Reducing Estrogen Synthesis in Developing Boars Increases Testis Size and Total Sperm Production

Abstract

The abundant production of testicular estrogens and the presence of both ESR1 and ESR2 within boar testes are consistent with a role for estrogen in testicular development and/or function in this species. This study was aimed at determining the role of endogenous estrogen in the regulation of testicular development and function, including the effects on testis weight, histology, sperm production (detergent-resistant spermatid numbers), Sertoli cell numbers, and Leydig cell volume in the boar. Twenty-eight littermate pairs of boars were assigned to groups as follows: 1 boar from each pair was assigned to the control group (vehicle) and the other was assigned to treatment and received 0.1 mg/kg body weight of an aromatase enzyme inhibitor (letrozole) orally each week beginning at 1 week of age until castration at 2, 3, 4, 5, 6, 7, or 8 months of age. Testes were weighed and testicular parenchyma was recovered for determination of histology and detergent-resistant spermatid numbers, and for determination of Sertoli cell number and Leydig cell volume by staining for GATA-4 and 17-a hydroxylase/17-20 lyase respectively. Testes of aromatase-inhibited boars initially exhibited delayed lumen formation, lower testicular weight, fewer detergentresistant spermatids, and fewer Sertoli cells, but by 7 to 8 months, these boars had recovered and had larger testes, more detergentresistant spermatids per testis, and more Sertoli cells. Total Leydig cell volume increased in proportion to testis size. Reducing endogenous estrogen is consistent with a delay in testicular maturation/puberty that allows for a longer window for the proliferation of Sertoli cells and maturation of Leydig cells, resulting in larger testes and higher spermatid production.

Testis morphology in rats chronically treated with letrozole, an aromatase inhibitor

“…The aro- www.fhc.viamedica.pl matase inhibition also affected sperm production, as has been evidenced in boars by At-Taras [35]. The levels of circulating and intratesticular estradiol were significantly decreased (43% and 48%, respectively) in letrozole-treated rats in our experiment.…”

Postnatal somatic cell proliferation and seminiferous tubule maturation in pigs: A non-random event

“…Particularly for pigs, in which the use of AI is a key tool for increasing reproduction efficiency, understanding the regulation of postnatal testis development is crucial to increasing the total number of sperm per ejaculate. However, studies related to the regulation of mitotic activity of Sertoli cells in pigs are inconclusive [3,25,26], although important advances have recently been made regarding the possible role of estrogens in Sertoli cell proliferation and maturation [27–30]. Based on ongoing studies in our laboratory, we inferred that the establishment of spermatogenesis may not be a synchronous event in the testicular parenchyma in pigs.…”

Effects of Panax ginseng, zearalenol, and estradiol on sperm function

“…The seminal plasma of breeding boars had 92 pg/mL E 2 and the seminal plasma of bulls was found to contain 568 pg/mL [10]. Concentrations of E 2 range from 8 to 300 ng/mL in sows [11] and up to 2,295 ng/mL in mature human ovarian follicles [12]. During in vitro maturation of oocytes, E 2 concentrations of 1–10 μg/mL have been used in culture media [13], [14], [15].…”