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Biomedical subjects

P J Sharp

Publications and source records attributed to P J Sharp.

At least 163 records · Page 9Linked to original sources
PubMed1981

Lack of a relationship between concentrations of plasma luteinising hormone, thyroxine and prolactin at nine week's of age and subsequent egg production in the domestic hen.

1. The concentrations of plasma luteinising hormone (LH), thyroxine and prolactin were measured in about 200 birds from each of two homogenous strains of White Leghorn hens at 9 weeks of age and related to subsequent egg production. 2. Within each strain, no relationships were found in individual birds between the concentrations of the plasma hormones and subsequent egg production after 90, 180 and 270 d of laying. 3. Single measurements of plasma LH, thyroxine or prolactin before the onset of lay do not appear to be useful criteria for the selection of egg-laying strains.

Animals↗
PubMed1981

Concentrations of plasma luteinising hormone, prolactin, progesterone and androgens during the ovulatory cycle of the turkey.

1. Changes in the concentrations of plasma luteinising hormone (LH), prolactin, androgen and progesterone were measured during the ovulatory cycle of the turkey. 2. Single pre-ovulatory peaks of plasma LH, androgen an progesterone were observed which took 8, 8 and 12 h respectively, to increase and return to base-line values. The concentration of plasma prolactin tended to be elevated between 6 h before and 6 h after the LH peak with the maximum values occurring after the peak. 3. The changes in the concentrations of plasma LH and progesterone were 3- and 7-fold respectively while 2-fold changes were observed in the concentrations of plasma androgen and prolactin. 4. The pre-ovulatory concentration of plasma progesterone and prolactin began to decrease 4 and 6 h respectively, after the pre-ovulatory peak of LH. 5. Ovulation and oviposition occurred 6 to 8 h and 36.10 +/- 0.57 h (SEM) (n = 11) respectively after the pre-ovulatory peak of LH. 6. In birds kept on 14 h light/d, pre-ovulatory peaks of LH were initiated only during a 10 to 11-h period starting within 2 h after the onset of darkness. 7. A comparison between these data and those from the fowl suggest that the egg is retained in the turkey's oviduct for about 3 to 4 h longer than in the fowl.

Androgens↗
PubMed1981

Conversion of testosterone to 5 beta-reduced metabolites in the neuroendocrine tissues of the maturing cockerel.

The metabolism in vitro of [4-14C]testosterone to reduced derivatives was studied in the pituitary gland, hypothalamus and hyperstriatum dorsale of cockerels from hatch to sexual maturity. The most important metabolites were 5 beta-dihydrotestosterone (5 beta-DHT), 5 beta-androstane-3 alpha, 17 beta-diol (5 beta-3 alpha-diol) and 5 beta-androstane-3 beta, 17 beta-diol. Trace amounts of androstenedione and, in the hypothalamus only, of 5 alpha-DHT were also detected. The amounts of 5 beta-reduced metabolites produced by all neuroendocrine tissues declined progressively during maturation with the steepest fall occurring during the first 2 weeks after hatch. At all ages studied, 5 beta-DHT was formed to the greatest extent by the hyperstriatum dorsale, to a lesser extent by the hypothalamus and in the smallest quantities by the pituitary gland. In the three tissues studied, 5 beta-3 alpha-diol tended to be formed to the greatest extent by the pituitary gland. No significant change was observed in the metabolism of testosterone to reduced derivatives in any of the neuroendocrine tissues after castration. It was concluded that in the cockerel, unlike the rat, a change in 5 alpha-reductase activity of the neuroendocrine tissues is unlikely to be involved in the initiation of puberty. The physiological significance of 5 beta-reductase activity in the neuroendocrine tissues remains to be established.

Animals↗
PubMed1981

The possible role of prolactin in the regulation of nesting behaviour and the secretion of luteinizing hormone in broody bantams.

The time spent each day on the nest and the rate of formation of the brood patch before the onset of incubation were measured in bantams (Gallus domesticus) and related to changes in the concentrations of plasma LH and prolactin. The hens spent progressively more time on the nest in the 5 days before the onset of incubation so that by the first day of incubation they were spending more than 90% of their time in this way. The concentration of plasma prolactin increased while that of LH fell on successive days before the onset of incubation: the increase in plasma prolactin preceded the fall in plasma LH by 2 days. The formation of the brood patch closely followed the increase in the concentration of plasma prolactin. In four out of five bantams the increase in nesting behavior was preceded by an increase in the secretion of prolactin. An injection of chicken prolactin antiserum into bantams incubating eggs resulted in a significant (P less than 0.05) increase in the plasma concentration of LH. The observations suggest that, in the bantam, the onset of incubation is initiated by an increase in the secretion of prolactin which also suppresses the secretion of LH.

Animals↗
PubMed1980

Conversion of progesterone to 5 alpha- and 5 beta-reduced metabolites in the hen and its potential role in the induction of the preovulatory release of luteinizing hormone.

In the laying hen, progesterone was shown to be converted in vitro in the pituitary gland and the hypothalamus to 5 beta-pregnane-3,20-dione (5 beta-pregnane-3 alpha-ol-20-one (5 beta,3 alpha-ol) and 5 alpha-pregnane-3,20-dione (5 alpha-DHP) and in the hyperstriatum dorsale to 5 beta-DHP and 5 beta,3 alpha-ol. The conversion of progesterone to 5 beta-reduced metabolites was greater in the hyperstriatum dorsale than in the hypothalamus (P < 0.001) and greater in the hypothalamus than in the pituitary gland (P < 0.01). The conversion of progesterone to 5 beta-reduced metabolites was greater than its conversion to 5 alpha-DHP in the pituitary gland (P < 0.01) and the hypothalamus (P < 0.001). The possibility was investigated that 5 alpha-DHP and 5 beta-DHP may act as metabolic intermediaries in the mechanism by which progesterone exerts a positive feedback effect on LH release. Progesterone, 5 alpha-DHP and 5 beta-DHP were injected into laying hens at doses of 0.05, 0.25 and 1.25 mg/kg and the changes in the concentration of plasma LH were followed for 4 h thereafter. Secretion of LH was stimulated after treatment with progesterone or 5 alpha-DHP but not 5 beta-DHP. Progesterone stimulated Lh release more effectively than did 5 alpha-DHP, since an increase in the concentration of plasma LH was observed after 0.25 mg progesterone/kg but not after the same dose of 5 alpha-DHP. It was concluded that in the hen 5 alpa-DHP is unlikely to play a role in the induction of the preovulatory release of LH.

Animals↗
PubMed1979

Localization of cells producting thyroid stimulating hormone in the pituitary gland of the domestic drake.

Cells binding anti-bovine TASH beta serum were found exclusively in the rostral lobe of the adenohypophysis of the drake using the peroxidase-antiperoxidase complex unlabelled antibody method. The specificity of the binding of the anti-serum to TSH cells was established by relating the morphology and relative abundance of immunochemically stained cells to the TSH content of the adenohypophysis after experimentally altering the activity of the pituitary-thyroid axis. The TSH activity of the adenohypophysis was assessed indirectly, by the weight of the thyroid glands, and directly, by bioassay. As determined by bioassay, the TSH content of the rostral lobe of the adenohypophysis was much greater than that of the caudal lobe. Compared with control drakes, immunochemically stained cells in birds fed a goitrogen, methimazole, seemed to be enlarged and were closer together, while the stained cells in drakes injected with thyroxine were shrunken and less intensely stained. The TSH content of the adenohypophysis was increased in drakes fed methimazole. Castration did not alter the TSH content of the adenohypophysis or change the morphology of immunochemically stained cells. These observations suggest that in the drake: 1) anti-bovine TSH beta serum binds specifically to TSH cells; 2) the TSH cells occur in the rostral and not in the caudal lobe of the adenohypophysis; and 3) the activity of TSH cells is not inhibited by the feedback effects of gonadal steroids.

Animals↗
PubMed1979

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods.

1. Concentrations of prolactin, growth hormone, testosterone, progesterone, thyroxine and triiodothyronine were measured in the blood plasma of female turkeys during successive periods of egg laying, a decline in lay, a moult induced by a short photoperiod (6 light: 18 dark) and a resumption of egg laying induced by a long photoperiod (16L:8D). 2. Concentrations of prolactin, growth hormone, testosterone and progesterone were higher in laying birds than in birds which were moulting or not laying. 3. The concentration of testosterone, but not of the other hormones studied, increased significantly during the period of profuse moult. 4. Concentrations of the thyroid hormones did not change with the varying physiological condition of the birds. However, the concentration of thyroxine was depressed by the long photoperiod.

Animals↗
PubMed1979

Variations in plasma growth hormone concentrations in laying hens.

1. Variations in plasma concentrations of growth hormone (GH) and luteinising hormone (LH) were measured by radioimmunoassay in blood samples taken during the ovulatory cycle of the domestic hen. 2. A peak in LH concentrationas observed 4 h prior to ovulation. 3. Plasma GH concentrations were quite variable but a significant increase was observed between 2 h before and 2 h after ovulation and the concentration remained elevated for about 4 h thereafter.

Animals↗
PubMed1979

Variations in concentrations of prolactin, luteinizing hormone, growth hormone and progesterone in the plasma of broody bantams (Gallus domesticus).

The concentrations of prolactin, LH, progesterone and GH were measured in the blood of broody bantam hens. The concentration of prolactin was at its highest when the birds began to incubate their eggs and in six out of nine hens it tended to remain raised until the eggs hatched. The increase in the concentration of prolactin was small: in incubating hens it was only 23% higher than in hens caring for their young and 14% higher than in laying hens (P less than 0.05 for both comparisons). The concentration of GH tended to be depressed in hens caring for young but otherwise was not related to reproductive activity. The concentrations of LH and progesterone decreased at the onset of incubation and remained depressed while the hens sat on their eggs (P less than 0.001) for both comparisons). After the chicks hatched, the level of LH began to increase slowly whereas the level of progesterone remained low. The hens stopped showing broody behaviour between 4 and 10 weeks after the chicks had hatched; this corresponded to the time when the concentration of LH had increased to values found in laying hens. These observations provide some evidence that prolactin secretion increases at the onset of incubation and support the view that the hormone is not secreted at an increased rate while hens are caring for their young.

Animals↗
PubMed1979

The effect of rapeseed meal and methimazole on levels of plasma hormones in growing broiler cockerels.

The effects of feeding a heat treated rapeseed meal, which has goitrogenic properties, on the concentrations of plasma pituitary and thyroid gland hormones was investigated in broiler cockerels of between 3 and 10 weeks of age. For purposes of comparison, two other groups were included in the study; one was fed the goitrogen, methimazole, and the other a normal control diet. The hormones measured were thyroxine (T4), triiodothyronine (T3), growth hormone (GH), prolactin, and luteinizing hormone (LH). In birds fed methimazole the thyroid glands were greatly enlarged, the concentrations of plasma T4 and T3 were depressed and the concentrations of growth hormone, prolactin, and LH were elevated. The high level of plasma LH in the birds fed methimazole was not due to the absence of sufficient concentrations of plasma testosterone to exert a negative feedback effect. Although the inclusion of rapeseed meal in the diet caused the thyroid glands to enlarge, the concentrations of all the hormones studied, with the exception of T3, were similar to those in the control birds. However, there was a tendency, which was more pronounced in birds of between 3 and 5 weeks of age, for rapeseed meal to depress the concentrations of plasma T4, GH, and LH and to increase the concentration of plasma prolactin. The most significant observation was that between 3 and 5 weeks of age the inclusion of rapeseed meal in the diet significantly (P less than .001) depressed the concentration of plasma T3.

Age Factors↗