Search PubMed⌕ Search

Biomedical subjects

H Dobson

Publications and source records attributed to H Dobson.

At least 127 records · Page 7Linked to original sources
PubMed1987

Early pituitary follicle stimulating hormone response to gonadotrophin releasing hormone in ewes.

The object of our experiments was to characterize the response of plasma follicle stimulating hormone (FSH) within minutes of an i.v. injection of high or low doses of gonadotrophin releasing hormone (GnRH), especially in relation to contemporary changes in luteinizing hormone (LH) concentrations. In the deep anoestrous period (June), three intact ewes and two ovariectomized ewes were injected with 1 mug synthetic GnRH followed 2 h later by a second identical injection. A week later, the same regimen was repeated with the same sheep but with 50 mug GnRH after an interval of 5 h 20 min. Blood samples were collected every 15 sec for 15 min after each injection (early release), then at longer intervals (main release) till the next treatment, followed by sampling for a further 6-h period after the second treatment. FSH was released as soon as the second minute after GnRH injection in all ewes. The mean pituitary FSH response, during this early release, in intact and ovariectomized ewes was similar after either 1 or 50 mug GnRH. However, the main release was less pronounced in the ovariectomized sheep and was not stimulated after the second treatment in all sheep. Three other ewes were injected with 40 mug GnRH and sampled every 15 sec for seven, 6-min periods during the period of release to compare FSH and LH secretion. The profiles reflected a similarity in sensitivity and responsiveness to GnRH, especially soon after GnRH injection. Increases in both hormones were formed by several grouped associated spikes. It is suggested that a readily releasable pool of FSH exists in the ewe. There are probably differences in the mechanisms of synthesis and/or release between pituitary FSH and LH.

Journal Article↗
PubMed1987

Effect of transport stress on luteinizing hormone released by GnRH in dairy cows.

Stress is thought to reduce gonadotrophin secretion in ruminants. So far, only prolonged administration of ACTH or cortisol have been shown experimentally to reduce LH release. The present experiment studied the effects of an acutely stressful situation. Fifteen min after the start of a 30 min truck journey for dairy cows plasma cortisol values exceeded 55 nmol/l, as measured by RIA. Values began to decline 15-45 min after return to the barn and reached baseline (2.5 to 20 nmol/l) 1-2 h later. Responses to 20 or 40 micrograms GnRH administered on day 10 of the cycle, or 48 h after prostaglandin analogue, were significantly reduced on a within-animal basis when given during the truck journey. Hence acute endogenous stimulation of pituitary-adrenal activity can interfere with pituitary LH release.

Animals↗
PubMed1987

Effect of betamethasone treatment on luteal lifespan and the LH response to GnRH in dairy cows.

Betamethasone (a synthetic glucocorticoid, 15 mg) was administered i.m. twice daily for 10 days to 4 regularly cycling dairy cows, beginning on Day 10 of the oestrous cycle. Luteal function, monitored by plasma progesterone, was extended by 7, 9, 19 and 20 days, respectively. Luteal function in the next cycle was normal. Endogenous cortisol values were suppressed for 14, 13, 34 and 27 days, respectively. Pituitary responsiveness to 20 micrograms GnRH was assessed by LH measurement on Days -1, +3 and +7 relative to the start of betamethasone treatment. There was a progressive decrease in peak LH concentrations after each GnRH challenge compared to control cows. Hourly measurements of PGF-2 alpha metabolite during the expected period of luteolysis failed to reveal normal increases. It is suggested that betamethasone caused prolonged luteal function, either by directly inhibiting PGF-2 alpha release, or by suppressing pituitary stimulation of follicular growth and hence lowering oestradiol concentrations, since it is known that PGF-2 alpha and oestradiol act synergistically to cause luteolysis.

Animals↗
PubMed1987

Preliminary investigations into the endocrine systems of subfertile cattle: location of a common lesion (rate-limiting step).

Dairy cows with a variety of clinical conditions were investigated in an attempt to identify the cause(s) of subfertility. Sequential or simultaneous injections of 20 micrograms gonadotrophin-releasing hormone (GnRH), 1 mg oestradiol benzoate and 0.06 mg ACTH(1-24) into five clinical cases of ovarian follicular cysts, two cases of poor body condition and one case of lameness and into control cows revealed a failure in the LH positive-feedback response to oestradiol in all eight clinical cases, but in only two out of twelve control cows. Two of the clinical cases and the two non-responding control cows had high or rising initial progesterone concentrations which would explain the absence of response. All cows studied responded similarly to GnRH and ACTH(1-24). It is suggested that hypothalamus-pituitary control of LH release may involve a rate-limiting step (in the oestradiol positive-feedback system) and that lesions at this point result in subfertility in a variety of clinical situations.

Animals↗
PubMed1986

Effect of various veterinary procedures on plasma concentrations of cortisol, luteinising hormone and prostaglandin F2 alpha metabolite in the cow.

Five commonly practised veterinary procedures were studied: Palpation per rectum of the reproductive tract, intramuscular injection, single venepuncture, repeated venepuncture and jugular vein catheterisation. Plasma cortisol concentrations increased from baseline values of approximately 2 ng/ml to maximum mean values between 6.5 +/- 2.5 ng/ml and 13.8 +/- 5.6 ng/ml approximately 13 to 27 minutes after each manipulation. Baseline values occurred approximately 80 minutes later. In the control bleeding periods unacclimatised cows initially had high values of plasma cortisol (5 to 10 ng/ml) which returned to baseline after two hours, ie, before beginning any procedure. There were no statistically significant changes in luteinising hormone concentrations. The concentration of 13,14 dihydro, 15-keto prostaglandin F2 alpha (PGFM) increased from 61.0 +/- 4.6 pg/ml to 209.8 +/- 152.1 pg/ml in three out of five cows palpated on days 16 and 19 of the oestrous cycle. Increases did not occur in five other cows palpated during the follicular phase, nor in five cows palpated on day 12. However, after palpation on day 8, one animal did have concentrations of PGFM similar to those occurring during spontaneous release on days 18 to 20 of the oestrous cycle.

Animals↗
PubMed1986

Food iron and lead absorption in humans.

Food iron and lead absorption were measured simultaneously in 28 subjects by extrinsically labeling three consecutive meals with the radioactive tracers, iron 59-sulfate and lead 203-chloride. Absorption was measured directly in all subjects by whole-body counting and indirectly in 15 subjects by assessing subsequent levels of tracer in blood. Iron status of the subjects ranged from iron deficient to replete, thus providing a wide range of iron absorption. Statistically significant positive correlations were obtained between food-iron and lead absorption measured by whole-body counting and also between the tracer levels of iron and lead in the blood. However, the correlation between the absorption of the two elements was not strong, as evidenced by the fact that only 50% of the subjects who hyperabsorbed iron also hyperabsorbed lead.

Administration, Oral↗
PubMed1985

Effects of chronic treatment with a GnRH agonist on oestrous behaviour and on the secretion of LH and progesterone in the ewe.

A study was carried out to investigate a novel approach to oestrus synchronization in the ewe by treatment with a gonadotrophin releasing hormone (GnRH) agonist. Groups of ewes were initially treated on Day 2, 10 or 14 of the oestrous cycle with 10 mug GnRH analogue (D-Ser(Bu(t)) 6 des Gly GnRH ethylamide) per ewe per day for 14 days. Behavioural oestrus was inhibited during GnRH agonist treatment and recurred from 8 to 38 days after the treatment in an unsynchronized manner. Luteal activity during treatment was not impaired but reduced progesterone concentrations occurred in cycles after the treatment. The rhythm of ovarian function, generally characterized by prolonged follicular development, was impaired. During the treatment and subsequent recovery period, integrity of pituitary function was examined by measuring luteinizing hormone (LH) after GnRH agonist was injected, and after stimulation test doses of 150 ng natural GnRH were administered. During treatment there was, with time, a decline in pituitary response to the agonist which suggested that pituitary release of LH was exhausted. After the 14-day treatment the stimulation test with GnRH revealed a gradual return to normal responsiveness although this was not complete three weeks after the treatment when compared to control ewes. This lowered pituitary activity could cause the impaired ovarian function.

Journal Article↗
PubMed1984

Plasma hormone changes in cows during induced or spontaneous calvings and the early post partum period.

Plasma progesterone, oestradiol, 13,14-dihydro, 15-keto, prostaglandin F2 alpha (PGFM) and luteinising hormone were measured in daily samples from eight dairy cows for 15 days before and after spontaneous calving, and compared to patterns obtained from 15 cows during and after induction of parturition with dexamethasone +/- prostaglandin. The average (+/- sd) length of pregnancy in the control cows was 285 +/- 3.04 days compared to 264 +/- 7.4 days in the induced group. Only nine cows required prostaglandin on day 11 after dexamethasone, which resulted in all nine calving 1.7 +/- 0.3 days later. Eight of the 15 treated cows retained the fetal membranes; however, the calving to first heat interval for all treated cows was 46.7 +/- 10 days (range 30 to 66 days) and calving to conception 52.4 +/- 17 days (range 30 to 85 days) compared to 42.1 +/- 15 days (range 28 to 64 days) and 76.5 +/- 24 days (range 54 to 115 days) respectively for the eight cows which calved without induction. The pre-partum hormone profiles were similar in all cows. Hormone profiles in the post partum period were also similar in all cows, irrespective of previous history. Baseline values for progesterone and oestradiol were not reached until 4.6 +/- 1.7 days and 2.75 +/- 0.7 days post partum respectively, whereas PGFM values increased for two or three days, reaching baseline levels 8.87 +/- 2.10 days later. Five cows had secondary peaks of PGFM on days 5,6 and 7. Luteinising hormone values increased steadily after calving in all cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Early pituitary LH response to injections of GnRH in ewes.

In the deep anoestrous period (June), five intact ewes and five ovariectomized ewes received 50 ug synthetic gonadotrophin-releasing hormone (GnRH). In the mid-breeding season (October), the GnRH administrations were repeated in five intact and four ovariectomized ewes; the former were in the luteal phase of the cycle. Blood samples were collected every 30 sec for 15 min, then at 15-min intervals. Release of luteinizing hormone (LH) occurred as soon as the second minute after injection in all ewes. This early response was earlier and more abrupt in the ovariectomized ewes than in the intact animals. In a second experiment three intact ewes that were in deep anoestrus received 50 ug GnRH followed 5 h 20 min later by a second identical injection. Another three intact ewes in deep anoestrus received two injections of 1 ug GnRH. Blood samples were taken every 15 sec for 15 min, then every 20 min until the next injection, and for a further 5 h after the second injection. This regimen was repeated in mid-breeding season during the luteal phase. There was again a very early release of LH; the magnitude of response was similar after the first injection of either 50 ug or 1 ug GnRH to intact ewes either in the breeding season or during deep anoestrus. However, a greater early release of LH was obtained at the lower dose only after the second injection of GnRH. Apart from this exception, the similar early release of LH occurred in spite of different amounts of LH released thereafter in response to the two doses of GnRH. It is suggested that the early response to GnRH consists of LH stored in a "readily releasable" pool in the pituitary, whereas the main release of LH may be a result of increased synthesis and/or release of a more stable pool.

Journal Article↗
PubMed1983

Mania in Cushing's syndrome: case report.

A case is described of recurrent mania without depressive episodes in a patient subsequently diagnosed as having an ACTH-producing basophil adenoma. The difficulties involved in the clinical and laboratory diagnosis of Cushing's syndrome, and the ramifications of neuroendocrinopathies' ability to mimic symptoms of functional psychosis, are discussed.

Adenoma, Basophil↗
PubMed1978

Radioimmunoassay of FSH in the plasma of post-partum dairy cows.

A method for measurement of bovine plasma FSH has been established with an interassay coefficient of variation of 15.5% over the workable range of the assay. Compared to values at the end of pregnancy (42-122 ng/ml), FSH concentrations were greater (P less than 0.01) between 0 and 20 days post partum in 3 cows.

Animals↗
PubMed1978

Effect of active immunization against oestrogens on plasma gonadotrophins in the ewe and the response to synthetic oestrogen or LH.

Immunization against oestrogen resulted in elevated LH concentrations, in the form of a pulsatile release, which rose from 3 to as much as 41 ng/ml approximately every 1.5 h, even in the presence of high plasma progesterone concentrations. Elevated FSH concentrations showed only minor oscillations without consistent synchrony to the LH pulses. Injection of 250 microgram stilboestrol did not abolish the LH pulses but in 2 out of 8 ewes FSH was initially lowered. Injection of 1 mg stilboestrol abolished the LH pulses within 11 h and decreased FSH values in 2 out of 4 ewes. Between 16 and 35 h after injection there was a large increase in LH and FSH concentrations. Thus, in the ewe, the tonic secretion of LH and FSH is controlled by a negative feedback action of oestrogen, and diethylstilboestrol will exert both dose. Infusion of LH was unable to alter the frequency or height of the LH pulses, thereby excluding regulation of the LH pulses by a short feedback mechanism.

Animals↗