Passive immunization against inhibin increases testicular blood flow in male goats
Introduction
Adequate blood supply to the testis is crucial to its function because the seminiferous tubules compromise 70%–80% of the testicular mass with very little oxygen concentration [1,2]. Previous reports have found that decreases in testicular blood flow can cause ischemic damage of the testis and impairments in spermatogenesis due to defective energy metabolism in the testicular microcirculation [3,4]. Therefore, various treatments that induce improvements in testicular blood flow, and in turn, improvement in testicular function are of great values for animal fertility [5]. Among the different methods of assessment of testicular function, color Doppler ultrasonography is considered a noninvasive tool for measurement of the blood perfusion to the testis in different animal species such as sheep [6], goats [7], bulls [8], horses [9], and dogs [10]. In previous literatures, Doppler indices of the blood flow (resistance index; RI and pulsatility index; PI) of testicular arteries were considered potential markers of seminal quality [8,11], and also as valuable parameters for the diagnosis of testicular dysfunction and to identify various infertility problems in males by clinical practitioners [9,10]. In addition, assessment of the testicular hemodynamics by color Doppler ultrasonography has been suggested as a very important way to indirectly assess gonadal function if sperm count is not available [4].
Inhibin is a heterodimeric glycoprotein hormone of gonadal origin. The name ‘inhibin’ is derived from its ability to inhibit or decrease the release of follicle-stimulating hormone (FSH) from the pituitary via a negative feedback mechanism [[12], [13], [14]]. Also, there are shreds of evidence supporting an autocrine or paracrine role for inhibin in the regulation of testicular function such as modulation of steroidogenesis [15,16], spermatogonial development [16], and sperm production [17,18]. Few previous studies have declared the importance of immunization against inhibin in male goats, for the purpose of elucidating its function in their reproduction [19,20]. However, there is no previous literature that has focused on its role in testicular hemodynamic. By bibliographical search, a few articles on the impact of inhibin on blood flow in other organs or even systems were found. For example, in patients that suffered from atherosclerotic vascular alterations (such as coronary artery disease), reductions in the testicular arterial blood flow were observed concomitantly with impairments of testicular function and significantly lower levels of circulating inhibin [21]. Moreover, in another study on women [22], ovarian blood flow was found to be negatively correlated with the serum inhibin levels. Our study [23] also showed a strong positive correlation between plasma inhibin levels and the RI of the supratesticular artery in male goats. Based on the aforementioned literature, we hypothesized that passive immunization against inhibin may neutralize the circulating inhibin, thus, leading to increases in blood flow within the testicular arteries. Therefore, the objectives of the current study were to determine the effect of passive inhibin immunization on testicular blood flow in male goats using color-pulsed Doppler ultrasonography and declaring changes in circulating hormones.
Section snippets
Material and methods
This study was performed on male Shiba goats (Capra hircus), a Japanese nonseasonal breeder miniature goats. Shiba goats reach puberty at about 3.5 months and are considered a useful model animal for studying the physiology of ruminants [24]. All procedures in this study were carried out according to the guidelines of the Tokyo University of Agriculture and Technology, Japan, for the use of animals.
Plasma inhibin binding capacity and circulating hormones
The effect of passive immunization against inhibin on plasma inhibin binding activity and circulating hormones in the present study is shown in Fig. 1. There were treatment (P < 0.0001), time (P < 0.0001), and treatment-by-time effects (P < 0.0001) on plasma inhibin binding activity. After administration of inhibin antiserum, % of inhibin binding activity in plasma increased (P < 0.05) continuously from 1 h till 168 h after treatment in the INH group and it was greater (P < 0.05) than those in
Discussion
The current study is the first, according to the authors’ knowledge, to monitor changes in testicular blood flow after immunization against inhibin. The results of the present study supported the hypothesis that intravenous injection of inhibin antiserum significantly modulates testicular hemodynamics in Shiba goats, and also influences circulating hormones. Providing such data is important for understanding the potential roles of inhibin on testicular blood flow and evaluates all aspects of
Conclusion
Overall, the results of the present study have illustrated the indirect stimulatory effect of passive inhibin immunization on testicular blood flow (through decreases in the values of RI of the STA and MTA) in goats. Concomitantly, significant increases in the concentrations of FSH and E2 were found. Thus, inhibin immunization may have merit as a therapeutic route to enhance testicular blood flow and need further investigations to confirm the mechanism.
Authors’ contributions
H. Samir: Conceptualization, Project administration, Methodology, Investigation, Visualization, Data curation, Formal analysis, Validation, Writing - original draft, Writing - review & editing. M.A.I. El Sayed: Visualization, Data curation, Validation, Writing - review & editing. K. Nagaoka: Visualization, Validation, Writing - review & editing. K. Sasaki: Visualization, Validation, Resources. A.M. Abo El-Maaty:Validation, Writing - review & editing. A. Karen: Visualization, Validation, Writing
Acknowledgement
We are grateful to Dr. A.F. Parlow (National Institute of Diabetes and Digestive and Kidney Diseases, Beltsville, MD) for providing the RIA materials for ovine FSH and LH, Dr. G.D. Niswender (Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, CO) for providing antisera to estradiol-17β (GDN 244) and testosterone (GDN 250), Dr. Y. Mori (University of Tokyo, Bunkyo-Ku, Tokyo, Japan) for antiserum to ovine LH (YM-18). We are grateful Dr. S. Kobayashi (United
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