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The effects of a GnRH analog (GnRHA), D-Ser-t-Bu6,desGly-NH2(10) (HOE 766) on spermatogenesis were analyzed in the frog, Rana esculenta. Intact animals caught at two different periods of the year (January and March) were treated with HOE 766 (GnRHA, 45 ng/g BW) at low (4 +/- 1 C) and high (22 +/- 2 C) temperatures. Hypophysectomized frogs were used also and, in addition to GnRHA, these animals were treated with crude pars distalis homogenate. In vitro incubations were carried out at 15 C, for 0, 6, and 24 h with the addition of 1 microgram GnRHA. Half of each testis was used as the untreated control. Histological sections of the testes were analyzed for the evaluation of the mitotic index of the primary spermatogonia. Intact March animals had mitotic indices higher than January animals. GnRHA treatment elicited an increase of the mitotic index in both intact and hypophysectomized animals. High temperature potentiated the GnRHA effect while low temperature favored pars distalis treatment. In conclusion, the present results are consistent with the fact that in the frog, R. esculenta, the magnitude of spermatogonial proliferation is temperature dependent, and for the first time it is shown that GnRH-like substances have direct stimulatory effect on the mitotic activity of the primary spermatogonia in a vertebrate.
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