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Biomedical subjects

I A Cumming

Publications and source records attributed to I A Cumming.

At least 19 recordsLinked to original sources
PubMed1982

The time of oestrus and ovulation following various synchronisation techniques using progesterone impregnated intravaginal devices.

Progesterone releasing intravaginal devices (PRIDs) were used in 4 experiments involving 67 cattle to study the effect of the stage of the oestrous cycle and of oestradiol benzoate (ODB) administration on the time interval from PRID removal to oestrus and/or ovulation. Cows in which PRIDs were inserted on days 2 to 4 of the oestrous cycle for 14 days were subsequently observed by endoscopy to ovulate significantly later than cows given identical treatments on days 13 and 14 of the cycle. The concentration of progesterone was higher in the former group at the time PRIDs were removed and remained at a higher level for 3 days thereafter. The length of the oestrous cycle of untreated heifers was significantly longer than in heifers treated for 12 days with PRIDs only inserted on day 3 of cycle (19.7 v 18.2; p less than 0.01). Treatment with PRIDs inserted for 12 days together with ODB further shortened the cycle length from 18.2 days to 16.9 days (p less than 0.01). The intervals from PRID removal to onset of standing oestrus in heifers treated with PRID only and those treated with PRID and ODB were 80h and 45h, respectively (p less than 0.01); the respective variances were 280 and 4; p less than 0.01). Plasma progesterone concentration, at PRID removal, was 3 times higher in heifers treated with PRID only than in heifers treated with PRID and ODB (p less than 0.01) and the interval from PRID removal to the lowest progesterone value following it was 3.8 ad 1.2 days for the 2 groups, respectively (p less than 0.05). The study indicated that the stage of oestrous cycle at PRID insertion is an important factor which influences the interval from withdrawal of PRIDs to ovulation. The results suggest closer synchronisation would follow insertion in the mid-luteal phase (Day 13 to 14) or use of ODB treatment at the time of insertion of PRIDs.

Animals↗
PubMed1981

Fertility and tubal morphology after microsurgical removal of segments of the porcine fallopian tube.

A controlled study was carried out in the pig to determine the effect on fertility of resecting either the ampullary-isthmic junction or the isthmus. In both treated groups, the nidation index was lower than that in the control animals. The index was not significantly lower in the isthmic resection group than in the ampullary-isthmic junction group. The implications of these findings in terms of fallopian tube physiology and human tubal reconstructive surgery are discussed.

Animals↗
PubMed1981

Effects of LH-RH infusion, castration and cryptorchidism on gonadotrophin and testosterone secretion in developing rams.

The relationship between the pituitary gland and testis in rams was studied from birth to sexual maturity. The concentrations of LH, FSH and testosterone increased between 5 and 7 weeks of age; the rise was not correlated with any specific cytological change in the testis. An augmented pituitary response to LH-RH was demonstrated as levels of gonadotrophin increased. It is unclear whether this change in sensitivity plays a role in initiation of the pubertal process because Sertoli cell maturation, the earliest detectable change in the seminiferous epithelium, occurs between 17 and 21 weeks of age. Spermatocytes were first seen in biopsies taken at 31-36 weeks and spermatogenesis was established fully by 45 weeks. This second phase of testicular development was characterized by increases in prolactin, testosterone and LH. Leydig cells previously difficult to identify became recognizable at the time of sexual maturation. In newborn rams, castration produced significant increases in LH and FSH levels within 2-3 weeks, but higher basal FSH levels (2- to 3-fold) were observed at 5 than at 3 weeks of age. Cryptorchidism did not elevate LH or FSH significantly during the first year of life. FSH rose after this period to levels 2- to 3-fold higher than in normal rams, while LH and testosterone values remained in the normal range in spite of diminished spermatogenic activity; spermatids were absent and testis size was approximately 60% of that recorded in a normal ram. These studies demonstrate a rise in gonadotrophin and testosterone secretion in rams during the first 5-7 weeks of life, followed by a quiescent period of 8-9 months before a secondary increase occurs coincident with the establishment of sexual maturity.

Aging↗
PubMed1981

The effect of intrauterine gonadectomy on fetal and neonatal gonadotrophin secretion in the lamb.

In Exp. 1, sheep fetuses (2 male and 3 female) were gonadectomized between Days 70 and 120 of gestation and their blood LH and FSH levels were compared to those of control animals (4 male, 6 female) at regular times during the first year after birth. In Exp. 2, fetuses (3 male and 5 female) were gonadectomized between Days 50 and 60 of gestation and gonadotrophin levels at Day 90 of gestation were compared to those of control fetuses of the same age. In neither study did the blood LH and FSH levels differ significantly between gonadectomized and intact lambs of either sex in utero or in the first week of life. However, by 2 weeks of age in the males and by 5 weeks of age in the females, gonadotrophin levels were higher in the gonadectomized than in the intact animals and this difference persisted throughout the first year of life. These results imply that fetal and neonatal gonadotrophin levels are suppressed by maternal and placental steroids in the sheep, and not by fetal gonadal hormones.

Aging↗
PubMed1980

Plasma LH and FSH in ewes that were either fertile or infertile after long-term grazing of oestrogenic pasture.

The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock 1, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml-1 x 1 h) was significantly (P < 0.05) greater in clover-infertile ewes (10.4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5.4 area units). Tonic LH and FSH secretions during the bleeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0.05) elevated in clover-infertile ewes (10.9 area units) compared to normal ewes (5.4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7.8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 beta (E2) during the breeding season were similar in the three groups. In another experiment, the positive feedback release of LH following administration of E2 (12.5, 25 or 50 micrograms per ewe) was measured in anoestrous ewes of flock 2. Significantly (P < 0.01) more clover-infertile ewes demonstrated a positive feedback effect than control ewes when given 12.5 micrograms E2 but not when given higher doses. The elevation of LH secretion in permanently affected clover-infertile ewes is inconsistent with the hypothesis that the hypothalamo-pituitary axis of these ewes is less responsive to the negative feedback effect of oestrogen. Furthermore, the patency of the positive feedback loop is consistent with the ability to ovulate.

Animal Feed↗
PubMed1978

The nature and role of pregnancy-associated antigens and the endocrinology of early pregnancy in the ewe.

Depite descriptions of many of the physiological events of early pregnancy in the ewe, the way in which the immunological and endocrine adjustments are brought about is not well understood. Obviously, specific effects--for example, maintenance of the corpus luteum--are brought about by the presence of a conceptus in the uterus. This has led to a search for substances produced by the conceptus or induced by the presence of the conceptus in the uterus which could be involved in establishing pregnancy. This paper describes the presence in sheep of substances associated with pregnancy and discusses the origin and characterization of these substances and their role in ovine pregnancy.

Animals↗
PubMed1978

Inhibition of fetal growth and survival by testosterone administration to pregnant sheep.

Testosterone (as testosterone enanthate, 250 mg i.m. every 2 wk) was administered to pregnant ewes (n = 16), and injections of vehicle were used in 10 control pregnant ewes between days 75 of gestation and term (day 147). Fetal survival (7 of 16 in the treated group versus 10 of 10 in the controls) and growth (birth weights 4.00 +- 0.51 kg in the treated group versus 5.79 +- 0.93, mean +- SD, in the controls) were markedly impaired by testosterone administration. The mechanism of the testosterone effect is unknown, but could be through metabolism to estrogens by the feto-placental unit. These results imply that alterations in the production or metabolism of androgens by the mother or the feto-placement unit may exert important effects on fetal growth and survival.

Animals↗
PubMed1977

The physiological release of specific individual neurophysins into the circulation of pigs.

Specific homologous radioimmunoassays for the two major porcine neurophysins have been developed and utilized to measure plasma neurophysins during events known to release vasopressin (dehydration and hemorrhage) and oxytocin (parturition and suckling). During hemorrhage plasma neurophysin I increased 2-25 times and decreased toward basal levels after reinfusion of the blood while plasma neurophysin II was low and showed only minor fluctuations. Neurophysin II was released during parturition and suckling in a pattern similar to that reported for oxytocin release during these events. A rise in plasma neurophysin II occurred towards the end of parturition and spurt release occurred in suckling. The function of neurophysins in the plasma is unknown but porcine neurophysin I has been shown to be released independently into the circulation in response to hemorrhage. Independent release of neurophysin II during parturition and suckling was not demonstrated. In the pig, release of neurophysin I may be associated with vasopressin release and neurophysin II associated with oxytocin release.

Animals↗
PubMed1977

Concentrations of luteinizing hormone in ovariectomized ewes and the effect of disturbance, starvation and vascular cannulation.

Neither routine experimental procedures, including vascular cannulation and venipuncture, nor starvation or disturbance caused significant fluctuations in luteinizing hormone (LH) concentrations in ovariectomized ewes. Samples obtained at 5-min intervals revealed episodic LH releases occurring every 10-35 min. Hourly sampling over 3 days revealed large LH variations but no distinct diurnal variation.

Animals↗
PubMed1976

Regulation of gonadotrophin secretion in rams from birth to sexual maturity. I. Plasma LH, FSH and testosterone levels.

Plasma LH, FSH and testosterone concentrations were measured by radioimmunoassays in male crossbred Merino/Corriedale sheep from birth to 45 weeks of age. FSH levels were 11 and 22 ng/ml at birth, increased to peak levels (mean value of 47 ng/ml) at 5 weeks and fluctuated between 25 and 35 ng/ml for the next 40 weeks. Similarly, LH (less than 0-5 ng/ml) and testosterone (less than 38 ng/100 ml) levels were low at birth and were significantly elevated by 5 weeks of age. LH values varied betwen 0-9 and 3-0 ng/ml for the next 30 weeks and then a secondary rise occurred reaching levels of 2-4 ng/ml by the 41st week after birth. Concentrations of LH subsequently fell to levels observed in adult rams. Testosterone levels rose gradually between the 5th and the 25th week, and then increased rapidly to values of 270-517 ng/100 ml by the 41st week after birth, a time coincident with the peak LH levels. Histological examination of testicular biopsies demonstrated that Sertoli cell maturation occurred 17-21 weeks after birth and was followed by activation of spermatogenesis leading to the presence of spermatozoa in the seminiferous epithelium by 39-42 weeks of age.

Age Factors↗
PubMed1976

Regulation of gonadotrophin secretion in rams from birth to sexual maturity. II. Response of the pituitary-testicular axis to LH-RH infusion.

The response of the pituitary-testicular axis to LH-RH infusion was investigated in rams from birth to sexual maturity. During early postnatal life ram lambs were responsive to LH-RH stimulation and heightened pituitary sensitivity was observed in rams aged 2-3 months. It is suggested that a change in sensitivity of the pituitary-testicular axis occurs at this time and perhaps represents the time of initiation of the pubertal process.

Age Factors↗