A. Chadwick

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.

Plasma levels of arginine vasotocin, prolactin, aldosterone and corticosterone during prolonged dehydration in the domestic flowl: effect of dietary NaCl

Summary1.Three groups of White Plymouth Rock laying hens were adapted to three levels of dietary NaCl: low-NaCl food with tap water (LOW), high-NaCl food (1% NaCl w/w added) with tap water (HT), and high-NaCl food with 0.5% NaCl for drinking (HS). The birds were subjected to water deprivation (dehydration) for 18 days. Blood sampling was done at 2–4 day intervals. Plasma concentrations of arginine vasotocin (AVT), prolactin (PRL), aldosterone (ALDO) and corticosterone (CS) were determined by radioimmunoassay. Plasma osmolality, sodium, chloride, and potassium were also determined.2.In the normally hydrated hens fully adapted to the diets, there was a stepwise increase from LOW to HS in plasma osmolality (305, 315, 332 mOsm, for LOW, HT and HS, respectively), [Na+] (144, 153, 161 mM) and [Cl−] (109, 119, 127 mM) as well as in [AVT] (6, 14, 18 pg/ml) and [PRL] (16, 24, 34 ng/ml). Regressing [AVT] on osmolality gave a slope of 0.30 pg·ml−1/mOsm and a threshold of 273 mOsm. The slope of [PRL] on osmolality was 0.73 ng·ml−1/mOsm. The correlation coefficient of [AVT] and [PRL] was 0.67. LOW had high [ALDO] (165 pg/ml) which was suppressed to low levels in HT and HS (5–8 pg/ml), while [CS] was the same in all groups (0.9–1.1 ng/ml). Plasma [K+] was decreased in the high-NaCl groups (5.8 mM in LOW, 4.4 and 4.7 mM in HT and HS).

Ontogeny of growth hormone and prolactin secretion in the domestic fowl (Gallus domesticus).

Abstract Concentration of growth hormone (GH) and prolactin were measured in plasma from embryonic and neonatal chicks. GH was not detectable (

Radioimmunoassay of prolactin in the plasma of the domestic fowl.

Abstract A homologous radioimmunoassay for chicken prolactin is described. Chicken pituitary prolactin reacts strongly in the assay but chicken pituitary growth hormone does not. Pituitary prolactin from sheep, and plasma from ducks and pigeons do not cross-react, but plasma from the turkey reacts well. Immunoreactive prolactin in chicken plasma is greatly elevated after administration of a salt load. Prolactin levels are high in laying hens. Gonadectomy has no significant effect on circulating prolactin levels. Immature cockerels of different ages show different mean prolactin levels, prolactin being high at 8 weeks old, when mean luteinising hormone levels are low, and low at 14 weeks old, when LH levels are high.

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.

Osmotic and hormonal responses to heat and dehydration in the fowl

Summary1.This study reports on osmotic and hormonal responses to heat and dehydration in birds.2.Heat exposure did not affect the osmotic and hormonal status of normally hydrated fowls.3.Dehydration for 48 h (normothermia, ca. 13% body weight loss) significantly (P<0.001) increased plasma osmolality and concentrations of sodium and chloride, and consequently the plasma concentrations of the antidiuretic hormone (AVT) and prolactin. Additional heat exposure of the dehydrated fowls further accelerated these changes, together with significantly (P<0.01) increasing plasma aldosterone concentration.4.Upon recovery (30 min of drinking) the osmotic and hormonal responses were significantly (P<0.001) diminished.5.Body temperature was not significantly affected by dehydration, yet during heat exposure the dehydrated fowls were significantly hyperthermic (P<0.05) compared with normally hydrated heat exposed fowls.6.A significant overall correlation (r=0.43,P<0.02) between body temperature and plasma sodium-to-calcium ratio suggests this ratio to be involved in the control of the hypothalamic thermoregulatory set-point.7.The associated thermoregulatory, osmoregulatory and hormonal changes revealed in the present study, together with literature information, are integrated into a model summarizing the operating mechanisms in dehydrated heat exposed birds.

Daily variations in the concentrations of plasma prolactin in broody bantams

Daily variations in the concentration of plasma prolactin were measured in bantam hens exposed to 14 hr light/day when they were laying, between 1 and 6 days before starting to incubate their eggs, 1 or 2 days after incubation had begun, and when they were brooding their chicks, 9–10 days after hatching. The mean concentration of plasma prolactin over 24 hr increased three- to fourfold at the onset of incubation, from 24.8 ± 1.2 ng/ml (mean ± SE, n = 7) to 100.3 ± 23.5 ng/ml (n = 7) but fell to 41.6 ± 6.9 ng/ml (n = 7) in brooding birds. The concentration of plasma prolactin did not vary over 24 hr in laying or incubating hens although in the former, the highest values consistently occurred during the night. A significant (P < 0.001) daily variation in the concentration of plasma prolactin occurred in hens which were within 6 days of the onset of incubation or which were brooding chicks: prolactin levels increased steeply immediately after the lights went out and remained high during the dark period. Observations on individual bantams showed that about 6 days before incubation began, the secretion of prolactin increased at night and during successive days, this increase persisted for longer periods into the light period until on the first day of incubation, the concentration of plasma prolactin was high throughout the light and dark periods. These observations support the view that in the hen, an increase in the secretion of prolactin plays a key role in the induction of incubation behaviour. Further, a nocturnal increase in prolactin secretion may be involved in the maintenance of brooding behaviour.

Prolactin release in vitro and in vivo in the pigeon and the domestic fowl following administration of synthetic thyrotrophin-releasing factor (TRF)

Chicken and pigeon pituitaries were incubated in vitro in the presence of different concentrations of hypothalamic extract and of synthetic thyrotrophin-releasing factor (TRF). It was found that prolactin, measured by pigeon crop-sac bioassay, was released in both species. The amount of prolactin released from the chicken pituitaries was increased at the higher doses of TRF, the increase occurring at a dose which corresponded to the decrease in the biphasic TSH secretion. In the pigeon, prolactin and growth hormone release in vitro were measured by an electrophoretic-densitometric method. Both prolactin synthesis and release showed a biphasic response to the dose level of TRF, as did growth hormone synthesis. Thyrotrophin-releasing factor administered in vivo in pigeons resulted in a significant cropsac response, which was biphasic with respect to dose of TRF. There were also corresponding changes in pituitary prolactin content.

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.

Purification and properties of an avian prolactin

Abstract Prolactin was isolated from chicken adenohypophyses by extraction of the frozen glands with alkaline ethanol and chromatography on Sephadex G100 and DEAE-cellulose. The resulting preparation was homogeneous in disc electrophoresis on polyacrylamide gel and had strong pigeon crop sac stimulating activity. The chicken prolactin had significant mammotrophic activity in pseudopregnant rabbits. Furthermore, a radioactively labeled preparation showed binding to mammary tissue in vivo . The amino acid composition of the purified avian prolactin closely resembles that of mammalian prolactin preparations and the isoelectric point is also similar in both cases.