Inhibition of the basal and oestradiol-stimulated mitotic activity of primary spermatogonia by melatonin in the testis of the frog, Rana esculenta, in vivo and in vitro

Abstract

Melatonin has a direct inhibitory effect on the basal and oestradiol-stimulated mitotic activity of primary spermatogonia in the testis of the frog, Rana esculenta. In this study oestradiol was used to induce spermatogonial proliferation to verify the anti-proliferative effect of melatonin. The colchicine metaphase arrest technique was used. The results obtained from in vivo experiments confirm that oestradiol increases the mitotic index of primary spermatogonia and, for the first time, indicate that melatonin has an inhibitory role on the proliferation of primary spermatogonia in the frog testis. Similar results were obtained from testes of melatonin-injected frogs that were exposed to oestradiol in vitro; in fact spermatogonia were unresponsive to hormonal stimulation. In addition, in short-term cultured testes, melatonin (at physiological concentration) interferes with the effects of oestradiol on spermatogonial proliferation, supporting the hypothesis that melatonin exerts the inhibitory effect directly via its local action on the frog gonads. Morphological observation after in vivo or in vitro melatonin treatments indicates that Leydig cells display degenerative features, whereas in adjacent germinal tubules, Sertoli cells show heterochromatic nuclei. These results indicate that melatonin may act on Leydig cells and confirm that there is a paracrine interaction between interstitial and germinal compartments. The results of the present study indicate, for the first time, that melatonin may be directly involved in the inhibitory control of spermatogonial proliferation in the testis of the frog, R. esculenta.

Effect of estradiol on apoptosis, proliferation and steroidogenic enzymes in the testes of the toad Rhinella arenarum (Amphibia, Anura)

“…In P. esculentus, besides the role of estradiol on proliferation previously described, spermatogonial proliferation is also associated with seasonal changes in testosterone (Raucci and Di Fiore, 2007) while in L. catesbeianus both testosterone and E 2 control proliferation (Caneguim et al, 2013a). Melatonin is another hormone that has also been suggested to regulate proliferation by inhibiting estradiol-stimulated mitotic activity of spermatogonia in P. esculentus (d Istria et al, 2003). Overall, amphibian spermatogenesis is a highly complex event, and the regulation of proliferation in R. arenarum may involve interactions between different factors.…”

“…Besides, in P. esculentus there is a strong mitogenic activity of spermatogonia in the period of the year characterized by high concentrations of estradiol (Fasano et al, 1989;Rastogi et al, 1985;Varriale et al, 1986). In this species, estradiol promotes spermatogonial proliferation through the activity of Fos protein and the activation of mitogen-activated protein kinase in spermatogonia (Chieffi et al, 1995(Chieffi et al, , 2000Cobellis et al, 1999;Minucci et al, 1997) and proliferation is inhibited by melatonin (d Istria et al, 2003). Moreover, estradiol regulates the expression of Fra-1, which is located in peritubular myoid cells, efferent ducts and blood vessels and may be involved in sperm transport.…”

Primordial Germ Cells (Spermatogonial Stem Cells) of Bullfrogs Express Sex Hormone-Binding Globulin and Steroid Receptors during Seasonal Spermatogenesis

“…It has been suggested that estrogens may play a role in regulating spermatogenesis and that this hormone induces murine gonocyte proliferation [Li et al, 1997]. In anurans, estrogen plays a role during early spermatogenesis [Callard, 1992;Polzonetti-Magni et al, 1998] and stimulates the mitotic activity of primordial spermatogonia of Rana esculenta [Minucci et al, 1997;d'Istria et al, 2003]. Thus, a possible direct role of estrogen in the mitotic activity of PGCs in the bullfrogs needs to be further confirmed.…”

Environmental influence on testicular MAP kinase (ERK1) activity in the frogRana esculenta

“…In fact, the light influences the hypotalamo-hypophyseal system, with the mediation of pineal gland/eyes (Rastogi, 1976;d'Istria et al, 2003), in the secretion of gonadotropins that regulate the synthesis of mitogen factors (i.e. growth factors, estrogens) by Sertoli and Leydig cells that induce and regulate spermatogonial proliferation (Rastogi, 1976).…”