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Biomedical subjects

P J Sharp

Publications and source records attributed to P J Sharp.

At least 181 records · Page 10Linked to original sources
PubMed1978

Age-dependent changes in the hypothalamo-pituitary-ovarian axis of the laying hen.

The functional integrity of the components of the hypothalamo-pituitary-ovarian axis was examined in young and old laying hens. Ovarian function was tested by measuring the amount of progesterone released in response to an injection of LH, and pituitary function was investigated by measuring the increase in the plasma LH level after an injection of LH-RH. There were no differences between young and old birds in the response of the pituitary gland or the ovary to these stimuli. Hypothalamic function was investigated by studying the positive feedback action of a standard dose of progesterone on LH release; the positive feedback response was smaller (P less than 0.05) in old hens. It is suggested that the fall in the rate of lay in hens towards the end of their laying year is caused partly by a decrease in the response of the LH-positive feedback mechanism to progesterone.

Aging↗
PubMed1978

The role of corticosterone in the ovulatory cycle of the hen.

This study was undertaken in laying hens to investigate the possibility that a diurnal increase in the concentration of plasma corticosterone is directly responsible for timing the preovulatory surge of LH which results in the first egg of a sequence. Provided that the ovary contained a mature follicle, i.m. injection of 0.5 or 2.0 but not 0.1 mg corticosterone/kg stimulated a preovulatory release of LH. The dose of 0.5 mg/kg was less effective than that of 2 mg/kg and induced release of LH in only four out of eight hens. However, it resulted in concentrations of plasma corticosterone which were outside the physiological range. Variations in the concentrations of plasma corticosterone were measured in ten hens on two successive nights for 8.5 h starting at the onset of darkness. The birds were maintained on a lighting regimen of 14 h light/day. The hens were selected so that on the first night there was no preovulatory release of LH of a sequence starting soon after the onset od darkness. No diurnal increase in the concentration of plasma corticosterone was observed during the first 6 h of darkness on either night nor was any increase seen before the preovulatory release of LH. These observations suggest that corticosterone is not directly involved in the timing of the first preovulatory surge of LH of a sequence.

Animals↗
PubMed1977

Immunofluorescent localization and ultrastructural characterization of gonadotrophe cells in the adenohypophysis of the barbary drake (Cairina moschata L.) using anti-chicken LH serum.

An indirect immunofluorescence technique and an anti-chicken LH serum were used to localize cells in the adenohypophyses of drakes at different stages of their breeding cycle, after castration, and after castration combined with thyroxine treatment. Immunofluorescent cells were distributed throughout both lobes of the adenohypophyses from control and experimental birds and were shown to be alcian blue positive. PAS negative, basophiles. Immunofluorescent cells were as numerous in castrated birds as in castrated birds treated with thyroxine. Adjacent thin and semi-thin sections were used to study the cells binding anti-LH serum at light microscope and ultrastructural levels. The cells contained spherical granules with variable densities and diameters ranging between 40 and 280 nm in the rostral (=cephalic) lobe, and between 60 and 260 nm in the caudal lobe. The light microscope and ultrastructural observations showed that the anti-LH serum binds to cells which have been classified by other authors in the Pekin duck, quail and pigeon as TSH producing delta cells. The experimental technique used did not permit a distinction to be made between cells producing FSH and LH.

Animals↗
PubMed1977

An homologous radioimmunoassay for chicken follicle-stimulating hormone: observations on the ovulatory cycle.

A highly purified FSH preparation has been used to develop a specific homologous radioimmunoassay for chicken FSH which is sufficiently sensitive and precise to measure the hormone in small sample (10-100 microliter) of plasma. The assay was used to measure plasma FSH in the chicken and turkey. The FSH concentration was higher in sexually mature chickens than in juvenile birds and further elevated after castration or ovariectomy. In turkeys, it was lower in birds held on a short daily photoperiod than in birds held on a long daily photoperiod. FSH rose in sexually quiescent female turkeys after injection of synthetic LH-releasing hormone and was increased in laying hens after injection of progesterone. No major changes were observed in FSH concentration during the chicken ovulatory cycle, although there was a small increase 15 and 14 h before ovulation.

Animals↗
PubMed1976

Effects of seasonal and social factors on testicular activity and hormone levels in domestic pigeons.

Testicular morphology and plasma concentrations of luteinizing hormone (LH), testosterone, progesterone, and estradiol-17beta were compared in paired (n = 8) and unpaired (n = 7) racing pigeons killed in December. The birds were housed mixed together under natural lighting conditions in two unheated lofts which contained no nesting facilities, in Kiel (54 degrees N), Germany. The paired birds had been paired for at least two months. Testicular weights and diameters of tubules were significantly higher (p less than 0.05) in paired (1.64 +/- 0.25 gm; 218 +/- 12 mum) than in unpaired birds (0.79 +/- 0.25 gm; 165 +/- 20 mum). The testes of paired birds were spermatogenetically more active than those of unpaired birds. Plasma concentrations of some hormones concerned with reproduction were, in paired and unpaired birds respectively: LH, 2.28 +/- 0.43 ng/ml and 0.98 +/- 0.36 ng/ml (significantly different, p less than 0.1); testosterone, 1.24 +/- 0.51 ng/ml and 0.59 +/- 0.12 ng/ml (not significantly different); progesterone, 0.58 +/- 0.08 ng/ml and 0.90 +/- 0.12 ng/ml (sifnificantly different, p less than 0.05); and estradiol-17beta, 16.3 +/- 0.95 pg/ml and 18.7 +/- 2.25 pg/ml (not significantly different). Thus, the stimulatory effects of a mate on gonadotropin secretion and gonadal activity which have often been reported for female ring doves and domestic pigeons are also demonstrable in males during the late fall. Seasonal testicular regression in the unpaired males at this time of year was not prevented by the presence of paired females.

Animals↗
PubMed1976

The effects of progesterone on oviposition and ovulation in the domestic fowl (Gallus domesticus).

1. Following an injection of 0.5 or 0.1 mg progesterone/kg between 0 and 6 h after ovulation, oviposition of the resulting egg was delayed by 1 to 11 h and occurred 26 to 31 h after injection, depending on the dose. The injection terminated the laying of a sequence of eggs by causing the next ovulation to occur a day late. The delayed ovulation occurred at the time normally expected for the first ovulation a sequence and became the first of a new sequence. 2. Following an injection of 0.5 or 0.1 mg progesterone/kg between 6 and 15 h after ovulation, oviposition of the resulting egg was generally delayed by between 15 and 28 h and occurred at the same time of day as the next ovulation, which was delayed as in the first experimental situation. Subsequent ovulations were resynchronised and followed at intervals according to the normal sequence established before the injection. 3. Injection of 0.5, 0.1 or 0.05 mg progesterone/kg between 12 and 9 h before expected ovulation advanced the oviposition of the egg already in the uterus (shell gland) by about 3 h. The succeeding ovulation was either advanced or blocked. 4. These observations suggest that the pre-ovulatory surge of progesterone is directly or indirectly involved in the timing of oviposition and ovulation.

Animals↗
PubMed1976

An assessment of the optimal range of dietary sodium for inducing a pause in laying.

Laying hens were fed on a diet containing 0-9 g sodium/kg until 34 weeks of age, then groups were fed on diets containing 0-2, 0-3,0-4, 0-5, 0-6 or 0-9 g sodium/kg for 16 weeks before that containing 0-9 g sodium/kg was reintroduced for all birds. 2. Egg production and food consumption were depressed by the low-sodium diets in proportion to the dietary sodium content. 3. Birds receiving 0-3 to 0-6 g sodium/kg diet lost weight initially but subsequently gained weight; birds receiving 0-2 sodium/kg diet lost weight continouosly. 4. In birds receiving 0-2 g sodium/kg diet, the reproductive organs were completely regressed, whereas these organs resembled those of point-of-lay pullets in birds fed on 0-3 or 0-4 g sodium/kg. 5. When the control diet was reintroduced, birds which had received the low-sodium diets resumed normal egg production and food consumption and regained body weight. 6. The optimal range of dietary sodium for inducing a pause in egg laying is 0-3 to 0-4 g/kg.

Animal Feed↗
PubMed1976

Effects of androgens, oestrogens and deoxycorticosterone acetate on plasma concentrations of luteinizing hormone in laying hens.

Testosterone, androstenedione, oestrone, oestradiol-17beta or deoxycorticosterone acetate (DOCA) were injected intramuscularly at several dose-levels and at various stages of the ovulatory cycle, and subsequent changes in plasma LH concentration were measured by radioimmunoassay. In 19 out of 24 hens, injection of 0.1, 0.5 or 1.0 mg DOCA/kg resulted in a mean maximal increase in plasma LH concentration of between 0.47 and 2.10 ng/ml. The magnitude of this response was not related to either the dose or the stage of the cycle at which the DOCA was injected. In the remaining five hens DOCA failed to stimulate LH secretion. Injection of either androstenedione, oestrone or oestradiol did not result in any increase in LH level in the circulation. In contrast, injection of 0.5, 1.0 or 2.0 mg testosterone/kg between 22 and 26 h after the terminal ovulation of a sequence resulted in mean maximal incremental changes in plasma LH level of 1.98 +/- 0.17, 2.17 +/- 0.21 and 2.41 +/- 0.31 (S.E.M.) ng/ml from pre-injection values of 1.38 +/- 0.16, 1.58 +/- 0.30 and 1.43 +/- 0.39 ng/ml (n=7, 6 and 5, respectively). The interval between the injection and the resulting rise in LH level was inversely proportional to the dose. The same doses of testosterone injected between 0 and 8 h after ovulation failed to stimulate LH secretion. There was also no significant increase in LH levels after injection of 0.5 and 1.0 mg testosterone/kg between 8 and 9 h after ovulation. However, injection of 2 mg testosterone/kg at this time resulted in a small but significant (P is less than 0.05) increase in LH levels. Since the largest ovarian follicle is more mature at 22-26 h after ovulation than at 0-9 h after ovulation, the ability of testosterone to cause the release of LH therefore appears to depend upon the degree of maturation of the ovarian follicle next due to ovulate.

Androgens↗