Biomedical subjects

A Sahu

Publications and source records attributed to A Sahu.

At least 73 records · Page 4Linked to original sources

PubMed1994

Evidence in support of nitric oxide (NO) involvement in the cyclic release of prolactin and LH surges.

Studies were undertaken to determine whether nitric oxide (NO) is involved in induction of the prolactin surge on proestrus and in that induced by ovarian steroids in ovariectomized (ovx) rats, by using inhibitors of NO synthase, the enzyme that generates NO. Two week-ovariectomized rats were treated either with estradiol benzoate (EB, 30 micrograms/rat, s.c.) alone, or with EB and 2 days later with progesterone (P, 2 mg/rat, s.c.) to evoke a prolactin surge in the afternoon. Injections of the NO synthase inhibitor Nw-nitro-L-arginine methyl ester (40 mg/kg, s.c.) at 10.000, 12.00, and 14.00 h completely suppressed the steroid-induced prolactin surge in the afternoon. Similarly, another NO synthase inhibitor, Nw-nitro-L-arginine (100 mg/kg, s.c.), injected at 1000, 1200, and 1400 h on proestrus suppressed prolactin and luteinizing hormone (LH) surges, but failed to alter the daily increase of corticosterone. These studies confirm our earlier report and show that NO is involved in the complex processes that initiate the afternoon prolactin and LH surges of proestrus.

Animals↗

PubMed1994

Specificity of the thioester-containing reactive site of human C3 and its significance to complement activation.

The specificity of the thioester-containing site in three plasma proteins is regulated by elements of their protein structures other than the thioester bond itself. Human C4A and alpha 2-macroglobulin preferentially form amide linkages while human C3 primarily forms ester linkages with hydroxyl groups. We have examined the thioester in C3 and found evidence of strong preferences for certain carbohydrates, indications of selectivity for specific positions on those carbohydrates and a preference for terminal sugars in polysaccharides. A testable set of rules are derived from these findings which predict preferred attachment sites on polysaccharides. A computer model of the effect of different reactivities on activation of the alternative pathway of complement suggested that organisms might greatly alter their susceptibility to complement with small changes in carbohydrate structure. While a random selection of 20 biological particles showed no correlation between activation and C3b attachment efficiency, subsets of related organisms differing primarily in their surface polysaccharide exhibited stronger correlations. The strongest correlation occurred in a series of the yeasts (Cryptococcus neoformans) possessing capsular polysaccharides with one, two, three or four branching xylose sugars per repeating unit. These organisms exhibited capture efficiencies for metastable C3b from 12% (one-xylose strain) to 41% (four-xylose strain).

Alcohols↗

PubMed1994

The hypothalamic peptides, beta-endorphin, neuropeptide K and interleukin-1 beta, and the opiate morphine, enhance the excitatory amino acid-induced LH release under the influence of gonadal steroids.

Several hypothalamic neuropeptides and amino acids are known to inhibit or excite pituitary luteinizing hormone (LH) release, but the precise interplay between these 2 classes of signals in episodic LH discharge is not known. In this study, we have evaluated the interaction between neuropeptides shown previously to inhibit LH release in castrated rats and the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA), on LH release in intact male rats. Rats received a permanent intracerebroventricular (i.c.v.) cannula and 9-12 days later an intrajugular cannula for frequent blood sampling. The next day, rats received i.c.v. either saline (SAL, 3 microliters, controls) or a neuropeptide: the opioid beta-endorphin (beta-END; 2.9 nmol), the tachykinin neuropeptide K (NPK, 2.5 nmol) or the cytokine interleukin-1 beta (IL-1 beta, 5.9 pmol) in SAL. The LH response to 2 consecutive i.v. injections of NMDA (5 mg/kg) at 30 min intervals was evaluated. In control rats, each NMDA injection evoked a significant release of LH at 10 min. Quite unexpectedly, the three peptides, instead of exerting an inhibitory effect, enhanced the LH response to NMDA. The peak plasma LH levels after each NMDA injection and the cumulative LH responses were significantly higher in peptide-treated than in control rats. This peculiar ability of the peptides that inhibit LH release in castrated rats, to potentiate the NMDA-induced LH release in the presence of gonadal steroids was further validated in female rats treated with an opiate receptor agonist, morphine (MOR) which is also known to suppress LH release in ovariectomized rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Role of galanin in stimulation of pituitary luteinizing hormone secretion as revealed by a specific receptor antagonist, galantide.

In this study, a specific galanin (GAL) receptor antagonist, galantide, was employed to evaluate the role of endogenous GAL in episodic basal and phasic LH release in rats. To assess the specificity of galantide, a series of experiments was performed. In the first experiment, we observed that administration of GAL (0.62 nm) intracerebroventricularly (icv) in ovarian steroid-primed ovariectomized (ovx) rats rapidly increased plasma LH levels between 10-30 min, and prior injection of galantide icv (5 nm) blocked the GAL-induced LH release. In the second experiment, galantide inhibited the GAL-evoked in vitro release of LHRH from the median eminence-arcuate nucleus (ME-ARC) of ovarian steroid-primed ovx rats. In addition, galantide on its own significantly decreased the basal efflux of LHRH from the ME-ARC of similarly treated rats, thereby suggesting that even the basal LHRH secretion may be a GAL-dependent event. In the third experiment, the effects of galantide on the phasic LH surge elicited by progesterone (P) in estradiol benzoate-primed ovx rats and that occurring spontaneously on proestrus were examined. Ovx rats bearing icv cannulae were primed with estradiol benzoate (30 micrograms/rat, sc) and 2 days later received a P (2 mg/rat, sc) injection at 1000 h to evoke a LH surge in the afternoon. Galantide (1 or 5 nm) in 3 microliters saline or saline was injected icv at 1300, 1400, and 1500 h. The results showed that the two dosages of galantide suppressed the LH surge in the afternoon. On the other hand, only a very high dose of galantide (15 nm) injected iv at 1300, 1400, and 1500 h blunted the P-induced LH hypersecretion. Central injections of galantide (1 or 5 nm) at 1300, 1400, and 1500 h on proestrus also inhibited the preovulatory LH surge and significantly reduced the numbers of rats ovulating the following day. In the final experiment, the role of GAL receptors in modulation of episodic LH release was analyzed in ovx rats. The results showed that an injection of galantide (5 nm, icv) significantly decreased both the mean LH levels and the amplitude of LH episodes during the 3-h observation period. Cumulatively, these results show that normally GAL stimulates LHRH release by activation of a specific receptor located in the ME-ARC, and that GAL may be a key excitatory signal in the hypothalamic neural circuitry involved in the regulation of basal episodic and phasic LHRH secretion in cycling female rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Hypothalamic neuropeptide-Y gene expression increases before the onset of the ovarian steroid-induced luteinizing hormone surge.

Neuropeptide-Y (NPY), a hypothalamic peptide, is involved in stimulation of LHRH and LH surges during proestrus and those induced by ovarian steroids in ovariectomized (ovx) rats. The NPY neurons that reside in the arcuate nucleus of the medial basal hypothalamus (MBH) and accumulate 17 beta-estradiol participate in the initiation of LHRH and LH surges. To determine whether NPY synthesis is altered in conjunction with the LH surge, we studied the dynamic changes in prepro-NPY mRNA levels in the MBH in association with the LH surge elicited by estradiol benzoate (EB) alone or by progesterone (P) in EB-primed ovx rats. Five days after ovariectomy, rats received oil or EB (30 micrograms/rat) at 1000 h on day 0. On day 2, these rats were injected with either oil or P (2 mg/rat) at 1000 h. Rats were killed before (1000 h) and at 2-h intervals after oil or P injection. The MBHs were dissected out and processed for determination of prepro-NPY mRNA levels by solution hybridization/RNase protection assay using a cRNA probe. Although in control ovx rats, prepro-NPY mRNA levels remained unchanged between 1000-1600 h, prepro-NPY mRNA levels showed dynamic changes in steroid-primed rats. In the EB-primed rats, prepro-NPY mRNA levels rose significantly (100%) at 1200 and 1400 h before the LH rise at 1600 h, and the levels remained elevated up to 1800 h. After P injection to the EB-primed rats, this response was further augmented, with a slightly different temporal pattern. Prepro-NPY mRNA levels rose at 1400 h (600%) before the onset of the LH rise at 1600 h and declined steadily to significantly lower values at 1800 h, coincident with the highest rate of LH secretion. These studies demonstrate dynamic shifts in hypothalamic NPY gene expression in association with the LH (LHRH) surge, and that maximal increases occur before the onset of the LH rise, but thereafter, NPY gene expression diverged in the two ovarian-steroid treatment models. These findings along with previous evidence of similar antecedent increases in NPY content in the median eminence, followed by release, suggest that augmented NPY synthesis and release are two temporally dissociable neural events for the LHRH and LH surges.

Animals↗

PubMed1993

Antibody dependent haemolysin, complement and opsonin in sera of a major carp, Cirrhina mrigala and catfish, Clarias batrachus and Heteropneustes fossilis.

The present communication is a continuation of our earlier study on the natural serum haemagglutinin/lectins of Cirrhina mrigala, Clarias batrachus and Heteropneustes fossilis. Sera of Cirrhina mrigala, belonging to the major carp family, could not only agglutinate heterologous rabbit erythrocytes, but also lyse them spontaneously. This lysis of rabbit RBC by Cirrhina mrigala sera was calcium ion dependent and heat sensitive, indicating thereby that the haemolysis was mediated by the fish serum complement system via the classical pathway. Quantification of CH50 and APCH50 levels in the sera of Clarias batrachus and Heteropneustes fossilis as well as in the sera of amphibia, aves and mammals showed that lower vertebrates predominantly possessed an alternative pathway of the complement system, while on the other hand, in the higher vertebrates the major pathway of complement activation was classical. Furthermore sera of Clarias batrachus and Heteropneustes fossilis had opsonins, which could stimulate heterologous rat peritoneal macrophages to engulf Staphylococcus aureus with the production of superoxide anion. From this study we concluded that fishes have been armed with various powerful natural humoral defense systems for their protection against environmental pathogens.

Animals↗

PubMed1993

Identification of multiple sites of interaction between heparin and the complement system.

Many diverse effects of heparin on the complement system have been reported. In only a few cases have the sites or the mechanisms of these effects been identified. In order to understand these results we sought to comprehensively analyze which complement proteins interact with heparin and which do not. Purified components of the classical, alternative and terminal pathways of complement were radiolabeled and their affinity for heparin determined. Affinity chromatography of normal human serum on heparin-agarose allowed a complete analysis of complement proteins and confirmed the results obtained with radiolabeled purified components. Of the 22 complement proteins examined, 13 bound heparin (C1q, C2, C4, C4bp, C1INH, B, D, H, P, C6, C8, C9, and vitronectin) while 9 did not bind heparin (C1r, C1s, C3, Factor I, C5, C7, C3b, Ba and Bb). These observations help explain the many effects heparin has on the complement system and they identify the proteins which need to be examined in order to explain these effects.

Chromatography, Affinity↗

PubMed1993

Role of neuropeptide-Y in episodic luteinizing hormone release in ovariectomized rats: an excitatory component and opioid involvement.

We tested the hypothesis that hypothalamic neuropeptide-Y (NPY) is an excitatory signal in the episodic secretion of LH in ovariectomized (ovx) rats and that the suppression of LH secretion that consistently follows intracerebroventricular administration of NPY is due to concurrent release of opioids or CRH, both previously shown to readily inhibit LH release. In the first experiment, ovx rats received continuous intraventricular infusion of either serum containing NPY antibodies (NPY-Ab) or normal rabbit serum (control) at dilutions of 1:5 or 1:1. NPY-Ab infusion at a 1:5 dilution significantly decreased mean plasma LH levels and LH pulse amplitude without affecting LH pulse frequency over a 3-h period of observation. However, infusion of relatively more concentrated NPY-Ab (1:1) markedly decreased not only mean plasma LH levels and LH pulse amplitude, but also the frequency of LH episodes. In the next experiment, we observed that intraventricular administration of NPY (0.2 nmol) suppressed LH release for 60 min. However, blockade of opiate receptors with iv infusion of naloxone (2 mg/h) before and after NPY injection completely counteracted the NPY-induced inhibition of LH release. On the other hand, prior blockade of the CRH receptors with alpha-helical CRH-(9-41) (25 or 100 micrograms/rat) was ineffective in reversing the inhibitory LH response of NPY (0.125 nmol). These results together with our previous demonstration of morphological communication between NPY and beta-endorphin neurons, show that suppression of LH by exogenous NPY in ovx rats may result from concurrent stimulation of opioids, primarily beta-endorphin. However, diminution of all parameters of episodic LH secretion by NPY-Ab affirms the notion that the NPY network is a physiologically important excitatory component of the hypothalamic pulse generator circuitry that regulates episodic LH secretion in rats.

Animals↗

PubMed1993

Evidence that nitric oxide may mediate the ovarian steroid-induced luteinizing hormone surge: involvement of excitatory amino acids.

The involvement of excitatory N-methyl-D-aspartate (NMDA) receptors in the hypothalamic control of pituitary LH secretion is well recognized. Recent evidence shows that nitric oxide (NO), a free radical gas, may act as neurotransmitter in the brain, and its efflux is stimulated by activation of NMDA receptors. Studies were undertaken to determine whether NO is involved in the hypothalamic release of LHRH and in the LH surge induced by progesterone (P) in estrogen-primed ovariectomized rats. Rats were ovariectomized and 2 weeks later received estradiol benzoate (30 micrograms sc) at 1000 h. Two days later, P was injected at 1000 h to potentiate the estradiol benzoate-induced LH surge in the afternoon. Serial blood samples were collected at hourly intervals from 1400-1800 h via an intraatrial cannula implanted the day before P injection. Additionally, at various times before onset of the LH surge at 1400 h, the rats were injected sc with one of three inhibitors of NO synthase, the enzyme that generates NO. Control, saline-injected rats showed unambiguous LH surges in the afternoon. However, either a single injection at 1000 h of NG-methyl-L-arginine (20 mg/kg) or three injections at 1000, 1200, and 1400 h of either Nw-nitro-L-arginine methyl ester (NAME, 40 mg/kg) or Nw-nitro-L-arginine (60 mg/kg) to inhibit NO efflux markedly suppressed the P-induced LH surge in the afternoon. To ascertain whether suppression of LH surge was due to blockade of hypothalamic LHRH release, a series of in vitro studies were performed in steroid-primed rats. First we examined the effects of sodium nitroprusside (NPS), a compound that spontaneously generates and releases NO. NPS increased basal and KCl-induced LHRH release in vitro from the medial basal hypothalamus-preoptic area and median eminence fragments. No direct effect of NO at the pituitary level was seen, since NPS did not alter basal or LHRH-induced LH in vitro release from hemipituitaries. In addition, we tested the effects of NAME on NMDA-induced LHRH release in vitro from the median eminence-arcuate nucleus fragments. As expected, NMDA alone (50 mM) induced a significant increase in LHRH release. Addition of NO synthase inhibitor, NAME (1 or 10 mM) to suppress NO efflux, significantly diminished the NMDA-induced LHRH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Ageing of the neuropeptidergic signals in rats.

With advancing age, subtle and progressive disintegration of several components of peptidergic signals that drive luteinizing-hormone-releasing hormone (LHRH) secretion contribute to diminished pituitary-gonadal function in both sexes of the rat. The results show that in female rats, ageing per se and unopposed exposure to oestrogen disrupt different loci in the transmission line to neurones that release LHRH. Ageing per se appears to abolish the restraint on the influence of inhibitory opioids induced by a neural clock--an event necessary for the preovulatory surge of luteinizing hormone to occur in young rats. By contrast, unopposed exposure to oestrogen disrupts the progression and transduction of information at hypothalamic loci downstream from the neural clock-opioid link. In male rats, the age-related diminution in pituitary-gonadal function is probably due to a gradual decrease in release of neuropeptide Y, an excitatory peptidergic signal to LHRH-expressing neurones. Further studies have revealed that this decline is a consequence of age-related acquisition of refractoriness to testosterone by neurones producing neuropeptide Y. Cumulatively, these findings underscore the key roles of hypothalamic peptidergic signals to LHRH-expressing neurones in the ageing process of the reproductive system in rats.

Aging↗

PubMed1992

Evidence that long-term estrogen treatment disrupts opioid involvement in the induction of pituitary LH surge.

Recent evidence suggests that a decrease in the inhibitory opioid influence is a necessary hypothalamic neural event in the preovulatory and ovarian steroid-induced luteinizing hormone (LH) surge. Whether shifts in ovarian steroidal milieu disrupts this neural event is not known. Therefore, the effects of short-term (3 days) and long-term (13 or 17 days) estradiol 17 beta (E2) exposure on spontaneous, naloxone (NAL) and progesterone (P)-induced LH surges were assessed in ovariectomized (ovx) rats. Two weeks after ovariectomy, rats received subcutaneous Silastic capsules filled with crystalline E2. In rats exposed to E2 for 3 days and infused with saline intravenously between 11.00-14.00 h, plasma LH rose significantly at 17.00 h. NAL infusion between 11.00-14.00 h in these rats to decrease the inhibitory opioid influence, advanced both the onset of LH rise and amplified the secretion of LH in the afternoon. Continuation of E2 exposure for 13 days produced no deleterious effects on either the spontaneous or NAL-induced augmentation in LH responses. However, uninterrupted E2 exposure for 17 days abolished the spontaneous afternoon LH rise and drastically diminished the ability of NAL to advance and amplify the LH response. In the next experiment, we evaluated the effect of P injection (2 mg/rat) at 11.00 h on the afternoon LH release in rats similarly exposed to E2 for either 3 or 17 days. In rats exposed to E2 for 3 days, the P-induced LH release was significantly greater than that observed after saline or NAL infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

A selective sexually dimorphic response in the median eminence neuropeptide Y.

Recent studies show that neuropeptide Y (NPY) is widely distributed in the hypothalamus and that it stimulates luteinizing hormone-releasing hormone (LHRH) release from the medial basal hypothalamus (MBH) of male and female rats. The neuroendocrine factors that regulate NPY neurosecretion in two sexes are not well understood. We have previously observed that orchidectomy (orch) in male rats decreased and testosterone (T) replacement increased NPY levels selectively in the median eminence (ME), arcuate nucleus (ARC) and ventromedial nucleus (VMN) and the KCl-evoked in vitro release of NPY from the MBH was likewise decreased after orch and restored by testosterone replacement. Now we report that these NPY responses are different in female rats following removal of the ovaries. Ovariectomy (ovx) decreased NPY concentrations in the ARC and VMN and not in the ME. Estrogen replacement restored NPY concentrations in the ARC and VMN, however, in the ME NPY concentration decreased significantly. Further, the KCl-evoked NPY release in vitro from either the MBH or ME of intact and ovx rats was similar. In an additional concurrent comparative study in male and female rats, we observed that of the 6 microdissected hypothalamic sites, NPY levels were approximately 50% less in the ME of intact females than in those of intact male rats. Again, in male rats there was a significant decrease in NPY levels in the ME, ARC and VMN after orch, whereas in female rats, NPY levels in the ARC and VMN, but not in the ME decreased after ovx.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Hypothalamic neuropeptide Y gene expression in rats on scheduled feeding regimen.

Recent evidence suggests that neuropeptide Y (NPY) is an important signal in the neural circuitry that controls feeding behavior. Previously we observed that in rats entrained to 4 h daily scheduled feeding regimen (SFR), NPY content and release in the paraventricular nucleus (PVN) was elevated but decreased rapidly in association with food consumption. In the present study, we investigated the pattern of hypothalamic NPY gene expression in SFR rats before and after food consumption by measuring the content of preproNPY mRNA in the medial basal hypothalamus (MBH). Adult male rats were maintained on either ad libitum diet (control) or on SFR. Rats were killed before food presentation at 11.00 h and at the end of 4 h food consumption at 15.00 h. The levels of preproNPY mRNA in the MBH were determined by solution hybridization/RNase protection assay using a cRNA probe complementary to rat NPY precursor mRNA. We observed that, as compared to that in control rats on ad libitum diet, preproNPY mRNA levels in the MBH were increased two-fold in the SFR rat at 11.00 h and remained elevated even after 4 h of food consumption. These results show a simultaneous enhancement in PVN NPY release and hypothalamic gene expression in advance of scheduled feeding time, but food intake rapidly decreases PVN NPY release and content, with little impact on hypothalamic gene expression.

Animals↗

PubMed1992

Anti-leprosy drugs inhibit the complement-mediated solubilization of pre-formed immune complexes in vitro.

Incubation of pre-formed immune complexes (IC) (125I-HSA--anti-HSA) with normal human serum resulted in solubilization of IC. When various anti-leprosy drugs were added to human sera, solubilization of IC was fairly explicit with clofazimine, whereas this effect was marginal with dapsone. Rifampicin hardly displayed this effect. Aspirin, chloroquine, and prednisolone, the drugs used in addition to multi-drug therapy to control reactions in leprosy, were in a position to inhibit the solubilization of 125I HSA--anti-HSA by normal serum only at a very high dose. From the current data of the inhibition of solubilization of pre-formed IC along with our earlier observations on the modulation of complement-mediated haemolysis by these drugs, it may be possible to postulate that clofazimine as well as chloroquine affect early complement components. This may in turn be responsible for preventing the deposition of C3 complement onto IC.

Antigen-Antibody Complex↗

PubMed1992

In vivo effects of anti-leprosy drugs on the rat peritoneal macrophages and lymphocyte subpopulations.

The present study describes the in vivo effects of anti-leprosy drugs on rat peritoneal macrophages and T-cell homeostasis. It was observed that BCG-elicited rat peritoneal macrophages produced more H2O2 and expressed more Ia antigen on their cell surfaces compared with resident peritoneal macrophages. Furthermore, elicited macrophages isolated from rats administered multidrug therapy (MDT), consisting of dapsone, clofazimine and rifampicin in high dose (10 x MDT) released more O2-. On the contrary, there was a significant decrease in the Ia antigen expression on these macrophages. Anti-leprosy drug treatment in high dose (10 x MDT) decreased the total number of blood T-helper (W3/25+) cells and increased the total number of blood T-suppressor (OX-8+) cells which resulted in a significant decrease in a W3/25: OX-8 ratio. Electron microscopy of elicited macrophages isolated from 10 x MDT treated rats showed development of many filipodia compared with control macrophages. These data show that 10 x MDT treatment in rats for 1 month alters the homeostasis of blood T-cell subpopulations which perhaps decreases the Ia expression on macrophages. However, the increase in O2- production and the appearance of filipodia on the macrophages is due to a direct effect of drugs on the macrophages. MDT treatment for 1 month in a therapeutic dose has no effect on the above-mentioned parameters.

Animals↗

PubMed1992

Effect of d-fenfluramine on neuropeptide Y concentration and release in the paraventricular nucleus of food-deprived rats.

Recent evidence indicates that Neuropeptide Y (NPY) is an important signal in the hypothalamic neural circuitry that stimulates feeding in the rat. Administration of d-fenfluramine (FEN) has been shown to rapidly inhibit feeding in the rat. Because food deprivation increases the levels and release of NPY in the paraventricular nucleus (PVN) of the hypothalamus, the aim of this study was to investigate whether the rapid anorectic effects of FEN in food-deprived (FD) rats are associated with alterations in the hypothalamic NPYergic system. In the first experiment, the effect of FEN (10 mg/kg) on NPY concentrations in nine microdissected hypothalamic sites was assessed by radioimmunoassay (RIA) in rats either food deprived for 3 days or fed ad lib during the experimental period. In response to food deprivation, NPY concentrations increased significantly in the PVN and arcuate nucleus, but NPY levels remained unchanged in the remaining seven hypothalamic sites. In control rats maintained on ad lib food supply, FEN injection produced little effect on NPY concentration in hypothalamic sites. However, FEN suppressed NPY levels selectively in the PVN of FD rats, so that NPY concentrations measured in the nucleus were within the range found in satiated control rats. In the second experiment, the effect of FEN on NPY release in the PVN was examined in FD rats by the push-pull cannula (PPC) technique. NPY levels in the PPC perfusate were unchanged in FD rats during the period 30-120 min after saline or FEN injection. Also, the mean rate of NPY release was similar in vehicle- and FEN-treated FD rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1992

Effects of tachykinins on luteinizing hormone release in female rats: potent inhibitory action of neuropeptide K.

Tachykinins, a family of biologically active related peptides, are found in variable amounts in the rat hypothalamus. We assessed the effects of five tachykinins, substance P (SP), neurokinin A (NKA), neuropeptide K (NPK), neuropeptide gamma (NP gamma), and neurokinin B (NKB), on LH release in different experimental model systems in ovariectomized rats. In the first series of experiments rats were ovariectomized and implanted with permanent cannulae in the third cerebroventricle of the rat brain. Two weeks later, the effects of intracerebroventricular injection of 0.5 or 1.25 nm various tachykinins on LH release were studied. The results showed that whereas SP, NKA, and NKB were ineffective, and NP gamma was marginally effective, NPK produced a long-lasting suppression of LH release. NPK decreased LH release in a dose- and time-related fashion. Similarly, in the second series of experiments, whereas SP and NKA were inactive, NPK completely suppressed the LH surge induced by progesterone in estrogen-primed ovariectomized rats. In the third series of experiments we observed that NK-2 receptor agonist [Nle10]NKA4-10, and not NK-1 receptor agonist [Sar9,Met(O2)11]SP, suppressed both the release of LH in vivo and basal and KCl-induced hypothalamic LHRH release in vitro. These results show that NPK is the most effective tachykinin in suppressing LH release, and the inhibitory response is mediated by hypothalamic NK-2 receptors. These findings are in accord with the hypothesis that NPK may serve as a hypothalamic inhibitory neurotransmitter/neuromodulator of LHRH secretion.

Animals↗

PubMed1992

Steroidal regulation of hypothalamic neuropeptide Y release and gene expression.

Neuropeptide Y (NPY) readily stimulates the release of hypothalamic LHRH and pituitary LH release in intact and gonadal steroid-primed gonadectomized rats. We have now tested the hypothesis that the release and synthesis of hypothalamic NPY may be regulated by gonadal steroids. To measure the effects of gonadal hormones on NPY release, a permanent push-pull cannula was implanted in the anterior pituitary (AP) of sham castrated (controls) or castrated (CAST) male rats, and 1 week later, the AP was perfused with artificial cerebrospinal fluid over a 3-4 h period. NPY concentrations in the perfusates collected at 10-min intervals were measured by RIAs. The NPY release pattern in the AP was episodic in both intact and CAST rats, and the frequency of NPY episodes was similar in two groups. However, the amount of NPY detected in the AP of CAST rats was significantly less than that of intact rats because the mean rate of release and the amplitude of NPY episodes in the perfusates of CAST rats were significantly reduced. This observation of attenuated hypothalamic NPY output in vivo and previous evidence of decreased hypothalamic NPY contents after CAST implied that the synthesis of hypothalamic NPY may be regulated by testicular secretions. Therefore, the effects of testosterone (T)-replacement on preproNPY messenger RNA (mRNA) in the medial basal hypothalamus (MBH) was evaluated. Rats were CAST and received either empty or T-filled Silastic capsules sc. Two weeks later, the level of perproNPY mRNA in the MBH was determined by solution hybridization/ribonuclease protection assay using a complementary RNA probe complementary to the rat NPY precursor mRNA. We observed that the levels of preproNPY mRNA were 2-fold higher in the MBH of T-replaced CAST as compared to control CAST rats. These findings are consistent with the hypothesis that gonadal steroids enhance the neurosecretory activity of hypothalamic NPYergic neurons, and for the first time reveal a coupling between the level of gene expression and the secretion of a neuropeptide involved in the regulation of hypothalamic LHRH and pituitary LH release.

Animals↗