Biomedical subjects

C K Murthy

Publications and source records attributed to C K Murthy.

13 recordsLinked to original sources

PubMed1996

Sexual dimorphism of galanin-like immunoreactivity in the brain and pituitary of goldfish, Carassius auratus.

A sexually dimorphic distribution of galanin (GAL)-like immunoreactive (ir) neurons and fibers was found in the brain and pituitary of goldfish. The rostralmost GAL-ir perikarya were found in the area ventralis telencephali pars supracommissuralis dorsal to the anterior commissure. In the diencephalon, there was several GAL-ir perikarya in the nucleus preopticus periventricularis (NPP). Males had many GAL-ir perikarya in the nucleus preopticus pars parvocellularis (NPOpp) and isolated GAL-ir perikarya in the NPO pars magnocellularis, and lateral to the NPO; in females GAL-ir perikarya were not found in these sites. A large GAL-ir neuronal aggregation was observed in the nucleus lateralis tuberis pars posterioris (NLTp). Several ir perikarya were present in the nucleus posterioris tuberis; however, unlike in other regions the males revealed fewer neurons than females. Besides the established innervation of the pituitary gland by the NPP, NPO and NLT, the present study revealed GAL-ir perikarya of these nuclei apparently also innervating the telencephalon, thalamus, optic tectum, tegmentum and even some areas of the rhombencephalon. Isolated perikarya were found in the nucleus posterioris periventricularis, the dorsal vicinities of the nucleus recessus lateralis (NRL), nucleus recessus posterioris, and nucleus saccus vasculosus, and in the medulla oblongata ventral to the vagal lobes. In the pituitary gland, GAL-ir fibers ramify and terminate among the pars distalis cells. A small percentage of growth hormone-secreting cells colocalize GAL. In males, most GAL-ir cells of the proximal pars distalis (PPD) showed granular ir product in the entire cell, and some had one or two large granules; in females the ir PPD cells showed clusters of a few fine ir granules of uniform size in each. Sexual dimorphism was also found in the olfactory bulb, telencephalon, infundibulum, mesencephalic tegmentum, optic tectum and medulla oblongata, the males having a more extensive GAL-ir fiber system than the females. Galanin may play a role in both hypophysiotropic and motor functions.

Animals↗

PubMed1994

A new gonadotropin-releasing hormone (GnRH) superagonist in goldfish: influence of dialkyl-D-homoarginine at position 6 on gonadotropin-II and growth hormone release.

The two native forms of gonadotropin-releasing hormones (GnRH) present in goldfish, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate gonadotropin-II (GTH-II) and growth hormone (GH) release both in vivo and in vitro. In our previous study using perifused goldfish pituitary fragments, many mammalian GnRH antagonists, especially those with D-Arg6, showed weak to strong stimulation of GTH-II and GH release. In the present study, the dose-related stimulation of GTH-II and GH release by [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-Arg6, Trp7, D-Ala10] mGnRH (analog J) and [Ac-D(2)-Nal1, 4Cl-D-Phe2, D-Trp3, D-hArg(Et2)6, D-Ala10] mGnRH (analog K) was demonstrated; the stimulatory potency of both analogs was significantly lower than that of native sGnRH. In the presence of analogs J and K, cGnRH-II stimulated GTH-II release was significantly suppressed. Further, GTH-II and GH stimulation by 2 microM of analog K was significantly suppressed by a 'true' GnRH antagonist, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6] mGnRH (analog E). These results indicate that analogs J and K increase GTH-II and GH release in goldfish by acting on GnRH receptors on gonadotrophs and somatotrophs. Since analog K, having [D-hArg(Et2)6], strongly stimulated GTH-II release, the potency of [D-hArg(Et2)6] or [D-hArg(CH2CF3)2(6)] substituted analogs to stimulate GTH-II and GH release from the perifused goldfish pituitary fragments was tested. Among the peptides tested, [D-hArg(Et2)6, Pro9-NHEt] sGnRH had a higher potency in stimulating GTH-II release than any other analog tested in the present or in previous studies. For stimulation of GH release, [D-hArg(Et2)6, Pro9-NHEt] sGnRH and [D-Arg6, Pro9-NHEt] sGnRH were the most potent analogs tested; analogs of mGnRH were less potent than sGnRH, indicating the importance of Trp7, Leu8 residues in the native peptide. These results suggest the importance of [D-Arg6] or alkylated [D-Arg6] in determining the intrinsic activity and potency of GnRH peptides in goldfish.

Amino Acid Sequence↗

PubMed1994

Functional evidence regarding receptor subtypes mediating the actions of native gonadotropin-releasing hormones (GnRH) in goldfish, Carassius auratus.

In goldfish, two native gonadotropin-releasing hormone (GnRH) peptides, salmon GnRH (sGnRH) and chicken-II GnRH (cGnRH-II), stimulate gonadotropin (GTH-II) and growth hormone (GH) secretion. In the present study we tested whether sGnRH and cGnRH-II act through different or the same population of GnRH receptors on GTH and GH cells, using various approaches. A GnRH antagonist [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH (analog C) equally inhibited GTH-II release by sGnRH and cGnRH-II. Similarly, [Ac-D(2)Nal1,4Cl-D-Phe2,D-(3)Pal3,6]cGnRH-II (analog N) suppressed GTH-II stimulation by the two GnRH peptides equally. Further, in the continued presence of 100 nM sGnRH, a 100 nM pulse of cGnRH-II failed to cause additional GTH-II release and vice versa. Prolonged exposure of pituitary fragments to 100 nM sGnRH or cGnRH-II resulted in desensitization and reduced the GTH-II response to a subsequent pulse of either sGnRH or cGnRH-II equally. All these results indicate that both sGnRH and cGnRH-II act through the same population of GnRH receptors on gonadotrophs. Similarly, the GH responses obtained with (i) analog N treatment, (ii) pulse challenge to cGnRH-II during prolonged sGnRH treatment and vice versa, and (iii) desensitization studies suggest that both sGnRH and cGnRH-II act through the same population of GnRH receptors on somatotrophs. However, the properties of GnRH receptors on GTH-II and GH cells are different. Analog C stimulated GH release but not GTH-II release. In contrast, [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,D-Arg6]mGnRH stimulated GTH-II release but weakly suppressed GH release. These results indicate that sGnRH and cGnRH-II act on the same population of receptors on GTH cells and on a functionally distinct population of receptors on GH cells.

Amino Acid Sequence↗

PubMed1994

In vivo actions of a gonadotropin-releasing hormone (GnRH) antagonist on gonadotropin-II and growth hormone secretion in goldfish, Carassius auratus.

In our previous in vitro studies, [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E) suppressed both gonadotropin-II (GTH-II) and growth hormone (GH) release stimulated by sGnRH and cGnRH-II. In the present study analog E significantly inhibited the increases in plasma GTH-II levels stimulated by sGnRH in sexually mature female and sexually recrudescent goldfish. Treatment of goldfish with alpha-methyl-p-tyrosin methyl ester (alpha-MPT) inhibits dopamine synthesis and abolishes the inhibitory actions of dopamine on GTH-II release, resulting in a potentiation of the GTH-II response to sGnRH. Following alpha-MPT pretreatment, analog E significantly reduced basal plasma GTH-II levels, and suppressed both sGnRH and cGnRH-II actions on GTH-II release. Analog E also inhibited the increase in plasma GTH-II levels in sexually mature male goldfish exposed to the female sexual pheromone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha 20 beta-P), demonstrating that the increase in plasma GTH-II levels is due to release of endogenous GnRH. Analog E significantly inhibited the increases in plasma GH levels stimulated by treatment with sGnRH. Implantation of estradiol pellets increases basal plasma GH levels and increases the GH responsiveness to sGnRH in sexually recrudescent goldfish; analog E also suppressed the increase in plasma GH levels stimulated by injection of sGnRH in estradiol-treated fish. Analog E suppressed basal GTH-II and GH levels in fish that were unhandled prior to injection; however, analog E was not effective in reducing basal plasma GTH-II or GH levels in experiments in which the fish were blood sampled or subjected to some experimental manipulation prior to injection of analog E. Analog E also suppressed basal levels of GTH-II in alpha-MPT-treated fish, suggesting that stress inhibition of GTH-II release may be mediated by the dopaminergic system. In summary, the results demonstrate that (i) analog E can suppress the actions of exogenous sGnRH and cGnRH-II on GTH-II and GH release in vivo, (ii) the GnRH system mediates, at least in part, the plasma GTH-II response in sexually mature male goldfish following exposure to the female sexual pheromone 17 alpha 20 beta-P, and (iii) endogenous GnRH peptides are important in the regulation of basal plasma levels of GTH-II as well as GH, particularly in low stress conditions.

Animals↗

PubMed1994

Receptor binding of gonadotropin-releasing hormone antagonists that inhibit release of gonadotropin-II and growth hormone in goldfish, Carassius auratus.

In goldfish, GnRH stimulates gonadotropin-II (GTH-II) and growth hormone (GH) release. The two native forms of GnRH, salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), bind to two classes of GnRH binding sites: high-affinity/low-capacity sites and low-affinity/high-capacity sites. Our previous in vitro perifusion studies of goldfish pituitary fragments showed that [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-mGnRH (analog E), [Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6]-sGnRH (analog C), and [Ac-D(2)Nal1, 4Cl-D-Phe2, D-(3)Pal3,6]-cGnRH-II (analog N) inhibited both sGnRH- and cGnRH-II-stimulated GTH-II and GH release. Interestingly, analog C stimulated GH release but not GTH-II release. The objectives of the present study were 1) to test the site of action of GnRH antagonists in goldfish, 2) to test the relationship between receptor binding affinity of antagonists and their in vitro inhibitory potencies and apparent duration of action, and 3) to compare the binding characteristics of analog C with its differential action on GTH-II and GH release. As in previous studies, analog E suppressed sGnRH-stimulated GTH-II and GH release from perifused pituitary fragments. Similarly, analog E suppressed both sGnRH- and cGnRH-II-stimulated GTH-II and GH release from perifused dispersed goldfish pituitary cells, indicating the direct action of GnRH antagonists at the pituitary cell level. In the receptor binding studies, analog E displaced 125I-[D-Arg6, Pro9NHEt]-sGnRH (sGnRH-A) from crude goldfish pituitary membrane preparations in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Differential actions of a mammalian gonadotropin-releasing hormone antagonist on gonadotropin-II and growth hormone release in goldfish, Carassius auratus.

In goldfish the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate both gonadotropin-II (GTH-II) and growth hormone (GH) release. Modifications of GnRH structure at positions 1, 2, 3, and 6 often result in an antagonist in goldfish, an observation well documented in mammalian studies. In a preliminary study in goldfish, a mammalian GnRH antagonist, [Ac-D(2)Nal1, 4Cl-D-Phe2, D(3)-Pal3,6, Arg5, D-Ala10]-mGnRH (analog L) weakly stimulated GTH-II release, and strongly inhibited GH release. The objectives of the present study were to study the dose-related actions of analog L on GTH-II and GH release in the goldfish, the specificity of inhibition of native GnRH actions, and to test whether analog L can act directly on goldfish pituitary cells. In a goldfish pituitary fragments perifusion system, analog L at different concentrations, given as 2-min pulses or as 30-min prolonged treatments, stimulated GTH-II and inhibited GH release in a dose-dependent manner. Analog L at 2 microM concentration (45 min) significantly suppressed sGnRH- and cGnRH-II-stimulated GTH-II as well as GH release. Analog L specifically inhibited GnRH-stimulated GH release, without having any significant effects on the GH release induced by either SKF38393, a dopamine D1 receptor agonist, or thyrotropin-releasing hormone. The GTH-II stimulatory and GH-inhibitory actions of analog L were significantly suppressed by a 'true' GnRH antagonist (Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6)-mGnRH. Further, analog L stimulated GTH-II release and suppressed GH release from the enzymatically dispersed goldfish pituitary cells, indicating the direct actions of analog L at the pituitary cell level. Analog L also displaced 125I-(D-Arg6, Pro9 NHEt)-sGnRH bound to crude goldfish pituitary membrane preparations in a dose-related manner. In conclusion, contrary to its action as a potent GnRH antagonist in mammals, analog L has GTH-II stimulatory action in goldfish. Analog L by acting via GnRH receptors at the pituitary cell level differentially acts on GTH-II and GH release, suggesting functional differences in the properties of the GnRH receptors on GTH and GH cells. Analog L also specifically inhibits sGnRH and cGnRH-II actions on GTH-II and GH release.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1993

Effects of sex steroid treatments on gonadotropin-releasing hormone-stimulated gonadotropin secretion from the goldfish pituitary.

The effects of gonadal steroids on the gonadotropin (GTH) release response to salmon gonadotropin-releasing hormone (sGnRH), chicken gonadotropin-releasing hormone-II (cGnRH-II), and the sGnRH analogue, [D-Arg6, Trp7, Leu epsilon, Pro9]-N-ethylamide-GnRH (sGnRH-A), were investigated using an in vitro perifusion system for goldfish pituitary fragments. Gonad-intact male and female goldfish were implanted intraperitoneally (i.p.) with silastic pellets containing no steroid (blank), testosterone (T; 100 micrograms/g), or estradiol (E2; 100 micrograms/g); pituitaries were removed 5 days later for perifusion experiments. In vivo treatment with T or E2 potentiates sGnRH-, cGnRH-II-, and sGnRH-A-induced GTH secretion from pituitary fragments of sexually regressed and sexually recrudescent goldfish in vitro. Testosterone (100 nM; 24 h) treatment in vitro has a direct effect on the pituitary to increase sGnRH responsiveness, and this potentiating effect of T was blocked by the protein synthesis inhibitor cycloheximide (25 microM). In sexually regressed goldfish, in vivo T implantation enhanced the serum GTH response to sGnRH-A (0.01 microgram/g; 6 h) 7-fold. ED50 estimates for in vitro pituitary GTH responsiveness to sGnRH-A were 1.0 +/- 0.1 nM and 0.1 +/- 0.1 nM (p < 0.05) for blank and T-implanted groups, respectively. Radioligand (125I-sGnRH-A) binding studies demonstrated that enhanced pituitary responsiveness was independent of changes in pituitary GnRH receptor affinity or number. These results demonstrate that sex steroids increase pituitary sensitivity to GnRH peptides in the goldfish.

Animals↗

PubMed1993

In vitro characterization of gonadotropin-releasing hormone antagonists in goldfish, Carassius auratus.

The two native forms of GnRH, salmon GnRH and chicken GnRH-II, in the brain and pituitary of goldfish are both active in stimulating gonadotropin-II (GTH-II) and GH release. The objective of the present study was to characterize GnRH antagonists for their ability to inhibit sGnRH- and cGnRH-II-induced GTH-II and GH release in goldfish using a pituitary fragments perifusion system. Contrary to expectations, putative GnRH antagonists with D-Arg6 stimulated GTH-II and GH release in nearly all cases. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mammalian (m) GnRH inhibited sGnRH- and cGnRH-II-stimulated GTH-II release in a dose-dependent manner, with ED50 values of 242 +/- 48 and 169 +/- 17 nM, respectively. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mGnRH also inhibited GH release stimulated by sGnRH (ED50, 128 +/- 74 nM) and cGnRH-II (ED50, 157 +/- 67 nM). The degree of inhibition was higher in sexually regressed fish compared to postspawning fish. [D-p-Glu1,D-Phe2,D-Trp3,6]mGnRH suppressed both sGnRH- and cGnRH-II-induced GTH-II release with ED50 values of 326 +/- 96 and 249 +/- 74 nM, respectively. [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]sGnRH inhibited sGnRH and cGnRH-II stimulated GTH-II release, but stimulated GH release. On the other hand, [Ac-D(2)-Nal1,4Cl-D-Phe2,D-(3)Pal3,6,Arg5,D-A la10]mGnRH weakly stimulated GTH-II release, but strongly inhibited basal GH release. These results indicate that [Ac-delta 3-Pro1,4FD-Phe2,D-Trp3,6]mGnRH has clear antagonistic activity on sGnRH and cGnRH-II stimulation of GTH-II and GH release in vitro. The differential actions of a few GnRH analogs on GTH-II and GH release indicate that the properties of the GnRH receptors on GTH and GH cells may be different. The amino acid in position 6 plays an important role in determining the nature of intrinsic activity of GnRH peptides, and substitution of D-Arg6 normally produces agonistic analogs.

Amino Acid Sequence↗

PubMed1978