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Biomedical subjects

H Opel

Publications and source records attributed to H Opel.

At least 19 recordsLinked to original sources
PubMed1990

Effect of peptide histidine isoleucine on in vitro and in vivo prolactin secretion in the turkey.

Studies were conducted both in vitro, using monolayer cultures of turkey pituitary cells, and in vivo, using ovariectomized turkey hens, steroid-primed ovariectomized hens, and immature toms to compared the effectiveness of peptide histidine isoleucine (PHI) with that of vasoactive intestinal peptide (VIP) in stimulating prolactin (PRL) secretion. Vasoactive intestinal peptide, a putative PRL-releasing factor (PRF) in the turkey, was approximately 1000-fold more effective than PHI in stimulating PRL secretion in vitro. Prolactin secretion was significantly enhanced by the exposure of pituitary cells to 10(-7) M PHI and a similar stimulation was observed with 10(-10) M VIP. Injection of cannulated, unrestrained turkeys with PHI at doses up to 100 micrograms per kg of BW caused no significant change in circulating PRL concentrations, but injection of 10 micrograms of VIP per kg resulted in a 7 to 22-fold increase in plasma PRL concentration within 10 to 30 min following injection. These results demonstrate a marked difference between the turkey and the rat in their response to a PRL-stimulating neuropeptide. In contrast to what was observed in the turkey, PHI is a strong PRF in the rat, with a potency equal to or greater than that of VIP. Earlier studies have shown that thyrotropin-releasing hormone, another strong PRF in mammals, has little consistent PRF activity in the turkey. Thus, the present studies add additional evidence of major differences between mammals and birds in the control of PRL secretion by hypothalamic neuropeptides.

Animals↗
PubMed1990

Half-life and metabolic clearance rate of recombinant-derived chicken growth hormone and purified turkey growth hormone in intact and hypophysectomized turkeys.

The half-life and metabolic clearance rate (MCR) of natural turkey growth hormone (tGH) were compared with those of recombinant-derived chicken growth hormone (rcGH) in intact and hypophysectomized (hypox) turkey poults at 8 and 13 wk of age. The hypox poults used were all hypophysectomized at 8 wk of age. The purpose of the experiment was to determine whether the source of growth hormone (GH) or the physiological changes associated with hypophysectomy might affect the disappearance of the hormone from the circulation and, hence, alter the biological response of the bird to exogenous GH. The mean half-life of GH in the growing turkey was 12.88 +/- .54 (SE) min. The source of GH had no effect on half-life, and GH half-life did not vary significantly between poults sampled at 8 and 13 wk. Hypophysectomy significantly (P less than .01) increased the half-life of administered GH from 11.21 +/- .50 min in intact poults to 14.70 +/- .84 min in hypox poults. The MCR of GH in hypox poults 2 days following hypophysectomy was markedly lower than that of intact birds (1.08 versus 2.95 mL/min; P less than .001). The GH clearance in hypox birds increased during the 5 wk following hypophysectomy but still remained somewhat lower than that of intact birds (2.55 versus 3.00 mL/min; P = .06). The MCR of GH did not change in intact birds between 8 and 13 wk of age, and the MCR of rcGH and tGH did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Plasma prolactin levels in incubating turkey hens during pipping of the eggs and after introduction of poults into the nest.

Plasma levels of prolactin (Prl) associated with incubation and maternal behavior were compared in turkey hens allowed to incubate 10 fertile eggs (Group I, n = 9) or 10 infertile eggs (Group II, n = 7) in open nest boxes. At the end of the day that the first egg hatched, all unhatched eggs were removed from Group I hens and each hen was given 10 poults. At the end of the following day, infertile eggs were removed from Group II hens and each hen was given 10 poults. Although pipping of the eggs changed the incubation behavior of Group I hens, it had no effect on plasma Prl. Subsequent hatch of the eggs and/or presence of poults resulted, within 24 h, in a sharp fall in Prl levels, abandonment of the nests, and a shift to maternal behavior. Visual and auditory exposure to Group I poults had no effect on plasma Prl or incubation behavior of Group II hens incubating infertile eggs in adjacent pens. However, within 24 h after the infertile eggs were exchanged for newly hatched poults, Prl levels in Group II hens declined sharply and the hens abandoned the nests and showed maternal behavior similar to that observed in Group I hens. No significant relationships were found in either group between plasma Prl levels and quality of incubation or maternal behavior.

Animals↗
PubMed1989

Daily changes in plasma prolactin, corticosterone, and luteinizing hormone in the unrestrained, ovariectomized turkey hen.

Plasma concentrations of prolactin (PRL), corticosterone (B), and luteinizing hormone (LH) were determined in hourly samples collected over a 24-h period from unrestrained, long-term ovariectomized (OVX) turkey hens maintained in cages in an isolation room on a 14 h light: 10 h dark photoperiod. Mean plasma concentrations of all three hormones were found to vary significantly with the time of sampling. Mean plasma PRL levels reached a peak (6.50 +/- 1.70 ng/mL, means +/- SEM) during the latter half of the photophase, declined to a nadir (5.22 +/- 1.20 ng/mL) prior to the onset of darkness, and then rose gradually during the scotophase to reach another peak (8.96 +/- 1.80 ng/mL) 1 h prior to lights on. Mean plasma LH levels rose significantly (P less than .001) from a nadir of 4.11 + .29 ng/mL prior to lights out to a peak of 4.74 + .34 ng/mL during the dark period. No evidence of random fluctuations in LH levels was observed in any individual, suggesting that episodic LH release may not occur in OVX turkey hens. Individual patterns of B secretion varied substantially so that, although significant increases and decreases in mean plasma B levels were observed, no clearly defined peaks in mean plasma B levels were identified. Individual secretory profiles revealed that peaks in PRL secretion often coincided with peaks in B secretion, but B peaks were usually more numerous. It is concluded that PRL and LH are secreted in a daily rhythm in the OVX turkey hen, with the highest levels of both hormones occurring during the scotophase.

Animals↗
PubMed1988

Effects of poults on plasma concentrations of prolactin in turkey hens incubating without eggs or a nest.

1. Plasma prolactin (PRL) concentrations, total daylight sitting time and extent of brood patch development were compared in singly caged hens incubating without a nest or eggs and in penned hens incubating eggs in nest boxes. No significant differences were found in any of the three measures of incubation intensity. 2. When 10 newly-hatched poults were placed in the cages of incubating hens their plasma PRL concentrations fell rapidly. No fall in plasma PRL was observed in hens that could see and hear, but not touch the poults. 3. When physical contact between hens and poults was maintained, visual isolation of hens from poults, surgical devocalisation of poults, or the combination of visual isolation and devocalisation of poults had no effect on the poult-stimulated decline in plasma PRL concentrations. 4. Sensory cues from poults that evoke the PRL response in incubating hens are primarily tactile.

Animals↗
PubMed1988

Stimulation of prolactin secretion from turkey anterior pituitary cells in culture.

Prolactin (PRL) secretion by monolayer cultures of turkey anterior pituitary cells was significantly increased (up to 44-fold) by vasoactive intestinal peptide (VIP), arginine vasotocin (AVT), and by an extract of turkey hypothalami (HE). Several other neuropeptides (including thyrotropin-releasing hormone) and neurotransmitters were ineffective in influencing PRL secretion at doses up to 10(-6) M. The dynamic PRL response to HE and VIP was studied using superfused pituitary cells attached to microcarrier beads. HE, administered in 30-min pulses, resulted in a significant, dose-related increase in PRL secretion from a basal secretion rate of 2.32 ng/min/10(7) cells to a peak secretion rate of 127.13 ng/min/10(7) cells at the highest dose of HE tested (1 mg tissue-equivalent weight/ml). VIP significantly increased PRL secretion at all doses studied (from 10(-10) to 10(-6) M), with 10(-8) M VIP producing a response similar to that observed with 1 mg/ml HE. A highly significant (P less than 0.001) linear relationship was demonstrated between the log-dose of VIP administered and peak PRL secretion rate. These studies suggest that VIP, but not TRH, may be a physiological stimulus for PRL release in the turkey.

Animals↗
PubMed1988

Stimulation of prolactin release in turkeys by vasoactive intestinal peptide.

Vasoactive intestinal peptide (VIP) is a potent releasor of prolactin in birds. The main purpose of this study was to identify its site of action. Synthetic porcine VIP administered intraatrially to freely moving ovariectomized (OVX) turkeys induced an elevation of circulating PRL within 15 min in a dose-related manner. Removal of hypothalamic control of PRL release by surgical disconnection of the neurohemal regions of the median eminence did not significantly diminish the PRL response to VIP. Intraatrial injection of eledoisin or bradykinin into OVX hens did not influence PRL secretion, indicating that the PRL releasing activity of VIP is probably not attributable to its vasodilatory action. These results support the possibility that VIP is an authentic prolactin releasing factor (PRF) in birds.

Animals↗
PubMed1984

Hormonal mediation of reproductive behavior.

Reproductive capability requires synchronization of both endocrine and behavioral components of reproduction. The classic view of reproductive behavior was that there was simply direct stimulation of a behavioral response by the appropriate gonadal steroid. However, it has become clear with recent developments in the field of behavioral endocrinology that the relationship of hormonal and behavioral processes is complex. In addition to the complexity of the mechanisms involved, other factors, both social and environmental, influence both the endocrine and behavioral responses. This paper provides an overview of selected issues within the field of behavioral endocrinology which deal with mechanisms of hormonal induction of behavior at various stages of the life cycle and with factors that interact with these processes.

Aging↗
PubMed1984

Evidence against a role of prolactin in the timing of ovulation in the turkey.

Two separate experiments in which blood was sampled at 2-h intervals from turkeys hens failed to show a significant change in plasma prolactin (Prl) concentrations in relation to the preovulatory surge of luteinizing hormone (LH) for the first (C1) ovulation of a sequence. Intravenous injection of 125 IU of ovine Prl (NIH-P-S10) or of 1 or 2 ml of antiserum to turkey Prl at varying intervals before C1 ovulation had no effect on the timing or incidence of C1 ovulation. However, injection of Prl before C1 ovulation tended to inhibit ovulation of the second (C2) egg of the sequence, while injection of antiserum to Prl before C1 ovulation tended to either advance or inhibit C2 ovulation. Possibly, the effects of Prl and Prl antiserum on C2 ovulation reflect interference with maturation of the C2 ovarian follicle rather than interference with neuroendocrine processes that regulate the timing of the preovulatory surge of LH. The data for C1 ovulation argue against a change in circulating levels of Prl as a factor in the timing of the preovulatory surge of LH.

Animals↗
PubMed1984

Two avian luteinizing hormone radioimmunoassay procedures compared by measurement of changes during the ovulatory cycle of turkey and broiler hens.

Two radioimmunoassay (RIA) procedures for measuring avian luteinizing hormone (LH) were compared using divided aliquots of plasma samples collected during the ovulatory cycles of turkey and broiler breeder hens in three separate experiments. The RIA systems compared were the homologous turkey LH assay Wentworth et al. (1976) and the homologous chicken LH assay of Follett et al. (1972). Both assays provided the same assessment of circulating LH changes. The preovulatory surge of LH was observed 6 hr before ovulation in turkeys and 4 hr before ovulation in chickens. In addition, both assays detected an increase in chicken LH after ovulation, followed by a gradual decline prior to the next preovulatory surge. The correlation between RIA were highly significant (P less than .001) in each experiment. The crossreaction of purified ostrich LH, FSH, and TSH and of the alpha and beta subunits of turkey LH was assessed in each assay system. Ostrich LH, FSH, and TSH crossreacted in the chicken LH assay in a dose-related manner: ostrich LH showed the highest activity. Only ostrich TSH produced a response in the turkey assay that was dose related. The alpha subunit, but not the beta subunit, of turkey LH was quite potent in the chicken LH RIA, but neither subunit competed as well as the native hormone in the turkey RIA. Thus, the two LH antisera recognize different portions of the LH molecule. The chicken antiserum apparently recognizes a site on the alpha subunit that may be at least partially masked in the FSH and TSH molecules. The turkey antiserum recognizes a site on the native LH molecule that is altered when the subunits are separated.

Animals↗
PubMed1984

Two methods for serial blood sampling from unrestrained, undisturbed turkeys with notes on the effects of acute stressors on plasma levels of prolactin.

A method was developed for chronic cannulation of the atrium of the turkey. Two methods, one employing a headmount swivel-tethering system and the other a backmount swivel-tethering system, were developed for serial bleeding from cannulated turkeys kept in an environmental cubicle. To validate the methods for serial bleeding from undisturbed, unrestrained turkeys, the effects were examined of several stressors on plasma prolactin (PRL) levels in adult toms. Serial bleeding at 2-min intervals followed by withdrawal of one sample of 50 ml at 2 hr after initiation of bleeding had no effect on plasma PRL. Water deprivation for 24 hr or intraatrial infusion of hypertonic saline had no effect on plasma PRL. Intraatrial injection of 10 mg/kg of epinephrine bitartrate resulted in a significant elevation of plasma concentrations of PRL.

Animals↗
PubMed1983

Endocrine changes in the incubating and brooding turkey hen.

Turkey hens were allowed to incubate eggs and to hatch and rear young. Plasma prolactin (Prl) levels increased prior to the start of continuous incubation and rose sharply as incubation progressed to reach a peak of 1178.2 +/- 221.8 ng/ml (mean +/- SEM) just before hatching. Prl levels then fell precipitously before the hens left the nest, and returned to preincubation levels (36.8 +/- 3.4 ng/ml) by the time the poults were 2 weeks old. These results show that the high plasma concentrations of Prl found during incubation are not initiated or maintained only by the stimulus of nesting. We suggest that the decline in Prl levels at the end of incubation could be related to the pipping and hatching of eggs, and the consequent shift to maternal behavior. Plasma growth hormone (GH) levels were significantly increased in hens which were brooding poults, but not in hens incubating eggs. An elevenfold, 1-day increase in plasma GH was observed immediately after the hens left the nests. Mean plasma GH levels rose from 12.0 +/- 4.7 ng/ml on the day that the hens left the nests to 133.0 +/- 32.0 ng/ml on the following day, and then declined to 23.1 +/- 9.6 ng/ml after an additional day. There were no significant changes in plasma thyroxine levels during laying, incubation and brooding. Plasma glucose concentration was significantly depressed during incubation.

Animals↗
PubMed1981

Effect of feed or water restriction on basal and TRH-stimulated growth hormone secretion in the growing turkey poult.

Both feed and water restriction of growing turkeys resulted in an increase in the basal levels of plasma growth hormone (GH). Restricted birds also showed an increased response to thyrotropin-releasing hormone (TRH) stimulation. These changes were significantly greater in feed-restricted birds than in the water-restricted birds. After return to ad lib conditions, basal plasma GH levels remained elevated above control levels in both previously restricted groups. However, the GH response to TRH stimulation returned to normal during this period. The increase in GH secretion during undernutrition is a metabolic adjustment consistent with the known role of GH in glucose, protein and fat metabolism. The elevated GH levels present after return to adequate nutrition may aid compensatory growth. Feed and water restriction were equally effective in limiting the growth of young turkey poults. Body weight gain and feed efficiency were severely affected during the first 3 weeks of restriction, but improved during the 4th week. Return to ad lib conditions resulted in compensatory growth and markedly improved feed efficiency in both restricted groups. Feed-restricted birds showed a significant increase in water consumption after 8 days of restriction. This polydipsia may result from intermittent feeding of hungary animals. Water consumption returned to normal after 1 week of ad lip feeding. Birds restricted in water consumption voluntarily limited their feed intake to a level only slightly higher than that of the feed-restricted group. When water was supplied ad lib, these birds immediately resumed normal feed consumption.

Animal Feed↗
PubMed1980

Failure of mammalian prolactin to induce incubation behavior in chickens and turkeys.

Three experiments on a high-broody strains of chickens that had not been selected for egg production for 50 generations and one experiment on a commercial strain of turkeys were conducted to test the effectiveness of mammalian prolactin (NIH-S10) in inducing regression of the ovary and incubation behavior. In two experiments on chickens, environmental factors known to favor the expression of broodiness were provided, and four components of nesting or incubation behavior were monitored continuously during the light period with a closed-circuit television system and timelapse videotape recorder. Although all doses of prolactin used caused regression of large ovarian follicles, none induced incubation behavior in either chickens or turkeys. Some prolactin-injected chickens occasionally displayed the covering stance of maternal behavior. An explanation for the discrepancy between these results and the results of studies conducted more than 20 years ago, in which mammalian prolactin was highly effective in inducing incubation behavior in chickens, may lie in differences in purity of the prolactin preparations used.

Animals↗
PubMed1979

On hypothalamic control of ovulation in the turkey.

Small bilateral lesions of the ventromedial preoptic hypothalamus consistently blocked ovulation. Lesions that completely cut the supraoptico-hypophyseal tract or that were placed throughout the tuberal hypothalamus and median eminence had no effect on ovulation. Lesions placed in the posterodorsal, medial, and ventral parts of the infundibular nuclear complex and in the medial and posteria divisions of the median eminence resulted in slight to moderate atresia of rapidly growing follicles within 38 to 40 hr after surgery.

Animals↗
PubMed1979

Effects of hypothalamic deafferentation on light-stimulated ovarian function in turkeys.

Previous studies in the turkey have shown that lesions placed in the preoptic brain (POR) block ovulation, while lesions placed in the tuberal hypothalamus (TH) induce regression of rapidly growing ovarian follicles. In the present experiments, the nature of the neural pathways to and between these regions is explored by the method of neural transection performed with a small, stereotaxically positioned knife. Superior deafferentation of the POR allowed light-stimulated rapid growth of ovarian follicles but appeared to block or suppress ovulation. Complete deafferentation of the TH prevented development of the ovary as indicated by the failure of ovarian follicles to enter the phase of rapid growth. Partial cuts that severed anterior inputs to the TH blocked follicular growth, whereas cuts that severed lateral and posterodorsal connections or posterior connections to this region had no effect on development of a functional ovary. Deafferentation of the posterior two-thirds of the TH, which created an island including the posterodorsal region of the infundibular nuclear complex, did not block ovulation.

Animals↗