The Goitrogen 6-n-Propyl-2-Thiouracil (PTU) Given during Testis Development Increases Sertoli and Germ Cell Numbers per Cyst in Fish: The Tilapia (Oreochromis niloticus) Model

Abstract

The main objectives of the present study were to investigate the effects of 6-n-propyl-2-thiouracil (PTU) on Sertoli cell proliferation, germ cell number, and testis size in Nile tilapias (Oreochromis niloticus). In this regard, young fish (approximately 1 g BW and approximately 3.5 cm total in length) were treated for a period of 40 d with different concentrations (100 and 150 ppm) of PTU. The animals were killed and analyzed on d 1, 30, 40, 98, and 208 after the beginning of the treatment. On d 30 and 40 the spermatogenic process was delayed in fish treated with PTU compared with the control group. Also at these periods, treated tilapia had decreased (P < 0.05) body weight and total length. On d 98 body weight and total length had recovered in PTU-treated fish and were similar (P > 0.05) to those of the controls. However, testis weight and gonadosomatic index (testis mass/body weight) were approximately 100% higher (P < 0.05) in treated tilapia. Similarly, the area occupied by seminiferous tubules, the number of Sertoli cells and germ cells per cyst, and the number of Leydig cells per testis were significantly (P < 0.05) greater in treated fish. Nevertheless, nuclear volume and individual Leydig cell volume were significantly lower (P < 0.05) in tilapia receiving PTU treatment. Compared with controls, at 208 d all parameters analyzed presented the same trend as that observed at 98 d. In general, at 98 d the different PTU concentrations used during the treatment period induced similar effects. However, at 208 d the mean values observed for several parameters were significantly higher (P < 0.05) in fish exposed to 150 ppm. Probably due to the higher density of Sertoli cells per cyst in treated tilapia, these cells presented a smaller (P < 0.05) nucleolus and a trend to decrease its support capacity (efficiency). However, the meiotic index (germ cell loss during the two meiotic divisions) was similar (P > 0.05) in the three groups of fish investigated. Remarkably, the results found in tilapia were similar to those found for rats treated with PTU. This suggests strongly that the mechanisms of control of Sertoli cell and Leydig cell proliferation seem to be preserved during vertebrate evolution.

Microscopic morphology and testis morphometry of captivity-bred Adult bullfrogs (Lithobates catesbeianus Shaw, 1802)

“…A measurement of the nucleolar diameter of the Sertoli cell was important since it was observed that treatments could reduce it. Matta et al (2002) observed a reduction in the nucleolar diameter of this cell when they treated Nile tilapia with goitrogen drugs. Ko et al (1998) Kanamadi and Jirankali (1992) found around five spermatid cysts per tubule and as many primary spermatogonium and secondary spermatocide cysts.…”

“…The testes were fixed in 2.5% glutaraldehyde in 0.1M sodium phosphate buffer (pH 7.4) and included in glycol methacrylate (Historesin®, Reichert-Jung) following routine procedures. Serial longitudinal sections (3 µm and 4 µm) were obtained using rotary microtome (Reichert-Jung, Multicut® -2045) and glass razor, according to MATTA et al (2002). The sections were stained with 1% toluidine blue-sodium borate and mounted in Entellan® (Merck).…”

“…The main measurable parameters are number, area, length, volume, and diameter of structures (Bozzola and Russell, 1998). Its application in testis analysis deepened the comprehension of gonadal dynamics, making a comparison of testicular structure and function possible (Matta et al, 2002). Costa (1992) studied aspects of bullfrog spermatogenesis in the testicular cycle as well as reproductive biology, but did not deal with morphometrical approaches.…”

Thyroid hormone regulation of mRNAs encoding thyrotropin β-subunit, glycoprotein α-subunit, and thyroid hormone receptors α and β in brain, pituitary gland, liver, and gonads of an adult teleost, Pimephales promelas

“…In addition to their well-established roles in influencing growth and morphology, THs have been shown to promote neural stem cell proliferation in the olfactory system of salmon indicating a role for THs in neurogenesis (Lema & Nevitt 2004), and to mediate the rheotactic shifts and migratory behaviors of salmon and other diadromous fishes (McCormick et al 1998, Edeline et al 2005. THs also appear to influence reproductive function in teleost fish, since inhibition of endogenous TH production during the time of gonadal germ cell differentiation leads to an increased density of Sertoli and germ cells per cyst in the testis (Matta et al 2002).…”

Sertoli cell proliferation in the adult testis is induced by unilateral gonadectomy in African catfish

“…each Sertoli cell supports a certain, species-specific number of germ cells during spermatogenesis in 11 mammals and fish [15,29,33,41,25], the Sertoli cell number per testis ultimately dictates the 12 magnitude of testis size and sperm production [15,22,33]. In mammals, the pituitary gonadotropin 13 follicle-stimulating hormone (FSH) is a major stimulator of the proliferation of Sertoli cells [32,50], 14 until they attain a non-mitotic state during puberty [9,23].…”