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Biomedical subjects

A Chadwick

Publications and source records attributed to A Chadwick.

At least 73 records · Page 4Linked to original sources
PubMed1979

Growth hormone and prolactin secretion in growing domestic fowl: influence of sex and breed.

Plasma growth hormone (GH) and prolactin concentrations were measured between 1 and 24 weeks of age in both sexes of a laying strain of chickens and from 1 to 9 weeks of age in broiler cockerels. 2. GH and prolactin concentrations were highest in young birds and higher in males than in females. 3. In both sexes GH and prolactin concentrations were correlated inversely with age and body weight and positively with relative weight gain. 4. Differences in growth rate between broilers and layers were related to differences in blood GH concentrations. 5. Water deprivation for periods of 6, 12, 18 or 24 h increases plasma prolactin markedly but did not affect GH secretion significantly.

Age Factors↗
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 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

Effect of chicken hypothalamus on prolactin and growth hormone secretion in male chickens.

The effects of a chicken hypothalamic extract (HE) on the secretion of prolactin and growth hormone (GH) in vivo have been investigated by radioimmunoassay in the domestic fowl. Different i.v. doses of HE (0.25--25 HE equivalents/kg body weight) had no effect on GH secretion in conscious or anaesthetized cockerels. In both groups of birds the concentration of plasma prolactin was significantly increased within 10 min of administration of the extract. Extracts of other brain tissues (cerebral cortex, cerebellum and medulla oblongata) had no stimulatory effect on prolactin or GH secretion. Release of both prolactin and GH by dispersed pituitary cells and by hemipituitary glands in vitro was enhanced following incubation with HE (5 hypothalami equivalents/ml) or with single whole hypothalami respectively. Other brain tissues (cerebellum, optic lobes and medulla oblongata) had no effect on the concentration of prolactin or GH released by incubated hemipituitary glands.

Animals↗
PubMed1978

The effect of thyrotropin-releasing hormone (TRH) and somatostatin (GHRIH) on growth hormone and prolactin secretion in vitro and in vivo in the domestic fowl (Gallus domesticus).

The effects of thyrotropin-releasing hormone (TRH) on growth hormone (GH) and prolactin (Prl) secretion have been investigated in vitro and in vivo in domestic fowl. In both conscious and anaesthetized immature chickens the administration (i.v.) of TRH (2.5 and 25 microgram/kg) significantly increased the concentration of plasma GH. The simultaneous administration of somatostatin (GHRIH), 2.5 microgram/kg, to conscious birds significantly reduced the magnitude of the GH response to TRH treatment, but had no effect on the basal levels of plasma GH. The repeated injection of TRH (10 microgram/kg) every 20 min over a 100-min period failed to maintain the concentration of plasma GH at a high level. Prl secretion was not stimulated in any of these experiments, and in anaesthetized birds TRH (2.5 and 25 microgram/kg) treatment was followed by a depression in the level of plasma Prl. The effects of TRH and GHRIH on GH secretion by an in vitro dispersed pituitary cell suspension system were very similar to the in vivo studies. TRH stimulated Prl release in vitro, in contrast to the in vivo studies, and the response was dose related. GHRIH had no effect on the basal release of Prl in vitro but significantly inhibited the response to TRH treatment.

Anesthesia, General↗
PubMed1978

Influence of fasting, glucose and insulin on the levels of growth hormone and prolactin in the plasma of the domestic fowl (Gallus domesticus).

The concentrations of both GH and prolactin in the circulation of the domestic fowl have been determined after various treatments known to affect carbohydrate metabolism. Fasting decreased the level of glucose, stimulated the secretion of GH and inhibited the secretion of prolactin. Administration of insulin significantly depressed the level of GH in the plasma of normal or fasted birds and also in chickens which had received simultaneous injections of glucose or 2-deoxy-D-glucose. No consistent effect of insulin on the secretion of prolactin was observed. Hyperglycaemia subsequent to administration of glucose had no effect on the levels of either GH or prolactin. Glucagon-induced hyperglycaemia suppressed the level of GH in the plasma and stimulated that of prolactin.

Animals↗