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PubMed1975

Episodic release of luteinizing hormone in the domestic fowl.

Plasma luteinizing hormone (LH) levels were measured by radioimmunoassay in serial samples taken from intact adult cockerels, gonadectomized fowl of both sexes and laying hens. By sampling at 30 and 10 min intervals, it was shown that in cockerels LH is released episodically. Each secretory episode lasted 90-120 min and was characterized by a 100-200% rise in LH levels over a period of 10-15 min followed by a more gradual, exponential decline. Mean plasma LH levels were found to be depressed in cockerels as a result of the handling associated with taking blood samples; in cases where LH levels were most depressed, an episodic pattern of secretion could not be demonstrated. In the gonadectomized fowl, an episodic pattern of LH secretion was shown when blood samples were taken at 10 or 5 min intervals. During each secretory episode, which lasted 20-45 min, LH levels rose by 20-60%. It is suggested that the increase in mean plasma LH levels in gonadectomized fowl (30-77 ng/ml) over those in cockerels (7-16 ng/ml) is related to an increase in the frequency of the episodic release of the hormone. Episodic discharges of LH could not be demonstrated in laying hens. In these birds the mean LH levels are low (1-5--2-4 ng/ml) and consequently may be maintained by secretory episodes which are of too low an amplitude to be detectable.

Animals↗
PubMed1975

Aspects of the adrenal function in the domestic fowl.

Chromatographic purification of extracts of hen peripheral plasma on Florisil columns before measurement by spectrofluorometry showed a basal level for corticosterone of 1-3 mug/100 ml, which is much lower than concentrations previously reported using acid fluorescence. Neither handling, restraint nor repeated bleeding affected the concentration of this hormone or of glucose. Adrenal function tests with two preparations of synthetic corticotrophin showed that they caused a rapid rise in blood corticosterone and eventually of glucose. Results of studies using insulin or tolbutamide i.v. suggest that there is a threshold concentration of plasma glucose (about 70 mg/100 ml) below which hypoglycaemia stimulates the hypothalamic-pituitary-adrenal system in fowls. Prolonged treatment of laying hens with protamine zinc insulin led to aphagia and cessation of egg-laying; increased concentrations of corticosterone were observed 2 days after the administration of insulin ceased, coinciding with the return to normal plasma levels of glucose. 'Chemical adrenalectomy' with metyrapone showed that the restoration of plasma glucose to a normal concentration after insulin treatment is dependent upon fully functional adrenal cortical tissue. It appears likely that the adrenal medulla is a target for corticosterone which probably regulates the tissue levels of phenylethanolamine-N-methyltransferase, one of the enzymes necessary for the biosynthesis of adrenaline.

Adrenal Cortex Function Tests↗
PubMed1977

Circadian rhythm of pineal uptake of 32P in domestic fowl.

The uptake of radioactive phosphorus by the pineal gland in White Leghorn cockerels (Gallus domesticus) showed a diurnal variation with maxima in the light phase and minima in the dark phase of the light: dark cycle. Constant light caused the rhythm to disappear while constant dark had no effect other than lowering the amplitude of the variations. These data indicate that the rhythm in pineal uptake of 32P is circadian.

Animals↗
PubMed1979

Acute effects of aldosterone on water and electrolyte transport in the colon and coprodeum of the domestic fowl (Gallus domesticus) in vivo.

White Leghorn laying hens were maintained on commercial poultry food (medium-Na+ diet) and fresh water. High-Na+ diet birds received, in addition, 10 ml 9% (w/v) NaCl/kg by stomach load for 2 days before perfusion experiments. The lumen of the coprodeum and colon of anaesthetized birds was perfused with a hyperosmotic solution resembling ureteral urine. Transmural solute and water fluxes and potential difference (p.d.) values were measured for 2.5 h before and for 8 h after i.v. injection of aldosterone (120 microgram/kg). After administration of aldosterone, the lag, increasing and stabilized plateau phases were identified for Na+, K+ and Cl- fluxes (which together formed an electroneutral ion-exchange system); plateau flux values were significantly greater than preinjection values and were comparable to values for birds maintained on low-Na+ diets in parallel experiments. Ammonium, phosphate and water fluxes were unresponsive to aldosterone and p.d. values showed a transient increase in medium-Na+ diet birds only. In parallel experiments on birds on low sodium diets the ammonium flux and p.d. increased but the osmotic flow and phosphate transfer did not respond. Therefore acute injection of aldosterone reproduced some but not all of the responses to dietary Na+ restriction in fowls.

Aldosterone↗
PubMed1981

Conversion of [4-14C]progesterone to androstenedione in vitro by thecal tissue from the ovary of the domestic fowl (Gallus domesticus).

The conversion of [4-14C]progesterone to androstenedione by thecal tissue homogenates from the large yellow follicles of the hen ovary was measured at two periods of the ovulatory cycle after incubation for 1 h in the presence of cofactors. Production of androstenedione by the largest follicle, F1, was reduced significantly 1-2 h before ovulation compared with 15 h before ovulation, whereas production of an unidentified androgen increased. These differences were not observed in the next largest follicles, F2 and F3. Thecal tissue homogenates from all the follicles converted [4-14C]progesterone to 17 alpha-hydroxyprogesterone, androstenedione and testosterone.

Androgens↗
PubMed1983

Thyroid hormones inhibit growth hormone secretion in domestic fowl (Gallus domesticus).

The influence of thyroxine (T4) and tri-iodothyronine (T3) on the secretion of GH in immature fowl was investigated. In birds pretreated with i.m. injections of T4 (100 micrograms/day for 10 days or 250 micrograms/kg for 7 days) or T3 (250 micrograms/kg for 7 days) the basal plasma GH level was markedly reduced. A similar reduction in the basal plasma GH level was also observed 60 min after a single injection or T3 (25 and 250 micrograms/kg) or T4 (250 micrograms/kg). In control birds the concentration of plasma GH was greatly increased (greater than 450 micrograms/l) within 10 min of an i.v. injection of thyrotrophin releasing hormone (TRH; 10 micrograms/kg). In birds pretreated with T3 or T4 the increase in GH concentration after TRH treatment was significantly less than that in the controls. In birds pretreated for 60 min with T3 or T4 the GH response to TRH was inversely dose-related and lowest in T3-treated birds. These results demonstrate that T3 and T4 inhibit GH secretion in birds, which is an effect not observed in mammalian species.

Animals↗
PubMed1983

Abnormalities in the plasma concentrations of thyroxine, tri-iodothyronine and growth hormone in sex-linked dwarf and autosomal dwarf White Leghorn domestic fowl (Gallus domesticus).

Plasma concentrations of GH were high in young birds (2-12 weeks old) and low in older birds (15 and 18 weeks old) in the control Cornell K strain of White Leghorn fowl. There was little variation in the plasma concentrations of tri-iodothyronine (T3) and thyroxine (T4) with age in this strain. Similar patterns of plasma hormone concentrations with age were observed in autosomal recessive dwarf chickens. However, the plasma concentrations of T3 and T4 tended to be depressed while that of GH was raised. There was little age-related change in the plasma concentrations of GH, T3 and T4 in sex-linked recessive dwarf chickens. Throughout growth and maturation the plasma concentrations of T3 in the sex-linked dwarf birds were less 40% of those observed in the control strain. Plasma concentrations of T4 tended to be raised relative to the control in the sex-linked dwarf at each age examined. The plasma concentration of GH was raised only in older (12, 15 and 18 weeks old) sex-linked dwarfs. Liver T4-5' monodeiodinase activity was slightly depressed in autosomal dwarf chickens and very low in the sex-linked dwarf fowl. Neither autosomal nor sex-linked dwarfism appears to be due to hypopituitarism. It is probable that the depressed liver 5' monodeiodinase activity and the concomitant low plasma concentrations of T3 are a causative factor in the reduced growth and stature of the sex-linked dwarf chicken.

Animals↗
PubMed1983

Antagonism of serum tri-iodothyronine changes after injections of prolactin in the domestic fowl before and after hatching.

The influence of an intravenous injection of ovine prolactin on circulating levels of thyroid hormones was studied in Rhode Island Red embryos and chicks after hatching. In the chick embryo, 2 h after injection of 0.1 microgram prolactin (on incubation day 19), serum triiodothyronine (T3) increased threefold; after 10 or 100 micrograms prolactin (on incubation day 18) serum T3 increased 15- to 25-fold. These profound increases were not observed in chicks after hatching. Serum concentrations and thyroid content of thyroxine (T4) in embryos and chicks of all ages studied were not influenced by the prolactin injections. Maximal serum concentrations of reverse T3 (rT3) were found on incubation day 18 (110.25 +/- 23.36 pmol/l; 71.66 +/- 15.18 pg/ml; n = 8), whereas after hatching no rT3 could be detected. An injection of 10 micrograms prolactin on day 18 depressed serum rT3 after 2 h to 5.68 +/- 3.20 pmol/l (3.69 +/- 2.08 pg/ml; n = 8; P less than 0.001); the effect of 100 micrograms prolactin was less pronounced. After hatching, chronic administration of prolactin resulted in decreased serum levels of T3, but not of T4, and hypertrophy of the follicles in the thyroid gland. It is concluded that prolactin plays a major role in the maturation of embryonic thyroid metabolism by changing the T4-5-monodeiodination into a T4-5'-monodeiodination. The hypertrophy of the thyroid gland observed after hatching following prolonged prolactin administration may be due to decreased negative feedback of T3 on the hypophysis.

Animals↗
PubMed1984

Ovarian aromatase activity in the domestic fowl (Gallus domesticus).

Fowl ovarian aromatase activity was measured by an assay based on the stereospecific elimination of tritium from [1,2-3H]testosterone. The production of tritiated water was shown to provide a valid estimate of aromatase activity under the conditions used. The small yellow follicles and ovarian stroma contained 50% of the total ovarian aromatase activity. The activity in the thecal tissue from the rapidly growing follicles reached a maximum level in the fourth largest follicles (17% of the total ovarian activity) and thereafter declined to low levels in the largest follicle and first post-ovulatory follicle. No activity was detected in the granulosa tissue from the rapidly growing follicles. It is proposed that the basal levels of plasma oestrogen in hens are maintained by production in the small yellow follicles and/or ovarian stroma. The variation in plasma oestrogen during the ovulatory cycle probably arises from secretion by the rapidly growing follicles.

Animals↗
PubMed1984

Dopaminergic inhibition of prolactin release from pituitary glands of the domestic fowl incubated in vitro.

Anterior pituitary glands from broiler fowl were incubated by themselves, with hypothalamic tissue or with thyrotrophin releasing hormone (TRH) in medium containing dopamine and its antagonist pimozide. The presence of hypothalamic tissue or TRH resulted in a stimulation of release of prolactin. Neither dopamine nor pimozide affected prolactin release directly from the pituitary gland. Dopamine inhibited the release of prolactin stimulated by hypothalamic tissue or TRH, in a concentration-dependent fashion. Pimozide diminished the response to dopamine. After pituitary glands were preincubated for 20 h in medium containing oestradiol-17 beta, the basal release of prolactin was enhanced as was the response to TRH. Both basal and TRH-stimulated release of prolactin from the oestrogen-primed pituitary glands was inhibited by dopamine, an effect blocked by pimozide. Hypothalami from broiler fowl were incubated for up to 8 h in medium containing dopaminergic drugs and pituitary glands were incubated in this medium, alone or with pimozide. As indicated by the prolactin released by the pituitary glands, the hypothalami appeared to secrete prolactin-releasing activity in a time-related fashion. Dopaminergic activity was also present in the hypothalami, since pimozide enhanced the prolactin-releasing activity of the medium. Dopamine apparently inhibited and pimozide stimulated the secretion of releasing activity from the hypothalamus. These results suggest that dopamine inhibits release of prolactin directly from the pituitary gland only when prolactin secretion is high. The hypothalamus secretes at least two factors regulating prolactin secretion, a prolactin-releasing factor and a dopaminergic prolactin-inhibiting factor. Dopamine may also play an inhibitory role in the regulation of secretion of the prolactin-releasing factor.

Animals↗
PubMed1985

Effect of a single injection of prolactin on the serum concentrations of thyroid hormones and corticosterone and liver monodeiodinase in the domestic fowl before and after hatching.

The influence of an intravenous injection of ovine prolactin on the liver monodeiodinase activity and serum concentrations of thyroid hormones and corticosterone was studied in Hisex embryos and chicks after hatching. An injection of 1 and 10 micrograms ovine prolactin into 18-day-old chick embryos increased serum concentrations of tri-iodothyronine (T3) five- and eightfold respectively after 2 h. At the same time serum concentrations of thyroxine (T4) and reverse T3 (rT3) were decreased in the chick embryo, but only with 10 micrograms prolactin. This was accompanied by a doubling of the liver monodeiodinase activity. Serum concentrations of corticosterone, however, were not influenced by the prolactin injections. In the 5-day-old chicken, serum concentrations of T3, rT3, T4 and liver T4-5'-monodeiodinase activity were not influenced by 1 or 10 micrograms prolactin. Serum concentrations of corticosterone after injection of 1 or 10 micrograms prolactin were doubled compared with controls. These results are compatible with a prolactin-induced shift from a T4-5-monodeiodination into a T4-5'-monodeiodination in the liver at the end of incubation. This effect, however, is not mediated through a prolactin-induced corticosterone release.

Animals↗
PubMed1986

Somatostatin tonically inhibits growth hormone secretion in domestic fowl.

Passive immunization of immature chickens with sheep somatostatin (SRIF) antiserum promptly increased the basal plasma GH concentration and augmented TRH-induced GH secretion. Although exogenous SRIF had no inhibitory effect on the basal GH concentration in untreated birds or birds pretreated with non-immune sheep serum, it suppressed the stimulatory effect of SRIF immunoneutralization on GH secretion. These results suggest that SRIF is physiologically involved in the control of GH secretion in birds, in which it appears to inhibit GH release tonically.

Animals↗
PubMed1988

The role of thyroid hormones in the growth hormone response to protein restriction in the domestic fowl (Gallus domesticus).

The possible role of thyroid hormones in the rise in plasma GH observed in protein-restricted chicks was examined. Increased sensitivity of protein-restricted chicks to secretagogue challenge (TRH or GH-releasing factor) appears to account, at least in part, for increased GH concentrations in protein-restricted chicks. Thyroid hormones administered acutely were able to suppress plasma GH concentrations in protein-restricted chicks. Further, chronic thyroid hormone supplementation to low protein diets normalized circulating thyroid hormone concentrations and also normalized the response to GH secretagogue challenge. This decreased sensitivity to TRH provocation occurred without an accompanying change in plasma concentrations of insulin-like growth factor-I, a reputed inhibitor of GH secretion in the chicken.

Animals↗