Role of catecholestrogens on ovarian prostaglandin secretion in vitro in the catfish Heteropneustes fossilis and possible mechanism of regulation

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Seasonal, periovulatory and 2-hydroxyestradiol-17β (2-OHE2)-induced changes on ovarian prostaglandin (PG) E2 and F2α were investigated under in vivo or in vitro in the female catfish Heteropneustes fossilis. Both PGE2 and PGF2α increased significantly during ovarian recrudescence with the peak levels in spawning phase. The PGs showed periovulatory changes with the peak levels at 16h after the hCG treatment. Incubation of postvitellogenic ovary fragments with estradiol-17β (E2), 2-OHE2 or 2-methoxyE2 produced concentration-dependent increases in PG levels; 2-OHE2 was more effective. In order to identify the receptor mechanism involved in the 2-OHE2-induced PG stimulation, the ovarian pieces were incubated with phentolamine (an α-adrenergic antagonist), propranolol (a β-adrenergic antagonist) or tamoxifen (an estrogen receptor blocker) alone or in combination with 2-OHE2. The incubation of the tissues with the receptor blockers alone did not produce any significant effect on basal PG levels. However, co- and pre-incubation of the tissues with the blockers resulted in inhibition of the stimulatory effect of 2-OHE2 on the PGs. Phentolamine was more effective than propranolol. The signal transduction pathway(s) involved in the 2-OHE2-induced PG secretion was investigated. The incubation of the ovarian pieces with 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor), chelerythrine (a protein kinase C inhibitor) and PD098059 (a mitogen-activated protein kinase inhibitor) significantly lowered the basal secretion of PGF2α and PGE2. In contrast, H89 (a protein kinase A inhibitor) increased the basal secretion of PGs at 1 and 5μM concentration and decreased it at 10μM concentration. The co- or pre-incubation with IBMX, H89, chelerythrine and PD098059 significantly inhibited the stimulatory effect of 2-OHE2 on PGF2α and PGE2 levels. The inhibition was higher in the pre-incubation groups. Chelerythrine was the most effective followed by PD098059, IBMX and H89. The results suggest that 2-OHE2 may employ both adrenergic and estrogen receptors, or a novel receptor mechanism having properties of both adrenergic and estrogen receptors.