rate was not different (P > 0.1) during the third and fourth oestrous cycles, nor were there differences (P > 0.1) in the mean cycle length over the first three cycles. Overall changes in plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH) and oestradiol did not differ significantly (P > 0.1) between the breeds (MS, n = 6; LW, n = 5) during the periovulatory period, but plasma inhibin concentrations were significantly (P < 0.05) higher in the MS. The time intervals from the oestradiol peak concentration and the onset of the LH surge until the onset of behavioural oestrus were significantly different (P < 0.005) between the breeds, with oestrus occurring earlier in the MS. However, no difference (P > 0.1) was found between the groups when the intervals from the peak oestradiol concentration to the onset of the LH surge were compared. These results indicate differences between the breeds, particularly in terms of the age of attainment of puberty and the timing of the onset of behavioural oestrus relative to the oestradiol and LH surges.

Animals↗

PubMed1993

Endocrine and follicular studies in Meishan pigs.

The enhanced early embryonic survival in Chinese Meishan compared with Large-White gilts may be due, in part, to differences in ovarian and endocrine function, particularly during the periovulatory period. The overall patterns of oestradiol, LH and FSH secretion were not different between Meishan and Large-White hybrid controls during this period, although circulating inhibin concentrations were higher in Meishan gilts. Thus, there appeared to be a decreased sensitivity to inhibin feedback on FSH secretion in Meishan gilts. Behavioural oestrus was exhibited earlier relative to the LH surge in Meishan gilts than in Large-White hybrid gilts, but the time interval from the oestradiol peak until the LH surge was similar in both breeds. This finding suggests that Meishan gilts are more sensitive in terms of initiating a behavioural response, but not in terms of positive feedback. Although preovulatory follicular characteristics were as variable in Meishan as in Large-White hybrid gilts, follicles from Meishan gilts were smaller, but contained a higher concentration of oestradiol in the follicular fluid. This was probably due to increased aromatase activity in both granulosa and theca cells of Meishan follicles. The enhanced maturation of the intrafollicular environment in Meishan gilts was reflected in the oocyte population which was at a more advanced stage of development in the period preceding ovulation. In addition to decreasing the time between onset of oestrus and ovulation, advancing the LH surge to coincide with onset of oestrus (via hCG administration) decreased embryo survival at day 30 of gestation. It is concluded that both endocrine and follicular mechanisms have a role in ensuring the prolificacy in the Meishan breed.

Animals↗

PubMed1992

Biological and structural properties of MIP-1 alpha expressed in yeast.

The murine macrophage inflammatory proteins-1 alpha (MIP-1 alpha) and MIP-1 beta are distinct but closely related cytokines. Partially purified mixtures of the two proteins affect neutrophil function and cause local inflammation and fever. The particular properties of MIP-1 alpha have not been well studied, although it has been identified as being identical to an inhibitor of haemopoietic stem cell growth. We have expressed MIP-1 alpha in yeast cells and purified it to sequence homogeneity. Structural analysis of this biologically active material by circular dichroism and fluorescence spectroscopy confirms that MIP-1 alpha has a very similar secondary and tertiary structure to platelet factor 4 and interleukin 8 with which it shares limited sequence homology. The in-vitro stem cell inhibitory properties have been confirmed using a range of murine progenitor cells including purified bone marrow progenitor cells (FACS-1), the FDCP-mix A4 cell line, and spleen colony forming unit (CFU-S) populations. Plateau levels of inhibition of stem cell growth were achieved using concentrations of 0.15 micrograms/ml MIP-1 alpha. We have also demonstrated that MIP-1 alpha is active in vivo: 5 micrograms of MIP-1 alpha per mouse given as a bolus injection, protects stem cells from subsequent in-vitro killing by tritiated thymidine. MIP-1 alpha was also shown to enhance the proliferation of more committed progenitor granulocyte macrophage-colony forming cells (GM-CFC) in response to granulocyte macrophage-colony stimulating factor (GM-CSF).

Animals↗

PubMed1992

Gonadotropin-independent mechanisms participate in ovarian responses to realimentation in feed-restricted prepubertal gilts.

Short-term feed restriction in prepubertal gilts suppresses episodic LH secretion in the absence of changes in body weight or composition. To assess non-gonadotropin-mediated effects of realimentation at the ovarian level, 52 gilts were assigned to six treatments after 7 days (Days 1-7) of maintenance feeding (approximately 30% ad libitum). Groups R12 and R9 were maintenance-fed Days 8-12 or Days 8-9, respectively; A12 and A9 were fed to appetite Days 8-12 or Days 8-9, respectively. Groups R9P and A9P were fed as groups R9 and A9 were but received 750 IU eCG at 1500 h on Day 8. Groups R12 and A12 were ovariectomized at 1500 h on Day 12, and all other groups were ovariectomized at 1500 h on Day 9. All gilts received oral progestogen (15 mg allyl trenbolone) from Day 1 to ovariectomy, to antagonize the usual increases in endogenous gonadotropins that follow realimentation. Blood samples were obtained at 10-min intervals during selected windows during the experiment. Ovarian follicles were analyzed for development and steroidogenesis, and plasma samples were analyzed by RIA to determine concentrations of LH, FSH, insulin, and insulin-like growth factor-1 (IGF-1). Allyl trenbolone abolished pulsatile LH secretion, and realimentation did not stimulate LH or FSH secretion, with the exception of FSH secretion on Day 8 in A9 gilts. Postprandial insulin concentrations on Day 9 were greater after feeding to appetite (A9, A9P, and A12) than after feed restriction (R9, R9P, and R12). Pre- and postprandial IGF-1 concentrations were higher in re-fed gilts on Day 9 (A9 and A12) and Day 12 (A12) than in feed-restricted gilts. Follicular diameter, fluid volume, and basal granulosa cell estradiol synthesis per follicle were greater in A12 gilts than in R12 gilts, although there was no difference between A9 and R9 gilts. There was no effect of realimentation on follicular fluid concentrations of estradiol or testosterone, or on androgen-driven granulosa cell estradiol synthesis. Treatment with eCG increased follicular diameter, fluid volume, basal and androgen-driven estradiol synthesis, and fluid estradiol concentrations without interaction with feeding level. In conclusion, in the absence of LH elevations, realimentation over 5 days exerts effects at the ovary, increasing follicular growth and estradiol synthesis. These effects may be mediated by insulin, IGF-1, or unmeasured growth factors and would be expected to synergize with increases in endogenous gonadotropin that follow realimentation.

Analysis of Variance↗

PubMed1992

Lack of stimulation of relaxin secretion in lactating sows by suckling in vivo or by oxytocin in vitro.

After parturition, eight sows were zero weaned by removing all piglets 6 h after birth; a further 18 sows suckled at least ten piglets each. Blood samples were collected on Day 4 after zero weaning or on Days 4, 14 and 21 of lactation and the sampling frequency increased during suckling bouts. Ovaries were recovered from sows on these days and corpora lutea were either extracted for estimation of relaxin and progesterone concentration, fixed for immunohistochemical analysis or incubated in vitro in the presence or absence of luteinizing hormone (LH) or oxytocin. Luteal weight and progesterone were higher in the zero-weaned sows than in lactating sows (P less than 0.05 and less than 0.001, respectively); relaxin content was below detection by Day 14. This was supported by immunohistochemical staining for relaxin, which showed limited immunostaining in zero-weaned and Day 4 sows, but none in the tissue recovered on Days 14 and 21, which showed typical signs of regression. Secretion of progesterone and relaxin by luteal tissue in vitro was highest in zero-weaned sows (P less than 0.05), decreased as lactation progressed and neither LH nor oxytocin had any significant effect. Concentrations of plasma relaxin were all less than 0.2 ng/ml in three of the four zero-weaned and Day-4-suckled sows assayed; there was no detectable increase during suckling bouts. It was concluded that during lactation the old corpus luteum of pregnancy is not able to release relaxin in response to suckling in vivo or to oxytocin treatment in vitro.

Animals↗

PubMed1992

Effect of prostaglandins on luteal function during early pregnancy in pigs.

Luteal cells were obtained by digestion of luteal tissue of cyclic (day 12) and early pregnant (days 12, 20 and 30) pigs. Suspensions of the dispersed luteal cells (5 x 10(4) cells ml-1) were incubated for 2 h in minimum essential medium (MEM) alone (control) and MEM with different concentrations of prostaglandin F2 alpha (PGF2 alpha) and PGE2 (0.01, 0.1, 1, 10, 100 and 1000 ng ml-1) and luteinizing hormone (LH) 100 and 1000 ng ml-1, or with combinations of LH + PGF2 alpha and LH + PGE2. Net progesterone production was measured in the incubation media by direct radioimmunoassay. The overall response pattern of the luteal cells to exogenous hormones on day 12 of the oestrous cycle and pregnancy differed (P < 0.05) from treatment on day 20 and 30 of pregnancy. In general progesterone production was higher (P < 0.05) and the response to PGF2 alpha and PGE2 treatment was most obvious on day 12 of the oestrous cycle and pregnancy. Overall, PGF2 alpha stimulated progesterone production in a dose-dependent manner (P < 0.05). The response to PGE2 was of a quadratic nature (P < 0.05) in which the lowest and the highest doses of PGE2 were associated with a greater production of progesterone than were the intermediate doses. Treatment of luteal cells with PGF2 alpha + LH or PGE2 + LH caused overall inhibition (P < 0.05) of progesterone production compared with treatment with each hormone alone. This interaction was not affected by the dose of LH used. These findings indicate that PGF2 alpha and PGE2 are involved in the autocrine control of corpus luteum function.

Animals↗

PubMed1992

Preovulatory follicle development and luteal function in ewes immunized against a synthetic peptide sequence of the alpha subunit of bovine inhibin.

Immunization against inhibin consistently results in an increase in ovulation rate in sheep, but the effects that this treatment has on follicle development are unknown. In order to determine the influence of inhibin, parameters of follicle development were assessed in ewes that had been actively immunized against a synthetic peptide homologous to the N-terminal sequence (alpha 1-29, Tyr30) of the alpha subunit of bovine inhibin, a treatment that neutralizes the biological activity of endogenous inhibin. The final stages of preovulatory follicle development that culminate in ovulation were induced in seasonally anoestrous ewes, and follicles were recovered prior to the predicted time of ovulation. After priming with progestagen, inhibin-immunized and control ewes were treated with gonadotrophin-releasing hormone (GnRH) by continuous infusion (200 ng/h). The ovaries were recovered at slaughter 24 h after the start of GnRH treatment and all follicles greater than or equal to 2.0 mm diameter were dissected out and their capacity to produce oestradiol in vitro was assessed. Further groups of similarly treated animals were blood-sampled daily to determine luteal function following GnRH-induced ovulation. The ovaries were recovered from these ewes at slaughter 10 days after the start of GnRH treatment, the corpora lutea were dissected out and their progesterone content was assessed. There were more (P less than 0.01) follicles of 5-6 mm diameter (3.2 +/- 0.45 (S.E.M.) compared with 1.1 +/- 0.25 follicles/ewe) and more (P less than 0.001) follicles of greater than 6 mm diameter (2.8 +/- 0.56 compared with 0.9 +/- 0.17 follicles/ewe) in inhibin-immunized than in control ewes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Current concepts of folliculogenesis in monovular and polyovular farm species.

Follicular growth in sheep and pigs is under both endocrine and paracrine control, and the local factors involved include steroids, growth factors and other regulatory peptides such as the putative follicle regulatory protein. These factors can act either directly on ovarian cells, or by modulating the response to circulating gonadotrophins. It is suggested that during the early stages of development in sheep and pigs, follicles pass through a stage at which they are modulated by growth factors, after which endocrine control mechanisms become more important. There is evidence that interactions between follicle-stimulating hormone, insulin-like growth factor-1 and oestradiol further enhance development and steroidogenesis. Interfollicular relationships in polyovular pigs may differ from those in sheep, in that the more mature follicles may act to enhance development of the less mature in the selected population. Although it is unclear whether similar mechanisms operate in both hyperprolific pigs and prolific breeds of sheep, Meishan pigs and Booroola ewes do exhibit similar follicular characteristics compared with those of nonprolific breeds. The significance of this in relation to prolificacy requires further investigation.

Androgens↗

PubMed1991

Effect of estrogen administration on endogenous and luteinizing hormone-releasing-hormone-induced luteinizing hormone secretion and follicular development in the lactating sow.

The objectives of this study were to investigate whether estradiol treatment during lactation modifies 1) the patterns of endogenous LH, FSH, and prolactin (PRL) release; 2) the sensitivity of the pituitary to exogenous injections of LHRH; and 3) the responsiveness of the ovarian follicles to gonadotropin. Plasma LH, FSH, and PRL were determined in samples taken repeatedly from 18 sows on Days 24-27 of lactation. Ovaries were then recovered, and follicular development was assessed by measuring the follicular diameter (FFD) and follicular fluid estradiol-17 beta concentration (FFE) of the ten largest follicles dissected from each ovary. Sows were randomly allocated to one of four treatments: 1) Group C (4 sows) received no treatment; 2) Group LHRH (5 sows) received 800 ng of LHRH every 2 h throughout the sampling period; 3) Group E2 (4 sows) received subcutaneous implants containing estradiol-17 beta 24 h after start of sampling; 4) Group LHRH + E2 (5 sows) were administered a combination of LHRH and estradiol-17 beta implants. Between-animal variability for plasma LH, FSH, and PRL was considerable. LH concentration and LH pulse frequency increased (p less than 0.05) after LHRH treatment in the LHRH and LHRH + E2 groups; however, an acute inhibition of LH secretion was observed in the latter group immediately after estradiol implant application. In the absence of LHRH treatment, estradiol caused chronic inhibition of LH secretion. Follicular development was greater in the LHRH and LHRH + E2 groups compared to the C and E2 groups (p less than 0.05 for both FFD and FFE).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Evidence against a role for blastocyst-secreted oxytocin in early pregnancy maintenance in sheep.

Analysis of ovine conceptus RNA by slot blotting, Northern analysis and nested polymerase chain reaction failed to detect oxytocin-neurophysin prohormone mRNA. Probes used hybridized with both the 3' end of the prohormone mRNA and the oxytocin-coding sequence. Northern analysis of bovine and porcine conceptus RNA was also negative, and polymerase chain reaction demonstrated oxytocin-neurophysin mRNA in ovine corpus luteum, but not in human corpus luteum or decidua, or in ovine endometrium. Infusion of oxytocin into the uterine lumen in cyclic ewes between days 9 and 19 or 20 after oestrus failed to prolong the luteal phase of the cycle and had no effect on endometrial oxytocin receptor concentrations or uterine prostaglandin F secretion. Oxytocin administered systematically prevented luteolysis and reduced uterine prostaglandin F secretion. Taken together, these data suggest that blastocyst-derived oxytocin is unlikely to contribute to corpus luteum maintenance in early pregnancy. They are inconsistent with a previous report that the ovine blastocyst synthesizes and secretes oxytocin.

Animals↗

PubMed1991

Catecholamines regulate the steroidogenesis by luteal cells from early pregnant pig.

Luteal cells (10(6)/chamber) from pregnant pigs (Day 18, n = 5) were incubated in a perfusion system with a flow rate of 0.11 ml/min and samples collected every 10 min. This medium 199 had been supplemented with 1% BSA, 0.1% ascorbic acid and 10 mM Hepes buffer. The effects in vitro of adrenergic agonists (adrenaline, noradrenaline and isoproterenol) at concentrations of 10(-5) M on progesterone (P4) production by pig luteal cells were studied. The alpha or beta receptors were blocked by pretreatment of the luteal cells with phentolamine or propranolol for 30 min and then the cells were treated with adrenergic agonists for 60 min followed by a further 80 min with medium alone. The steroidogenic response to noradrenaline in terms of increased P4 production was greater than that for adrenaline and isoproterenol (P less than 0.05). Response to both natural and synthetic catecholamines was suppressed by pretreatment of luteal cells with propranolol but after pretreatment with phentolamine all the agonists significantly (P less than 0.05) elevated P4 production. The results demonstrate that catecholamines can affect steroidogenesis in luteal cells from the early pregnant pig and their action is mediated by beta adrenergic receptors.

Animals↗

PubMed1991

Characteristics and causes of the inadequate corpus luteum.

An inadequate luteal phase occurs in domestic ruminants in several physiological situations (e.g. puberty, post partum), and also following the induction of ovulation in anoestrous ewes with GnRH treatment. The induced corpora lutea (CL) initially developed, but then regressed rapidly after Day 4, unless the animals had been primed with progesterone before GnRH therapy or hysterectomized. Significant increases in prostaglandin F-2 alpha metabolite (PGFM) secretion and coincident peaks of oxytocin and PGFM occurred around the time of premature regression. Endometrial oxytocin receptors were also detectable at this time in ewes which had abnormal luteal phases, but not in ewes which had been progesterone primed and thus had normal luteal phases. This suggests that the presence or otherwise of the oxytocin receptor during the early luteal phase may be crucial in determining whether the CL has a short or normal lifespan. These results show that an inadequate luteal phase is often caused by the premature induction of luteolysis and the presence of the endometrial oxytocin receptor in necessary for this occurrence. This receptor in turn is controlled by the steroid environment to which the uterus has previously been exposed.

Animals↗

PubMed1990

Immunocytochemical localization of oxytocin in corpora lutea and luteinized cysts from anoestrous ewes stimulated with gonadotrophin-releasing hormone.

Anoestrous Romney Marsh ewes with or without progesterone pretreatment were injected with multiple low-doses of gonadotrophin-releasing hormone followed by a single, larger bolus. Blood samples were taken at twelve-hourly intervals for progesterone radioimmunoassay. Ewes were slaughtered on day 3 or 5 after the bolus injection, and the ovaries were collected for histology and immunocytochemical examination for oxytocin-immunoreactivity. The corpora lutea of all ewes killed on day 3 had similar weights and morphology. The ovaries of those ewes which were not pretreated with progesterone also contained some luteinized cysts. Ewes slaughtered on day 5 were separated into 2 groups according to plasma progesterone profiles, which were either rising ('normal'), or falling after a transitory rise ('abnormal'). Those ewes pretreated with progesterone all had a 'normal' progesterone profile whereas, of 14 ewes not pretreated with progesterone, 6 were 'normal' and 8 'abnormal'. Corpora lutea were significantly lighter in the 'abnormal' group and the ovaries of most of these ewes also contained luteinized cysts. All corpora lutea and luteinized cysts showed staining for oxytocin-immunoreactivity although the staining intensity was variable. In corpora lutea from 'normal' ewes oxytocin was restricted to large luteal cells. In addition tissues from 'abnormal' ewes also contained many cells with an atypical elongated shape which stained for oxytocin-immunoreactivity. These results show that progesterone pretreatment is needed for both normal morphological and endocrine development of corpora lutea in anoestrous ewes stimulated with gonadotrophin-releasing hormone.

Anestrus↗

PubMed1990

Differences in follicular morphology, steroidogenesis and oocyte maturation in naturally cyclic and PMSG/hCG-treated prepubertal gilts.

Ovaries were obtained from naturally cyclic pigs on Days 16-17, 18, 19, 20 and 21 of the oestrous cycle and on the basis of observed follicular characteristics were assigned as representative of the early (Group 1), mid- (Groups 2 and 3) or late (after LH; Group 4) follicular phase. Follicular development in cyclic gilts was compared with that in ovaries obtained from late prepubertal gilts 36 (Group 5) or 72 (Group 6) h after treatment with 750 i.u. PMSG alone, or with a combination of 500 i.u. hCG 72 h after PMSG and slaughter 30-40 h later (Group 7). After dissection of all follicles greater than 2 mm diameter, follicular diameter, follicular fluid volume, follicular fluid concentrations of progesterone, oestradiol and testosterone, and the stage of oocyte maturation were determined. Combined PMSG/hCG treatment of immature gilts resulted in a pattern of follicular development different from that in naturally cyclic gilts during the follicular phase. Overall exogenous gonadotrophin treatment also increased (P less than 0.001) the variability in follicular diameter and fluid volume. Comparisons between appropriate groups also established differences in the variability of both morphological (diameter and volume, Group 1 vs Group 5; P less than 0.05) and biochemical development (follicular fluid oestradiol, Group 3 vs Group 6 and Group 4 vs Group 7; both P less than 0.05). Such differences in both morphological and biochemical characteristics between cyclic and PMSG/hCG-treated gilts were particularly evident in the population of larger (greater than 6 mm) follicles. These results indicate that the pattern of follicular development in naturally cyclic and in PMSG/hCG-treated gilts is dissimilar and suggests that the ovaries of gonadotrophin-treated prepubertal gilts are functionally different from the ovaries of mature females.

Animals↗

PubMed1990

Luteal inadequacy during the early luteal phase of subfertile cows.

A study was made of early luteal function (up to Day 6) in cyclic and pregnant heifers and also in older, subfertile cows. There were no differences in vivo or in vitro between cyclic and pregnant heifers, indicating no luteotrophic effect of the embryo at this stage, but the increase in postovulatory peripheral progesterone concentrations was delayed (P less than 0.01) and occurred more slowly (P less than 0.001) in the subfertile cows than in the heifers. The corpora lutea of the subfertile cows were heavier (P less than 0.001) than those of the heifers on Day 6. Basal progesterone production by dispersed luteal cells was similar between heifers and subfertile cows, but there was a difference (P less than 0.001) in the pattern of response to exogenous LH and PGE-2. Cells from subfertile cows were less sensitive to the stimulatory effects of PGE-2 and although LH increased (P less than 0.001) progesterone production by all cells, this stimulation by a low dose of LH was inhibited by PGE-2 in luteal cells from subfertile cows. This effect did not occur in the luteal cells from heifers. These results indicate the possibility that luteal inadequacy, due to a diminished response to circulating luteotrophic hormones, may contribute to embryo mortality in subfertile cows.

Animals↗