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

The role of neurokinin A and its receptor in the regulation of prolactin secretion by the anterior pituitary of cyclic pigs

In pigs, plasma prolactin concentration markedly changes during the oestrous cycle and the regulation of its secretion is very complex. The contribution of neurokinins in this process has not been sufficiently delineated. The aim of the study was to examine the effects of neurokinin A (NKA) on prolactin synthesis and secretion in cyclic gilts. The expression of NKA precursor (Ppta) and receptor (Tacr2) genes as well as NKA and TACR proteins content in the porcine pituitaries (days 2-3, 9-10, 12-13, 15-16 and 19-20 of the cycle) was determined. Furthermore, the in vitro influence of NKA on the expression of prolactin (Prl), dopamine receptor (D2r), TRH receptor (Trhr) genes and prolactin secretion by the porcine pituitary cells (days 9-10, 15-16 and 19-20 of the cycle) was assessed. The expression of Ppta and Tacr2 as well as NKA and TACR proteins in the pituitary tissue has been changing throughout the oestrous cycle. NKA affected in vitro the expression of studied genes and prolactin secretion depending on the stage of the cycle, dose of NKA and/or duration of the cell incubation. Altogether, the study indicates that NKA is engaged in the modulation of prolactin secretion in the pig during the oestrous cycle.

Prenatal melatonin and its interaction with tachykinins in the hypothalamic-pituitary-gonadal axis

The pineal gland, through its hormone melatonin, influences the function of the hypothalamic-pituitary-gonadal axis. Tachykinins are bioactive peptides whose presence has been demonstrated in the pineal gland, hypothalamus, anterior pituitary gland and the gonads, in addition to other central and peripheral structures. Tachykinins have been demonstrated to influence the function of the hypothalamic-pituitary-gonadal axis, acting as paracrine factors at each of these levels. In the present review, we examine the available evidence supporting a role for melatonin in the regulation of reproductive functions, the possible role of tachykinins in pineal function and the possible interactions between melatonin and tachykinins in the hypothalamic-pituitary-gonadal axis. Evidence is presented showing that melatonin, given to pregnant rats, influences the developmental pattern of tachykinins in the hypothalamus and the anterior pituitary gland of the offspring during postnatal life. In the gonads, the effects of melatonin on the tachykinin developmental pattern were rather modest. In particular, in the present review, we have included a summary of our own work performed in the past few years on the effect of melatonin on tachykinin levels in the hypothalamic-pituitary-gonadal axis.

Tachykinins and ovarian function in mammals

Tachykinins are bioactive peptides whose presence has been demonstrated in endocrine glands, where they likely exert a paracrine modulatory activity on hormonal secretions. In the ovary, tachykinins have been shown to be present in nerve fibers, blood vessels, and in granulosa, luteal and interstitial cells. Tachykinin gene expression was shown in granulosa and luteal cells. Tachykinins have also been found in the follicular fluid. Substance P (SP) has been demonstrated to significantly affect the release of hormonal steroids by ovarian cells in vitro. While some authors found that SP stimulated the release of steroids, others found an inhibitory effect by the same tachykinin. Gonadotropins decrease tachykinin concentrations in the ovary. The neonatal treatment of rats with capsaicin, a drug that depletes SP in primary afferent neurons, resulted in a modest reduction in the reproductive success in rats. The experimental results listed in this review suggest that tachykinins are synthesized in the ovary, in the granulosa and luteal cells. Tachykinins are likely intraovarian modulators of the secretion of hormonal steroids. Their stores in the ovary are likely regulated by pituitary gonadotropins.

NMDA and group I metabotropic glutamate receptors activation modulates substance P release from the arcuate nucleus and median eminence

Glutamate participates in the regulation of secretion of several neuropeptides, including substance P (SP). Glutamate acts through ionotropic (iGluR) and metabotropic (mGluR) receptors. We have investigated whether glutamate receptor agonists and antagonists could affect SP release from the arcuate nucleus and the median eminence (ARC/ME). An increase in SP-like immunoreactivity (SP-LI) release from ARC/ME was induced by glutamate and N-methyl-D-aspartate (NMDA). This increase was prevented by D-(-)-2-amino-5-phosphono pentanoic acid (DAP5) (0.1mM), a specific NMDA antagonist and by (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) (0.1 mM), a selective antagonist of group I mGluR. The selective non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3(1H-4H)-dione (DNQX) (0.1mM) and (RS)-alpha-methyl-4-tetrazolylphenylglycine (MTPG) (0.1 mM), a group II and III mGluRs antagonist, did not affect the stimulatory effect of glutamate. A group I selective agonist, (S)-3,5-dihydroxyphenylglycine (DHPG) induced a significant increase in SP-LI release. Supporting the participation of nitric oxide (NO) in the effect of glutamate on SP-LI release, NAME (0.5 mM), a NO synthase inhibitor, reduced the glutamate-induced increase in SP-LI release from ARC/ME. Similarly, glutamate did not induce an increase in SP-LI release in the presence of meloxicam (0.1 mM) (a cyclooxygenase-2 (COX-2) specific inhibitor) indicating that prostaglandins production may also be involved in the glutamate effect. These data indicate that glutamate increases SP-LI release from the ARC/ME by acting through NMDA and group I mGluRs in the male rat. This stimulatory effect could be mediated by nitric oxide and prostaglandin production.

Intra-pituitary regulation of gonadotrophs in male rodents and primates

Paracrine and autocrine regulation is well established in many organs including the gonads, but the notion of communication among pituitary cells is a relatively new concept. The FSH-beta and GnRH-receptor genes are up-regulated by pituitary activin and down-regulated by pituitary follistatin, and circulating inhibin disrupts this local regulation by functioning as an endogenous competitor of the activin receptor. Activin and follistatin production by folliculostellate cells may play a central role in these responses. alpha-Subunit expression is maintained at high levels in the absence of GnRH through unknown mechanisms. There is evidence that the intra-pituitary regulation of FSH-beta and GnRH-receptor gene expression may activate pubertal maturation in male rats. Finally, there are marked differences in follistatin expression and its regulation by GnRH and androgens in male primates and rats that appear to explain species differences in the differential secretion of FSH and LH, although the physiological significance of these differences is not yet known.

Influence of maternal pineal gland on the developmental pattern of neurokinin A (NKA) and substance P (SP) in male-rat-offspring: relationship to the season of the year

The present study examines the influence of maternal pineal gland on the frontal cortex, striatal and testicular concentrations of the tachykinins, neurokinin A (NKA) and substance P (SP). Control, pinealectomized (PIN-X) and PIN-X plus melatonin-treated (PIN-X + MEL) mother rats were prepared. Male offspring rats were studied at 21, 31 and 60 days of age, during the four seasons of the year. In control-offspring tachykinin concentrations in frontal cortex were found at their highest levels in 21-day-old rats with a moderate decrease up to 60 days of age. This developmental pattern was season-dependent, observed only during summer and fall. Maternal PIN-X or PIN-X + MEL resulted in alterations in the offspring, showing during spring and summer significantly higher concentrations (P < 0.01) and during fall significantly lower concentrations of tachykinins in the frontal cortex (P < 0.05, P < 0.01) as compared to control-offspring. The tachykinin concentration in the striatum of control-offspring showed no major modifications throughout the ages studied in the four seasons of the year. With very few exceptions, PIN-X- and PIN-X + MEL did not alter tachykinin concentrations in striatum. Testicular SP concentrations showed a decrease from 21 to 60 days of age. PIN-X or PIN-X + MEL only caused minor and inconsistent modifications in testicular SP levels. In conclusion, our data clearly indicate for the first time that the maternal pineal gland participates in the regulation of the postnatal tachykinin development in some areas of the central nervous system. This effect was more evident in the frontal cortex than in the striatum and testes.

Seasonal changes of SP and NKA in frontal cortex, striatum and testes in the rat. Role of maternal pineal gland

The concentrations of neurokinin A (NKA) and substance P (SP), members of tachykinins family, have been studied in all seasons of the year in frontal cortex, striatum and testes of male offspring 21-, 31-, or 60 days old of mother Wistar rats: control, pinealectomized (PIN-X) and pinealectomized + melatonin during pregnancy (PIN- X + MEL) kept under 12h:12h L:D. Control-offspring: in spite of having been kept under constant environmental conditions throughout the year, had marked differences in tachykinin concentrations. The highest tachykinin concentrations in the frontal cortex were found in summer and fall and the lowest in winter and spring. Maternal PIN-X resulted in alterations of this developmental pattern, mainly in PIN-X- and PIN- X + MEL-offspring in which the highest tachykinin concentrations at 21 and 31 days of age were only observed during summer. The alterations were observed up to 60 days of age for both tachykinins, when at this age control-offspring showed similar NKA concentrations. Seasonal variations were still observed in PIN-X- and PIN- X + MEL-offspring. In striatum and testes no mayor modifications throughout the four seasons of the year were found, with very few exceptions. PIN-X did not alter tachykinin concentrations, neither treatment with melatonin did it. In conclusion, our data clearly indicate for the first time that NKA and SP do indeed have seasonal rhythms in frontal cortex and that the maternal pineal gland plays a role in their entrainment already during fetal life.

Tachykinins in the normal and gonadotropin-stimulated ovary of the mouse

In this investigation, substance P (SP) and neurokinin A (NKA) concentrations have been determined in the ovary of control prepubertal mice, and prepubertal mice injected with pregnant mare serum (PMS) gonadotropin, an equine gonadotropin with predominant FSH action, or with PMS followed by human chorionic gonadotropin (hCG), which produces heavily luteinized ovaries after the stimulation with PMS. Control animals were injected with saline. The ovaries of animals treated with gonadotropins were heavier than the control ovaries, the combination of PMS plus hCG produced significantly heavier ovaries than PMS alone. The concentrations of SP and NKA in the ovaries of the animals treated with PMS or PMS/hCG were significantly lower than in control ovaries. No significant differences in ovarian tachykinin concentrations were observed between PMS and PMS/hCG-treated animals. The total ovarian content of SP was lower in PMS-injected animals as compared with the controls. The total ovarian content of NKA was not significantly different in the three groups of animals studied. These results show that ovaries stimulated with gonadotropins have lower concentrations of tachykinins than normal ovaries at the same age. It is therefore evident that gonadotropins can affect tachykinin stores in the ovaries of mice.

Tachykinins and their possible modulatory role on testicular function: a review

Tachykinins are vasoactive and smooth muscle-contracting peptides with widespread localizations. Tachykinins have been localized in the nerve fibres that supply the testes, in the Leydig cells of different animal species, and also in Sertoli cells of the Siberian hamster testes. The presence of substance P (SP) has also been demonstrated in ejaculated human spermatozoa and in the seminal plasma. Tachykinins have been shown to inhibit the release of testosterone by testicular fragments or by isolated Leydig cells in vitro. Acting on Sertoli cells, tachykinins have been shown to stimulate the release of lactate and transferrin by these cells in vitro, and also to stimulate aromatase activity. Leydig and Sertoli cells express the Preprotachykinin A gene, and this fact strongly suggests that tachykinins can be synthesized in the testes. These findings suggest that tachykinins may have a physiological function in the testes as modulators of the functions of the different cell types contained in these organs.

Age differences in neurokinin A and substance P from the hypothalamus, pituitary, pineal gland, and striatum of the rat. Effect of exogenous melatonin

Previous data showed that aging of the central nervous system (CNS) is associated with widespread changes in tachykinin gene expression. However, there are no data about the possible role of exogenous melatonin in modulating the tachykinergic system during aging. The aim of this work was to analyze the age-dependent changes on neurokinin A (NKA) and substance P (SP) levels in hypothalamus, pituitary, pineal gland and striatum and the role of exogenous melatonin on these changes. We studied female rats at three different ages: 5-month-old (cyclic), 15-month-old (preacyclic) and 25-month-old (acyclic). Hypothalamic tachykinin levels increase when female rats reached acyclicity, this increase was blunted in acyclic-melatonin-treated rats. However, melatonin treatment in young cyclic rats resulted in significantly increased values as compared to controls. Pituitary NKA concentrations did no show age-dependent changes in control rats, however, in both, preacyclic and acyclic-melatonin-treated rats significantly increased values of pituitary NKA were found compared to controls. In the pineal gland, a marked decrease of NKA levels was observed in acyclic-control rats. Melatonin treatment did not alter this decrease. In the striatum, NKA and SP concentrations were significantly reduced in preacyclic- and acyclic-control rats compared to young cyclic rats, melatonin had no effect on striatal tachykinins. Our results indicate that melatonin may regulate tachykinin stores during aging mainly on structures of the neuroendocrine-reproductive axis.

Intercellular communication in the anterior pituitary

In addition to hypothalamic and feedback inputs, the secretory cells of the anterior pituitary are influenced by the activity of factors secreted within the gland. The list of putative intrapituitary factors has been expanding steadily over the past decade, although until recently much of the work was limited to descriptions of potential interactions. This took the form of evidence of production within the pituitary of factors already known to influence activity of secretory cells, or further descriptions of actions on pituitary cells by such factors when added exogenously. A new phase of discovery has been entered, with extensive efforts being made to delineate the control of the synthesis and secretion of the pituitary factors within the gland, regulation of the receptors and response mechanisms for the factors in pituitary cells, and measurements of the endogenous actions of the factors through the use of specific immunoneutralization, receptor blockade, tissue from transgenic animals, and other means. Taken together, these findings are producing blueprints of the intrapituitary interactions that influence each of the individual types of secretory cells, leading toward an understanding of the physiological significance of the interactions. The purpose of this article is to review the recent literature on many of the factors acting as intrapituitary signals and to present such finding in the context of the physiology of the secretory cells.

Effect of progesterone on tachykinin concentrations in the hypothalamus and anterior pituitary of female siberian hamsters

The effect of progesterone on SP- and NKA-like immunoreactive substances in the hypothalamus and anterior pituitary was studied in ovariectomized and in ovariectomized, estrogen treated Siberian hamsters. Neither ovariectomy nor progesterone or estradiol treatment resulted in apparent changes in the tachykinin concentration in the hypothalamus. No effect of the treatments was seen on the release of tachykinins by hypothalami incubated in vitro in presence of high KCl concentrations. Ovariectomy resulted in a significant increase in the concentrations of both tachykinins in the anterior pituitary, as compared with intact animals. Progesterone (5 mg/animal) significantly reduced tachykinin concentrations in the anterior pituitary, as compared with the values found in ovariectomized animals. Estradiol completely suppressed the post-ovariectomy increase in anterior pituitary tachykinins, and progesterone did not significantly modify the response to estradiol. Lower doses of progesterone (250 microg or 1 mg/animal) significantly reduced NKA concentrations in the anterior pituitary of ovariectomized Siberian hamsters, but SP concentrations, although showing a similar tendency, were not significantly different in progesterone-treated as compared with ovariectomized, control animals. These results suggest that progesterone may modulate tachykinin stores in the anterior pituitary gland of Siberian hamsters.

Developmental changes of hypothalamic, pituitary and striatal tachykinins in response to testosterone: influence of prenatal melatonin

Substance P (SP) and neurokinin A (NKA), members of the family of mammalian tachykinins, are involved in the regulation of many physiological functions and are widely distributed in mammalian tissues. In this report, the effects of prenatal melatonin on the postnatal developmental pattern of NKA, and SP, and on testosterone secretion were investigated. Also, tachykinin response to the administration of testosterone propionate (TP) was studied. The brain areas studied were medio-basal-hypothalamus, pituitary gland and striatum. Male rat offspring of control or melatonin treated mother rats were studied at different ages of the sexual development: infantile, juvenile or prepubertal periods, and pubertal period. Both groups received exogenous TP (control-offspring+TP and MEL-offspring+TP), or the vehicle (control-offspring+placebo and MEL-offspring+placebo). Hypothalamic concentrations of all peptides studied in control-offspring+placebo remained at low levels until the juvenile period, days 30-31 of age. After this age, increasing concentrations of these peptides were found, with peak values at puberty, 40-41 days of age, then declining until adulthood. In the MEL-offspring+placebo a different pattern of development was observed; hypothalamic concentrations of NKA and SP from the infantile period until the end of juvenile period were significantly higher than in control-offspring+placebo. TP administration exerted a more marked influence on MEL-offspring than on control-offspring and prevented the elevation in tachykinin concentrations associated with prenatal melatonin treatment. TP administration to control-offspring resulted in significantly reduced (P < 0.05) tachykinin concentration only at 40-41 days of age, and increased (P < 0.01) during infantile period as compared to control-offspring+placebo. Pituitary NKA concentrations were lower than in the hypothalamus. In control-offspring+placebo pituitary NKA levels did not show significant changes throughout sexual development. A different developmental pattern was observed in MEL-offspring+placebo, with significantly increased (P < 0.05) pituitary NKA concentrations at 35-36 days of age than in control-offspring+placebo. TP administration to control-offspring influenced pituitary NKA levels at the end of the infantile and pubertal periods, showing at both stages significantly higher (P < 0.05) NKA levels as compared to control-offspring+placebo. NKA levels in MEL-offspring+TP were only affected at 21-22 days of age, showing significantly increased (P < 0.01) values as compared to MEL-offspring+placebo. Striatal tachykinin concentrations in control-offspring did not undergo important modifications throughout sexual development, but during the prepubertal period they started to increase. Maternal melatonin and TP injections produced short-lived alterations during the infantile period. The results showed that prenatal melatonin delayed the postnatal testosterone secretion pattern until the end of the pubertal period and postnatal peptide secretion in brain structures. Consequently, all functions depending of the affected areas will in turn, be affected.

Modulation of the hypothalamo-pituitary-gonadal axis and the pineal gland by neurokinin A, neuropeptide K and neuropeptide gamma

Modulation of the hypothalamo-pituitary-gonadal axis and the pineal gland by neurokinin A, neuropeptide K, and neuropeptide gamma. PEPTIDES 1999. Neurokinin A (NKA), neuropeptide K (NPK) and neuropeptide gamma (NPG) are members of the family of tachykinins, and act preferentially on NK-2 tachykinin receptors. These peptides are widely distributed and are potent stimulators of smooth muscle contraction, especially in the respiratory and gastrointestinal tract. They also induce vasodilatation and plasma extravasation. Through their effects on the vascular tone, they are also potential regulators of the blood flow and therefore of the function of many organs and tissues. Tachykinins have been demonstrated to influence the secretory activity of endocrine cells, and they may have a physiological role as regulators of endocrine functions. A number of reports have indicated that NPK, NKA and NPG act on the hypothalamo-pituitary gonadal axis to regulate functions related to reproduction. Therefore, we thought that, at this point, it was important to review the available evidence suggesting the role of these tachykinins on reproductive functions by effects exerted at 3 different levels of regulation: the hypothalamus, the anterior pituitary and the gonads. These 3 tachykinin peptides were reported to have effects on reproductive functions, acting on the control of the secretion of gonadotropin and prolactin at the level of the hypothalamo-pituitary axis, and on the steroid secretion by the testes and the ovaries. Acting on the hypothalamus, tachykinins, mainly NPK, were reported to inhibit LH secretion, but this effect is dependent on the presence of gonadal steroids. On the anterior pituitary gland, however, tachykinins were shown to stimulate LH and prolactin secretion, and this effect is also dependent on the presence of gonadal steroids. Tachykinin concentrations in the hypothalamus and pituitary are regulated by steroid hormones. In the hypothalamus, estrogens and testosterone increase tachykinin concentration. In the anterior pituitary gland, estradiol and thyroid hormones markedly depress tachykinin concentrations. Ovariectomy and exposure to short photoperiods significantly increase anterior pituitary tachykinins in the Siberian hamster. In the pineal gland, SP and NK-1 receptors are present and, more recently, the presence of NKA and probably also NPK was demonstrated. Castration and steroid replacement modified the content of tachykinins in the pineal gland. The removal of the superior cervical ganglia was followed by an increase in NKA content in the pineal gland. These results suggest that gonadal steroids may influence tachykinins in the pineal gland. In the gonads, tachykinins stimulated the secretory activity of Sertoli cells, but inhibited testosterone secretion by Leydig cells. There are very few reports on the role of tachykinins in the ovary, but some of them indicated that these peptides are present in some of the ovarian structures, and they may affect the secretion of ovarian steroids. Thus, NKA, NPK and NPG appear to have a modulatory role, mainly acting as paracrine factors, on the hypothalamo-pituitary-gonadal axis.

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.

Plasma substance-P and substance-K and gonadal steroids in relation to the gonadotropin surge in normal human reproductive cycles

PURPOSE

This study was designed to examine changes in peripheral plasma substance-P and -K levels, their association with follicle-stimulating hormone and luteinizing hormone release in normal reproductive cycles in humans, and their correlation with plasma estradiol and progesterone.

METHODS

Fourteen healthy, normally menstruating women underwent daily blood sampling (cycle day 4, 4-14 days) for measurement of estradiol, progesterone, luteinizing hormone, and follicle-stimulating hormone, substances-P and -K, and daily transvaginal ultrasounds assessing follicular growth and documentation of ovulation.

RESULTS

Estradiol peaked on day 13, luteinizing hormone and follicle-stimulating hormone peaked on day 14, and progesterone began an exponential increase on about day 13.

CONCLUSIONS

In contrast to other experimental designs using in vitro or in vivo rat or monkey tissue, peripheral levels of substances-P (P = 0.8391) and -K (P = 0.3205) reflected no modulation related to midcycle gonadotropin release in cycling woman.

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.

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.

Tachykinins and their gene expression in the anterior pituitary of the siberian hamster-Effects of photoperiod, thyroid hormones, and analogs of hypothalamic hormones

The anterior pituitary gland of the Siberian hamster contains high concentrations of tachykinins compared to other laboratory rodents. In this investigation we studied the relative quantities of neurokinin A (NKA), neuropeptide gamma (NPG), and neuropeptide K (NPK) present in extracts of anterior pituitaries from this species. The anterior pituitary extracts, purified by HPLC, contained similar quantities of NKA and NPG, and lower quantities of NPK. The anterior pituitary gland of the Siberian hamster contained mRNA encoding β-preprotachykinin A, which is a precursor of substance P, NKA, and NPK. This fact proves that the anterior pituitary gland of the Siberian hamster has the ability to synthesize tachykinins. Animals exposed to short photoperiods had higher concentrations of tachykinins in the pituitary gland, and triiodothyronine markedly depressed the stores of these peptides in the anterior pituitary. In some groups of animals, the somatostatin analog octreotide induced a small, but significant decrease of the levels of NKA in the pituitary. The present results, together with previously published findings, indicate that thyroid hormones and estrogens are the most active endogenous substances to suppress the levels of anterior pituitary tachykinins in the Siberian hamster.

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)