Biomedical subjects

B Senthilkumaran

Publications and source records attributed to B Senthilkumaran.

13 recordsLinked to original sources

PubMed2001

Periovulatory changes in catfish ovarian oestradiol-17beta, oestrogen-2-hydroxylase and catechol-O-methyltransferase during GnRH analogue-induced ovulation and in vitro induction of oocyte maturation by catecholoestrogens.

In the catfish Heteropneustes fossilis and Clarias batrachus, ovarian oestrogen-2-hydroxylase (OE-2-H) activity increased significantly at 8 h after the injection of an ovulatory dose (0.15 microg/g body weight) of a mammalian GnRH analogue ([d -Ala(6)-Pro(9)]-LHRH ethylamide) and was restored to the 0 h (control) level after egg-stripping at 16 h. On the other hand, ovarian oestradiol-17beta (OE2) level and catechol-O-methyltransferase (COMT) activity decreased significantly at 8 h. While the OE2 level was restored to the 0 h level, COMT activity increased significantly at 16 h. Changes in ovarian OE2 level and enzymes indicate higher synthesis of 2-hydroxylated catecholoestrogens and their degradation during the periovulatory period. Under in vitro conditions, the synthetic catecholoestrogens (CEs, 2- and 4-hydroxylated oestradiol17beta and oestrone (OE1)) induced germinal vesicle break down (GVBD) in a dose- (0.01-10 microg/ml) and duration- (1-36 h) dependent manner, the mean values of the responses being in the order 2-OH OE2>4-OH OE2> 2-OH OE1>4-OH OE1. The CE-induced GVBD response (8 h induction) was not blocked by prior and subsequent incubations with steroid synthesis inhibitors (cyanoketone, epostane and aminoglutethimide) up to 36 h, suggesting that de novo steroidogenesis is not essential for the response. The percentage of GVBD response to 2-h induction by CEs was significantly inhibited by actinomycin D (a transcriptional inhibitor) and cycloheximide (a translational inhibitor), indicating the involvement of both RNA and protein synthesis. The CE-induced 8-h stimulation of GVBD was mildly blocked by propranolol, the beta-adrenergic inhibitor, suggesting the response was partly mediated through a beta-adrenergic receptor mechanism. Incubations with phentolamine, an alpha-adrenergic inhibitor, did not interfere with the CE-induced GVBD response. The results demonstrate CE-related enzymatic changes in teleost (catfish) ovaries and maturation-inducing substance activity of CEs.

Animals↗

PubMed2000

Thyroidectomy modulates rat prostatic monosaccharides.

Earlier studies have shown that thyroid hormones play an important role in glycoprotein metabolism in the prostate. In this paper, hypothyroidism induced changes in prostatic glycoprotein-associated monosaccharides and fructose concentrations were studied in 30-day-old peripubertal rats. Hypothyroidism was induced by total surgical thyroidectomy and confirmed by radioimmunoassay (RIA) of thyroid hormones and thyroid stimulating hormone (TSH). Animals were killed after 30 and 60 days post-thyroidectomy. To test the direct effect of thyroid hormones on prostatic monosaccharides, prostatic tissue was incubated for 24 h at 37 degrees C with 25, 50 or 100 ng/mL T3. Ventral prostatic hexosamines and sialic acid concentrations were significantly decreased in hypothyroid rats aged 30 and 60 days, whereas fucose concentration was increased at 30 days but decreased at 60 days in hypothyroid rats. In the case of the dorsolateral prostate, hypothyroidism enhanced the concentration of hexosamines but caused a decrease in levels of fucose, sialic acid and fructose, irrespective of the duration of hypothyroidism. Concentrations of fucose, fructose and hexosamines in the anterior prostate were decreased and sialic acid concentration was increased in 60-day hypothyroid rats. In in vitro studies, the concentrations of fucose, sialic acid and hexosamines were significantly increased in all three prostatic lobes irrespective of the T3 dose with which they had been incubated. A consistent increase in fructose concentration was observed in anterior and dorsolateral prostates when incubated with different doses of T3 stimulation. It is concluded that the influence of hypothyroidism on prostatic monosaccharides seems to be specific for each sugar in different lobes of the prostate. These results clearly show that thyroid hormones differentially regulate prostatic glycoprotein metabolism.

Animals↗

PubMed2000

Unique expression of gonadotropin-I and -II subunit genes in male and female red seabream (Pagrus major) during sexual maturation.

Two distinct gonadotropins (GTHs) have been demonstrated in a number of teleost fishes. Although the physiological roles of GTHs have been extensively studied in salmonids, little is known about their biological functions in nonsalmonid fishes. In this study, to elucidate the role of GTH-I and GTH-II in reproduction, we cloned the alpha-glycoprotein subunit (alphaGSU) and gonadotropin beta subunits (Ibeta and IIbeta) of red seabream using the 5'- and 3'-RACE methods and used these cDNA probes to reveal changes in mRNA levels of each subunit during sexual maturation of both male and female red seabream. The nucleotide sequences of alphaGSU, Ibeta, and IIbeta are 629, 531, and 557 base pairs long, encoding peptides of 117, 120, and 146 amino acids, respectively. The deduced amino acid sequence of each mature subunit showed high homology with those of other teleosts. Northern blot analysis showed that Ibeta mRNA levels of males increase in association with gonadal development, whereas those of females remain low throughout sexual maturation, indicating sexual dimorphism in the expression pattern of Ibeta. In contrast, IIbeta mRNA levels of both sexes are maintained at high levels from the beginning of gametogenesis to spawning season. These results are different than those of salmonids and suggest that GTH-I may have important roles in male, but not female, gametogenesis. GTH-II may be involved in regulation of early and late gametogenesis in both male and female red seabream.

Amino Acid Sequence↗

PubMed1999

Distribution and seasonal variations in levels of three native GnRHs in the brain and pituitary of perciform fish.

Specific and sensitive radioimmunoassays (RIAs) were newly developed for two types of gonadotropin-releasing hormone (GnRH), namely, seabream (sb) GnRH and chicken (c) GnRH-II. We employed these two RIAs together with a previously reported RIA for salmon (s) GnRH to study the presence and regional distribution of these three GnRHs in the brains and pituitaries of four perciform fishes (red seabream, Pagrus major; black seabream, Acanthopagrus schlegeli; striped knifejaw, Oplegnathus fasciatus; and Nile tilapia, Oreochromis niloticus), as well as clarify seasonal changes in levels of these GnRHs in the brain and pituitary of red seabream. All three GnRHs were found in brains of all fishes examined, with regional distributions in the brains of the three GnRHs being rather similar. sbGnRH was abundant in telencephalon and hypothalamus. cGnRH-II was concentrated from the middle to posterior part of the brain and distributed throughout the brain. sGnRH was concentrated in the olfactory bulb and distributed all over the brain, as was cGnRH-II. The dominant form of GnRH in the pituitary was sbGnRH, with levels 500- to 2400-fold higher than those of sGnRH, while cGnRH-II was undetectable in all four species. In the brain and pituitary of female red seabream, levels of both brain and pituitary sbGnRH increased from October (immature phase) and reached a peak in April (spawning phase), reflecting the increase in gonadosomatic index and vitellogenesis. However, levels of sbGnRH remained high only in the pituitary of completely regressed fish in June. Levels of both sGnRH and cGnRH-II in the brain were higher in the regressed phase and remained lower during the spawning phase. From these and previous results, it appears that sbGnRH is physiologically the most important form of GnRH in reproduction in red seabream and, probably, in other perciforms also.

Animals↗

PubMed1998

Annual and diurnal variations in, and effects of altered photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement on catechol-O-methyltransferase level in brain regions of the catfish, Heteropneustes fossilis.

The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region-specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 micrograms/g doses of E2, and none at week 2 and 5 of OVX and after 0.5 and 1 microgram/g doses of E2. The season-specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.

Animals↗

PubMed1998

Periovulatory changes in hypothalamic and pituitary monoamines following GnRH analogue treatment in the catfish Heteropneustes fossilis: a study correlating changes in plasma hormone profiles.

In Heteropneustes fossilis, administration of a single dose (0.15 micrograms/g body weight, i.p.) of [D-Ala6,Gly10]-gonadotrophin-releasing hormone analogue (GnRHa) induced ovulation (in 35 of 35 fish) when mild-stripped at 16 h. Plasma gonadotrophin II (GTH II) levels showed a highly significant increase at 2, 4, 8, 12 and 16 h with the peak at 8 h. Plasma cortisol, progesterone and testosterone showed significant elevations at 2, 4, 8 and 12 h with peaks at 8 h (cortisol and testosterone) and 4 h (progesterone). The levels declined to control values at 16 and 48 h except that of testosterone which decreased even further. In contrast, plasma levels of oestradiol-17 beta decreased significantly at 2, 4, 8 and 12 h, with the lowest value at 8 h, but increased at 16 and 18 h. The contents of hypothalamic and pituitary serotonin and noradrenaline increased at 8 h, coinciding with the peak GTH II rise, and decreased at 16 h. In contrast, dopamine content declined at 8 h in both the hypothalamus and pituitary, but increased at 16 h only in the hypothalamus. The hypothalamic adrenaline level decreased at 8 h but increased significantly at 16 h. Hypothalamic levels of monoamine oxidase, catechol O-methyltransferase and dopamine beta-hydroxylase were elevated significantly at 8 h; the dopamine beta-hydroxylase activity decreased at 16 h. Phenylethanolamine N-methyltransferase activity was elevated only at 16 h, coinciding with the rise in adrenaline content. It is inferred that the preovulatory decrease in dopamine content concomitant with rises in serotonin and noradrenaline levels, triggered by the low titre of oestradiol, might have potentiated the GnRHa/GnRH (endogenous)-induced release of GTH II for a prolonged period.

Animals↗

PubMed1996

Effects of administration of some monoamine-synthesis blockers and precursors on ovariectomy-induced rise in plasma gonadotropin II in the catfish Heteropneustes fossilis.

In the present study, effects of three daily i.p. injections of some monoamine (MA)-synthesis blockers and pre-cursors on plasma gonadotropin (GTH-II) levels were investigated in 3-week ovariectomized catfish, and the effects were correlated with changes in hypothalamic MA contents. Administration of alpha-methylparatyrosine (alpha-MPT; 250 micrograms/g BW, a tyrosine hydroxylase inhibitor) significantly decreased the ovariectomy-induced rise in GTH-II compared to that of the sham control group. Injection of L-dihydroxyphenylalanine (10 micrograms/g BW) in the alpha-MPT-treated fish elevated the GTH-II level significantly over that of the sham control group but not to the level of the ovariectomized fish. Administration of noradrenaline (NA; 5 micrograms/g BW) in combination with alpha-MPT counteracted the effect of the latter and maintained the plasma GTH-II level at that of the ovariectomized fish. Plasma GTH-II level was decreased significantly in the diethyldithiocarbamate (10 micrograms/g BW, a dopamine-beta-hydroxylase inhibitor)-injected fish compared to that of the sham and ovariectomized control groups. Administration of para-chlorophenylalanine (p-CPA; 100 micrograms/g BW, a tryptophan hydroxylase inhibitor) decreased the GTH-II level significantly compared to that of the ovariectomized group. Supplementation of 5-hydroxytryptophan (20 micrograms/g BW) with p-CPA nullified the latter's effect and maintained the GTH-II level at that of the ovariectomized fish. The administration of both p-CPA and alpha-MPT significantly reduced plasma GTH-II to the lowest mark compared to that of the sham, ovariectomized, and all other treatment groups. These results clearly show that the ovariectomy-induced rise in GTH-II was mediated through simultaneous activation of hypothalamic serotonergic and NA-ergic and suppression of dopaminergic mechanisms.

Animals↗

PubMed1995

A turnover study of hypothalamic monoamine oxidase (MAO) and effects of MAO inhibition on gonadotropin secretion in the female catfish, Heteropneustes fossilis.

In the present study, the rate constants of degradation (k) and synthesis (S) and half-life of hypothalamic monoamine oxidase were determined to explain annual variations and biphasic effects of the enzyme to low and high doses of estradiol-17 beta (E2) in 3-week ovariectomized Heteropneustes fossilis. In the preparatory phase, the half-life (t1/2) of the enzyme was the longest (21.16 days) with low k (0.03275 days-1) and S (0.000845 Units/day) values, suggesting a low turnover of the enzyme. In the prespawning phase the t1/2 was the shortest (11.65 days) with high k (0.0595 days-1) and S (0.011 Units/day) values. The low and high turnovers of the enzyme, respectively, in these two seasons could be correlated to low and high profiles of plasma E2 levels. In the resting phase, the values were in between (t1/2 = 18.83 days, k = 0.0368 days-1, S = 0.00211 Units/day) but the plasma E2 level was undetectable. Three weeks of ovariectomy increased the t1/2 (19.04 days) compared to that of the control (11.61 days) with decreases in both k and S values. The administration of a low dose of E2 (0.1 micrograms/g BW) further increased the t1/2 (19.63 days) over that of the ovariectomized fish with a significant rise in the S value. However, a high dose of E2 (1.0 micrograms/g BW) decreased it (13.33 days) by reducing the S and elevating the k values. These results suggest that the stimulatory effect of low doses of E2 on the enzyme activity is produced by elevating its synthesis rate and the inhibitory effect of high doses of E2 by simultaneously decreasing the synthesis and increasing the degradation rates of the enzyme. The administration of a single dose (75 mg/kg BW) of pargyline has elevated plasma gonadotropin (GTH) level after 3 and 6 hr and 7 days in the sham-ovariectomized (control), ovariectomized, and ovariectomized low-E2-dose groups; the peak increase was found at 6 hr. On the contrary, in the ovariectomized high-E2 group the GTH level was inhibited at 3 and 6 hr postinjection. These changes in the GTH level could be correlated with changes in the profiles of hypothalamic monoamines. The data show that E2 exerts its feedback regulation of GTH by modifying monoaminergic activity at the level of oxidative deamination.

Animals↗

PubMed1995

Changes in hypothalamic catecholamines, dopamine-beta-hydroxylase, and phenylethanolamine-N-methyltransferase in the catfish Heteropneustes fossilis in relation to season, raised photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement.

In Heteropneustes fossilis, contents and turnovers of hypothalamic catecholamines (CA) and activities of dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) showed significant seasonal variations with significantly high day values. The seasonal pattern of dopamine (DA) on one hand and that of noradrenaline (NA) and adrenaline (A) on the other hand showed an inverse relationship, the former decreasing and the latter increasing during the progress of gonadal recrudescence. The DBH and PNMT levels were low in the resting phase and increased to the peak in the prespawning (DBH) and spawning (PNMT) phases. Maintenance of the fish under long photoperiods (16L:8D) and high temperature (28 +/- 2 degrees) stimulated the NA and A, and DBH and PNMT activities, and suppressed the DA mechanism, the changes being maximal in the raised temperature groups. In the resting phase (December), ovariectomy (OVX) or estradiol-17 beta (E2) replacement in 4-week ovariectomized fish did not produce any significant effects on the CA and enzyme activities. On the contrary, in the prespawning phase (May), OVX produced differential and biphasic responses on CA and the enzymes. The contents and turnovers of both NA and A increased significantly at 2-5 weeks and decreased in the sixth week. However, the reverse was true for DA. The DBH and PNMT activities (assayed only 3, 4, and 6 weeks after OVX) were elevated significantly in the third and fourth weeks but decreased in the sixth week. Plasma levels of gonadotropin (GTH) increased significantly at all durations of OVX in a bimodal pattern while the E2 levels decreased consistently. Supplementation with a low dose (0.1 microgram/g BW) of E2 restored the NA and A and enzyme activities while the higher doses (0.5, 1.0, and 5.0 micrograms/g BW) depleted them. The reverse was true for DA. The low dose of E2 restored the GTH level while the higher ones inhibited it significantly. These results indicate that both environmental photoperiod and temperature and E2-negative feedback act on the CA to modulate GTH secretion.

Animals↗

PubMed1995

Circadian aspect of photoperiodic time measurement in a female house sparrow, Passer domesticus.

Endogenous circadian rhythms are involved in various photoperiodic responses of birds. Investigations involving the mechanisms of photoperiodic time measurement in birds have been confined mainly to temperate zone species using males exclusively. Due to the paucity of experimental evidence on subtropical birds that have very wide distribution, the present study was performed using subtropical female house sparrows. Photoperiodic sparrows were subjected to various T cycles for 60 days in which a fixed 3-h photophase was combined with scotophase in cycles of 20-30 h duration. Simultaneously, two groups of birds were also exposed to short days (light:dark = 8L:16D) or long days (15L:9D) as controls. Significant ovarian growth was found only in cycles of 3L:17D, 3L:23D, 3L:25D, and 3L:27D as well as in 15L:9D, whereas no positive response was detected in 3L:19D, 3L:21D, and 8L:16D. Plasma levels of estradiol showed a close relation to ovarian growth. The results indicate that photoperiodic time measurement in house sparrows involves an endogenous circadian rhythm.

Animals↗

PubMed1994

Effects of ovariectomy and oestradiol replacement on hypothalamic serotonergic and monoamine oxidase activity in the catfish, Heteropneustes fossilis: a study correlating plasma oestradiol and gonadotrophin levels.

Hypothalamic serotonin (5-HT; content and turnover) and monoamine oxidase (MAO) activity were measured in female catfish, Heteropneustes fossilis, after ovariectomy and supplementation with oestradiol-17 beta (OE2) in the recrudescent and quiescent phases. These factors were correlated with changes in plasma levels of OE2 and gonadotrophin. In the quiescent phase (December), neither ovariectomy nor OE2 supplementation had any significant effect on 5-HT content and MAO activity. Plasma levels of OE2 and gonadotrophin were undetectable in both control and treated fish, indicating that there was no feedback effect. In the recrudescent phase (prespawning, May), ovariectomy caused biphasic responses of MAO activity and 5-HT content. The enzyme activity decreased significantly after 2, 3, 4 and 5 weeks but increased significantly 6 weeks after ovariectomy. The 5-HT content varied in a biphasic manner with a significant increase at 2, 3 or 4 weeks and a significant decrease in week 6; there being no effect in week 5. 5-HT turnover was inhibited significantly only in week 4 after ovariectomy and did not show a biphasic pattern. In the ovariectomized groups, the OE2 level decreased significantly in a progressive manner with a maximum reduction in week 6. The plasma level of gonadotrophin showed a significant bimodal pattern of increase with the peak in week 4 after ovariectomy, indicating a strong negative feedback effect of OE2. The bimodal pattern of pituitary gonadotrophin release could be correlated with a similar pattern of increase in 5-HT content. OE2 treatment of fish which had been ovariectomized 3 weeks previously had dose-dependent effects on the enzyme; the low dose (0.1 microgram/g body weight) was stimulatory and the higher doses (0.5, 1.0 and 5.0 micrograms/g body weight) were inhibitory. The reverse was true for 5-HT content. Serotonergic turnover increased significantly only in the groups given high doses (1.0 and 5.0 micrograms/g body weight). The low dose of OE2 (0.1 micrograms/g body weight) restored the gonadotrophin and OE2 levels to those of the sham-ovariectomized vehicle-treated control group, whereas the high doses (0.5, 1.0 and 5.0 micrograms/g body weight) decreased the release of gonadotrophin in a dose-dependent manner. Our results suggest that OE2 modulates MAO activity to alter hypothalamic 5-HT in a seasonally dependent manner. The ovariectomy-induced changes in plasma levels of gonadotrophin appear to be mediated, at least partly, by the feedback action of OE2 on 5-HT metabolism.

Animals↗

PubMed1993

Annual variations in hypothalamic serotonin and monoamine oxidase in the catfish Heteropneustes fossilis with a note on brain regional differences of day-night variations in gonadal preparatory phase.

In Heteropneustes fossilis, significant annual variations in serotonin (5-HT) and monoamine oxidase (MAO) were found in the hypothalamus both at 12 and 24 hr with high values of content and turnover index (TI) during gonadal recrudescence, and low values during gonadal quiescence. The 5-HT content reached high levels during April-July (late preparatory, prespawning, and spawning phases). The TI of 5-HT showed two peaks in its midday value; a major peak occurred in March (midpreparatory phase) and a minor one in June (prespawning phase). High MAO activity was seen in June (prespawning phase) and low values during February, March, and April (preparatory phase). Significant day-night variations in 5-HT content and TI, and MAO activity were observed in the hypothalamus and telencephalon in February and March (early and midpreparatory phase), but not at other times of the year. In the whole brain and separate regions such as the thalamus, midbrain, and hindbrain no day-night patterns were seen. A comparison of the data shows that the increase in 5-HT content and TI from February to March was significantly higher in the hypothalamus than in telencephalon and the opposite is true for MAO. The results suggest that the high hypothalamic activities of 5-HT and MAO during recrudescence is related to breeding activity; the day-night variations during the early and midpreparatory phase in these variables may be related to initiation of breeding in this species.

Animals↗

PubMed1991

Influence of thyroidectomy on seminal vesicular glycosidases of young albino rats.

Impact of thyroidectomy (hypothyroidism) on few glycosidases was studied in the seminal vesicles of young albino rats. Thyroidectomy was performed at 30 days post partum. Seminal vesicular beta-D-glucosidase, beta-D-galactosidase, and N-acetyl-beta-D-galactosaminidase exhibited a similar response of decreased activities under short- (30 days) and long-term (60 days) hypothyroid conditions. On the other hand, N-acetyl-beta-D-glucosaminidase registered a temporal biphasic response of increased and decreased activities in the seminal vesicles of rats subjected to short- and long-term hypothyroidism, respectively. The data obtained in the present study suggest that thyroid hormones have specific influences on different glycosidases in the seminal vesicles of rats and euthyroid status is essential for the maintenance of normal activities of these enzymes.

Animals↗