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An in vitro study on catecholamine modulation of ovarian steroidogenic activity in the catfish Heteropneustes
1Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, India.
Abstract:
In the present study, α-methylparatyrosine (α-MPT), a tyrosine hydroxylase inhibitor was used to impair ovarian catecholaminergic activity in vitro. The consequent effects on catecholamine (CA) levels were correlated with follicular steroid production. l-dihdroxyphenylalanine (l-DOPA, the precursor of CA) and human gonadotropin (hCG) were supplemented to reverse the effect of α-MPT. The experiments were conducted in two reproductive phases, namely preparatory and pre-spawning phases in female catfish Heteropneustes fossilis. The incubation with α-MPT inhibited ovarian l-DOPA, dopamine (DA), norepinephrine (NE) and epinephrine (EP) levels and the l-DOPA supplementation compensated the inhibitory effect. The level of tyramine (TR) was increased by the α-MPT treatment but inhibited by the l-DOPA supplementation. α-MPT produced stage-specific (seasonal) effects on ovarian estradiol-17β (E2); in the preparatory phase, E2 was decreased significantly at both 12 and 24h and in the pre-spawning phase, the level was stimulated over the respective control groups. The changes were higher at 24h in both phases. l-DOPA and hCG increased the E2 level significantly in the preparatory phase and reversed the inhibitory effect of α-MPT in the co-incubation groups. In the pre-spawning phase, α-MPT-stimulated the E2 level compared to the control groups, which was reversed by l-DOPA, hCG, or by both, in co-incubations. In contrast, the α-MPT treatment decreased progesterone (P4), 17-hydroxyprogesterone and 17,20β-dihydroxy-4-prenen-3-one (17,20β-DP) in a duration-dependent manner while the co-incubations with l-DOPA, hCG, or by both, significantly reversed the inhibitory effect. These results suggest that ovarian CAs (DA, NE and EP) may exert differential and stage-specific effects on E2, inhibition in the preparative phase and stimulation in the pre-spawning phase. The progestin steroids appear to be stimulated by CAs. In conclusion, this study highlights a possible direct/causal functional interaction between CA activity and gonadotropin on steroidogenic activity, and that CAs may be involved in regulating temporal secretion of the hormones through causing the shift in steroidogenic pattern.
Insights
This study reveals that ovarian catecholamines (CAs) influence fish reproductive hormone production, with effects varying by reproductive stage. Inhibiting CAs altered steroid levels, but supplementation with l-DOPA or hCG modulated these changes.
Area of Science:
- Reproductive Biology
- Endocrinology
- Neuroendocrinology
Background:
- Ovarian catecholaminergic (CA) activity plays a role in regulating reproductive processes.
- Understanding the interplay between CAs and steroidogenesis is crucial for fish reproduction.
Purpose of the Study:
- To investigate the effects of inhibiting ovarian CA activity on catecholamine and steroid levels in catfish (Heteropneustes fossilis).
- To determine the influence of l-dihydroxyphenylalanine (l-DOPA) and human chorionic gonadotropin (hCG) in modulating these effects during different reproductive phases.
Main Methods:
- In vitro incubation of catfish ovaries with α-methylparatyrosine (α-MPT), a tyrosine hydroxylase inhibitor.
- Supplementation with l-DOPA (CA precursor) and hCG to counteract α-MPT effects.
- Analysis of ovarian catecholamine (dopamine, norepinephrine, epinephrine) and steroid hormone (estradiol-17β, progesterone, and progestins) levels.
- Experiments conducted during preparatory and pre-spawning reproductive phases.
Main Results:
- α-MPT inhibited ovarian catecholamine levels, which were partially restored by l-DOPA.
- α-MPT exhibited stage-specific effects on estradiol-17β (E2), decreasing it in the preparatory phase and increasing it in the pre-spawning phase.
- Progesterone and other progestins were decreased by α-MPT in a duration-dependent manner.
- l-DOPA and hCG reversed the inhibitory effects of α-MPT on steroidogenesis.
Conclusions:
- Ovarian catecholamines (DA, NE, EP) differentially regulate estradiol-17β secretion, with inhibitory effects in the preparatory phase and stimulatory effects in the pre-spawning phase.
- Progestin steroid synthesis appears to be stimulated by ovarian CAs.
- A direct functional interaction exists between CA activity and gonadotropin signaling in regulating steroidogenesis, influencing temporal hormone secretion patterns.
