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This study evaluates the transcriptional and post-transcriptional regulation of prolactin (PRL) by vasoactive intestinal peptide (VIP). Pituitary nuclei from laying (control), incubating (with enhanced VIP secretion), and VIP-immunized laying turkey hens, and from pituitary cells cultured with or without VIP were used in nuclear run-on transcription assays. Cytoplasmic PRL mRNA was analyzed by slot blot hybridization. PRL transcription was greater in hyperprolactinemic incubating birds (PRL/beta-actin=3.33) than in laying birds (PRL/beta-actin=1.83). VIP-immunoneutralized birds had 47% and 51% decreases in PRL transcription and cytoplasmic PRL mRNA, respectively when compared with laying birds. In primary pituitary cell cultures, VIP significantly increased the transcription rate of PRL (3.8-fold) and cytoplasmic PRL mRNA (3.2-fold) compared with that of non-VIP-treated pituitary cells. The stability of pre-existing PRL mRNA was measured by Northern blot analysis after addition of actinomycin D. PRL mRNA half-lives were calculated using a two-component model, with a first-long component of 18.0+/-1.0 h and a second-short component of 3.7+/-0.7 h in non-VIP-treated pituitary cells. Both half-lives were significantly increased (53. 2+/-6.9 and 26.3+/-4.3 h) in VIP-treated cells. The present data show that VIP acts to stimulate PRL expression by up-regulating the transcription rate of PRL and by enhancing PRL mRNA stability.

This study investigated the capability of dopamine (DA) to prevent avian prolactin (PRL) secretion by antagonizing the PRL-releasing factor, vasoactive intestinal peptide (VIP), at the level of the pituitary. To test this hypothesis, combined intracranial and intrapituitary infusions of DA, DA agonists, and VIP, plus electrical stimulation of the medial preoptic area (ES/POM), were used to characterize the actions of DA on PRL secretion in anesthetized laying turkey hens. Infused into the third ventricle at the rate of 10 nmol/min, DA induced a 2.8-fold increase in circulating PRL levels (63.8 ± 15.1 to 181.3 ± 44.3 ng/ml, p < 0.05), similar to the 3.1-fold PRL increase induced by ES/POM (65 ± 10.3 to 199.1 ± 57.3 ng/ml, p < 0.05). Infused into the anterior pituitary at the rate of 15 ng/min, VIP induced a 2.2-fold increase in PRL (78.6 ± 22.9 to 173.6 ± 39.5 ng/ml, p < 0.05). When DA (10 nmol/min) was infused into the anterior pituitary it completely blocked both ES/POM- and VIP-induced PRL secretion. The D2 DA receptor agonist R- (–) -Propylnorapomorphine HCl inhibited VIP-induced PRL secretion at the level of the anterior pituitary, allowing only an insignificant rise in PRL (54.8 ± 14.3 to 73.9 ± 21.6 ng/ml, p > 0.05), while the D1 DA receptor agonist (±)-SKF-38393 HCl failed to prevent VIP-induced PRL release, allowing PRL to rise 2.5-fold (49.1 ± 10.8 to 121.0 ± 34.8 ng/ml, p < 0.05). Pituitary infusion of DA, DA agonists or vehicle alone caused no change in PRL levels. The data showed that DA prevented avian PRL secretion by blocking the action of VIP at the level of the anterior pituitary. DA effected this blockade of PRL via D2 DA receptors residing within the anterior pituitary. The data also suggested that there were no stimulatory D1 DA receptors related to PRL secretion in the avian anterior pituitary.

The objective of this study was to culture turkey hypothalami and examine vasoactive intestinal peptide (VIP) release during the turkey reproductive cycle. The release of VIP was studied employing a computer-guided perifusion system. Hypothalami were perifused with Krebs-Ringer bicarbonate medium for 10 or 15 h at a flow rate of 40 microliter/min, and perifusate was collected at 5-min intervals. Basal VIP secretion increased (p0.05) over time, and no differences in release rate were noted between reproductive stages. Basal VIP release during perifusion was episodic throughout each experimental period. Perifusion with dopamine (DA; 10 and 100 nmol/min) in incubating hens stimulated VIP release in a dose-dependent manner. There were no significant differences (p0.05) in VIP release in response to DA stimulation between hypothalamic fragments obtained from nonphotostimulated and incubating birds. The data suggest that 1) a VIP pulse generator appears to be located within the turkey hypothalamus, on the basis of the observed pulsatile release of VIP; 2) hypothalamic secretion of VIP is augmented by removal of inhibitory factors residing outside of the hypothalamus, or by the loss of negative feedback mechanisms that inhibit VIP release; and 3) mechanisms responsible for altering VIP release during different reproductive conditions may lie external to the hypothalamus.

Both chicken gonadotropin-releasing hormones I and II (cGnRH I and II) were detected in abundant quantity by radioimmunoassay of extracts of Japanese quail medial basal hypothalamic/preoptic area (MBH/POA) fragments that included the median eminence (ME) region. However, in radioimmunoassayed extracts of Japanese quail ME alone, the concentration of cGnRH I greatly exceeded that of cGnRH II (approximately 450 pg/ME vs < 10 pg/ME). Likewise, cGnRH I and II were released into perifusates from quail an turkey MBH/POA explants maintained in short-term perifusion. Release of both forms occurred whether or not explants included the ME region, i.e., from quail POA explants did not include the ME or from turkey MBH/POA explants from which the ME region had been dissected out. This indicates that neuropeptides released from areas other than the ME can be a major source of neuropeptides detected in perifusates. Further, release of cGnRH I was altered following the addition of norepinephrine to perfusion media, whereas cGnRH II release was unaffected, again, whether or not explants included the ME. These results demonstrate that the release of neurohemoral substances from perifused explants cannot be assumed to represent regulated secretion from the ME.

The purpose of this study was to examine the role of vasoactive intestinal peptide (VIP) in prolactin (PRL) release in young turkey poults. Poults obtained from hens immunized with keyhole limpet hemocyanin (KLH)-chicken VIP (cVIP-KLH) conjugate or with KLH alone were used in this study. Plasma VIP antibody was tested by means of monoiodinated cVIP. Plasma samples were prediluted (1:100) in 0.05 EDTA PBS and used as a source of primary antibody in a cVIP-binding assay. Antibody levels averaged 50.8 +/- 10.3% at hatch and then declined with age to a level of 5.0 +/- 2.1% after 3 wk. Plasma PRL concentration was lower in cVIP-KLH-immunized poults (p0.05) than in KLH-immunized birds. Exogenous VIP administration at 7 days of age (7.8 micrograms/kg) increased plasma PRL level (p0.05) to a peak value of 359 +/- 32 ng/ml in the KLH-immunized birds. A smaller increase (p0.05) was obtained when the KLH-immunized poults received injections at 2 and 3 wk of age. The PRL response to cVIP administration was not observed in 1- and 2-wk-old poults maternally immunized with cVIP-KLH. Similarly, electrical stimulation of the ventromedial nucleus of the hypothalamus, at 1 and 8 days of age, induced a significant increase in the plasma PRL level of maternally KLH-immunized birds but not in maternally cVIP-KLH-immunized birds. These findings suggest that cVIP is a PRL-releasing factor in young turkey poults, similar to the finding in adult turkey hens.

The neuronal mechanisms that govern prolactin (PRL) secretion in the turkey appear to involve monoaminergic systems. Considerable evidence indicates that serotonin (5-HT), acting centrally, is a potent stimulator of PRL secretion. This study, using birds actively immunized against VIP, tests the hypothesis that 5-HT stimulates PRL secretion by releasing vasoactive intestinal peptide (VIP). Nonimmunized turkeys were injected ip with saline, quipazine (5-HT agonist; 5 mg/kg), methysergide (5-HT antagonist; 8 mg/kg), or methysergide plus quipazine, and VIP-immunized birds were injected with saline or quipazine. Quipazine increased plasma PRL levels from 26.8 ± 7.1 ng/ml at Time 0 to a peak value of 148.1 ± 31.4 ng/ml 2 hr after injection. Pretreatment with methysergide or VIP-immunoneutralization abolished the PRL response to quipazine. Intraventricular infusion of 5-HT (1 nmol/min) caused plasma PRL to rise from a baseline of 16.3 ± 2.6 ng/ml to 85.2 ± 14.3 ng/ml after 30 min in nonimmunized control birds. Serotonin infusion did not induce PRL secretion in the VIP immunized birds. These findings suggest that serotonergic stimulation of PRL secretion in the female turkey requires a functional VIPergic system.

cDNAs encoding the precursor molecule of the turkey LH β subunit (tLHβ) were cloned from a turkey pituitary cDNA library. The nucleotide sequence of the longest of two different tLHβ cDNA clones contained 592 bp, and included 23 bp of the 5′ untranslated region (UTR) and 92 bp of the 3′ UTR in addition to a 477 bp open reading frame that encoded a 39 amino acid leader polypeptide and a 120 amino acid mature apoprotein. Turkey and chicken LHβ sequences shared approximately 92 and 93% nucleotide and amino acid sequence similarities respectively. Northern blot analysis of total cellular anterior pituitary RNA showed that an approximate 800 base transcript hybridized to a 32P-labelled tLHβ cDNA probe. The gonadotrophin-releasing hormone (GnRH)-and prolactin (PRL)-regulated expression of LH and PRL in dispersed pituitary cells was determined by Northern blot analysis of tLHβ and PRL steady-state mRNA levels and by RIA analysis of secreted LH and PRL. GnRH-treated cells showed increased levels of both tLHβ mRNA and secreted LH, whereas mRNA and secreted levels of PRL did not change significantly. Cells treated with PRL showed lower levels of tLHβ and PRL mRNA as well as decreased release of LH and PRL. When cells were treated with both PRL and GnRH, increases in tLHβ mRNA and secreted levels of LH observed with GnRH alone were negated, whereas the decreases in mRNA and secreted levels of PRL observed with PRL alone were abrogated. These findings suggest that PRL can down-regulate tLHβ gene expression and spontaneous release of LH as well as autoregulate PRL gene expression and spontaneous release of PRL, while GnRH appears capable of modulating the effects of PRL-regulated LH and PRL gene expression and spontaneous release.

Vasoactive intestinal peptide (VIP) is a hypothalamic prolactin (PRL)-releasing factor in the turkey. The hypothesis in the present study was that active immunization of turkeys with VIP would neutralize endogenous VIP, decrease circulating PRI, and consequently prevent the expression of incubation behavior. Large white female turkeys were divided into three experimental groups comprising untreated controls, control turkeys immunized with keyhole limpet hemocyanin (KLH), and turkeys immunized with synthetic chicken VIP conjugate (KLH-cVIP). Each turkey received four injections at 4-wk intervals, starting on the day of photostimulation. The immune response, measured by the percentage binding of monoiodinated chicken VIP (cVIP) to plasma at a dilution of 1:1000, averaged 11.8 +/- 2.5% during the reproductive life cycle. Immunization against KLH-cVIP prevented the normal increases of PRL that are associated with the photo-induced reproductive cycle. Over a 21-wk period beginning at photostimulation, KLH-cVIP-immunized birds exhibited a maximal plasma PRL level of 82.2 +/- 29.5 ng/ml, compared to 367.7 +/- 66.6 ng/ml and 227.5 +/- 51.7 ng/ml for non- and KLH-immunized turkeys, respectively. The total number of nest visits per hen during the 147-day experimental period decreased from 320.0 +/- 48.2 in the nonimmunized controls to 180.7 +/- 53.7 and 149.4 +/- 13.1 visits in KLH- and KLH-cVIP conjugate-immunized turkeys. Turkeys that showed an immune response to KLH-cVIP immunization did not exhibit incubation behavior, whereas 54% and 33% of non- and KLH-immunized hens incubated their eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

This study was designed to examine changes in cytochrome P450 17 alpha-hydroxylase (C17) and aromatase (ARO) mRNA contents in the theca layer of preovulatory follicles (POF) as turkey hens transit from egg laying to incubation. Hens were grouped into the following categories: 1) laying hens--laid one egg per day and nested 1-2 times per day; 2) transitional hens--laid one egg per day and nested4 times per day; and 3) Day 1, Day 3, and Day 5 incubating hens--laid no eggs for 2, 4, or 6 days, respectively, and nested4 times per day. Small white follicles (SWF) and the theca layer from the largest (F1) and the third (F3), fifth (F5), and seventh (F7) largest POF were dispersed and challenged with testosterone (T) for 5 h. Relative levels of C17 and ARO mRNA were examined from the theca layers of F1, F3, F5, F7, and SWF. The number of atretic follicles increased from 0 (layers) to 8 (Day 5 incubating hens). Serum LH, progesterone (P), and estradiol (E), but not T, declined on Day 1 of incubation. Basal levels of P, T, and E from theca and SWF cells declined in incubating hens. Both basal and T-stimulated theca and SWF production of E decreased in incubating hens. C17 and ARO mRNA declined in SWF, F7, and F5 during follicular atresia. It is suggested that reduced gene expression of ovarian steroidogenic enzymes may be a partial determinant of reduced circulating sex steroid levels in incubating hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion. Ovine PRL induces incubation behavior in avian species. This study was designed to determine whether VIP can elevate plasma PRL for up to 3 h. Saline or porcine VIP (pVIP; 30, 60, or 150 ng/min) was infused into the median eminence of laying turkeys for 1 h. The 60- and 150-ng doses of pVIP increased plasma PRL (p0.01), whereas the 30-ng dose was insignificant. Pituitary PRL content decreased in pVIP-treated turkeys. Two-hour infusion of 60 or 150 ng chicken VIP (cVIP)/min produced similar elevations of plasma PRL (p0.001), which declined within 80 min. Both treatments induced insignificant increases in pituitary PRL mRNA. Saline or cVIP (30, 60, or 60 [pulsed] ng/min) was infused into the median eminence for 3 h. Sixty ng cVIP/min induced the largest PRL release (p0.05). The pulsatile and low-cVIP treatments resulted in release of a significant amount of PRL in comparison to the saline treatment (p0.01). All cVIP treatments resulted in decreased pituitary PRL content (p0.05). The 60-ng dose increased PRL mRNA (p0.1). This study shows that 60 ng VIP/min causes the maximum PRL release in laying turkeys. However, pituitary PRL content is depleted and PRL synthesis cannot maintain PRL secretion at high levels.

Hyperprolactinemia is associated with incubation behavior in avian species. Increased nesting activity is a major indication of incubation behavior. Vasoactive intestinal peptide (VIP) stimulates prolactin (PRL) secretion from the anterior pituitary. The goal of this study was to induce incubation behavior by stimulating PRL through chronically infusing VIP into the third ventricle of turkey brains. In experiment 1, porcine VIP (pVIP) was infused into the median eminence at a rate of 60 ng/min for 7 days by means of osmotic pumps implanted s.c.. Plasma PRL increased significantly in the pVIP-treated turkeys (p0.001). Although egg laying was not affected by the pVIP infusion, the mean oviduct weight decreased (p0.057). In experiment 2, saline or pVIP (30 or 60 ng/min) was infused into the third ventricle of laying turkeys for 12 days. Both pVIP treatments increased plasma PRL for 9 days (p0.05). The 30-ng pVIP/min infusion decreased nesting activity, plasma LH, ovary and oviduct weight, hypothalamic GnRH I, and anterior pituitary VIP receptors (p0.1). However, ovine PRL infusion (20.8 ng/min) into the same turkey flock increased nesting activity (p0.01). In conclusion, pVIP does not induce incubation behavior in laying turkeys.

An inverse relationship often exists between prolactin (Prl) and LH in avian species. Our study was designed to investigate the relationship between hypothalamic and posterior pituitary vasoactive intestinal peptide (VIP)--an endogenous Prl-releasing peptide--and chicken GnRH-I and GnRH-II. Hypothalamic VIP content was increased after photostimulation, reaching its highest levels in incubating and photorefractory birds. The highest hypothalamic GnRH-I content was in laying hens followed by that in photostimulated and incubating birds. The lowest levels were in the nonphotostimulated birds. Hypothalamic GnRH-II increased after photostimulation, then fell to nonphotostimulated levels during incubation and photorefractoriness. Posterior pituitary VIP content was elevated in response to photostimulation, reaching a peak value in the laying and incubating birds, then declining in the photorefractory hens. Posterior pituitary GnRH-I and GnRH-II content peaked in the incubating birds. Ovariectomy caused a significant reduction in hypothalamic GnRH-I and GnRH-II with no effect on VIP; no changes were found in the posterior pituitary due to ovariectomy. Reducing day length caused a significant decrease in the hypothalamic and the posterior pituitary content of VIP and GnRH-I, and GnRH-II. Ovine Prl (oPrl) administration to laying hens reduced the hypothalamic VIP and GnRH-I and GnRh-II content. Posterior pituitary GnRH-I content was also reduced. Although GnRH-II levels were reduced by Day 4 of injections, they rose to peak levels by Day 14 of oPrl administration. Posterior pituitary VIP content was not altered by oPrl.

A series of experiments were conducted to elucidate the role of the ovary in incubation behavior-associated luteinizing hormone (LH) suppression. Ovariectomy (Ovx) increased (p0.05) serum LH levels in nonphotostimulated, laying and photorefractory turkeys but not in incubating birds (p0.05). Ovx had no effect on intramuscularly injected mammalian luteinizing hormone-releasing hormone (4 micrograms/kg i.m.)-induced LH in incubating hens, but enhanced the LH response in laying hens. Serum LH and prolactin (Prl) were unaffected by Ovx, and nest deprivation (ND) decreased Prl levels (p0.05) with no effect on serum LH of incubating turkeys. However, serum LH increased (p0.05) and Prl decreased in Ovx-ND birds. Prl mRNA abundance (11.9 +/- 1.2 ng/microgram total RNA) decreased following Ovx (3.4 +/- 0.4 ng/microgram total RNA) or ND (3.6 +/- 0.5 ng/microgram total RNA). Nest deprivation increased LH beta mRNA (2.5-fold) which was further increased (4.8-fold) by Ovx. Hypothalamic GnRH-I and GnRH-II contents increased (p0.05) in Ovx-ND turkeys. We conclude that serum LH suppression during incubation behavior requires ovarian participation acting synergistically with elevated Prl and/or nesting stimulus on hypothalamic GnRH, and that the concentration fo LH beta mRNA may be a limiting factor in LH secretion.

The effect of ovine prolactin (oPRL) administration to laying and incubating turkey hens was studied. In experiment one, five treatment groups (n = 6) of laying hens received injections of vehicle or oPRL (4 mg/bird/day) for 2, 4, 8, or 14 days. Hypothalamic vasoactive intestinal peptide (VIP) content decreased to its lowest level (p0.05) by Day 2 of oPRL injection. Serum turkey PRL decreased by Day 8 of injection, reaching nadir by Day 14. Similar to the decline in hypothalamic VIP content, the maximal decline in the number of anterior pituitary VIP binding sites was achieved by Day 2 of oPRL administration. Hypothalamic GnRH-I content decreased after 2 days of oPRL injection and remained low through Day 14 of the experiment. GnRH-II levels declined with time, reaching significantly lower levels after 8 days of injections, and remained low through Day 14. Plasma LH levels also declined (p0.05) after Day 14 of oPRL administration. In experiment 2, two groups (n = 6) of incubating birds were used: controls receiving injections of vehicle only and birds receiving injections of oPRL (4 mg/bird/day) for 10 days. Exogenous oPRL had no effect on hypothalamic VIP, GnRH-I or II, anterior pituitary VIP binding sites, or plasma turkey PRL or LH. The findings suggest that in laying hens, PRL inhibits its own secretion by acting on both the hypothalamus and the anterior pituitary; this phenomenon does not occur in incubating birds. Furthermore, we provide evidence that pRL acts centrally to reduce LH levels by reducing GnRH levels in the hypothalamus.

Vasoactive intestinal peptide (VIP) is a prolactin-releasing factor in turkey hens. Membranes from anterior pituitaries of turkey hens were used to characterize VIP receptors. Using HPLC-purified monoiodinated VIP, we found specific VIP receptors in the anterior pituitary glands. Binding was saturable and was time- and temperature-dependent. Scatchard analysis of competitive binding studies indicated two binding sites, a high-affinity binding site (Kd1) of 6.6 +/- 1.8 pM and maximum binding (Bmax1) of 1.52 +/- 0.2 pM, and a low-affinity binding site (Kd2) of 542 +/- 200 pM and Bmax2 of 15.8 +/- 8.0 pM. Binding of VIp to pituitary membranes was specific, as compared to other peptides of the glucagon family. The rank order of potency of the peptides tested was chicken VIPporcine VIPpeptide histidine isoleucinesecretinglucagongrowth hormone-releasing factor. Two binding sites were found in all the examined reproductive stages. The lowest binding site levels were found in nonphotostimulated and photorefractory birds, followed by photostimulated birds and layers; highest levels were found in incubating birds. Nest deprivation significantly reduced Bmax1 levels without changing hypothalamic VIP content. These results suggest the involvement of the anterior pituitary VIP receptors in the regulation of prolactin secretion from the pituitary gland.

In the turkey, the onset of incubation behavior is associated with decreased luteinizing hormone (LH) and increased prolactin (PRL). This study was designed to clarify the contribution of the hypothalamus and the anterior pituitary to the changes in plasma LH during the reproductive cycle of the turkey. Plasma LH and PRL were measured in anesthetized turkey before, during, and after electrical stimulation in the median eminence. In one experiment, luteinizing hormone releasing hormone (LHRH; 4 micrograms/kg) was injected intramuscularly 30 min after termination of electrical stimulation, and blood samples were obtained 5, 10, 20, and 30 min after injection. Electrical stimulation in the median eminence significantly increased (P0.05) plasma LH of laying (LAY), nest-deprived, previously incubating (NEST DEP), and photorefractory (REFRAC) hens, but not of photosensitive short-day (SHORT DAY) birds (P0.05). Plasma LH of LAY hens peaked at 4.06 +/- 0.78 ng/ml from a prestimulation baseline of 2.30 +/- 0.21 ng/ml and that in NEST DEP birds increased from 1.08 +/- 0.18 ng/ml to 2.57 +/- 0.53 ng/ml. Administration of LHRH increased plasma LH levels in SHORT DAY, LAY, and NEST DEP hens with the increase being 2.0-, 2.5-, and 6.1-fold, respectively. Electrical stimulation in the median eminence increased plasma PRL (P0.05) in all the reproductive groups tested, with peak response being greatest for NEST DEP birds (661 +/- 126 ng/ml) followed by LAY (317 +/- 26 ng/ml), REFRAC (50 +/- 7 ng/ml), and SHORT DAY (39 +/- 12 ng/ml) hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood samples were taken from adult male and female geese, and from gonadectomized (GX), thyroidectomized (TX) and gonadectomized+thyroidectomized (GX+TX) ones during the reproduction peak period (March 16), at the beginning of photorefractoriness (June 14), in the second half of the photorefractory period (August 14), and at the beginning of the postrefractory period (October 2). Surgeries were carried out at the age of 10-13 weeks. The birds were kept under natural light conditions. From the blood plasma prolactin (PRL), luteinizing hormone (LH), testosterone (T), progesterone (P4), 17 beta-oestradiol (E2) as well as thyroxine (T4) and triiodo-tironine (T3) were determined by RIA methods. At the beginning of photorefractoriness in intact geese the LH and E2 levels significantly decrease, relative to sexually active period, whereas the P4 remains at a high level. In ganders the LH shows only a slight decrease but the T level is significantly lower than in spring. The PRL, T4 and T3 levels increase after reproduction and give a peak value in both sexes. In both GX ganders and geese decreased T, P4 and T3 levels are observable and the PRL is decreased in females, and the LH is increased in both sexes. Gonadectomy does not influence the E2 in females, the PRL in males and the T4 in both sexes. In TX birds the PRL is higher in March and lower in June than the control level, but these changes are significant only in females. In TX females the P4 level is lower during reproduction and at the beginning of photorefractoriness. The T and E2 levels do not change during the photorefractoriness. In the second half of photorefractoriness a low PRL and P4 level, an increasing LH, T and medium high T4 and T3 levels characterized the intact male and female geese. In GX animals an increase of LH levels is occurred in both sexes. The T4 is higher in castrated-, and lower in ovarectomized geese. In TX birds the P4 is higher than in controls, but the difference is significant only in males. The levels of PRL, LH, T and E2 remain unchanged in TX animals. At the beginning of the postrefractory phase the T (in males) and the P4 and the T4 level increase in both sexes. The PRL and LH show a low value. In GX animals the high LH level refer to the increased sensitivity of hypothalamo-gonadotropic system, because of the absence of negative feed-back of sexual steroids.4+ in both sexes and a high thyroid hormone level and a transitional slight reactivation of gonadotropic-gonadal system occur then.

The transition from egg laying to incubation activity in birds is associated with a dramatic rise in serum prolactin levels. To further our understanding of the regulation of prolactin gene expression in birds, a cDNA clone encoding turkey Pit-1/GHF-1 was isolated. The turkey cDNA, designated tPit-1/GHF-1, was 1,123 nucleotides in length and encoded a protein of 327 amino acids, including a conserved 80-amino-acid POU-specific domain and a 60-amino-acid POU homeodomain. tPit-1/GHF-1 POU-specific domain and POU-homeodomain showed 94-95% amino acid identity with the corresponding rat Pit-1/GHF-1 domains. At its amino terminus, tPit-1/GHF-1 contained a 26-amino-acid insertion comparable to that found in the rat variant isoform, Pit-1 beta. Two other insertions of 38 and 7 amino acids were present and were not found in the mammalian protein. Levels of tPit-1/GHF-1 mRNA in pituitary tissue were examined at different phases of the turkey reproductive cycle by Northern blotting. tPit-1/GHF-1 mRNA was expressed as a 3.5-kb transcript, whose abundance remained relatively constant throughout the reproductive cycle. Thus, the dramatic rise in prolactin mRNA, observed during hyperprolactinemia in incubating turkey hens, was not associated with a concomitant increase in tPit-1/GHF-1 gene expression.

The relationships of prolactin (PRL) and LH messenger (m) RNA to serum and pituitary content were determined for turkey hens at different phases of the reproductive cycle. In the nonphotostimulated, reproductively inactive hen, serum and pituitary PRL content and pituitary PRL mRNA levels were low. All three PRL values rose after photostimulation and peaked during the incubation phase. Relative to nonphotostimulated hens, hyperprolactinemic incubating hens showed 220-, 11-, and 57-fold increases in serum PRL, pituitary PRL content, and pituitary PRL mRNA levels, respectively. These peak levels declined 80-, 3-, and 6-fold, respectively, in photorefractory hens. In contrast to PRL levels, serum LH, pituitary LH, and pituitary LH beta-subunit mRNA levels did not change as dramatically. Serum LH showed no significant changes for the different reproductive phases. Pituitary LH peaked after photostimulation and declined to its lowest level in incubating hens. Pituitary LH-beta mRNA abundance was highest in photostimulated and laying hens and lowest in incubating and photorefractory hens. These results demonstrate that the abundance of LH-beta and PRL mRNA shows an inverse relationship in photostimulated/laying and incubating turkey hens.

The aims of this study were: (1) to examine whether the posterior pituitary contains prolactin releasing factor (PRF) activity, (2) to determine to what extent known neurohypophyseal peptides contribute to this activity, and (3) to compare posterior pituitary PRF activities of hens in different reproductive stages. Anterior pituitary cells derived from juvenile female turkeys were incubated with posterior pituitary extracts or test substances for 3 hr. Posterior pituitary extracts (0.1-0.8 equivalent) contained a potent substance(s) which stimulated PRL release in a concentration-dependent manner (2.4 +/- 0.08 to 6.5 +/- 0.23 micrograms/500 k cells). Arginine vasotocin (AVT) and vasoactive intestinal peptide (VIP) antisera (1:500) completely abolished the PRL-releasing activities of their respective peptides but partially reduced (P less than 0.05) the PRF activity of the posterior pituitary (AVT, 19.9%; VIP, 55.1%). Mesotocin antiserum did not alter (P greater than 0.05) PRL release induced by posterior pituitary extract. Posterior pituitary extract (0.01-0.5 equivalent) from hens in each of the various stages of the reproductive cycle induced a concentration dependent PRL release. The 0.5 posterior pituitary equivalent dose from reproductively quiescent (nonphotostimulated), laying, photorefractory, and incubating hens increased PRL release 2.4-, 2.9-, 3.8-, and 11.1-fold, respectively. The turkey posterior pituitary contains a potent PRF activity, partially accounted for by VIP and AVT, at the assayed concentrations, which varies with the reproductive cycle.

Controversy exists regarding the role of dopamine (DA) in the regulation of avian prolactin (PRL) secretion. Consequently, we injected apomorphine, a DA agonist, and pimozide, a DA receptor blocker, into laying and nest-deprived incubating turkeys and studied their effect on PRL secretion before (-20, -10, 0 min), during (5, 10, 20, 30 min), and after (5, 15, 30 min) electrical stimulation in the ventromedial nucleus of the hypothalamus. Apomorphine (10 mg/kg, ip) completely abolished the electrical stimulation-induced PRL increase in both laying and nest-deprived incubating hens. Pimozide (2 mg/kg, ip) potentiated electrical stimulation-induced PRL secretion in laying hens. In the two pimozide experiments, peak responses were 10.9-fold for the pimozide-treated group vs 2.9-fold for the control group, and 5.4-fold for the pimozide-treated group vs 2.6-fold for the control group. In nest-deprived incubating hens, PRL response to electrical stimulation was unaffected by pimozide treatment. These data support the concept that DA is inhibitory to the neuroendocrine system which stimulates PRL secretion in laying hens. In incubating hens, the dopaminergic inhibition is diminished, allowing for the increased PRL level observed during incubation.

In the turkey, the onset of incubation behavior is associated with altered ovarian steroidogenesis, ovarian regression, decreased, LH secretion, and increased serum prolactin (Prl) levels. To clarify the relative contribution of circulating LH and Prl to the initiation of ovarian regression, laying hens were exposed for 0, 3, 7, or 14 days to a forced molting procedure (exposure to reduced day length of 6L:18D and removal of feed and water for the initial 3 days) that induces ovarian regression and decreased LH levels but does not increase Prl levels. On each of these days, hens were killed and granulosa and theca interna cells from the largest (F1) and fifth largest (F5) preovulatory follicles and total cells from the small white follicles (SWF) were incubated for 5 h in the presence or absence of ovine LH (oLH; 0-1,000 ng/ml). Force-molted hens exhibited diminished levels of circulating LH, Prl, progesterone (P), androgen (A), and estradiol (E) by Day 3 of treatment. Ovarian atresia began in F1 by the third day of treatment, and included F1 and F5 by the seventh day. No preovulatory follicles were present on the fourteenth day. With both F1 and F5 granulosa cells, production of P in the presence of oLH was initially enhanced (Day 3) and later absent (Day 7). In contrast, production of A by F5 theca interna cells in the presence of oLH was initially suppressed (Day 3) and then returned to pretreatment levels (Day 7).(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism regulating ovarian regression during incubation behavior in the domestic turkey has not been elucidated. This study was designed to determine whether ovarian steroidogenic potential is depressed during gonadal regression associated with the onset of incubation behavior. Hens were housed in floor pens equipped with trap nests that were checked 7 times per day. Hens were grouped, according to nesting frequency and egg production, into the following classifications: laying (laid an egg every day and trapped in the nest only once/day); transitional (laid an egg every day but trapped in the nest 4 or more times/day); and Day 1, Day 3, and Day 5 incubating (no egg for 2, 4, or 6 days, respectively, while trapped in the nest at least 4 times/day). Follicular atresia was evident in the largest preovulatory follicle (F1) in transitional hens, extensive in F1 through the third largest follicle (F3) in Day 1 incubating hens, and extensive in F1 through F7in Day 3 incubating hens. Levels of circulating LH, progesterone (P), androgen (A), and estradiol (E) decreased in transitional hens relative to concentrations in laying hens and remained low thereafter. In contrast, levels of prolactin were greater in Day 3 and Day 5 incubating hens than in laying, transitional, or Day 1 incubating hens. Basal production of P by F1 granulosa cells was lower from Day 1 incubating hens than from the other groups. Production of P in response to porcine-luteinizing hormone (pLH) was greater by cells from transitional and Day 1 incubating hens than from those of laying hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Large White Nicholas male turkeys were reared at two stocking densities (.21 or .46 m2 per bird) and fed one of four diets: 1) control corn and soybean (mash) with 1% fat (CSM); 2) as Diet 1, pelleted (CSP); 3) as Diet 1 with supplemental fat increasing from 1 through 8% with age (CSF); and 4) as Diet 1 with barley at 0, 20, 35, 50, and 65% during successive 4-wk periods (CSB). The turkeys were reared in four environments: (A) intermittent light schedule [4(2 h light (L):4 h dark D))] with temperature at 7 or 21 C during light and dark photoperiod, respectively; (B) and (D) with intermittent light (2L:4D) with a constant 21 and 7 C temperatures, respectively; (C) continuous light cycle (18L:6D) with temperatures as in Environment A. At 20 wk of age, two turkeys per replicate pen, were killed for determination of body composition and meat yield. Compared with turkeys fed CSM diet, those on CSF and CSP diet had increased percentage carcass fat. Meat yield per bird and percentage carcass fat were greater for turkeys reared at .46 m2 per bird compared with rearing at .21 m2 per bird. Pelleting and fat supplementation resulted in significantly increased amounts of breast meat and leg compared with CSM. Breast meat yield (percentage) and amount were greater at 7 C (Environment D) than at 21 C (Environment B) and the cycling regimen (Environment A). Percentage abdominal fat was greatest at 7 C. Interactions of environment and diet were detected for breast meat yield percentage (P less than .023) and weight (P less than .036). Diet type had no effect on percentage breast meat or weight in Environment C. An increased amount of breast meat was obtained by feeding CSP in Environments A, B, and D, and dietary fat supplementation increased breast meat yield in Environments A and D over CSM treatment.

The performance of 1,312 male market turkeys (Large White, Nicholas strain) from 0 to 20 wk of age fed diets varying in feed form and energy level was measured under two stocking densities (.21 or .46 m2 per bird) and four lighting and temperature programs. The four diets were 1) corn and soybean meal with 1% supplemental fat, mash (CSM); 2) as 1, pelleted (CSP); 3) as Diet 1 but with 1, 2, 4, 6, and 8% supplemental fat during 0 to 4, 4 to 8, 8 to 12, 12 to 16, and 16 to 20 wk of age, respectively (CSF); and 4) as Diet 1 but with barely included at 0, 20, 35, 50, and 65% during the respective 4-wk age periods (CSB). The four light and temperature programs were 1) Environment A with intermittent light [4 [2 h light (L):4 h dark (D)]] in combination with cycling temperature at 7 and 21 C during light and dark photoperiod, respectively; Environment B with intermittent light, 21 C; Environment C with continuous light (18L:6D) and cycling temperature of 7 to 21 C; and Environment D with intermittent light, 7 C. Lighting and temperature programs started at 1 and 4 wk of age, respectively. Body weights at 20 wk of age decreased (P less than .05) with increasing temperature (13.86 versus 12.26 kg for Environments D and B, respectively) with cycling temperature intermediate (13.51 kg for Environment A). Intermittent light (P less than .05) improved BW and feed conversion by 3.4 and 2.0%, respectively, compared with continuous light. Rearing males at .21 m2 per bird versus .46 m2 per bird decreased weight (P less than .05) by 5.5%. Twenty-week BW of males fed the CSP (13.52 kg) and CSF (13.58 kg) diets were greater (P less than .05) than those fed CSM (12.90 kg) and CSB (12.69 kg) diets. Significant (P less than .05) interactions between diet, environment, and density were not detected for most performance characteristics. Environmental measurements indicated higher dust and ammonia levels in the warm environment (B). Isolates of aspergillus and incidence of airsacculitis at time of processing were greatest in Environment B.

A direct effect of prolactin (Prl) on gonadotropin secretion has been suggested but not convincingly demonstrated. The secretion of LH in response to photostimulation (phs) and ovariectomy (ovx) was evaluated in adult female turkeys that had received injections of ovine Prl (124 IU/bird/day for 14 days). In experiment 1, oPrl administration initiated on the day of ovx and phs in reproductively quiescent birds suppressed (p less than 0.05) the elevated LH from a peak level of 11.7 +/- 3.5 ng/ml to 5.1 +/- 0.8 ng/ml in ovx hens. The photo-induced LH increase was unaffected by the oPrl treatment in intact birds. In experiment 2, the oPrl treatment was initiated 7 days before ovx and/or phs. This treatment blunted the peak increase in LH level that follows phs in intact (p less than 0.05) and in ovx (p less than 0.05) hens. In both experiments, onset of lay following phs was delayed (p less than 0.05) in the oPrl-treated groups (29.4 +/- 0.9 days vs. 22.3 +/- 0.9 days; 34.8 +/- 0.5 days vs. 25.0 +/- 0.9 days). In experiment 3, administration of oPrl after ovx of laying hens suppressed the LH rise at essentially all sampling times tested. At the end of the experimental period, 6 of the 7 sham-operated, oPrl-treated laying hens, but none of the sham controls, displayed incubation behavior and had Prl levels of 1020 +/- 370 ng/ml compared to 34 +/- 7 ng/ml in vehicle-treated controls. The results suggest a role for Prl in incubation behavior and LH secretion in the turkey.

1. The incidence of broodiness was four times as high among turkey hens fed a complete control diet than among hens allowed to self-select their diet from two different feed sources, one being relatively high in protein and the other relatively high in energy (i.e. split-diet). 2. Among non-broody birds, hens fed the split-diet had a significantly lower serum prolactin concentration in the third month of production as compared to control hens. 3. Hens in their second season of egg production had significantly lower serum luteinizing hormone concentrations during the latter stages of egg production than did first season hens.

During incubation, female turkeys exhibit elevated circulating prolactin (PRL) which may be the result of enhanced pituitary responsiveness to vasoactive intestinal peptide (VIP). This hypothesis was tested by comparison of spontaneous and porcine VIP-induced PRL secretion from anterior pituitary cells of hens in various reproductive conditions. The effect of VIP and luteinizing hormone releasing hormone (LHRH), alone and in combination, on luteinizing hormone (LH) secretion was also examined. Incubation with pVIP (10(-10) to 10(-6) M) significantly stimulated PRL secretion at all incubation times tested (1-5 hr). This increase was greatest in cells from incubating hens, with those from laying, photorefractory, and quiescent (nonphotostimulated) hens secreting successively less PRL. These responses were obtained when spontaneous PRL secretions were compared. VIP induced approximately a similar 1.5-fold increase in LH secretion, in all reproductive groups. Also, VIP enhanced LHRH-induced LH secretion (1.2- to 1.6-fold; P less than 0.0001). It is concluded that PRL secretion in vitro by pituitary cells from turkey hens in various reproductive stages reflects the circulating levels of PRL at these stages.

Interferon-gamma (IFNgamma) has been demonstrated to have potent stimulatory effects on parameters of cell-mediated immunity in chickens (11). Protection of neonatal leghorn chickens against infection by invasive salmonellae has been associated with enhanced cell-mediated indices of immunity (5). The present investigation evaluated the effect of recombinant-turkey (rt) IFN-gamma on protection of neonatal leghorn chicks from Salmonella enteritidis (SE) organ invasion after experimental challenge in three experiments. In Expt. 1, intraperitoneal (i.p.) administration of 25 microg rtIFNgamma per chick 30 min prior to per os SE challenge resulted in a 35% reduction (P < 0.01) in SE organ invasion when compared with control (vehicle injected) chicks 24 hr post-SE challenge. However, i.p. administration of 2.5 microg rtIFNy per chick was not efficacious in reducing SE organ invasion. In Expt. 2 and Expt. 3, i.p. administration of 13.75 microg rtIFNgamma per chick 30 min prior to per os SE challenge resulted in significant reductions of 38.4% (P < 0.025) and 31.58% (P < 0.01), respectively, in SE organ invasion as compared with control chicks 24 hr post-SE challenge. Administration of 2.5 or 25 microg rtIFNgamma per chick i.p. had no effect on SE organ invasion in either Expt. 2 or Expt. 3 24 hr post-SE challenge. Additionally, i.p. administration of rtIFNgamma 30 min prior to SE challenge in Expt. 2 and Expt. 3 was not associated with protection against SE organ invasion when organ culture was performed 72 hr postchallenge. Further, the oral administration of 25 microg rtIFNgamma per chick was not efficacious in conferring protection against SE organ invasion at 24 or 72 hr postchallenge when this route of administration was evaluated in Expt. 2. Similarly, the subcutaneous administration of a potential repository injection of 13.75 or 25 microg rtIFNgamma per chick did not protect chicks against SE organ invasion when evaluated 72 hr postchallenge. These data indicate a potential acute immunostimulatory activity of rtIFNgamma in chickens experimentally challenged with SE. Further, these experiments, although preliminary, are suggestive of the potential involvement of IFNgamma in cell-mediated or innate mechanisms of protective immunity against salmonellosis in chickens.

The involvement of central biogenic amines in the mechanisms controlling photoperiodically-induced testicular development in Coturnix quail were studied employing pharmacological approaches. Daily administration of alpha-methyltyrosine (MT), which blocks catecholamine (CA) biosynthesis, to 6-week-old quail exposed to long daily photoperiods markedly depleted brain dopamine (DA), norepinephrine (NE) and epinephrine (E). This was associated with a partial suppression of testicular growth 7 days after light stimulation. Combined treatment with MT and L-dihydroxyphenylalanine (L-DOPA), a precursor of DA, NE and E, elevated the monoamine levels in the brain and prevented the blocking effect of MT on testicular growth. Selective blockade of NE and E biosynthesis with diethyl-dithiocarbamate (DDC) depleted both NE and E, while it elevated DA level. Furthermore, such treatment reduced testicular weight. In DDC-treated birds, D,L-dihydroxyphenylserine (DL-DOPS) administration, which bypasses the DDC block, restored only brain NE level and reversed the blocking action of DDC on testicular weight. It is concluded that central NE plays a role in transformation of the photoperiodic information affecting gonadal development in Coturnix quail.

Cytosolic progesterone receptors (PRcs) from the reproductive tract of the female turkey were analyzed by high-performance liquid chromatography using a diethylaminoethyl (DEAE) ion-exchange column. PRcs from oviduct tissue of laying, incubating, photorefractory and short-day turkey hens were compared. In general, three types of PRcs were identified: Receptor I, a partially displaceable species that was eluted at a 0.13 M salt concentration; and Receptors II and III, which were two specific binding species eluting at 0.23 M and 0.26 M, respectively, in the subdivided tissue from the laying hen oviduct, Receptor I was the major PRc species of the isthmus and Receptor III was the only receptor present in the uterus. The infundibulum and magnum each contained a small amount of Receptor II and a substantial amount of Receptor III. The whole oviduct of incubating hens contained a greater proportion of Receptor I than Receptor II or III, and these last two receptor types were present in equal quantity. The whole oviduct of the short-day hens had an equal distribution of the three receptor types. In the presence of sodium molybdate, an inhibitor of phosphatase and protease, only one sharp Receptor II species was seen in the magnum and uterus of the laying hen oviduct and in the whole oviducts of incubating and short-day hens. The transformation of Receptor II to Receptor III in the absence of sodium molybdate was facilitated by the aging of cytosol at 0-4#{176}C. Our results show that (1) three PRc forms are present in the reproductive tract of the turkey, (2) both qualitative and quantitative changes are observed in different sections of the reproductive tract, and (3) quantitative changes of receptor forms are noted for reproductively active and quiescent hens. We suggest that Receptor III isa modified form of the molybdate-stabilized Receptor Ii. Receptors II and III are possibly associated with the inactive and active stages of turkey reproduction, respectively.

The monoamine oxidase inhibitor tranylcypromine (TCP) increases brain dopamine (DA), norepinephrine (NE) and serotonin (5-HT) levels and inhibits photoperiodically-induced testicular growth in quail. Blockade of catecholamine synthesis by n-methyl-tyrosine (MT) in TCP treated quail preferentially elevates 5-HT levels and does not interfere with TCP inhibition of the gonads, however, treatment with parachlorophenylalanine (PCPA) reduces 5-HT and DA and antagonizes the action of TCP. Treatment with PCPA alone causes further augmentation of testicular response to photostimulation and reduces 5-HT and DA levels in the brain, whereas 5-hydroxytryptophan (5-HTP) administration elevates central 5-HT stores and partially inhibits testicular development. The results are consistent with the view that 5-HT may have an inhibitory effect on the process of gonadal development; in addition, an inhibitory influence of DA may also be involved.

The detachment process of the domestic chick from its mother, or any other imprinting object occurs between the sixth and tenth week after hatching. The present study (Experiment I), examines whether the detachment process parallels endocrine events that precede prepuberty. Immediately upon hatching, groups of heavy strain chicks were imprinted to a colored foam rubber ball for 72 hours. The bond between these chicks and the imprinting object was then tested, and plasma LH and testosterone were assayed once a week until the chicks were 10 weeks of age; the sexual development of chicks of the same strain was studied at the same time. At the outset of the detachment period (5–7 weeks) an increase in plasma testosterone and a decrease in plasma LH was found. In addition, the comb and testes showed a definite weight increase while the bursa of Fabricius showed a significant decline in weight. In Experiment II, the beginning of the detachment process was induced by injecting 3 to 4 week old chicks with testosterone-propionate, estradiol-benzoate and 5α-dihydrotestosterone. Our evidence therefore appears to demonstrate that testosterone and its metabolites induce the detachment process by the same mechanism used to stimulate sexual behavior in juvenile chicks.

Serum prolactin (PRL) and luteinizing hormone (LH) levels were measured in White Leghorn hens induced to pause by fasting and exposure to 8L:16D photoschedule. Both PRL and LH levels declined during the fast and increased upon refeeding. Prolactin levels changed primarily in response to the fasting/refeeding component of the pause-inducing procedure, as exposure of non-fasted hens to an 8L:16D photoschedule exerted little effect on serum PRL levels. Injections of ovine prolactin during the pause-inducing procedure significantly reduced the subsequent rate of loss of primary wing feathers, suggesting that in certain physiological states, PRL may function to suppress molting.

Prolactin (Pr!) is released by electrical stimulation in the turkey hypothalamus and preoptic area (POA). Possible trajectories for POA efferents to the median eminence (ME) were tested by placing lesions in the POA, the lateral hypothalamus (Lily), or the ventromedial nucleus of the hypothalamus (VMN) of reproductively quiescent turkey hens, then subjecting them to long photoperiods while monitoring their blood Pr! levels and nesting activities. in addition, lesions were made in the VMN of a group of incubating hens to learn whether the lesions would cause the elevated Pr! levels to fall or interfere with incubation behavior. Lesions in medial POA, Lily, or VMN prevented the onset of incubation and prevented the large rise in Pr! associated with it. However, these lesions did not interfere with the initial, more gradual Pr! rise caused by increasing daylengths. Lesions in Lily or VMN appeared to interfere with a pathway lying late rally from POA to ME. Electrical stimulation in medial POA, which caused an increase in circulating Prl,fai!ed to do so in hens with Lily or VMN lesions. Lesions in the VMN of incubating hens caused them to leave the nest and suffer a large decline in Prl, both within 48 h. it is tentatively suggested that incubation behavior and its associated elevated Prl are prevented by the POA lesions and that lesions in LJly or VMN, which mimic POA lesion effects, interfere with POA efferents projecting to ME.

Three experiments were conducted to evaluate the effect of immobilization on plasma prolactin (PRL) levels in the immature turkey. Acute immobilization for 120 min resulted in elevated PRL levels (P less than 0.05) starting 15 min after the onset of immobilization. Release from immobilization caused PRL levels to return to those of the nonimmobilized controls by 120-180 min following replacement of the turkeys in cages. Repeated immobilization for 3 or 5 consecutive days diminished PRL response (P less than 0.05) to subsequent immobilization. It is suggested that the PRL controlling mechanism(s) of the young turkey is both susceptible and able to habituate to changes induced by immobilization stress.

The age at which photosexual responsiveness occurs in juvenile male turkeys was investigated by determining the age at which a postcastration rise in serum luteinizing hormone (LH) was first evident. Birds were subjected to short (6L:18D) and long (16L:8D) photoperiods. In birds exposed to long photoperiod there was no castration-induced LH rise in 2-, 4-, and 6-week-old turkeys, but there was in such birds by 7–8 weeks. No postcastration increase occurred if castrated turkeys were held under 6L:18D. When 10-week-old castrated turkeys were switched from a long to a short photoperiod their serum LH levels fell to that of intact controls. Administration of synthetic luteinizing hormone-releasing hormone (LHRH) to 6-week-old turkeys increased serum LH about ninefold above the preinjection values. Hypothalamic LHRH content of 6- and 10-week-old males were similar. Thus, it is proposed that the absence of LH response to castration in these young birds is due to a failure to transduce or transmit the photoperiodic information necessary to activate the hypothalamic-pituitary axis.

The metabolism of dopamine (DA), norepinephrine (NE), epinephrine (E), and serotonin (5-HT) was determined in the brains of female turkeys before and after light stimulation, and during various phases of reproductive activity. Ten days of light stimulation increased oviduct weight 3.5 fold (P

1. Furazolidone or nitrofurazone were given orally to laying turkeys at doses of 7.5, 15 or 30 mg/kg for 7 d. Plasma concentrations of luteinising hormone (LH), prolactin (PRL) and egg production were measured before, during and after treatment. 2. Both drugs produced dose-dependent decreases in LH concentration which were statistically significant at doses of 15 and 30 mg/kg. Plasma PRL concentration was significantly increased in birds receiving 15 or 30 mg/kg of nitrofurazone, and tended to increase in the other treated groups, but this was not statistically significant. 3. Egg production was lowered in a dose-dependent manner by both drugs. However, nitrofurazone appeared to be more potent in reducing egg production than furazolidone. 4. Birds given 15 mg/kg of either drug were injected intramuscularly with luteinising hormone releasing hormone (LHRH) at a dose of 5 micrograms/kg and blood was collected immediately before and 30 min after LHRH administration. 5. Nitrofurazone significantly reduced the rise in LH induced by LHRH. Seven days after withdrawing the drug, the LHRH-induced LH release was not significantly different when compared to that in the control group or that seen on day 7 of treatment.

Vasoactive intestinal peptide (VIP) has potent PRL-releasing activity, but its physiological role in the regulation of PRL release during the avian reproductive cycle is not known. We used indirect immunofluorescence to determine if changes in hypothalamic VIP are associated with the shifts in circulating PRL during the reproductive cycle of the domestic turkey. In the naturally hyperprolactinemic incubating hen, the majority of VIP immunoreactivity (VIP-IR) existed within neurons of the infundibular nuclear complex (INF) and fibers in the external layer of the median eminence. Within the INF, the numbers of VIP-IR cells increased during the cycle, paralleling increases in serum PRL. In the reproductively inactive, nonphotostimulated hen with low serum PRL, essentially no positive cells were noted, whereas the incubating hen exhibited 32.1 +/- 2.2 cells/pair of adjacent sections in the anterior INF and 59.6 +/- 2.0 cells in the posterior INF. Exposure of inactive hens to a stimulatory photoperiod resulted in a 2.6-fold increase in serum PRL with the appearance of VIP-IR cells in the INF. During laying and incubation, further increases were observed in the number of positive cells in the INF and serum PRL as well as a greater fiber density in the median eminence. To further examine the association between changes in VIP-IR and serum PRL, circulating PRL was artificially lowered by depriving incubating hens of their nests for 0, 2, 5, and 10 days. On day 2 of nest deprivation, serum PRL declined markedly to 12% of day 0 levels, with VIP-IR cell numbers at 64% and 46% in the anterior and posterior INF, respectively. By day 10, birds exhibited cell numbers in the INF averaging 20% of those observed in the day 0 incubating hens, with serum PRL at 6% of day 0 levels. The results of these studies indicate a possible causal relationship between hypothalamic VIP and changes in PRL secretion during the avian reproductive cycle, providing a basis for further research on the importance of this peptide as well as factors responsible for the modulation of its expression in hypothalamic INF neurons.

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels. 2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca. 3. Doses of 0.1 and 1.0 mU MT/min/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone. 4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature. 5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT. 6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects aldosterone secretion. These neurohypophysical peptides are involved in thermoregulation.

To determine what role pituitary responsiveness plays in the suppression of gonadotropin level during incubation in the turkey, the ability of the pituitary to release luteinizing hormone (LH) in response to luteinizing hormone-releasing hormone (LHRH) was compared in incubating, laying, and photorefractory birds. In all three groups, the i.m. injection of LHRH (4 micrograms/kg) increased serum LH levels; however, the LH response was markedly enhanced in the incubating turkeys as compared with the laying (6.6-fold increase over preinjection levels vs. 1.9-fold; p less than 0.05) or the photorefractory birds (9.7-fold vs. 3.1-fold; p less than 0.05). The LHRH-induced LH release was also determined in turkeys as they shifted from the laying to the incubating phase of the reproductive cycle. This response increased (p less than 0.05) in magnitude as the birds started to incubate. The high prolactin level of incubating turkeys does not have a depressing effect on LHRH-stimulated LH release; thus, impaired LH response to LHRH is not a mechanism involved in the diminished gonadotropin secretion of incubating turkeys.

Pimozide, a dopamine receptor blocking agent, was administered to turkey hens which were judged, on the basis of an increased nesting frequency, to be in transition between the laying and broody phases of a reproductive cycle. Treatment of hens with pimozide, either by subcutaneous injection or oral administration significantly decreased daily nest visits and significantly increased daily egg production compared to control hens. However, when hens were given pimozide twice weekly for 8 weeks without regard to nesting frequency, no treatment effect was discernable. Thus, the efficacy of pimozide's effect on broodiness is related to time of administration during the reproductive cycle.

Serum prolactin (PRL) and luteinizing hormone (LH) levels from mature female turkeys were determined following ovariectomy and daily subcutaneous injections for 4 or 9 days of 0.002-2.0 mg/kg estradiol benzoate (EB), 0.05-2.0 mg/kg progesterone (P), or their combinations. Serum PRL levels were increased (P less than 0.05) at the onset of sexual maturity in intact controls, but not in ovariectomized turkeys. Injection of 0.02 mg/kg EB into ovariectomized turkeys resulted in elevated (P less than 0.05) serum PRL levels after 8 treatment days. Higher doses failed to elicit a response of greater magnitude. EB at doses of 0.02-2.0 mg/kg reduced LH levels while 0.002 mg/kg EB increased LH levels above (P less than 0.05) those of ovariectomized controls. The 1.0-mg/kg P dose increased (P less than 0.05) serum PRL within 24-48 hr of administration while the 0.05-, 0.5-, or 2.0-mg/kg P doses failed to elicit a response. When P was injected in doses of 0.5-2.0 mg/kg, LH levels were decreased in a dose-response manner. The injection of EB combined with P had a variable effect on serum PRL levels. The 0.5- or 1.0-mg/kg dose of P facilitated (advanced in time) the rise in serum PRL level induced by 0.02 mg/kg of EB. In contrast, the positive feedback effect of 0.2 mg/kg of EB was blocked when administered with 0.5 mg/kg of P. Serum LH levels were dramatically decreased by all steroid combinations used. These results indicate that daily injections of EB and/or P in ovariectomized turkeys have a variable effect on serum PRL and LH levels depending upon the dose, the duration of treatment, or the ratio between EB and P.

Adult male turkeys were treated orally with furazolidone at doses of 1, 2.5, 5 or 20 mg/kg for 14 days and their plasma analysed for luteinizing hormone (LH), testosterone and prolactin (PRL) concentrations before, during and after treatment. At 20 mg/kg the drug produced a significant decrease in the plasma levels of LH and testosterone at the end of treatment, whereas at 5 mg/kg the drug had no significant effect. Prolactin concentrations were unaffected by any of the drug doses used. Intramuscular injection of luteinizing hormone releasing hormone (LHRH) at a dose of 5 micrograms/kg produced after 30 min a significant rise in plasma levels of LH, an effect that was decreased significantly by treatment with 20 mg/kg furazolidone. Incubation of normal turkey semen with graded doses of furazolidone or nitrofurazone for up to 30 min resulted in a dose- and time-dependent decrease in sperm motility. At a concentration of 20 mg/ml a complete absence of sperm motility was observed after incubation with either drug, although, on the whole, nitrofurazone seemed more potent than furazolidone as a sperm-immobilizing agent. Histological changes occurred in the 20 mg/kg group and consisted of a decrease in spermatocyte production, corrugation of sperm cell nuclear envelopes and distention of the endoplasmic reticulum of elongate spermatids. It is concluded that furazolidone depresses pituitary LH output but may, in addition, directly affect spermatogenesis and sperm motility.

An ambient temperature of 30 degrees C compared to 18 degrees C accelerated the increase in serum prolactin (Prl) level induced by photostimulation of female turkeys. The contribution of reproductive stage and nesting behavior to this serum Prl elevation was assessed by housing adult female turkeys in individual wire cages while allowing other females free access to nests on the floor. Birds of both groups were exposed to 10 degrees C, 24 degrees C or 30 degrees C beginning 4 wk prior to photostimulation and continuing throughout the reproductive phase. Lapsed time between the onset of photostimulation and onset of sexual maturity, and between the onset of sexual maturity and onset of incubation behavior was shorter in birds housed at 30 degrees C with access to nests than in corresponding birds housed at 24 degrees C and 10 degrees C. The increases in serum Prl associated with sexual maturity or incubation behavior occurred at a greater rate in the birds maintained at 30 degrees C. Cage-reared birds had the same lapsed time between onset of photostimulation and onset of sexual maturity and the same sustained low Prl level regardless of ambient temperature exposure. All groups exhibited similar luteinizing hormone profiles. These findings indicate that the accelerated increase in Prl under elevated temperature in floor-reared turkeys is related to accelerated development of reproductive function, and not the direct effect of ambient temperature on mechanisms controlling Prl.

Primary anterior pituitary cell cultures were utilized to study the influence of serotonin (5-HT) directly on the pituitary. Cells incubated with 10(-5) and 10(-4) M 5-HT exhibited a significant prolactin (Prl) release, whereas cells incubated with 10(-10) to 10(-6) M 5-HT did not. Cells incubated with 10(-10) to 10(-4) M quipazine (5-HT agonist) or methysergide (MES; 5-HT antagonist) did not release Prl in amounts greater/less (P greater than 0.01) than spontaneous release. Luteinizing hormone (LH) release from cells incubated in the presence of 5-HT, quipazine, or MES was similar to spontaneous release. The hypothalamic extract-induced Prl and LH release from cells was not influenced by quipazine, but Prl release was diminished in a dose-related fashion by MES. The influence of 5-HT on hypothalamic induction of Prl and LH release was investigated utilizing in vitro culture of hypothalamic fragments (HF). Media samples from HF incubated with 10(-6) and 10(-4) M 5-HT induced a release of Prl. Media samples from HF incubated with 10(-4) M MES induced less Prl release than media samples from control fragments. When HF were incubated with both 10(-4) M 5-HT and 10(-4) M MES, the expected 5-HT-mediated Prl release was not evident. These culturing situations had no influence on LH release. In vitro Prl release from pituitary cells of the young turkey was stimulated through 5-HT activity at the hypothalamus, but not by direct 5-HT action on the pituitary cells.

Serum prolactin (PRL) levels were determined by homologous radioimmunoassay in 6- to 10-week-old domestic white turkeys treated by intraperitoneal injection of agents that alter serotonergic activity. Quipazine (0.1-10.0 mg/kg), a serotonin (5-hydroxytryptamine; 5-HT) agonist, induced a dose-dependent rise in serum PRL level 1 hr after injection. The 5-HT precursor, 5-hydroxytryptophan (5-HTP), at doses of 80 and 150 mg/kg produced over a twofold elevation in PRL level 1 hr after administration, though the 50 mg/kg dose failed to produce any change. Administration of fluoxetine (10 mg/kg), a 5-HT reuptake blocker, induced an elevation in PRL level persisting 3 hr. When fluoxetine injection preceded administration of a weakly stimulatory dose of 5-HTP, a prolonged elevation in PRL level was observed. methysergide (MES), a 5-HT antagonist, administered in a 10 mg/kg dose produced no change in PRL level, while the 25 mg/kg dose initially produced a spike in PRL level which subsequently dropped slightly below the control level. Prior injection of 20 mg/kg MES completely blocked the serum PRL rises induced by quipazine and 5-HTP. These results suggest that serotonergic mechanisms are involved in the regulation of pituitary PRL release beyond basal levels in young domestic turkeys.