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Biomedical subjects

G B Martin

Publications and source records attributed to G B Martin.

At least 199 records · Page 11Linked to original sources
PubMed1984

A new method for studying pituitary responsiveness in vivo using pulses of LH-RH analogue in ewes passively immunized against native LH-RH.

In two experiments with ovariectomized ewes, the plasma levels of LH and FSH were measured following passive immunization against LH-RH. The pulsatile secretion of LH was inhibited and the levels of the hormone fell quickly and were undetectable within 24 h. The levels of FSH fell more slowly and were always detectable. In the second of the experiments, pulses of LH of normal amplitude were re-established in the immunized ewes by hourly intravenous injections of 200 ng of Des-Gly10 (Pro9)-LH-RH Ethylamide, a synthetic analogue of LH-RH that does not cross-react with the antiserum yet has similar biological activity to native LH-RH. The analogue was injected over 6 h and had no detectable effect on the levels of FSH. When the ewes were injected with 50 micrograms of oestradiol benzoate, the LH responses to the analogue were completely inhibited for 4-5 h then slowly recovered to normal levels. The oestrogen injection also depressed the levels of FSH for varying amounts of time. On the basis of the normal LH patterns and responses to oestrogen, we conclude that combining passive immunization against LH-RH with injections of an LH-RH analogue provides a valuable model for testing factors that affect pituitary responsiveness to LH-RH.

Animals↗
PubMed1984

Effect of plasma proteins and buffer in flushing solutions on rat kidney preservation by cold storage.

The isolated rat kidney perfused at 37 C was used to evaluate the effect of adding plasma proteins to, and varying osmolality of, cold-storage flushing solutions with or without buffering. Addition of albumin improved immediate poststorage kidney function (glomerular filtration rate [GFR], fractional sodium reabsorption, and fractional protein clearance) of all flushing solutions tested after 6 hr and 24 hr of storage. At 6 hr, these improvements also correlated with less weight gain. Flushing solutions containing citrate and sulfate produced significantly better return of function after 24 hr of cold storage than Krebs' or Collins'-derived solutions. Osmolality was unimportant with solutions containing citrate. Collins' solution with reduced MgSO4 yielded better poststorage function than conventional solution. An all-citrate isotonic solution buffered with 15 mmol THAM preserved poststorage function at 48 hr better than a similarly buffered solution containing both citrate and sulfate. Loss of dry weight during storage and subsequent perfusion appeared to correlate, in these experiments, with loss of poststorage function. The isolated rat kidney provides discrimination among various flushing solutions. The technique might be useful in the assay of additional variables that might affect the quality of kidney preservation.

Animals↗
PubMed1983

Metastatic periosteal osteosarcoma causing cardiac and renal failure.

The case of a 25-year-old man who had periosteal osteogenic sarcoma with intravascular metastases in unusual locations is reported. The patient presented with acute renal failure, unilateral pulmonary edema, functional mitral stenosis, and low cardiac output. After successful surgical removal of a left atrial metastasis with subsequent improvement in cardiac output, renal function improved only transiently and urinary output varied markedly. At autopsy, metastatic osteogenic sarcoma was discovered within the lumen of the abdominal aorta obstructing both renal arteries. The case is the first report of a neoplasm metastatic to the aorta causing intermittent bilateral renal arterial obstruction; it illustrates the diagnostic difficulties presented by intravascular metastatic disease.

Acute Kidney Injury↗
PubMed1983

The induction of oestrus and ovulation in seasonally anovular ewes by exposure to rams.

In anoestrus ewes of many breeds, the introduction of rams will evoke an increase in the tonic secretion of LH, pre-ovulatory surges of LH and FSH, and ovulation, provided the ewes have been preconditioned by a period of complete isolation from the rams. The "ram effect" is apparently mediated by a pheromone which seems to inhibit or reverse the effects of photoperiod on the secretion of LH pulses. In the absence of progesterone "priming" the ewes rarely show oestrus behaviour around the time of the first ovulation. In some of the ewes, the corpus luteum formed at the first ovulation is apparently normal, and the second ovulation and first oestrus is observed about one oestrus cycle later. In the remainder of the ewes, the first corpus luteum regresses prematurely, a second ovulation is seen about 6 days after the first, and the third ovulation and first oestrus are seen after a further 17 days. Progesterone treatment prior to the introduction of rams prevents the occurrence of short cycles, apparently by delaying the LH surge. The combination of the ram effect and progesterone treatments can provide useful synchrony of oestrus for artificial insemination, and also some gains in fecundity. There is considerable potential for using the effect in intensive breeding programmes.

Animals↗
PubMed1983

Effects of oestradiol on plasma concentrations of luteinizing hormone in ovariectomized ewes with clover disease.

The effects of oestradiol on plasma luteinizing hormone (LH) concentrations were examined in 15 ovariectomized control ewes and 15 similar ewes with permanent infertility after prolonged grazing on oestrogenic clover pasture ('clover disease'). Before treatment, the plasma concentrations of LH were similar in the control and affected ewes. After intravenous injection with 40 micrograms oestradiol-17 beta during the anoestrous season, the decline in LH concentration was greater in the clover-affected ewes and the subsequent elevation above original baseline levels was smaller. After intramuscular injection with 15 or 30 micrograms oestradiol benzoate during the normal breeding season, fewer clover-affected ewes showed a surge of LH, and the response was both reduced and retarded. This difference between the two groups has not been observed in studies on intact ewes, and it is suggested that in intact ewes the difference is masked by a greater tonic LH activity in affected ewes. The results of the present study are consistent with the hypothesis that prolonged exposure to oestrogenic pasture has a differentiating, or 'androgenizing' effect on the adult ewe.

Animals↗
PubMed1983

Effects of progesterone on the responses of Merino ewes to the introduction of rams during anoestrus.

The effects of progesterone on the responses of Merino ewes to the introduction of rams during anoestrus were investigated in two experiments. In the first experiment, the introduction of rams induced an increase in the levels of LH in entire ewes. The mean levels increased from 0.68 +/- 0.04 ng/ml (mean +/- s.e.m.) to 4.49 +/- 1.32 ng/ml within 20 min in ewes not treated with progesterone (n = 10). In ewes bearing progesterone implants that provided a peripheral concentration of about 1.5 ng progesterone per millilitre plasma, the LH response to the introduction of rams was not prevented, but was reduced in size so that the concentration was 1.38 +/- 0.15 ng/ml after 20 min (n = 5). Progesterone treatment begun either 2 days before or 6 h after the introduction of rams and maintained for 4 days prevented ovulation. In the second experiment ovariectomized ewes were used to investigate further the mechanism by which the ram evoked increases in tonic LH secretion. In ovariectomized ewes treated with oestradiol implants, the introduction of rams increased the frequency of the LH pulses and the basal level of LH. In the absence of oestradiol there was no significant change in pulse frequency but a small increase in basal levels. Progesterone again did not prevent but reduced the responses in ewes treated with oestradiol. It is suggested that following the withdrawal of progesterone treatment, the secretion of LH pulses in response to the ram effect would be dampened. This effect could be a component of the reported long delay between the introduction of rams and the preovulatory surge of LH in ewes treated with progesterone. Continued progesterone treatment prevented ovulation, probably by blocking positive feedback by oestradiol.

Animals↗
PubMed1983

Effect of the introduction of rams during the anoestrous season on the pulsatile secretion of LH in ovariectomized ewes.

Introduction of rams to ovariectomized ewes treated with oestradiol implants (N = 10) increased the frequency of LH pulses from 4 X 8 to 10 X 6 pulses per 12 h. This effect was reflected by increases in mean levels of LH and the basal levels upon which the pulses were superimposed. In ewes that had not been treated with oestradiol (N = 5), there was no significant increase in pulse frequency but mean and basal levels of LH increased slightly after the introduction of rams. In a second experiment, similar effects of the introduction of rams were seen in ovariectomized ewes treated with oestradiol or oestradiol + androstenedione (N = 16), but no significant effects of the rams were observed in untreated ewes (N = 8) or ewes treated only with androstenedione (N = 7). No preovulatory surges of LH were observed in the 30-h period after the introduction of rams. It was concluded that the ram stimulus probably evokes the increase in pulse frequency by inhibiting the negative feedback action of oestradiol, and that the surge normally observed in entire ewes is dependent on the ovarian response to these pulses. However, the observation of responses in some ewes not treated with oestradiol also raises the possibility that the ram stimulus can act directly on the hypothalamic neurones that control the secretion of LH, and that this effect is enhanced in the presence of oestrogen.

Anestrus↗
PubMed1983

Effects of oestradiol, progesterone and androstenedione on the pulsatile secretion of luteinizing hormone in ovariectomized ewes during spring and autumn.

The effects of oestradiol-17 beta, androstenedione, progesterone and time of the year on the pulsatile secretion of LH were tested in ovariectomized Merino ewes (n = 32). The steroids were administered by small subcutaneous implants, and the LH pulses were observed in samples taken at intervals of 15 min for 12 h in spring 1979, autumn 1980 and spring 1980, seasons corresponding to successive periods of anoestrus, breeding season and anoestrus. During spring, oestradiol alone was able to reduce the frequency of the LH pulses, while progesterone, either alone or in combination with oestradiol, had little effect. During autumn, on the other hand, neither oestradiol nor progesterone could significantly reduce the frequency of the pulses when administered independently, whereas the combined treatment was very effective. Androstenedione had no significant effect on pulse frequency at either time of the year, either alone or in any combination with oestradiol and progesterone. The basal levels of LH, over which the pulses are superimposed, were reduced by oestradiol alone in both seasons. Progesterone alone had no consistent effects, but interacted significantly with oestradiol and this combined treatment maintained low basal levels most effectively at all times. Androstenedione had no significant effect. The amplitude of the pulses increased throughout the course of the experiment. Within seasons, the amplitudes were significantly higher in the presence of oestradiol and progesterone, but were not significantly affected by androstenedione. It was concluded that certain of the ovarian steroids exert negative feedback on the tonic secretion of LH primarily by reducing the frequency of the pulses, and that the changes in LH secretion attributable to season and phases of the oestrous cycle can be accounted for entirely by the responses of the hypothalamus to oestradiol and progesterone. The role of the androstenedione secreted by the ovary in the ewe remains obscure.

Androstenedione↗
PubMed1981

Effect of stress due to laparoscopy on plasma cortisol levels, the preovulatory surge of LH, and ovulation in the ewe.

The ovulation which is induced in seasonally anovular ewes by the introduction of rams was used as a model to examine the effects of the stress of repeated laparoscopy on the preovulatory surge of LH and ovulation. The number of ewes which experienced LH surges and ovulation was reduced (10/23 vs 1/20) when laparoscopy was repeated every four hours. Plasma cortisol levels were used as an indicator of stress, and were found to increase after laparoscopy: a single laparoscopy produced a transient rise, while repeated laparoscopy induced and maintained levels between 70 and 100 ng/ml.

Journal Article↗
PubMed1981

Induction of ovulation in seasonally anovular ewes by the introduction of rams: effects of progesterone and active immunization against androstenedione.

The effects of progesterone priming and active immunization against androstenedione on ovulation, oestrus ad premature luteal regression were observed in seasonally anovular Merino ewes which had been induced to ovulate by the introduction of rams. Ovulation was induced in 27 out of 36 ewes, and the response was not affected by either immunization or progesterone priming. The ovulation rate (mean number of ovulations per ewe ovulating) was higher in ewes immune to androstenedione, but there was no significant effect of this treatment on oestrus or luteal maintenance. Priming with progesterone prior to the introduction of rams prevented premature regression of the corpora lutea but had no effect on the other measures of reproductive function. If active immunization were to be applied on a commercial scale, it would not interfere with the practice of mating ewes during the anoestrous season. The increase in ovulation rate in these ewes, with no increase in the proportion of ewes ovulating, indicates that the mechanism for the control of ovulation is separate from that controlling ovulation rate. The mechanism by which progesterone pretreatment prevents premature luteal regression awaits further investigation.

Androstenedione↗