The effect of aromatase inhibitor, fadrozole, on sGnRHa stimulated LH secretion in goldfish (Carassius auratus) and common carp (Cyprinus carpio).

The aromatase inhibitor, fadrozole, was applied to common carp and goldfish in order to examine its ability to increase the spontaneous and sGnRHa stimulated LH secretion. First, trials in goldfish in 2003 showed fadrozole's moderate ability to potentiate sGnRHa-stimulated LH secretion. However, this ability was much weaker than that obtained with dopamine antagonist, pimozide. There was no ovulation in fadrozole-treated fish. Several experiments on goldfish and carp during the two consecutive years with the different treatment regimes and doses of fadrozole did not confirm the optimistic results obtained in 2003. This shows that fadrozole is unable to replace the antidopaminergic drugs being used in fisheries practice.

Influence of heavy metals and 4-nonylphenol on reproductive function in fish.

Many industrial and agricultural chemicals (including heavy metals and alkylphenols) present in the environment have adverse effects on the reproductive function in fish. Three studies were conducted to assess toxicity of these chemicals towards reproduction of freshwater fish. It was shown that heavy metals added to the diets accumulate in brain tissue of carp, and this accumulation results in inhibition of the secretion of noradrenaline and stimulation of the secretion of dopamine in the hypothalamus. These processes results in a disturbance of hormonal equilibrium of the hypothalamo-pituitary system, which can unfavorably influence the efficiency of artificial spawning in fish. Quality of salmonid and sturgeon sperm was impaired after in vitro exposure to heavy metals. The degree of this toxic effect was species-specific. It was demonstrated that sperm motility parameters appeared to be good indicators of adverse effects of heavy metals fish sperm. The protection role of seminal plasma against toxic effects of heavy metals was suggested for salmonid fish. Oral application of 4-nonylphenol (NP) disrupted reproduction in pikeperch. In juvenile fish a decrease in the percentage of males and an increase of intersex fish was observed in relation to dose of NP and time of exposure to this alkylphenol. Exposure of adult males to the NP led to the reduction in fecundity, milt quality and fertility.

Differential effects of morphine and naltrexone on the in vitro LH secretion from male and female carp pituitary gland.

The in vitro effects of morphine (10(-10), 10(-8), 10(-6) or 10(-5) M) or/and naltrexone (10(-6) or 10(-8) M) on LH release from male and female carp (Cyprinus carpio L.) dispersed pituitary cells (obtained from fish at the time of late gonad recrudescence) were investigated. Morphine alone at the lowest tested concentration (10(-10) M) increased LH secretion from the cells of males. On the contrary, in female cell incubations the highest concentrations of morphine (10(-6) or 10(-5) M) significantly lowered LH levels. Naltrexone alone (at both tested concentrations) had no influence on LH secretion, neither in males nor in females. However in the incubations of female cells it antagonised the influence of morphine at 10(-10) or 10(-8) M. In male cell incubations naltrexone abolished the stimulatory action of morphine at 10(-10) M. The results suggest that in the in vitro culture of carp pituitary cells LH secretion is modulated by the opioids which affect the release of this gonadotropin through the typical opioid receptors and that the mu type of these receptors is involved in this process. The effects of opioid agonist and antagonist depend on the stage of gonadal maturity and the sex of fish i.e. the actual level of sex steroids.

The effects of naltrexone, an opioid receptor antagonist, on plasma LH levels in common carp (Cyprinus carpio L.).

Naltrexone-an opioid receptor antagonist, was administered intraperitoneally to sexually mature male and female common carp in the prespawning period, in order to investigate its effects on spontaneous or sGnRH-A-stimulated LH secretion. Naltrexone and sGnRH-A were injected at the same time. The possible involvement of a dopaminergic system in this process was studied in males pre-treated with pimozide (a dopamine receptor antagonist) 12 h before naltrexone and/or sGnRH-A administration. Blood samples for the analysis of carp LH concentrations were taken just before the injections and then after the injections, serial sampling during 24 h was performed. In male carp, naltrexone (500 or 5000 microg kg(-1)) decreased spontaneous LH release, but there were no effects of naltrexone on sGnRH-A-stimulated LH secretion. In males pre-treated with pimozide, a similar response to naltrexone injection (500 microg kg(-1)) as in pirnozide non-treated fish, was observed. The highest dose of naltrexone, 5000 microg kg(-1), significantly stimulated LH release, in response to sGnRH-A administration in pimozide pre-treated males. In female carp, contrary to males, naltrexone at a dose of 500 microg kg(-1), caused significant stimulation of spontaneous LH release. These data indicate that endogenous opioid peptides modify LH secretion in sexually mature carp. In males, they stimulate LH secretion, acting rather on the hypothalamic GnRH system and in females, opioids inhibit LH release by the influence on the dopaminergic system.

Seasonal short-term effects of naltrexone on LH secretion in male carp (Cyprinus carpio L.).

In order to evaluate the influence of the season (the stage of gonad maturity) on the modulatory role of endogenous opioid peptides in LH secretion in fish, sexually mature male carp (Cyprinus carpio L.) were intravenously injected with naltrexone-opioid receptor antagonist (5 or 50 microg kg(-1)) in the period of natural spawning (June) or gonad recrudescence (December). Moreover, the possible involvement of the dopaminergic system was studied in fish pre-treated with pimozide (dopamine receptor antagonist) and in intact fish. Blood samples were taken every minute, up to 10 min after naltrexone injection. In June, naltrexone significantly lowered LH levels in comparison to saline injected males. In December, there were no differences between saline and naltrexone-injected carps. In fish pre-treated with pimozide, neither in June nor in December were any significant differences in LH levels between control group and the groups injected with naltrexone found. The results showed that, in male carp, LH secretion under the influence of naltrexone depends on the stage of gonad maturity what suggests that the feedback of gonadal steroids on LH release could be mediated by the endogenous opioids. The role of dopamine in these processes is also discussed.