Umesh Rai

In vitro effect of temperature on phagocytic and cytotoxic activities of splenic phagocytes of the wall lizard, Hemidactylus flaviviridis

The in vitro effect of temperature on phagocytosis, nitric oxide production and interleukin-1 (IL-1) secretion by splenic phagocytes isolated from the wall lizard (Hemidactylus flaviviridis) demonstrated that changes in temperature altered non-specific defenses. The LPS-induced percentage phagocytosis and phagocytic index were recorded maximum at 25 degrees C. The phagocytic activity declined considerably when the phagocytes were incubated at low (7 and 15 degrees C) or high (37 degrees C) temperatures. The presence of bacterial lipopolysaccharide (LPS) in the incubation medium could considerably enhance the phagocytic activity of splenic phagocytes. A similar temperature-related effect was also observed on LPS-induced cytotoxic activity of phagocytes. LPS could stimulate the nitrite release indicating nitric oxide production only at 25 degrees C. Likewise, the proliferative responses of immature rats thymocytes to LPS-induced phagocyte-conditioned medium suggest that IL-1 secretion was enhanced when phagocytes were cultured at 25 degrees C. This suggests that 25 degrees C is the optimal temperature for phagocyte functions in H. flaviviridis. The decrease or increase in temperature other than at 25 degrees C dramatically suppressed the phagocyte activities.

Genomic and non-genomic effect of cortisol on phagocytosis in freshwater teleost Channa punctatus: an in vitro study.

The non-genomic action of glucocorticoid, besides classical genomic action, is recently implicated in regulation of phagocyte activities in mammals. With regard to the non-mammalian vertebrates, this study in the teleost, Channa punctatus, for the first time demonstrates the regulation of innate immunity by cortisol following non-genomic pathway. Cortisol suppressed the phagocytic activity of splenic phagocytes in a time- and concentration-dependent manner. Intriguingly, it impeded the phagocytosis within 15 min which is too short for conventional genomic action. The cortisol-induced rapid inhibition could not be altered by transcription and translation inhibitors, suggesting the involvement of non-genomic pathway. Since membrane impermeable BSA-cortisol mimicked the rapid inhibitory effect of cortisol at 15 min, we speculated that cortisol exerted its non-genomic effect on phagocytosis by acting at membrane site. These membrane-bound glucocorticoid receptors seem similar to cytosolic GR, as rapid inhibitory effect of cortisol was blocked by the cytoplasmic glucocorticoid receptor blocker RU-486. Using inhibitors for adenylate cyclase/protein kinase A (PKA) and estimating intracellular cAMP, adenylate cyclase-PKA pathway was seen involved in mediating the rapid non-genomic action of cortisol in phagocytes of C. punctatus. In contrast to the rapid effect, inhibitory effect of cortisol on phagocytosis after 1h was blocked by protein synthesis inhibitors, thus implicating genomic regulation. An overview of our data suggests that cortisol regulates phagocytosis in C. punctatus via genomic as well as non-genomic mechanisms. Further, the non-genomic action of cortisol is mediated via membrane-bound GR coupled to cAMP-PKA system.

Differential effects of histamine on Leydig cell and testicular macrophage activities in wall lizards: precise role of H1/H2 receptor subtypes

The present study in the wall lizard, Hemidactylus flaviviridis, was aimed to understand the role of histamine (HA) in the regulation of Leydig cell and testicular macrophage activities, for the first time, in ectothermic vertebrates. Although HA did not affect the testosterone production from unstimulated Leydig cells, it had dual concentration-related effects, stimulatory at a low concentration of 10(-10) M while inhibitory at a high concentration of 10(-5) M, on FSH-induced testosterone production. This suggests that HA did not influence the basal Leydig cell steroidogenesis, but modulated the FSH-stimulated testosterone production in a biphasic manner depending upon its concentration. However, HA failed to affect the FSH-stimulated Leydig cell proliferation, indicating that HA modulated the testosterone production from Leydig cells without influencing their proliferation in wall lizards. HA, apart from Leydig cells, differentially regulated the testicular macrophage immune responses. It inhibited phagocytosis and superoxide production at high concentration (10(-5) M), while stimulated superoxide production and could not affect phagocytosis at low concentration (10(-10) M). Using selective H1 and H2 antagonists, pyrilamine and famotidine respectively, H1 receptor subtype was seen responsible for mediating the inhibitory effect of HA on Leydig cell steroidogenesis and testicular macrophage immune responses at high concentration, while H2 receptors were involved for the stimulation at low concentration.

Diurnal variation in phagocytic activity of splenic phagocytes in freshwater teleost Channa punctatus: melatonin and its signaling mechanism

The aim of the present study was to understand the rhythmic changes in innate immune response in freshwater fish Channa punctatus. Furthermore, the putative role of melatonin as the zeitgeber was explored. The phagocytic activity of splenic phagocytes assessed at 6-h intervals showed higher phagocytic activity during light phase than dark phase. The increased phagocytic activity during light phase was diminished by melatonin administration at 09:00 h. Implication of melatonin in control of diurnal variation in phagocytic activity was substantiated by administering irreversible tryptophan hydroxylase inhibitor, para-chlorophenylalanine (pCPA) at 18:00 h. pCPA abrogated the decrease of phagocytosis observed during dark phase, and the same was restored after melatonin administration. The direct involvement of melatonin in modulation of phagocytosis was demonstrated following in vitro experiments. Melatonin suppressed the phagocytic activity in a concentration-dependent manner without affecting the viability of phagocytes. The existence of functional membrane-bound melatonin receptors on fish phagocytes was pharmacologically demonstrated. Luzindole, melatonin membrane receptor antagonist, completely blocked the inhibitory effect of melatonin on phagocytosis. Further receptor-coupled adenylate cyclase-protein kinase A (PKA) pathway was implicated in transducing the melatonin effect as both adenylate cyclase and PKA inhibitor completely nullified the melatonin-induced suppression. An increased intracellular cAMP level in response to melatonin ascertained the second messenger status of cAMP for downstream signaling. However, manipulation of phospholipase C/PKC failed to influence the effect of melatonin on phagocytic activity. These observations in C. punctatus evidenced the diurnal rhythmicity in phagocytic activity that is regulated by melatonin following membrane-bound receptor-coupled cAMP-PKA pathway.

Hormonal Regulation of Testicular Functions in Reptiles

Publisher Summary Reptiles are the first phylogenetic group in which spermatogenesis occurs in seminiferous tubules lined by peritubular cells. Testicular functions are regulated by multifactor, environmentally important, hypothalamo–hypophysial, and testicular cells-secreted paracrine factors. The existence of different gonadotropins and their role in testicular functions are interesting in reptiles. In chelonians and crocodilians, two distinct pituitary gonadotropins similar to mammalian follicle-stimulating hormone (FSH) and luteinizing hormone (LH) regulate two different functions: spermatogenesis and steroidogenesis, respectively. Conversely, the purification and characterization of pituitary gonadotropin from different families of snake reveal the existence of a single gonadotropin that controls both testicular functions in squamates. To date, cDNA has been cloned for either FSH or LH but not for both FSH and LH from a single squamate. With respect to sex steroids, androgens differentially regulate spermatogenesis, depending on reproductive phases, while estrogens are implicated in post-spermatogenic testicular regression. In addition, several uncharacterized paracrine factors secreted by Leydig and Sertoli cells, macrophages, and mast cells play critical roles in the regulation of spermatogenesis, steroidogenesis, and testicular immune responses.

Dose and time-related in vitro effects of glucocorticoid on phagocytosis and nitrite release by splenic macrophages of wall lizard Hemidactylus flaviviridis.

Glucocorticoids (GC) are usually considered to be immunosuppressive and anti-inflammatory. However, recent studies in mammals have demonstrated the diverse effects of GC on non-specific host-defense mechanism, depending on dose or duration of treatment. Hence, in the present study in vitro dose and time-related effects of glucocorticoid, i.e. hydrocortisone (HC) on phagocytosis and nitrite production by LPS-induced splenic macrophages in wall lizard Hemidactylus flaviviridis has been investigated. Hydrocortisone suppressed percentage phagocytosis, phagocytic index and nitrite production by splenic macrophages even at the lowest concentration (10(-13) M) for a short-term exposure (4 h). Hydrocortisone-induced suppression enhanced with the increase of concentration or duration of exposure time. The suppressive effect of hydrocortisone on phagocytic and cytotoxic activities of splenic macrophages was further corroborated since the pre-exposure of macrophages to glucocorticoid-receptor blocker (RU 486) considerably reduced the hydrocortisone-induced suppression of phagocytosis and nitrite production. The present study suggests that GC instead of diverse effects, has dose- and time-dependent immunosuppressive effect on non-specific host-defense immune responses in wall lizard H. flaviviridis.

Clomiphene citrate potentiates the adverse effects of estrogen on rat testis and down-regulates the expression of steroidogenic enzyme genes

OBJECTIVE To investigate the antiestrogenic effect of clomiphene citrate (CC) in male rats estrogenized with estradiol-3-benzoate (EB). DESIGN Prospective experimental study. SETTING Laboratory. ANIMALS Adult male albino rats (Holtzman strain). INTERVENTION(S) CC was given alone or in combination with EB. MAIN OUTCOME MEASURE(S) Testicular function and steroidogenic enzyme gene expression were evaluated in control versus treated groups. RESULT(S) EB after 30 days of treatment induced a rise in TUNEL-positive germ cells adversely affecting spermatogenesis with complete absence of elongated spermatids or sperms. CC alone had only a moderate effect. In contrast, CC+EB synergistically inflicted more adverse effects as apoptotic germ cells per tubule rose further. Significant down-regulation in expression of testicular steroidogenic enzyme genes StAR, p450scc, 3β-HSD, and p450c17 was observed. In the EB-alone group, aromatase gene expression in the testis was up-regulated but reversed in brain and liver tissues. CC alone had little modulatory effect on aromatase expression. On the other hand, CC+EB countered the EB-induced rise of aromatase expression in the testis. CONCLUSION(S) The above findings indicate that CC in the presence of estrogen synergistically potentiates more adverse effects in testis, inhibiting expression of upstream steroidogenic enzyme genes and leading to disruption of steroidogenesis.

Quercetin supplementation restores testicular function and augments germ cell survival in the estrogenized rats.

Quercetin, as a flavonoid, has been recognized to possess dual properties of an oxidant and antioxidant as well. The role of quercetin (QC), as an antioxidant in countering estradiol-3-benzoate (EB) induced adverse effects and germ cell apoptosis in adult rat testis was presently investigated. Adult rats received EB (0.075 mg/rat/5th day) alone or EB+QC (15 mg/kg bw/alternate day) simultaneously for 30 days. Revival of spermatogenesis following QC intervention was associated with a significant restoration in serum and intra-testicular levels of testosterone. Decline in lipid peroxidation and simultaneous improvement in the activities of superoxide dismutase, catalase and glutathione s-transferase were very much evident. Identically, total antioxidant capacity and glutathione demonstrated a marked improvement. QC augmented germ cell survival leading to a decrease in cell apoptosis. Expression of downstream apoptotic markers, caspase-3 and poly-ADP-ribose polymerase (PARP) presented a significant reduction. Down regulation with respect to upstream markers, caspase-8 and -9, Fas, FasL, Bax, and p53 was similarly observed. Taken together, the above findings indicate that with the dose presently used quercetin with its antioxidant and antiestrogenic properties restored testicular function leading to revival of spermatogenesis. It also augmented germ cell survival primarily mediated through downregulation in the expressions of upstream, downstream and other markers in the pathways of metazoan apoptosis.

Dynorphin regulates the phagocytic activity of splenic phagocytes in wall lizards: involvement of a κ-opioid receptor-coupled adenylate-cyclase–cAMP–PKA pathway

SUMMARY This in vitro study of the wall lizard Hemidactylus flaviviridis demonstrates the role of the opioid peptide dynorphin A(1–17) [dyn A(1–17)] in the regulation of the phagocytic activity of splenic phagocytes. Dyn A(1–17) in a concentration-dependent manner inhibited the phagocytic activity, and the maximum inhibition was recorded at a concentration of 10–9 mol l–1. To explore the receptor-mediated effect of dyn A(1–17), cells were treated simultaneously with the non-selective opioid receptor blocker naltrexone and dyn A(1–17). Naltrexone completely blocked the inhibitory effect of dyn A(1–17) on phagocytosis. Moreover, the involvement of selective opioid receptors was investigated using selective opioid receptor antagonists. CTAP and naltrindole, selective μ- and δ-opioid receptor blockers, respectively, failed to block the inhibitory effect of dyn A(1–17) on phagocytosis. However, the selective κ-opioid receptor blocker NorBNI completely antagonized the inhibitory effect of dyn A(1–17). Regarding the κ-opioid receptor-coupled downstream signaling cascade, the adenylate cyclase (AC) inhibitor SQ 22536 and protein kinase A (PKA) inhibitor H-89 decreased the inhibitory effect of dyn A(1–17) on phagocytosis. Furthermore, treatment with dyn A(1–17) caused an increase in intracellular cAMP content in splenic phagocytes. Thus, it can be concluded that, in H. flaviviridis, dyn A(1–17) negatively regulates the phagocytic activity of splenic phagocytes by acting through κ-opioid receptors that are coupled with the AC–cAMP–PKA signal transduction mechanism.

Seasonality of reproduction in male spotted murrel Channa punctatus : correlation of environmental variables and plasma sex steroids with histological changes in testis

The present study was undertaken to develop a comprehensive understanding of how environmental cues and sex steroids relate with cyclic changes in spermatogenesis in freshwater spotted snakehead Channa punctatus that is nutritious and economically important. The seasonal histological changes in testis and annual profile of gonadosomatic index (GSI) of C. punctatus delineated the testicular cycle into four phases: regressed (December–March), preparatory (April–June), spawning (July and August) and postspawning (September–November). Among environmental variables, correlation and regression analyses exhibited an important relationship between photoperiod and testicular weight while role of rainfall was seen confined to spawning. The seasonal profile of plasma sex steroids when correlated with cyclic changes in spermatogenesis in spotted snakehead, testosterone (T) seems to be involved in controlling the major events of spermatogenesis from renewal of stem cells to spawning of spermatozoa. Another important androgen prevalent in teleosts, 11-ketotestosterone (11-KT), was high during preparatory phase, suggesting that 11-KT in addition to T plays an important role in progression of spermatogenesis and spermiation in C. punctatus. However, 11-KT was not seen to be associated with milt production and release of spermatozoa during spawning. Plasma profile of estradiol-17β (E2) during different reproductive phases revealed the involvement of E2 in repopulation of stem cells during postspawning phase and in maintaining quiescence of testis during regressed phase.