S. Harvey

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 (

Reproductive performance and endocrine responses to ingested petroleum in domestic ducks (Anas platyrhynchos)

Abstract The onset of lay by Khaki Campbell ducks transferred from a short-day (8L:16D) to a long-day photoperiod (16L:8D) was delayed by at least 4 weeks in birds fed 5 ml of North Sea Crude Oil per 100 g day wt of food, compared with birds fed an uncontaminated control diet. Over a 20-week period the oviposition rate and shell thickness of eggs laid by the birds fed 5% oil were greatly reduced. Refeeding the oil-fed birds with the uncontaminated diet increased oviposition rate and egg-shell thickness but not to the level in the controls. Throughout the experiment the plasma levels of prolactin and corticosterone in blood samples taken at weekly intervals were invariably less than those in the control birds. During photostimulation the mean plasma thyroxine concentration in the oil-fed birds was higher than the level in the controls but significant increases in the weekly concentration were only observed after the effects of petroleum on reproduction were manifest. The circulating concentrations of triiodothyronine were unaffected by oil ingestion. These results suggest that decreased ovarian activity in the oil-fed birds was not due to antigonadal effects of increased prolactin secretion or adrenocortical activity and an endocrine dysfunction of the thyroid is unlikely to be causally responsible for the effects of petroleum on avian reproduction.

Growth, growth hormone, and corticosterone secretion in freshwater and saline-adapted ducklings (Anas platyrhynchos)

Abstract Plasma growth hormone (GH) and corticosterone concentrations have been determined in growing male and female ducks during adaptation to hypersaline drinking water (0.1 – 0.4 M NaCl) and fresh water (FW). Saline adaptation resulted in growth retardation, adrenal hypertrophy, and lymphoid (bursa of Fabricus) involution. Basal plasma corticosterone levels increased with age in both FW- and saltwater (SW)-reared birds. Compared with the FW birds corticosterone was temporarily increased three- to fivefold during periods of saline adaptation. Plasma GH cocentrations decreased with age in birds reared on both FW and SW and in each group were directly related to the percentage weekly body weight gain. However, differences between the groups in growth rate were not reflected in corresponding differences in plasma GH level. No differences were seen between the sexes in circulating GH or corticosterone concentrations in the FW birds.

Concentrations of triiodothyronine, growth hormone, and luteinizing hormone in the plasma of thyroidectomised fowl (Gallus domesticus).

Surgical thyroidectomy increased (P less than 0.05) the basal concentrations of growth hormone (GH) and luteinizing hormone (LH) in the plasma of 10- to 12-week-old domestic fowl. The administration of thyrotrophin releasing hormone (TRH) (100 micrograms, sc) increased (P less than 0.01) the GH concentration in both intact and thyroidectomised birds. The magnitude of the TRH-induced increase in GH level was greater (P less than 0.01) in thyroidectomised birds than in intact controls. Although TRH had no effect on LH secretion in the controls, it induced a small (P less than 0.05) rise in the plasma LH level in thyroidectomised birds. In both the intact and thyroidectomised birds the LH concentration was enhanced (P less than 0.05) following the administration of LH-releasing hormone (LH-RH) (20 micrograms, sc). The increase in the LH level by LH-RH in the thyroidectomised birds was greater (P less than 0.001) than that in the intact controls. Plasma GH concentrations were unaffected by LH-RH treatment. These results suggest that thyroid hormones inhibit the secretion of LH and GH in birds. In thyroidectomised birds low levels of immunoreactive triiodothyronine (T3)-like material were measurable in the circulation, despite the absence of regenerated thyroid tissue. The administration of TRH (100 micrograms, sc) did not enhance the plasma level of this material in thyroidectomised birds, whereas plasma T3 concentrations were enhanced in intact birds following TRH treatment. These results suggest that the T3 immunoreactive substance in thyroidectomised birds is extrathyroidal in origin.

Diurnal variations in serum luteinizing hormone, growth hormone, and prolactin concentrations in intact and pinealectomised chickens

Abstract Diurnal variations in luteinizing hormone and prolactin have been demonstrated in sera from immature cockerels. Pinealectomy significantly altered these patterns of hormone secretion. No diurnal pattern in growth hormone concentration was seen in intact or pinealectomised birds.

Habituation of the corticosterone response of ducks (Anas platyrhynchos) to daily treadmill exercise.

The habituation of the corticosterone response of ducks to treadmill exercise (1.1 km/hr 0 degrees incline for 60 min) has been determined over a 28-day period. In untrained birds 30 min of treadmill exercise resulted in a marked (P less than 0.001) increase in the basal plasma corticosterone level. After 60 min of exercise the corticosterone concentration remained elevated (P less than 0.001) in comparison with basal and control (nonexercised) levels but was less (P less than 0.01) than that at 30 min. Following exercise the concentration declined to basal levels within 60 min. After 7 days of daily training the peak (30 min) corticosterone response to exercise diminished by greater than 50% and was absent in birds trained for 21 days. This habituation of the corticosterone response may be due to adrenocortical stimulation by pituitary adrenocorticotrophin (ACTH) being reduced. As the stimulatory effect of ACTH administration (8 IU/kg) on corticosterone secretion does not habituate in birds treated daily (for 28 days), the reduced corticosterone response to exercise may be due to decreased ACTH release rather than to a reduction in adrenal ACTH sensitivity.

Growth and the plasma concentrations of growth hormone and prolactin in chicks: effects of "environmental enrichment", sex and strain.

1. The effects of including novel objects in the environment (environmental enrichment) on body-weight gain, relative body-weight gain, gain: food ratio, plasma growth hormone (GH) and prolactin concentrations in male and female broiler and layer chicks was investigated. 2. Environmental enrichment improved body-weight gain, relative body-weight gain and gain : food ratio but had no effect on circulating GH or prolactin concentrations. 3. Weight gain and gain : food ratio were greater in the broilers than in the layer chicks, while plasma GH and prolactin (females only) concentrations were less. 4. There were no sex differences in weight gain and relative weight gain but gain : food ratio was significantly greater in females than in males. In both strains plasma GH concentrations were higher in male than in female broilers.

Effect of daily injections of ACTH on growth and on the adrenal and lymphoid tissues of two strains of immature fowls

1. The effects of daily injections of ACTH (30 IU/kg) or physiological saline on growth and on adrenal and lymphoid tissues of Rhode Island Red (RIR) and Light Sussex (LS) chickens were compared at 1, 2 and 3 weeks of age. 2. Saline injections retarded skeletal growth in both strains during the 1st week but only affected weight gain in LS birds. 3. Injections of ACTH depressed growth rate, caused adrenal enlargement and deplenished adrenal cholesterol to the same extent in both strains. 4. ACTH caused a greater reduction in bursal size in RIR than in LS birds. Spleen size was reduced by ACTH only in RIR birds. 5. At 2 and 3 weeks the plasma concentrations of corticosterone of RIR birds were greater than those of LS birds. Plasma corticosterone concentrations were within the normal range 24 h after the last injection of ACTH in both strains. 6. Plasma concentrations of growth hormone was unaffected by ACTH treatment in RIR birds, but it was increased in LS birds after 3 weeks of treatment.

Somatostatin inhibits thyroid function in fowl

Plasma concentrations of thyroxine (T4) and triiodothyronine (T3) were marginally (less than 25%) lowered 10 and 60 min, respectively, following somatostatin (SRIF) administration (at doses of 10-30 micrograms/kg) in immature domestic fowl. When plasma iodothyronine levels were elevated by the administration of anti-SRIF (1.0 ml/kg) 10 min prior to SRIF challenge, the inhibitory effect of SRIF on T4 and T3 concentrations was greatly augmented. The relative reduction in the T3 concentration was greater than the decline in the T4 level, resulting in a decline in the T3:T4 ratio. These data indicate that SRIF inhibits thyroid function in fowl, possibly by direct effects on the thyroid gland and by effects on the peripheral conversion of T4 to T3.

In vitro release of triiodothyronine and thyroxine from thyroid glands of the domestic fowl (Gallus domesticus)

Basal and thyrotrophin (TSH)-stimulated release of iodothyronines (triiodothyronine, T3, and thyroxine, T4) from intact chicken thyroid glands was determined in vitro. In the absence of TSH, T3 and T4 were released in measurable amounts in the incubation media. The release of both iodothyronines was directly related to the media TSH concentrations and incubation period. Lineweaver-Burke analysis revealed that the Vmax for T3 was 99.4 pg/gland, with an apparent Km of 17.8 mU TSH, and that the Vmax for T4 was 323.35 ng/gland, with an apparent Km of 51.5 mU TSH, demonstrating that T4 is the major iodothyronine released by avian thyroid glands. The basal release of T4 was suppressed by the addition of a calcium chelator (ethyleneglycol-bis-(beta-aminoethylether)-N,N,N, N-tetraacetic acid; EGTA), a calcium antagonist (cobalt chloride, CoCl2), or prostaglandin E1 (PGE1) to the incubation media. Basal T4 released was increased in the presence of a calcium agonist (lanthanum chloride, LaCl3), a calcium ionophore (A23187), dibutyryl cyclic adenosine 33-monophosphate (dbcAMP), isobutylmethylxanthine (IBMX), indomethacin, magnesium chloride (MgCl2), and potassium iodide (KI). Thyrotrophin-stimulated T4 release was reduced by CoCl2, PGE1, and indomethacin but enhanced by LaCl3, MgCl2, and KI. These results demonstrate that it is possible to measure the release of thyroid hormones in an in vitro system in the chicken. Basal and stimulated iodothyronine release from the chicken thyroid gland appears to be mediated by calcium- and cAMP-dependent mechanisms.