Inhibition of hCG-induced spawning by a-methylparatyrosine, a tyrosine hydroxylase inhibitor, in the catfish Heteropneustes fossilis (Bloch).

In this study, the effect of pharmacological inhibition of catecholaminergic activity on hCG-induced spawning was evaluated and correlated with tyrosine hydroxylase (TH) activity, the rate-limiting enzyme in catecholamine biosynthesis. Gravid female H. fossilis collected in both prespawning and spawning phases were given -methylparatyrosine (-MPT: 250g/g body weight, ip, an irreversible inhibitor of TH) and human chorionic gonadotropin (hCG: 100 IU/fish, ip) alone or in combination. The fish were sampled at different intervals for measuring hypothalamic and ovarian TH activity and checking spawning response. The administration of hCG resulted in ovulation and spawning in both phases with a higher response in the spawning phase. The administration of -MPT did not induce any response, like the control fish. In the hCG + -MPT groups, the spawning response of hCG was significantly inhibited and delayed by the inhibitor. The spawning response of hCG was accompanied by a significant increase in both hypothalamic and ovarian TH activity at 6 and 12 h of the injection. However, at 24hr the activity decreased except in the spawning phase. The -MPT treatment inhibited TH activity significantly in a duration–dependent manner. In the hCG + -MPT groups, enzyme activity was inhibited at all duration. The results indicate the involvement of catecholamines during the hCG-induced spawning and the specific functional nature of the involvement needs further investigation.

Ovarian monosaccharides (glucose and fructose): hormonal effects and their role in final oocyte maturation and egg quality in catfish Heteropneustes fossilis, Bloch.

In the catfish H. fossilis, ovarian glucose and fructose levels showed significant annual variations that could be correlated with the gonado-somatic index. The concentration of the sugars, which was low in resting phase of gonad increased with the onset of oogenesis, reaching the peak in prespawning (June) phase. Glucose is the predominant monosaccharide in the late oogenesis, while fructose in early oogenesis and resting phase. Administration of a single injection of HCG (100 IU/fish) decreased glucose at 4 hr but increased fructose (6 hr) in the resting phase. In the preparatory phase (active oogenesis), fructose decreased significantly at 4 hr and glucose at 6 and 12 hr. In the prespawning phase, HCG administration induced a significant decrease in glucose level at 2 hr but increased it significantly at 16 and 18 hr. Fructose concentration, on the other hand, decreased > or = 4 hr. The involvement of different energy substrates (glucose, fructose, 2-deoxyglucose and pyruvate) on final oocyte maturation and viability of eggs were demonstrated in an in vitro study, employing incubation of mature oocytes in medium containing one or the other energy substrates. Glucose at 4 and 8 mM concentrations increased the viability of eggs without affecting germinal vesicle break down (GVBD) and at high concentrations (16 and 32 mM) marginally increased GVBD but decreased viability. Pyruvate at high concentrations (> or = 8 mM) produced a positive effect on both GVBD and viability. Fructose and 2-deoxyglucose did not elicit any effect on these parameters. The results suggest that glucose has an active role in catfish oogenesis and maintaining egg quality and HCG influences monosaccharide metabolism in a season-dependent manner.

Effects of ovine LH, GH and prolactin, and testosterone on serum testosterone and estradiol-17 beta levels, and seminal vesicle and testicular activity in the catfish Clarias batrachus (L.).

Intraperitoneal administrations of testosterone (0.5 microgram/g body wt), and ovine LH (1.0 microgram/g body wt), GH (5 micrograms/g body wt) and prolactin (10 micrograms/g body wt) daily for 7 days during early prespawning phase (May) in C. batrachus produced varied effects on seminal vesicle (SVSI) and testicular (GSI) weights and biochemical correlates. Testosterone and LH treatments significantly increased serum testosterone level and concentrations of total proteins, fructose, hexosamines and sialic acid in both seminal vesicles and testis. Serum E2 levels increased significantly only after testosterone treatment. GH treatment increased significantly serum testosterone level and only the concentrations of SV hexosamines and testicular protein. Prolactin, however, significantly lowered serum testosterone level and concentrations of total protein, hexosamines in both SV and testis, and testicular fructose and sialic acid levels. The results show that the stimulating effect of LH and GH on SV and testicular activity is mediated through the increased secretion of testosterone and the inhibitory effect of prolactin by decreased testosterone secretion.

Effects of administration of testosterone on some biochemical correlates in seminal vesicle of Heteropneustes fossilis (Bloch) during preparatory phase: a study correlating changes in plasma testosterone level and testis activity.

In the catfish H. fossilis, administration of testosterone (0.25, 0.5, 1 and 2 micrograms/g body weight for 20 days) during mid-preparatory phase (March) increased plasma testosterone, gonadosomatic index, seminal vesicle-somatic index and concentrations of total proteins, fructose and hexosamines in seminal vesicle (SV) and testis in a dose-related manner. In the lowest dosage (0.25 microgram) group, only the hexosamine and SV protein levels were significantly high. Glucose level decreased in a dose-related manner, the decrease being not significant in the 0.25 microgram group. The results indicate that testosterone stimulates SV and testicular secretions of total proteins, hexosamines and fructose in catfish. Decrease in glucose content suggests its conversion into fructose under testosterone stimulation.

Precocious recrudescence of seminal vesicle and testis in catfish, Clarias batrachus (Linn.), subjected to a long photoperiod regime.

The catfish C. batrachus were exposed to a long photoperiod of 14 hr light during resting--early preparatory (December-February) phases of the reproductive cycle. At 70-day sampling, both the seminal vesicle (SV) and testis registered marked stimulatory effects in comparisons to control fish maintained under approximately 10.55 L:13.45D as shown by the increased size and weight. In both the SV and testis, concentrations of total proteins, fructose, hexosamines, and sialic acid were significantly high compared to those of the control fish indicating increased activities of the organs. Serum levels of gonadotropin-II, testosterone, and estradiol-17 beta were significantly high in the long photoperiod group. The results show that exposure to long photoperiod can stimulate early development of both the SV and testis by activating the pituitary--gonadal axis.

Effect of dexamethasone and metopirone on hypothalamic gamma-aminobutyric acid (GABA) and plasma cortisol levels in the female catfish, Clarias batrachus (L.)

Em C. batrachus, o GAMA hipotalâmico aumentou significativamente em resposta ao tratamento durante 7 dias com dexametasona (50 ug/peixe/dia : i.p.). Entretanto, a metopirona (CIBA, 50 ug/peixe/dia : i.p.) baixou acentuadamente o conteúdo do GABA hipotalâmico já a partir do 3. dia de tratamento. Nos peixes submetidos a tratamentos com dexametasona e metopirona o nível de cortisol plasmático apresentou-se significativamente menor. Estes resultados sugerem que o aumento e decréscimo dos níveis do GABA hipotalâmico podem ter um papel estimulador ou inibidor em resposta aos tratamentos com dexametasona ou metopirona