PubMed Health⌕ Search

Biomedical subjects

A Chadwick

Publications and source records attributed to A Chadwick.

At least 55 records · Page 3Linked to original sources
PubMed1983

Early changes in the adaptation to a low calcium diet in the chick.

Twelve hours after the diet of 3-week-old chicks was changed from a 1% to a 0.1% concentration of calcium (Ca), the growth rate and circulating levels of growth hormone had fallen while renal 25-hydroxecholecalciferol-24-hydroxylase had risen. The amount of 47Ca incorporated into bone from an injection given 18 h previously was lower than in the control birds. Over the following 2 1/2 days on the low Ca diet, the renal 1-hydroxylase activity rose and the plasma prolactin level fell, but the other parameters moved back toward the control level. It was concluded that early adjustments in hormonal and mineral metabolism counteract the acute effects of a dietary Ca shortage until longer-term adaptive changes begin to compensate for a continuing Ca deficiency. The renal hydroxylase activities were not directly influenced by the level of circulating growth hormone or prolactin.

Adaptation, Physiological↗
PubMed1983

Hypothalamic control of prolactin and growth hormone secretion in the pituitary gland of the pigeon and the chicken: in vitro studies.

Hypothalamic extracts stimulated the release of prolactin and growth hormone from pigeon and chicken pituitary glands incubated in vitro. Release of hormone was proportional to the amount of hypothalamic extract added. Pituitary glands from "lactating" pigeons released more prolactin and their hypothalami contained more prolactin-releasing activity compared with controls. Partial separation of prolactin releasing activity from growth hormone releasing activity in chicken hypothalamic extract was achieved using gel filtration chromatography. Co-incubation studies in vitro with hypothalamic tissue present showed that prolactin release from the pituitary was inhibited and growth hormone release was stimulated when dopamine was added to the medium. The effects of dopamine were blocked by the antagonist pimozide. The possible existence of hypothalamic releasing and inhibiting factors regulating secretion of prolactin and growth hormone is discussed.

Animals↗
PubMed1983

Serotoninergic drugs affect prolactin and growth hormone secretion in the domestic fowl.

Adult fowl of both sexes injected with the monoamine oxidase inhibitor pargyline showed elevated circulating prolactin concentrations and reduced growth hormone concentrations. Young cockerels injected with the serotonin agonist quipazine and the antagonist methysergide showed responses consistent with a serotoninergic stimulatory control of prolactin. Injection of the serotonin precursor tryptophan and the serotonin re-uptake blocker imipramine resulted in elevated prolactin and reduced growth hormone levels. The similarities and differences in the control of prolactin and growth hormone in birds and mammals were discussed.

Animals↗
PubMed1983

Effect of intermittent feeding on blood plasma growth hormone and prolactin in chickens of a heavy breed.

1. Variations in plasma growth hormone (GH) and prolactin concentrations were determined during growth (at 20, 33, 56 and 83 d of age) in ad libitum (control) and intermittently (alternate days) fed chicks. 2. In each group of birds the concentration of plasma GH was inversely related to age. The mean prolactin concentration was highest in the youngest (20-d-old) birds. 3. The concentration of plasma GH in the intermittently-fed birds deprived of food for 24 h (depleted birds) was significantly higher than that in the controls at 33, 56 and 83 d of age. The mean GH concentration in the intermittently-fed birds 24 h after refeeding (repleted birds) was less than that in the depleted ones. 4. The overall mean concentration of plasma prolactin in the depleted birds was significantly less than that in the control and repleted birds. 5. These results are consistent with the effects of fasting on GH and prolactin secretion and demonstrate that growth retardation in the intermittently-fed birds was not due to impaired GH secretion.

Age Factors↗
PubMed1983

Mechanism of serotonin effects on prolactin and growth hormone secretion in domestic fowl.

Brain serotonin levels were increased in immature chickens by ip injection of pargyline (75 mg/kg) and clorgyline (5 mg/kg) and by L-tryptophan (100 mg/kg) and imipramine (10 mg/kg) treatment. These treatments increased the circulating prolactin level and reduced the concentration of plasma growth hormone (GH). Treatment with para-chlorophenylalanine (PCPA, 100 mg/kg) reduced the brain serotonin content and the level of plasma prolactin. Treatment with these drugs in vivo similarly affected the basal level of prolactin release from pituitary glands in vitro, although it did not affect the basal level of GH release. The in vitro responsiveness of the pituitary gland to hypothalamic stimuli eliciting prolactin secretion was increased by in vivo pargyline and combined tryptophan: imipramine treatment but reduced by PCPA administration. The in vitro GH response to hypothalamic stimulation was reduced after the in vivo injection of pargyline, clorgyline and tryptophan: imipramine. The hypothalami from clorgyline and tryptophan: imipramine treated birds induced a greater stimulation of in vitro prolactin secretion from control pituitary glands than hypothalami from controls birds, whereas the GH releasing activity was reduced. These results suggest that serotonin stimulates prolactin secretion in chickens by increasing pituitary responsiveness to hypothalamic releasing factors and by increasing the prolactin releasing activity of the hypothalamus. Serotonin appears to suppress GH secretion by reducing pituitary sensitivity to releasing factors and by reducing hypothalamic GH releasing activity.

Animals↗
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

Serum concentrations of prolactin, luteinizing hormone, growth hormone, corticosterone, progesterone, testosterone and oestradiol in relation to broodiness in domestic turkeys (Meleagris gallopavo).

Variations in concentrations of LH, GH, prolactin, corticosterone, oestradiol, testosterone and progesterone in serum were followed over a 24 h period (14 h light:10 h darkness) in laying and broody turkeys and in turkeys suspected of becoming broody (pre-broody hens). In laying hens marked variations in LH and gonadal steroid levels were observed in relation to the ovulatory cycle of the bird. These patterns of hormone secretion were not seen in either group of broody birds. Levels of GH in serum were very variable and showed no correlation with the egg-laying or light:darkness cycle and the concentrations did not differ between the respective physiological states. A nocturnal increase in the concentration of corticosterone in serum was observed in all three groups of turkeys and the concentration was occasionally higher in the pre-broody and broody birds than in the laying hens. The serum prolactin concentration in each group was also very variable and showed no obvious relationship with the ovulatory or photoperiodic cycle. The mean circulating prolactin concentration throughout the 24 h period did not differ significantly between the groups. These results suggest that broodiness in the domestic turkey is not initiated or maintained by enhanced prolactin secretion.

Animals↗
PubMed1981

Concentrations of pituitary, gonadal and adrenal hormones in serum of laying and broody white rock hens (Gallus domesticus).

Diurnal variations in circulating concentrations of LH, GH, prolactin, corticosterone, oestradiol, progesterone and testosterone were followed in laying and broody White Rock domestic fowl. Throughout the 24 h study prolactin concentrations in serum were consistently (two- to fourfold) higher in broody than in laying birds, in which the prolactin level varied with the light:darkness or ovulatory cycles. Concentrations of GH in serum tended to be lower in broody birds but in both groups were very variable and showed no obvious relationship with either the lighting or ovulatory cycles. Broodiness was also characterized by low LH and gonadal steroid levels and by the absence of preovulatory peaks in the serum concentrations of these hormones. A diurnal rhythm in corticosterone was observed in both the laying and broody birds, with high levels during the period of darkness. Corticosterone concentrations were markedly higher in the broody birds than in laying birds during most of the 24 h study. No diurnal rhythm in the blood haematocrit level was observed in either group, although the level was generally lower in broody birds. This difference, however, was insufficient to account for the lower LH and gonadal steroid levels in the broody birds. The results suggest that prolactin is involved in the initiation or maintenance of broodiness in the fowl and the possibility of an antigonadal role for the hormone is discussed.

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

Circulating growth hormone and prolactin concentrations in turkeys and chickens infected with Histomonas meleagridis.

1. Histomonas meleagridis was inoculated into young chickens and turkeys and the effect of the infection (blackhead) on circulating growth hormone (GH) and prolactin concentrations determined. 2. During the course of the infection in turkeys there was a marked increase in plasma GH concentration which correlated with the severity of the disease, as judged by liver and caecal characteristics. The infection was less severe in chickens and no correlation between plasma GH and the degree of infection was observed. 3. The concentration of plasma prolactin was increased in the chicken, but not in the turkey, during the invasive period of infection.

Animals↗
PubMed1980

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.

Animals↗
PubMed1979

In vitro stimulation of chicken pituitary growth hormone and prolactin secretion by chicken hypothalamic extract.

The effect of an acid extract of chicken hypothalami on the in vitro secretion of prolactin and growth hormone (GH) by dispersed chicken pituitary cells has been investigated. Both prolactin and GH release were stimulated in a dose related manner in the presence of the hypothalamic extract (HE). Somatostatin had no effect on the basal or HE stimulated release of prolactin although it did inhibit the HE induced release of GH.

Animals↗