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Biomedical subjects

J K Findlay

Publications and source records attributed to J K Findlay.

At least 181 records · Page 10Linked to original sources
PubMed1981

Evidence for a change in oestradiol negative feedback and LH pulse frequency in post-partum ewes.

Plasma LH levels and the effects of ovariectomy and of chronic and acute administration of oestradiol-17 beta were compared in post-partum (anoestrous) and cyclic Merino ewes during the breeding season. Plasma LH and LH pulses were detected in more post-partum (anoestrous) than cyclic (dioestrous) ewes (10/10 and 4/10 respectively). The post-partum ewes had a greater pulse frequency (1.8 +/- 0.42 compared with 0.4 +/- 0.16 pulses/6 h) and higher plasma LH levels (1.16 +/- 0.32 compared with 0.17 +/- 0.05 ng/ml). Ovariectomized post-partum ewes demonstrated fewer LH pulses (3.8 +/- 0.36 compared with 5.0 +/- 0.15 pulses/6 h) than did ovariectomized cyclic ewes. The depression of plasma LH following acute i.v. injection of 3 micrograms oestradiol-17 beta was similar (0.05 < P < 0.1) for the two groups (80.5 +/- 3.6 and 66.3 +/- 4.1%). At 7 days after ovariectomy and an oestradiol implant more cyclic ewes than post-partum ewes showed detectable plasma LH and LH pulses (6/10 compared with 1/9 ewes). By 66 h after implant removal pulse frequency was less in the post-partum ewes (3.2 +/- 0.55 compared with 5.5 +/- 0.56 pulses/6 h). These findings indicate that in post-partum ewes there is an increased inhibitory (negative-feedback) effect of oestradiol on LH release and a lower intrinsic frequency of pulsatile release of LH. These factors may be casually related to ovarian acyclicity.

Anestrus↗
PubMed1981

Protein, prostaglandin and steroid synthesis in caruncular and intercaruncular endometrium of sheep before implantation.

The effect of the presence of a preimplantation embryo on protein concentration, rate of protein synthesis, beta-glucuronidase and acid phosphatase activities, steroid metabolism and prostaglandin F production in caruncular and intercaruncular tissue have been studied for sheep at Day 15 of pregnancy. The rate of protein synthesis in both tissues was greater in pregnant than in non-pregnant animals, although the difference was only significant in caruncular endometrium. The effect in caruncular tissue was mimicked in ovariectomized animals treated with oestradiol. Localized changes in the caruncular tissue were observed in respect of PGF with an increased tissue concentration, an enhanced basal release when the tissue was incubated in the presence of indomethacin, and a decreased net production. Maximum production of PGF in the 2 tissues was unaffected by the presence of an embryo but it was enhanced by oestradiol or progesterone treatment in intercaruncular tissue of ovariectomized ewes. beta-Glucuronidase and acid phosphatase activities and steroid metabolism were unaffected by pregnancy. However, in ovariectomized animals oestradiol treatment stimulated beta-glucuronidase activity in endometrium and myometrium. Progesterone treatment stimulated acid phosphatase activity in the intercaruncular endometrium. The results show that amongst several endometrial constituents investigated relatively few changes were detected by Day 15 post coitum, one day before definitive attachment. Those changes that did occur were associated with the dynamics of PGF production and the rate of protein synthesis, and were consistent with the production of a PGF binding component in caruncular endometrium which may be concerned with the protection of luteal function by redirection of uterine PGF production. Canonical variate analysis revealed that changes on Day 15 of pregnancy were mimicked most closely in caruncular tissue by treatment of ovariectomized ewes with oestradiol and progesterone, and in intercaruncular tissue by oestradiol treatment only.

Acid Phosphatase↗
PubMed1981

The failure of prolactin to enhance the inhibitory effect of oestradiol-17 beta on LH synthesis and release in ewes.

Groups of 5-6 ovariectomized ewes were treated with oestradiol-17 beta (100 mg implant) and/or bromocriptine (1 mg; 2 X daily) or with vehicle for 30 days during the anoestrous season. Oestradiol increased (P less than 0.05) the priming effect of 2 X 1 micrograms LH-RH on LH release and decreased (P less than 0.001) pituitary LH content, plasma LH levels, the frequency and amplitude of pulsatile LH release and the LH response to LH-RH. Bromocriptine decreased prolactin levels to less than 2.5 ng/ml (P less than 0.001) and increased the LH response to LH-RH (P less than 0.05). There were no significant treatment interactions. It is concluded that prolactin does not enhance the inhibitory effect of oestradiol on LH synthesis and release in the ewe.

Anestrus↗
PubMed1981

Immunoreactive growth hormone levels during the hormonal induction of lactation and during hand-milking in ewes.

Growth hormone was measured by radioimmunoassay in blood samples collected from ewes during the hormonal induction of lactation and during hand-milking post partum. Ovariectomized ewes were induced to lactate with injections of progesterone + oestradiol benzoate every 3 days for 30 days (priming phase) and then daily injections of dexamethasone for 5 days (trigger phase). The ewes were then milked daily. Immunoreactive GH levels fluctuated considerably but were generally in the range 1-15 ng/ml during all phases of lactation and were unaffected by bromocriptine treatment. Milk yield was unrelated to GH levels. Growth hormone was also measured in blood plasma taken at frequent intervals around the time of milking in lactating ewes approximately 4 weeks post partum. Although a clear prolactin response to milking was observed, there was no indication of a GH response. Although there is probably a minimum requirement for GH for lactation, a relationship between immunoreactive GH levels and milk yields was not established, perhaps because of limitations of the radioimmunoassay to detect all the biologically active GH

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

Blastocyst-endometrial interactions in early pregnancy in the sheep.

This review analyses the endocrine recognition of pregnancy in the sheep. Particular emphasis is placed on the effect of a blastocyst on prostaglandin and protein metabolism in the endometrium. The preimplantation period is associated with increased prostaglandin content in the endometrium and uterine lumen, increased leucine incorporation into endometrial protein and increased blood flow to the uterus. It is concluded that there are substantial alterations in endometrial function during the protracted preimplantation period and that these alterations constitute an endocrine form of maternal recognition of pregnancy. However, it is not yet possible to attribute these alterations to specific embryonic signals.

Animals↗
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↗
PubMed1980

Effects of heat stress on the lactation performance of ewes accustomed to tropical conditions and the total fluid intake of their lambs.

The impact of heat stress on the feed intake, milk production, water intake and urine output of undernourished lactating ewes and on the growth rate and water intake of their lambs was measured both in a climate chamber and during exposure to natural high ambient temperature conditions. Similar liveweight increases occurred in both stressed and unstressed lambs. Freed intake was depressed in heat-stressed ewes in the climate chamber but not under natural heat-stress conditions. During the first and second weeks of lactation calculated milk yield (200--500 ml/day) and composition were unaffected by heat stress per se. However, undernutrition due to the poor quality roughage offered apparently depressed milk production of all ewes. Increased water intake (27%) and plasma prolactin concentrations (220%) were recorded in heat-stressed ewes, but daily urine output (27--36 ml/kg body wt) was unaffected. No relationship between prolactin concentrations, milk production and antidiuretic activity was obvious. At the age of 5--6 weeks water intake accounted for 67% (500 ml/day) and 80% (1000 ml/day) of total fluid intake (water plus milk) of unstressed and heat-stressed lambs respectively. These data indicate the importance of making water freely available to lambs subjected to extensive grazing systems of tropical regions.

Animals↗
PubMed1980

Pitutary responsiveness to LH-RH, the occurrence of oestradiol- 17 beta-induced LH-positive feedback and the resumption of oestrous cycles in ewes post partum.

The relationship between pituitary responsiveness to exogenous LH-RH, return of oestradiol-17 beta-induced positive-feedback effect on LH release and the resumption of oestrous cycles were studied in Merino ewes lambing in the breeding season. The mean (+/- s.e.m.) increase in plasma LH 2 h after 50 micrograms LH-RH i.v. was reduced (P < 0.001) in ewes tested in the last 4 weeks of pregnancy (8.6 +/- 2.1 ng/ml, N = 29) but was similar (P > 0.05) for non-parturient dioestrous ewes (N = 31) and for anoestrous ewes tested around 14 (N = 50) and 28 (N = 51) days post partum (30 +/- 3.9, 37.8 +/- 4.0, 39. 0 +/- 3.2 ng/ml, respectively). Oestradiol-positive feedback was absent in 68.6% (35/51) and 54% (27/50) of ewes tested around 14 and 28 days post partum, respectively. Neither LH-RH responsiveness nor the presence of oestradiol-postive feedback was related to the incidence of 61.9%, 166/268) or interval to (62 +/- 2.2 days, N = 99) first oestrus post partum. We suggest that these endocrine responses do not represent factor limiting the resumption of ovarian cyclicity post partum.

Animals↗
PubMed1979

Pituitary response of prepuberal lambs to oestradiol-17 beta.

In two experiments 48 prepuberal Merino ewe lambs were injected with oestradiol-17 beta (E2) or saline to study the effect of E2 on their plasma LH levels and on oestrus and ovulation. In the three groups which received 30 (experiment I), 50 and 30 (experiment II) microgram E2 respectively, 27 out of 28 lambs showed an LH response, the corresponding mean LH peaks being 64.3 +/0 22.5, 153.6 +/-33.4 and 91.7 +/- 16.9 ng/ml at mean intervals of 11.1, 11.2 and 10.5 h, respectively, after injection. None of the 20 lambs in the control groups had an LH level higher than 18 ng/ml 12 h after injection. In the three E2 groups, 41.7, 62.5 and 37.5% of animals showed oestrus within 26 h of injection while in the control groups only one animal showed oestrus. Of 13 animals showing oestrus in the E2 groups, 11 failed to ovulate. The mean pre-injection plasma FSH level in experiment I was 102.7 ng/ml, and in four 5--7-month-old lambs over several weeks uas 155.3 ng/ml. Despite these high pre-injection levels of FSH, it appears that the follicles were unable to respond to the LH peak which followed the E2 injection.

Animals↗
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↗