Biomedical subjects

L Debeljuk

Publications and source records attributed to L Debeljuk.

At least 19 recordsLinked to original sources

PubMed1999

Prenatal melatonin influences developmental changes of tachykinins in response to estradiol benzoate.

The developmental changes of hypothalamic, pituitary, striatum and pineal gland tachykinin concentrations, as well as the response to estradiol-benzoate (EB) administration, were studied in offspring of control and melatonin (MEL) treated mother rats. Female rats were studied throughout different phases of the sexual development: infantile, prepubertal and pubertal periods, in the four following groups; control-offspring+vehicle; control-offspring+EB; MEL-offspring+vehicle; MEL-offspring+EB. Hypothalamic NKA in control-offspring+ vehicle was significantly increased only at 27 days of age and in control-offspring+EB at 27 days of age and during the infantile period. Hypothalamic SP levels increased similarly in control-offspring+EB during the infantile period but the EB influence was more pronounced with significantly increased concentrations at 32 days of age. Prenatal melatonin treatment produced major alterations in these patterns of postnatal development. In MEL-offspring+EB tachykinins concentrations in the hypothalamus during infantile and prepubertal periods did not increase, however at 37 days of age, they showed significantly higher values than in control-offspring+EB groups. The developmental pattern of pituitary NKA and SP concentrations in both; control-offspring+vehicle and control-offspring+EB groups, showed similar values from the infantile period to puberty, indicating that NKA and SP concentrations remained at similar levels independently of the sexual stage, only at 27 days of age in control-offspring+EB significantly increased values were found as compared to MEL-offspring+EB. Prenatal melatonin did not produce marked modifications, only significantly lower NKA and SP concentrations in MEL-offspring+EB group were observed at 25 days of age in comparison to control-offspring+EB group. Striatal NKA and SP concentrations showed a similar developmental pattern. In control-offspring, EB treatment produced NKA and SP decreased concentrations at the infantile period than in control-offspring+vehicle and significantly increased concentrations during the prepubertal period, then during the pubertal period NKA and SP concentrations decreased in control-group+EB. However, prenatal melatonin treatment reduced the levels of striatal NKA and SP during the prepubertal period after EB treatment and delayed until pubertal period the increase previously observed in control group during the prepubertal period. In MEL-offspring+vehicle group striatal concentrations of both tachykinins remained at low levels from infantile period until pubertal period. Prenatal melatonin and EB did not produce major alterations in SP pineal concentrations throughout sexual development. Plasma estradiol concentrations were significantly higher in the groups that received EB treatment than in those that received vehicle during prepubertal and juvenile periods in control-offspring+EB group and during the pubertal period in MEL-offspring+EB group. These data indicate that prenatal MEL treatment may influence NKA and SP developmental pattern from the infantile period until adulthood in the female rat.

Animals↗

PubMed1998

Tachykinins in the pineal gland: effect of castration and ganglionectomy.

In this investigation, the presence of NKA-immunoreactive substances was determined in pineal glands from intact, castrated and castrated, testosterone-treated male rats. The effect of environmental light, melatonin treatment and superior cervical ganglionectomy on pineal NKA-immunoreactive substances was also investigated. The results obtained show that NKA is present in measurable amounts in the rat pineal, and NPK is probably also present, Orchidectomy was followed by an increase in the content of NKA-immunoreactive substances in the pineal gland. The replacement treatment with testosterone propionate in castrated rats blocked this effect. NKA-immunoreactive substances were not significantly different quantitatively in pineals from rats killed under light or under darkness. The removal of the superior cervical ganglia was followed by a significant increase in the NKA-immunoreactive substance content in the pineal gland of male rats. These results indicate that NKA and other tachykinins are present in the pineal gland of the male rat, and they seem to be regulated by gonadal hormones and the innervation originated from the superior cervical ganglia.

Animals↗

PubMed1998

Effects of immunoneutralization of substance P on hypothalamic neurotransmitters in normal mice and in transgenic mice expressing bovine growth hormone.

It is well known that transgenic mice expressing bovine growth hormone have altered neuroendocrine functions. Substance P was shown to influence the secretion of gonadotropins. In this investigation, the effect of a single injection of an antiserum to substance P was investigated in intact and castrated transgenic (MT-bGH) mice and in their normal litter mates. In the median eminence, the administration of antisubstance P serum resulted in a decreased dihydroxyphenyl acetic acid/dopamine index in intact and castrated normal mice but was without effect in transgenics. The homovanillic/dopamine index was decreased in normal mice (intact or castrated) but unchanged in transgenics. Norepinephrine and epinephrine were increased in normal mice (intact and castrated) treated with the anti-SP serum, but in transgenic mice, the anti-SP serum induced significant changes of norepinephrine only in intact animals, with no modifications in epinephrine levels. In the whole hypothalamus (minus the median eminence), the injection of antisubstance P serum resulted in an increased dihydroxyphenyl acetic acid/dopamine index in castrated, but not in intact, normal mice. In transgenic mice, this index was increased in intact but decreased in castrated animals. The homovanillic/dopamine index was decreased in normal intact mice treated with the antiserum but increased in intact transgenic mice. Norepinephrine and epinephrine were decreased by the antiserum treatment in normal intact mice but were unchanged in transgenics, except for norepinephrine in castrated transgenics, in which it was found increased. The administration of the antiserum did not affect plasma LH, FSH, or prolactin in normal mice but it reduced LH levels in intact transgenic mice. These results indicate that the response to the treatment with the antiserum to substance P shows considerable alterations in transgenic mice as compared with their litter-mate, normal controls, producing divergent effects on hypothalamic catecholamine metabolism. The present findings confirm that transgenic mice overexpressing the bGH gene have marked neuroendocrine alterations as compared with their normal litter mates.

Animals↗

PubMed1997

The detection of thyrotropin-releasing hormone (TRH) and TRH receptor gene expression in Siberian hamster testes.

Thyrotropin-releasing hormone (TRH) from the hypothalamus is the major regulator of TSH synthesis and secretion. Most recently, TRH and TRH receptors (TRH-R), as well as their mRNAs, have been identified in rat testis. To expand our knowledge on the testicular TRH and TRH receptor gene expression in different species, in the present study the mRNA levels of testicular TRH and TRH-R were investigated in Siberian hamsters. To further localize the cellular sites of the gene expression, the animal model was treated with a single injection of ethylene dimethane sulfonate (EDS) (i.p., 80 mg/kg body weight), a compound known as to specifically eliminate testicular Leydig cells. The elimination of Leydig cells induced by EDS treatment was confirmed by histological studies of the testis sections and by serum hormonal analyses, which showed a dramatic reduction of serum testosterone (T) levels and significantly elevated serum LH concentrations. Messenger RNA levels of TRH and TRH-R in the testes were determined by Northern blot analyses quantitated with densitometry scanning. The results showed that specific TRH-R mRNA, 3.8 kb in size, was identified in Siberian hamster testes and the mRNA levels were significantly elevated in the EDS-treated testes compared to the controls (p < 0.01). Testicular TRH mRNA was also detected; however, no significant differences in TRH mRNA levels were found between EDS-treated and control groups. The size of TRH mRNA was characterized as about 1.2 kb in hamster testes, which was smaller than that observed in the rat hypothalamus (1.6 kb) and in the rat testis (2.0 kb). Further studies by RNase H digestion revealed the presence of smaller TRH transcripts in the hamster testes than those in the rat testis. No hybridization signal for TRH mRNA was detected by RNase protection assay, when a rat TRH riboprobe was applied to hamster testis RNA, suggesting the limited homology of TRH gene sequences between these two species. Our results demonstrate that both TRH and TRH-R genes are expressed in Siberian hamster testes, and a significant increase of TRH-R mRNA levels occurs in the Leydig cell eliminated hamster testes. Unlike the rat testicular TRH mRNA mainly detected in Leydig cells, in hamster TRH mRNA could also be detected in other testicular compartment.

Animals↗

PubMed1997

Neurohypophyseal vasopressin in the Syrian hamster: response to short photoperiod, pinealectomy, melatonin treatment, or osmotic stimulation.

In the present study, the effect of photoperiod on vasopressin content in the pituitary neurointermediate lobe (NIL), as well as the ability of pinealectomy to prevent and melatonin to mimic the short photoperiod-induced changes in NIL vasopressin were studied in male Syrian hamsters. The ability of melatonin to modify the hyperosmotically stimulated vasopressin release was also determined. Exposure to short photoperiod (SD) for 4 or 10 weeks increased vasopressin content in the hamster NIL. In long photoperiod (LD)-exposed hamsters, pinealectomy induced a decrease in NIL vasopressin content, whereas no effect of melatonin injections on vasopressin storage in the NIL was detected. In SD-exposed animals, pineal removal failed to alter vasopressin content in the NIL. Hypertonic saline administration led to the expected decrease in vasopressin content in the NIL both in vehicle- and melatonin-treated animals. The hyperosmotically stimulated release of vasopressin was not modified by previous treatment with melatonin. The data from the present study show that, in male Syrian hamsters, exposure of animals to SD increases the vasopressin content in the posterior pituitary, but these changes appear not to be mediated by SD-induced changes in melatonin secretion. Furthermore, the exposure of animals to SD prevents the pinealectomy-induced changes in NIL vasopressin content. Melatonin does not modify the hyperosmotically stimulated vasopressin release in the male Syrian hamster.

Animals↗

PubMed1997

Effect of a non-peptide NK-2 tachykinin receptor antagonist on LH, FSH, and prolactin release by rat hemipituitaries in vitro.

Tachykinins are present in the anterior pituitary gland and there is evidence that they may have a direct intrapituitary role influencing the secretion of some of the hormones released by this gland. In this investigation, we have studied the effect of the non-peptide NK-2 receptor antagonist SR 48,968 (Sanofi Recherche) on the basal release of LH, FSH, and prolactin by rat hemipituitaries incubated in vitro, and also on the response to GnRH. SR 48,968 significantly inhibited prolactin release into the medium. The highest doses of this compound stimulated the basal release of LH by hemipituitaries from castrated, castrated testosterone-treated, and ovariectomized estradiol-treated rats, but not from intact male rats. SR 48,968 significantly inhibited the release of LH in response to GnRH. Since some tachykinin receptor antagonists have been demonstrated to act also on calcium channels, studies with verapamil, a calcium channel antagonist, were also carried out for comparison. Verapamil inhibited prolactin release into the medium and decreased the LH response to GnRH. These results suggest that tachykinins that bind NK-2 receptors, may have an intrapituitary role stimulating the release of prolactin, and that they may also modulate the response of the gonadotrophs to GnRH. The fact that verapamil shares some of the actions exerted by NK-2 receptor antagonists on the pituitary glandm however, suggests the possibility that some of the effects of NK-2 receptor antagonists may be mediated through calcium channel antagonism. Therefore, the results observed with the use of some of these antagonists should be interpreted with great caution.

Animals↗

PubMed1996

Development of a specific radioimmunoassay for neuropeptide K: its application to Siberian hamster tissues.

In this report we describe the development of a radioimmunoassay for neuropeptide K (NPK) that is not influenced by the presence of free neurokinin A (NKA) or neuropeptide gamma (NPG). The antisera for the radioimmunoassay were obtained by immunizing rabbits with beta-preprotachykinin A fragment 69-91. This fragment contains the sequence 1-20 of NPK and has only the sequence 18-20 (Gly-His-Gly) in common with NPG. Two antisera were obtained, neither cross-reacting with NKA or NPG. The specificity of these antisera was confirmed by the finding of a major immunoreactive peak in the eluates obtained from HPLC separation, corresponding to NPK. This radioimmunoassay was applied to the determination of NPK in hypothalamic and anterior pituitary extracts from Siberian hamsters. Hypothalami from male and female hamsters contained similar concentrations of NPK, although slightly higher in males. NPK levels in the hypothalamus of female Siberian hamsters showed few fluctuations during the estrous cycle, with the levels measured at estrus being significantly lower than at proestrus, diestrus I, and diestrus II. In anterior pituitaries from Siberian hamsters the concentrations of NPK were significantly lower in females than in males. This radioimmunoassay has demonstrated the presence of NPK in the anterior pituitary gland of the Siberian hamster, and it should be very useful for future studies on mechanisms of regulation of NPK secretion in different tissues.

Amino Acid Sequence↗

PubMed1996

Effects of photoperiod on hypothalamic and anterior pituitary tachykinins of male Siberian hamsters during development.

In previous reports from our laboratory we showed that the hypothalamus and especially the anterior pituitary gland of the Siberian hamster contain very high concentrations of substance P- and neurokinin A-like immunoreactive substances, as compared with other common laboratory rodents. It was thought, therefore, that a study of the developmental changes of these two tachykinins in the hypothalamus and anterior pituitary of male Siberian hamsters would be of interest. In addition, as this species is very sensitive to changes in environmental light, these studies were carried out in animals kept under short or long daily photoperiods. The results of this investigation show that in male Siberian hamsters, photoperiod did not markedly influence the hypothalamic concentrations of substance P- and neurokinin A-like immunoreactive substances, which steadily increased from prepuberty up to 40-50 days of age. The influence of photoperiod, however, was much more marked on tachykinin levels in the anterior pituitary gland, because the developmental increase of tachykinins in this gland was significantly more evident in animals kept under short daily photoperiods than in animals under long daily exposure to light. These results are similar to those previously obtained in female Siberian hamsters, in spite of the fact that estradiol and testosterone seem to have opposite effects on anterior pituitary tachykinin concentrations. It seems, therefore, that, in addition to gonadal steroids, other factors may be important mediators of the tachykinin response to photoperiods in the anterior pituitary of the male Siberian hamster.

Aging↗

PubMed1995

Melatonin inhibits oxytocin and vasopressin release from the neurointermediate lobe of the hamster pituitary.

The aim of this investigation was to study whether melatonin affects the release of oxytocin and vasopressin by the pituitary neurointermediate lobe of the Syrian hamster in vitro. The effect of melatonin was studied on the unstimulated (pre- and post-K+ -stimulated) release of oxytocin and vasopressin and on the response to K+ stimulation. Melatonin significantly inhibited unstimulated release of these hormones in all concentrations (10(-11) M, 10(-9) M and 10(-7) M) studied. K+ -stimulated release of oxytocin and vasopressin was significantly decreased by the 10(-9) M dose of melatonin. It is concluded that melatonin is active in modifying the release of these peptides in the Syrian hamster neurointermediate lobe, as it has been previously demonstrated in the rat hypothalamus.

Animals↗

PubMed1995

In vivo and in vitro effects of neuropeptide K and neuropeptide gamma on the release of growth hormone.

There is anatomical and experimental evidence suggesting that tachykinins have a role in the regulation of secretion of anterior pituitary hormones. In this investigation, the effects of neuropeptide K and neuropeptide gamma on the secretion of GH were studied in vivo and in vitro. Injections of neuropeptide K into the third ventricle of freely moving, ovariectomized rats resulted in a significant increase of plasma GH, but neuropeptide gamma induced no significant changes in these levels, although it did induce a significant increase in GH pulse height. In vitro, neither neuropeptide K nor neuropeptide gamma had any apparent effect on GH release from hemipituitaries incubated for 2 h. These results suggest that neuropeptide K may have a modulatory function in the regulation of GH secretion from the anterior pituitary, through an action exerted at the hypothalamic level, and the effects of neuropeptide gamma seem to be more marginal.

Animals↗

PubMed1995

Developmental changes of tachykinins in the hypothalamus and anterior pituitary of female Siberian hamsters from prepuberty to adulthood.

The developmental changes of hypothalamic and anterior pituitary tachykinin concentrations were studied in female Siberian hamsters kept either under short (SD) or long (LD) daily photoperiods. The animals were killed between 15 and 70 days of age. Hypothalamic NKA sharply increased starting at 15 days up to 50 days in LD animals, and between 20 and 60 days in SD animals. Hypothalamic SP levels increased in a similar manner in SD animals, but in LD animals the increment was less pronounced, with increased levels from day 20 to 40, followed by a plateau. In the anterior pituitary gland, NKA concentrations in LD animals increased at 40 days of age, with only slight increases afterward, but overall the increment curve was considerably flatter than for hypothalamic NKA. In SD animals, the increase of anterior pituitary NKA was much steeper than in LD animals. However, the total content of NKA in the AP was similar in both SD and LD animals, because the AP weight was considerably higher in LD- than in SD-exposed hamsters. These results showed that photoperiod did not markedly affect the developmental changes in hypothalamic NKA. The developmental changes in anterior pituitary NKA concentrations were considerably smaller than in the hypothalamus in LD animals, but in SD animals they were much steeper. NKA concentrations in the anterior pituitary were markedly affected by the photoperiod. Concentrations of NKA in the anterior pituitary of the Siberian hamster at the age of 15 days of age were already higher than in the anterior pituitary of adult rats or Syrian hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1995

Effects of tachykinins on the secretory activity of rat Sertoli cells in vitro.

In the present study we investigated the effects of various tachykinins on the secretory activity of rat Sertoli cells in vitro. Sertoli cells were isolated from testes of immature Sprague Dawley rats, cultured for 4 days and thereafter incubated with three concentrations (0.1 pM, 1 pM or 100 pM) of substance P (SP), neurokinin A (NKA), neuropeptide K (NPK) or neuropeptide gamma (NPG) for 24 h. Levels of transferrin and lactic acid were determined in the culture media and expressed per micrograms of cellular DNA. Among all the peptides studied, NPG exhibited the greatest stimulatory effect on the release of transferrin and lactate, with NKA and NPK being less potent and SP being the least potent. Also, the effects of tachykinins on the aromatase activity of cultured Sertoli cells, as reflected by their ability to metabolize testosterone to estradiol (E2), were studied. No stimulatory effect was observed at lower concentrations (1 pM), while at 100 pM both NPG and NKA increased estradiol levels in the medium. SP and NPK had no significant effect on estradiol levels in the medium. This study reveals that tachykinins are able to influence the secretory activity of Sertoli cells, and that some of these peptides can also enhance the aromatase activity. Thus there is a possibility that tachykinins may have a physiological role as modulators of the function of Sertoli cells.

Animals↗

PubMed1994

GABA transport and subcellular distribution in the rat anterior pituitary gland.

In this investigation we have studied the uptake of gamma aminobutyric acid (GABA) into anterior pituitary slices. Tissue:medium ratios of about 45:1 were obtained after a 30-min incubation. The process responsible for 3H-GABA uptake was temperature-sensitive and sodium-dependent. The kinetic constants of saturable GABA transport were: Km 4.141 microM and Vmax 0.973 pmol/min/mg protein, at 25 degrees C. The incorporation of GABA into anterior pituitary was inhibited by specific inhibitors of neuronal and/or glial uptake. The subcellular distribution of GABA was investigated by continuous sucrose density gradients and differential centrifugation. Most of the endogenous and labelled GABA was present in the soluble fraction. However, a small part of GABA was found in the particulate fraction. These observations indicate that the anterior pituitary gland is able to concentrate GABA which interacts with intracellular particles.

Animals↗

PubMed1994

Immunoreactive substance P and neurokinin A in the hypothalamus and anterior pituitary gland of Siberian and Syrian hamsters and of rats.

In this investigation the concentrations of immunoreactive substance P and neurokinin A in the hypothalamus and anterior pituitary of the Siberian hamster were compared with those in the rat and Syrian hamster. The concentrations of immunoreactive neurokinin A in the hypothalamus of Siberian hamsters were significantly higher than those of rats and Syrian hamsters, while male Siberian hamsters had similar amounts of substance P in the hypothalamus to those of male Syrian hamsters, but had higher amounts than those in male rats. However, female Siberian hamsters and significantly higher hypothalamic concentrations of both substance P and neurokinin A than did female Syrian hamsters and rats. In the anterior pituitary glands of Siberian hamsters, concentrations of substance P and neurokinin A were markedly higher than they were in rats and even more so more in Syrian hamsters. Ovariectomy further increased tachykinin concentrations in the anterior pituitary gland of female Siberian hamsters, and this was completely prevented by oestradiol replacement. Female Siberian hamsters kept under conditions of reduced photoperiod had significantly higher tachykinin concentrations in the anterior pituitary than did animals kept under daily photoperiods of 16 h light:8 h dark. The incubation of anterior pituitaries from female Siberian hamsters with a neurokinin A receptor antagonist resulted in a partial blockade of the LH and FSH release in response to LHRH. Thus, the high concentration of tachykinins present in the anterior pituitary of the Siberian hamster may have a local role in modulating the secretion or release of gonadotrophins.

Animals↗

PubMed1992

Substance P variations in the hypothalamus of golden hamsters at different stages of the estrous cycle.

The changes in substance P concentrations in the hypothalamus of female golden hamsters were studied at the different stages of the estrous cycle. Substance P levels in the hypothalamus of hamsters were highest during estrus and lowest during diestrus I and proestrus. The concentrations of substance P during diestrus II were not significantly different from those observed during estrus. These results show that substance P levels in the hypothalamus of female hamsters undergo significant changes during the estrous cycle.

Animals↗

PubMed1991

Possible role of vasoactive intestinal peptide in the hyperprolactinemia induced by ethanol.

The effect of the blockade of endogenous VIP by injecting a specific rabbit anti-VIP serum (A-VIP) was studied in rats receiving an acute injection of ethanol. A-VIP administration decreased serum prolactin levels and reduced the hyperprolactinemia induced by ethanol. We also investigated the effect of the acute administration of ethanol on the concentration and release of VIP from the mediobasal hypothalamus. Ethanol decreased VIP concentration in the mediobasal hypothalamus, whereas it stimulated the in vitro K(+)-evoked release of VIP from this tissue. Conversely, ethanol increased VIP concentration in the anterior pituitary gland. The data indicate that VIP may be involved in the pituitary response to ethanol. The increased anterior pituitary VIP after ethanol may be due to an augmented release from the mediobasal hypothalamus.

Animals↗

PubMed1991

Effect of immunoneutralization of neuropeptide Y on gonadotropin and prolactin secretion in normal mice and in transgenic mice bearing bovine growth hormone gene.

Immunoneutralization of endogenous neuropeptide Y (NPY) with specific antibodies was used to evaluate the possible physiological role of this neuropeptide in the regulation of gonadotropin and PRL secretion in the mouse. Because regulation of anterior pituitary function can be profoundly altered by chronic GH excess, we felt it was also of interest to have examined the effects of immunoneutralization of NPY in transgenic mice expressing bovine (b) GH gene with mouse metallothionein-I promotor. Intact or castrated transgenic and normal (nontransgenic) littermate adult male mice were injected with control rabbit serum or anti-NPY rabbit serum (anti-NPY). Blood samples were obtained 24 h later for hormone measurements. In intact transgenic mice expressing bGH gene, plasma LH levels were reduced and plasma PRL levels were increased, as compared to their normal littermates. Plasma levels of FSH were similar in normal and transgenic animals. Injection of anti-NPY increased plasma LH levels significantly in both intact normal and intact transgenic mice. However, plasma levels of FSH and PRL were increased significantly after anti-NPY treatment only in intact normal mice. In both normal and transgenic males, castration lead to the expected increase in plasma FSH and LH levels, whereas plasma levels of PRL remained unaltered. Administration of anti-NPY to castrated animals was followed by a significant increase in circulating LH levels in both transgenic and normal mice, whereas plasma levels of PRL were not changed. The results suggest that NPY plays a physiological role in the control of gonadotropin and PRL release in the adult male mouse, and that expression of the bGH gene in transgenic mice is associated with altered role of endogenous NPY in the control of pituitary function.

Animals↗

PubMed1990

Neurokinin A in the hypothalamus and anterior pituitary during the estrous cycle in the golden hamster.

The fluctuations in the neurokinin A concentrations in the hypothalamus and anterior pituitary of female golden hamsters were studied in the different stages of the estrous cycle, and they were correlated with the changes in serum estradiol levels. Neurokinin A levels in the hypothalamus were lowest at day 4 of the cycle (proestrus), when serum estradiol levels were highest. Neurokinin A levels in the hypothalamus of hamsters in day 1 (estrus), day 2 (diestrus I), and day 3 (diestrus II) were not significantly different from each other. In the anterior pituitary, the highest neurokinin A concentrations were found during day 1 of the cycle (estrus), the levels in day 2 (diestrus I), day 3 (diestrus II), and day 4 (proestrus) were significantly lower than at estrus, again showing the lowest levels during proestrus, when estradiol levels were maximal. These results show that neurokinin A levels in the hypothalamus and anterior pituitary of the female hamster undergo significant changes during the estrous cycle.

Animals↗