Biomedical subjects

P J Sharp

Publications and source records attributed to P J Sharp.

At least 73 records · Page 4Linked to original sources

PubMed1998

The role of prolactin in the development of reproductive photorefractoriness and postnuptial molt in the European starling (Sturnus vulgaris).

Seasonal breeding in many birds, including the European starling, is terminated by the development of absolute reproductive photorefractoriness, followed by a postnuptial molt, when photo-induced PRL secretion is at its seasonal maximum. To determine whether this photo-induced increase in PRL secretion has a causal role in the development of photorefractoriness or molt, European starlings were actively immunized against vasoactive intestinal polypeptide (VIP), the PRL releasing hormone in birds, or against PRL, during a photo-induced breeding cycle. In half of the VIP-immunized birds, the photo-induced increase in PRL was completely suppressed. Although these birds became photorefractory, the rate of gonadal regression was markedly slowed. These birds did not molt. In the remaining VIP-immunized birds, the photo-induced increase in PRL was inhibited but not completely suppressed. In these birds, and in those immunized against PRL, gonadal regression was also slowed, but molt progressed as normal. There were no significant differences in concentrations of plasma thyroxine between treatment and control groups, indicating that the effects of immunization on gonadal regression were not mediated by the induction of hypothyroidism. These results are consistent with the view that in the European starling the seasonal photo-induced increase in PRL accelerates gonadal regression during the onset of photorefractoriness but does not itself cause photorefractoriness. Further, the seasonal increase in PRL is required for the induction of the postnuptial molt.

Animals↗

PubMed1997

Sites of gene expression for vasoactive intestinal polypeptide throughout the brain of the chick (Gallus domesticus).

The peptide neurotransmitter vasoactive intestinal polypeptide (VIP) has several important functions in vertebrates, particularly, influencing the neuroendocrine and autonomic nervous systems both in developing and in adult animals. To document potential brain areas that might play significant functional roles, the distribution of VIP mRNA was examined throughout the entire chick brain by using in situ hybridization histochemistry (ISHH). In addition, a VIP binding-site study was completed that focused on the lateral septal organ (LSO), a circumventricular organ of potential significance in avian species. The areas where VIP message was found included the olfactory bulbs, posterior hippocampus, parahippocampal area, hyperstriatum, archistriatum/nucleus (n.) taenia (amygdala), medial part of the LSO, organum vasculosum of the lamina terminalis, medial preoptic region, bed n. of the pallial commissure, anterior hypothalamic (hypo.) n., lateral hypo. area (most extensive and dense message), periventricular hypo. n., lateral to the paraventricular n., ventromedial hypo. n., stratum cellulare externum, inferior hypo. n., infundibular hypo. n., median eminence, three layers within the stratum griseum et fibrosum superficiale, area ventralis of Tsai, n. tegmenti pedunculopontinus pars compacta (substantia nigra), intercollicular n., central gray, locus ceruleus, parabrachial n., ventrolateral medulla, reticular pontine area, in and about the n. vestibularis descendens. When compared with immunocytochemistry that detected the presence of the peptide product VIP, more areas of the brain were found to contain perikarya expressing VIP by using ISHH, particularly in the telencephalon and the mesencephalon. VIP binding sites were found in the lateral portion of the LSO where the blood-brain barrier is not fully developed. Hence, the LSO was found to contain neural elements that synthesize as well as bind VIP. VIP appears to be a useful peptide for defining major components of the visceral forebrain system in birds.

Animals↗

PubMed1997

Photorefractoriness in European starlings (Sturnus vulgaris) is not dependent upon the long-day-induced rise in plasma thyroxine.

Transfer of intact, photosensitive starlings from short to long days causes an increase in plasma thyroxine and gonadal maturation and later induces photorefractoriness. Thyroidectomy of starlings prevents the induction of photorefractoriness. This study investigated whether the long-day-induced increase in plasma thyroxine is necessary for the induction of photorefractoriness. Photosensitive starlings were thyroidectomised, given thyroxine in their drinking water at concentrations that result in plasma thyroxine at short-day physiological concentrations or lower, and transferred to long days. Plasma thyroxine and prolactin, gonadal size, and moult were monitored. The group with short-day concentrations of plasma thyroxine became photorefractory at the same time as intact controls transferred to long days. The other groups, with lower plasma thyroxine, also became photorefractory, but the onset of photorefractoriness was delayed. The increase in plasma prolactin following photostimulation was proportional to plasma thyroxine concentrations. The onset of moult was also related to plasma thyroxine. We conclude that the long-day concentrations of plasma thyroxine observed in the plasma of intact starlings are not necessary for the induction of photorefractoriness. This suggests that thyroxine acts as a permissive factor rather than actively driving the photorefractory process.

Animals↗

PubMed1997

Localization of progesterone receptor in brain and pituitary of the ring dove: influence of breeding cycle and estrogen.

An immunocytochemical method was used in male and female ring doves (Streptopelia risoria) to localize progesterone receptor immunoreactivity (PR-ir) in the brain and anterior pituitary gland in nonbreeding, incubating, brooding, and estrogen (E2)-treated nonbreeding birds. Progesterone receptor was found in four regions of the brain in males and females: the preoptic area (POA), nucleus preopticus paraventricularis magnocellularis (PPM), nucleus hypothalami lateralis (PLH), and the tuberal region (TR). Quantitative analysis demonstrated that the density of cell nuclei containing PR-ir in the POA, PPM, and PLH in brooding birds was significantly higher than in E2-treated doves or in birds at other stages of the reproductive cycle. The density of PR-containing cell nuclei in the TR of male ring doves was significantly higher on day 1 of incubation than in nonincubating males. In brooding birds, there was a significant decrease in PR-ir in the TR, particularly in the ventral region where nuclei containing PR-ir disappeared. In the anterior pituitary gland the density of cell nuclei containing PR-ir was higher in females than in males at the onset of incubation. E2 treatment resulted in an increase in the density of PR-containing cell nuclei in both males and females. Brooding females had a lower concentration of PR-containing cell nuclei than did females at other stages of the breeding cycle. It is suggested that progesterone receptor in the POA mediates the expression of incubation behavior while progesterone receptor in the TR is involved in the control of neuroendocrine function. The source of estrogen which increases PR appears to be of central nervous origin in the male and may be predominantly peripheral in the female.

Animals↗

PubMed1996

Immunocytochemical localization of androgen receptor in the comb, uropygial gland, testis, and epididymis in the domestic chicken.

Nuclear, but not cytoplasmic androgen receptors (AR), were localized immunocytochemically in the comb, uropygial (preen) gland, testis, and epididymis of juvenile and adult cockerels. Androgen receptor immunoreactivity (AR-ir) was seen in the comb, in the stratum germinativum of the epidermis and in fibromucoid cells in the dermis in juvenile and adult cockerels. AR-ir was observed in the glandular epithelial (sebum-producing) cells lining the peripheral and middle sections of the tubules in the uropygial gland. AR-ir was not detected in innermost part of the tubules which conduct the sebum to the surface of the skin. AR-ir labeling was not observed in the uropygial gland of juveniles. In the testis, AR-ir was seen in the Leydig cells, in adults but not juveniles. The epithelial cells lining the tubules in the epididymis contained AR-ir in both juveniles and adults.

Aging↗

PubMed1996

The effect of ovariectomy on concentrations of plasma prolactin and LH and parental behavior in the domestic fowl.

The role of ovarian hormones in the expression of parental behavior and in the regulation of LH secretion was investigated in incubating commercial meat-type hens. After ovariectomy, incubating hens continued to incubate eggs normally and brooded day-old chicks given to replace eggs, in a manner similar to sham-ovariectomized control hens. The concentration of plasma LH increased significantly in incubating hens after ovariectomy while the concentration of plasma prolactin remained high. Plasma LH remained depressed in sham-ovariectomized incubating control hens. The increase in plasma LH in incubating hens after ovariectomy (3.92 +/- 0.7 ng/ml) was less than that following the ovariectomy of nonincubating, nonlaying hens (5.3 +/- 1.2 ng/ml). The two groups of hens differed in that plasma prolactin concentrations were high (527 +/- 7.4 ng/ml) in the incubating hens and low (70 +/- 9 ng/ml) in the nonincubating hens. Nest deprivation resulted in an increase in plasma LH in both ovariectomized and sham-ovariectomized incubating hens with a significantly larger increase occurring in the ovariectomized hens (8.5 +/- 1.41 ng/ml compared to 2.48 +/- 0.65 ng/ml). Nest deprivation resulted in a similar rapid decrease in plasma prolactin in both ovariectomized and sham-ovariectomized hens. Replacement of eggs with day-old chicks in ovariectomized or sham-ovariectomized incubating hens resulted in a rapid decrease in plasma prolactin and after 6 days, in an increase in plasma LH in the ovariectomized but not sham-operated hens. It is concluded that once incubation behavior is established, ovarian hormones are not required for its maintenance or the readiness to brood day-old chicks. Ovarian hormones do, however, suppress LH release during incubation while the high concentration of plasma prolactin supplements this suppression.

Animals↗

PubMed1996

Plasma thyroxine concentrations in farmed ostriches in relation to age, body weight, and growth hormone.

Thyroid hormones are of interest in ostriches because, in common with other ratites, ostriches are believed to have evolved through neoteny, a process which, in amphibia, is related to thyroid function. Farmed ostriches show marked differences in growth rates, a problem which also could be related to abnormal thyroid function. In adult farmed ostriches (more than 3 years old), mean plasma thyroxine concentration was 1.8 nmol middle dot liter-1 (range 0.2 to 6.5 nmol middle dot liter-1). This is a lower mean and a much greater range than those in adult starlings or Japanese quail measured at the same time. No sex differences were observed. In 5-month-old ostriches (approximately half grown) mean levels were again low (3.1 nmol x liter-1, range 0.2 to 9.9 nmol x liter-1). There was a correlation (P < 0.0005) between thyroxine and body weight, which ranged from 10.8 to 51.5 kg. Growth hormone in this group ranged from 0.7 to 45.6 microg x liter-1, but there was no correlation with body weight or with thyroxine. In the same group of birds at 10 months of age, plasma thyroxine concentrations were similar, but were not correlated with body weight. In young birds sampled between hatch and 13 weeks, mean thyroxine decreased from 7.6 nmol x liter-1 soon after hatching to less than 2 nmol x liter-1 at 2 weeks and remained less than 2 nmol x liter-1 for the following 3 months. Thyroxine was highly variable within and between individuals. There was no correlation with body weight or growth rate. There were no significant differences between values at 13 weeks, 5 months, 10 months, or in adults. The results do not suggest that slow growth is directly related to low thyroxine. However, the low means and wide range of values do suggest that thyroid function in the ostrich is abnormal compared to other birds.

Aging↗

PubMed1996

Expression of fos-like immunoreactivity in the hypothalamus of the ring dove (Streptopelia risoria) at the onset of incubation.

Fos immunocytochemistry was used in the ring dove (Streptopelia risoria) to identify areas in the forebrain and hypothalamus which might be involved in the expression of incubation behaviour and the associated changes in neuroendocrine function. In this species, both sexes participate in incubation which becomes fully established after laying the second egg in the two egg clutch. The eggs hatch after 14-15 days incubation. Observations were made in both sexes 16-18 h after laying the first egg, 3-5 h after laying the second egg, and after 12-14 days of incubation. Non-breeding birds were used as controls. Fos-labelled cells were observed in several forebrain areas in both sexes irrespective of reproductive status but their numbers did not change during incubation. In the hypothalamus, very few fos-labelled cells were seen in non-breeding birds but appeared in both sexes in the nucleus preopticus medialis after egg laying and after 12-14 days of incubation. Fos-labelled cells also appeared in the nucleus tuberis (=arcuate nucleus) in both sexes after laying the first or second egg and less abundantly, after 12-14 days incubation. Additionally, in males only, fos-labelled cells were seen after the laying of the first and second eggs in the rostral area of the nucleus tuberis close to the walls of the third ventricle. These observations suggest that the fos-labelled cells in the nucleus preopticus medialis may be involved in the expression of incubation behaviour while those in the nucleus tuberis may be involved in the regulation of gonadotrophin or prolactin secretion.

Animals↗

PubMed1996

Effect of age of donor on the responsiveness of dispersed and cultured chicken anterior pituitary cells to GnRH-I.

1. The aim of this study was to devise a method to prepare and culture anterior pituitary cells from juvenile and adult chickens in order to investigate mechanisms controlling gonadotrophin-releasing hormone-I (GnRH-I)-induced luteinising hormone (LH) release in vitro. 2. The optimum culture medium for maintaining gonadotroph responsiveness to GnRH-I was bicarbonate-buffered and phenol red-free Medium 199 supplemented with 10% foetal calf serum. 3. Cultured pituitary cells from juvenile chickens were more responsive to GnRH-I than cells from adult cockerels, while no LH was released in response to GnRH-I from pituitary cells from laying hens. 4. Cultured pituitary cells from adult chickens of both sexes released LH in response to 12-O-tetradecanoyl-13-phorbol acetate (TPA), an activator of an enzyme involved in intracellular signalling, protein kinase C. 5. It is concluded that freshly-dispersed and cultured gonadotrophs from adult chickens do not regain their responsiveness to GnRH-I as well as freshly-dispersed and cultured gonadotrophs from juvenile chickens. It appears that the stimulus-secretion coupling pathway between the GnRH-receptor and the activation of protein kinase C in gonadotrophs from adult chickens is more easily disrupted by dispersion and culture than in gonadotrophs from juvenile chickens.

Aging↗

PubMed1996

Regulation of chicken gonadotropin-releasing hormone-I mRNA in incubating, nest-deprived and laying bantam hens.

Secretion of luteinizing hormone is decreased when hens start to incubate their eggs and is increased after nest deprivation or hatching of the eggs. The purpose of this study was to determine whether decreased luteinizing hormone (LH) secretion during incubation in the domestic hen is associated with a decrease in hypothalamic chicken gonadotropin-releasing hormone-I (cGnRH-I) mRNA or peptide. A semiquantitative competitive PCR assay was developed to measure cGnRH-I mRNA. Hypothalamic mRNA was quantified as the amount of GnRH cDNA obtained by reverse transcription of cGnRH-I mRNA. The amount of hypothalamic cGnRH-I mRNA was significantly higher in laying than in incubating hens (38.7 +/- 10.3 vs. 7.7 +/- 1.6 x 10(-17) mol cDNA, p = 0.01, n = 8). The hypothalamic GnRH peptide content was not significantly different between laying and incubating hens in either the preoptic area (286.9 +/- 24.01 vs. 269.3 +/- 29.3 pg, n = 8) or the basal hypothalamus (1.67 +/- 0.19 vs. 1.54 +/- 0.21 ng, n = 8). Five days after incubating hens were deprived of their eggs, the resulting increase in LH secretion was associated with a significant increase in hypothalamic content of cGnRH-I mRNA (22.8 +/- 2.2 vs. 6.7 +/- 1.7 x 10(-17) mol cDNA, p < 0.001, n = 8). These observations suggest that a decrease in the expression of the cGnRH-I gene is a major factor in maintaining depressed LH secretion in incubating domestic chickens.

Animals↗

PubMed1995

[14C]2-deoxyglucose uptake in the brain of the ring dove (Streptopelia risoria). I. Prolactin-induced uptake.

Quantitative [14C]2-deoxyglucose (2DG) autoradiography was used to identify areas of the ring dove brain involved in the expression of incubation behavior. Compared with non-breeding controls, 2DG uptake was increased in birds of both sexes during late incubation in all areas of the fore, mid- and hind-brain examined. This increase occurred irrespective of whether the birds were sitting on their eggs at the time of 2DG administration. A similar pattern of 2DG uptake into the brain was observed in non-breeding females treated with 30 I.U. ovine prolactin (i.p.) twice daily for 5 days. It is concluded that there is a generalised increase in neural activity in the brain of doves during late incubation which may be dependent on increased concentrations of plasma prolactin.

Animals↗

PubMed1995

[14C]2-deoxyglucose uptake in the brain of the ring dove (Streptopelia risoria). II. Differential uptake at the onset of incubation.

Brain areas involved in the expression of incubation behaviour were identified in male ring dove at the onset of incubation using quantitative [14C]2-deoxyglucose (2DG) autoradiography. The uptake of 2DG in twenty-eight areas found in the hypothalamus and thalamus, and six areas in the forebrain were compared in control non-breeding and incubating birds. Although 2DG utilisation varied significantly between brain areas, significant differences between non-breeding males and incubating males were observed only in 4 of them. These were the nucleus tuberis, nucleus preopticus medialis, nucleus ovoidalis and paleostriatum primitivum. The uptake of 2DG was increased at the onset of incubation in the nucleus tuberis, nucleus preopticus medialis and nucleus ovoidalis and decrease in the paleostriatum primitivum. These findings are consistent with the hypothesis that these brain areas play a role in the initiation of incubation behaviour.

Analysis of Variance↗

PubMed1995

Sexually differentiated role of calcium ions in chicken GnRH-I-stimulated release of LH from anterior pituitary glands from adult domestic chickens.

Continuous perifusion of quartered anterior pituitary glands from juvenile and adult chickens of both sexes with chicken gonadotrophin-releasing hormone-I (cGnRH-I) stimulated a spike-plateau profile of luteinizing hormone (LH) secretion. When perifused in Ca(2+)-free medium, pituitary glands from juveniles of both sexes and from adult cockerels but not those from laying hens, released LH in response to cGnRH-I. This release occurred at the same time as the spike phase of the response seen in the presence of extracellular Ca2+ and was not accompanied by a plateau phase of secretion. The magnitude of the plateau but not the spike phase of LH secretion from pituitary glands from adult males and females was reduced by the L-type Ca2+ channel blocker, nifedipine. This suggests that the mechanism of cGnRH-I-induced LH release from pituitary glands from laying hens is independent of mobilization of intracellular Ca2+, and that entry of Ca2+ during the spike phase of LH secretion occurs through non-L-type Ca2+ channels. Both non-L-type and L-type Ca2+ channels operate during the plateau phase of secretion in adults of both sexes. The duration of the spike phase of LH release from pituitary glands from adult cockerels was curtailed in the presence of nifedipine. The spike phase of LH release from the adult cockerel pituitary therefore involves three modes of Ca2+ flux, comprising an intracellular Ca(2+)-dependent component and extracellular components involving Ca2+ entry through L-type and non-L-type Ca2+ channels. The finding that the extracellular Ca(2+)-independent component of cGnRH-I-stimulated LH release from pituitary glands from juvenile hens is not present in adult hens suggests that this difference is related to sexual maturation. The maturational and sexual differences in the LH response to cGnRH-I could be mediated through the high concentrations of plasma 17 beta-oestradiol in adult hens which suppress the mobilization of intracellular stores of Ca2+ in the gonadotrophes.

Animals↗

PubMed1995

A test for photorefractoriness in high-producing stocks of laying pullets.

1. Pullets of 2 high-producing commercial stocks (both brown-egg layers) were exposed to 5 different lighting patterns between 18 and 72 weeks to test the hypothesis that photoperiods used in commercial lighting programmes early in the laying year may be unnecessarily long and, by accelerating the development of photorefractoriness, may contribute to the decline in egg production observed after the initial peak. Two rooms of 288 pullets were allocated to each treatment. 2. The rate of lay observed with a Step-Up treatment which gave increases in photoperiod from 8L:16D at 18 weeks to 15L:9D at 27 weeks of age was not significantly different from that of treatments which held the birds on 11L:13D during peak egg production but gave increments up to 15L:9D later in the laying year. 3. A control group maintained on 11L:13D from 20 to 72 weeks laid 295 eggs per bird housed and a further group held on 8L:16D from 0 to 72 weeks laid 284 eggs per bird. These yields were lower than the Step-Up treatment (299 eggs) but show the potential of modern hybrid stocks to lay prolifically even without light stimulation. 4. It is concluded that the stocks tested in this experiment showed no advantage when given lighting programmes in the first laying year which were designed to minimise the adverse effects of photorefractoriness.

Aging↗

PubMed1995

Evidence for alternative splicing of the chicken vasoactive intestinal polypeptide gene transcript.

Two forms of chicken vasoactive intestinal polypeptide (VIP) mRNA have been identified by reverse transcription (RT)-PCR and RNase protection assay. The shorter form of chicken VIP mRNA encodes a protein that does not contain an analogue of rat peptide histidine isoleucine (PHI) 1-27 or human peptide histidine methionine 1-27. The larger form encodes both VIP and a chicken analogue of PHI 1-27 in the same protein product. Three VIP cDNAs isolated from a chicken hypothalamic cDNA library were derived from the shorter mRNA. Sequence analysis of the longest clone identified an open reading frame that codes for a 165 amino acid preproVIP protein and contains two polyadenylation signals. In situ hybridisation with an oligonucleotide probe from the VIP cDNA sequence showed that VIP-encoding mRNA occurs in cells in the basal hypothalamus, an area of the brain known to contain VIP neurosecretory neurones. RT-PCR of total RNA from liver, kidney, gut, pancreas, pituitary, cerebellum, forebrain and hypothalamus, using primers derived from the VIP cDNA sequence, showed that the shorter form of VIP mRNA is present in all of these tissues. The sequence of the longer form of VIP mRNA was obtained by sequencing a portion of the VIP gene from genomic DNA. This revealed a potential exon that was not represented in the VIP cDNA clones analysed. RT-PCR with primers from this sequence showed that it was expressed in the gut and hypothalamus. RNase protection assays confirmed the presence of the two forms of mRNA in gut and hypothalamus. The relative proportions of the two mRNA forms were: 97.8% VIP only, 2.2% PHI/VIP in the hypothalamus and 98.5% VIP only, 1.5% PHI/VIP in the gut. In conclusion, chicken VIP mRNA is alternatively spliced. The shortest form, which encodes a preproprotein containing only the VIP peptide, is the most abundant. The longer form of chicken VIP mRNA encodes a preproprotein containing sequences for both VIP and a chicken form of PHI.

Alternative Splicing↗

PubMed1995

Migratory fat deposition in European quail: a role for prolactin?

The present study addresses the role of prolactin as a regulator of migratory fattening in European quail (Coturnix coturnix). Plasma prolactin levels in captive birds undergoing migratory fattening in an outdoor aviary and in the laboratory were measured by radioimmunoassay with an antibody raised against recombinant-derived chicken prolactin. No strong association between prolactin and migratory fattening was apparent, and prolactin levels were more closely related to daylength, with the highest concentrations being reached on long days. Plasma prolactin profiles were similar in intact and castrated male quail. Prolactin was secreted in a daily rhythm, with the highest concentrations occurring early in the photophase. However, when birds were food-restricted for 50 days during a migratory phase, there was no difference in fat deposition between birds food-deprived for the first half of the daily photophase compared with those deprived for the second half. Fattening was reduced in the food-restricted birds relative to ad libitum-fed controls, but there was no difference in plasma prolactin levels between the groups. Injections of ovine prolactin (4 mg/kg) significantly increased food intake and body mass of birds maintained on long days, but there were no differences in fattening between birds injected in the morning compared with those injected in the afternoon. Collectively, these results do not support a major role for prolactin in the regulation of migratory fat deposition in European quail.

Adaptation, Physiological↗

PubMed1994

Insulin-like growth factor-I in the ovary of the laying hen: gene expression and biological actions on granulosa and thecal cells.

Concentrations of insulin-like growth factor-I (IGF-I) were measured in granulosa and thecal tissue dissected from the three largest follicles in the ovaries of laying hens. The higher concentration was found in extracts of granulosa (0.82 +/- 0.01 pmol/g wet wt) and theca (0.36 +/- 0.02), both of which were greater than that in liver extracts (0.25 +/- 0.01). RNA was extracted from these tissues, and by using reverse transcription and the polymerase chain reaction with primers specific for chicken IGF-I, both granulosa and thecal tissue were shown to express chicken IGF-I mRNA. Granulosa and thecal cell cultures were established and used to measure IGF binding sites and the response to exogenous IGF peptides in terms of DNA synthesis. Both cell types bound [125I]IGF-I, which was displaced by IGF-I, IGF-II, and insulin in descending order of potency, characteristic of a type-I IGF receptor. Treatment of granulosa and thecal cell cultures with IGF-I resulted in a dose-dependent increase in [3H]thymidine incorporation into DNA by both cell types. LH, but not FSH, stimulated DNA synthesis in cultured granulosa cells but not in cultured thecal cells. This effect was enhanced in granulosa cells by the addition of IGF-I to the culture medium. These data are consistent with an autocrine or paracrine role for IGF-I within the developing ovarian follicle of the domestic hen.

Animals↗

PubMed1994

A radioimmunoassay for recombinant-derived chicken prolactin suitable for the measurement of prolactin in other avian species.

A homologous radioimmunoassay for chicken prolactin is described. The assay is based on recombinant-derived chicken prolactin that has been used to raise an antibody and produce 125I-labeled tracer and assay standards. The radioimmunoassay measures a minimum of 0.03 +/- 0.01 ng of the recombinant prolactin with 50% displacement of binding by 0.6 +/- 0.1 ng. Chicken plasma and pituitary immunoreactivity dilute in parallel with the standard curve. The mean (+/- SE) concentrations of plasma prolactin were 12.1 +/- 1.5, 433.2 +/- 5.5, and 1609.8 +/- 18.5 ng/ml in out-of-lay, laying, and incubating bantam hens, respectively. The binding of recombinant prolactin was not displaced by extracts of neural lobe or plasma from a hypophysectomized hen. Plasma prolactin concentrations were increased after intravenous administration of chicken vasoactive intestinal polypeptide or quipazine, a 5-HT agonist. The assay measures immunoreactive prolactin in other birds. Plasma from quail, turkey, great tit, and wryneck displaced the 125I-labeled prolactin tracer parallel to the standard curve. Starling, ring dove, and penguin plasma displaced the binding in a nonparallel manner.

Animals↗