Supraphysiological concentration of urea affects the functional competence of Holstein-Friesian (Bos taurus) sperm

• Published in: Theriogenology Vol. 176; pp. 104 - 114
• Main Authors: Lavanya, Maharajan, Swathi, Divakar, Archana, Santhanahalli Siddalingappa, Ramya, Laxman, Ranjithkumaran, Rajan, Krishnaswamy, Narayanan, Singh, Sanjay Kumar, Krishnappa, Balaganur, Rajendran, Duraisamy, Kumar, Harendra, Selvaraju, Sellappan
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-12-2021
• Subjects: Bull; Ejaculate rejection rate; Sperm functional attributes; Sperm head area; Urea; Urea; Sperm functional attributes; Sperm head area; Bull; Ejaculate rejection rate
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2021.09.020

To understand the effects of urea on sperm functional attributes, fresh bull semen (n = 12) was subjected to four different concentrations (mg/mL) of urea to mimic the physiological (0.04 and 0.13), supraphysiological (0.43) concentrations and control (0 mg/mL). Sperm membrane integrity, kinematics, chromatin integrity, and mitochondrial membrane potential were assessed at different time points (before incubation, 0, 1, 2, and 4 h) of incubation. The concentration of urea in serum and seminal plasma was estimated and correlated with the ejaculate rejection rate and sperm functional attributes. The relative expression of urea transporter gene transcripts (UT-A and UT-B) was assessed in sperm and testis (control) using real-time PCR. The supraphysiological concentration of urea affected sperm kinematics, viability, functional membrane integrity, and acrosome integrity within 1 h of incubation (p < 0.05). Sperm head area decreased (p < 0.05) at 0 h and subsequently increased at 1 h of incubation in all media except supraphysiological (0.43 mg/dL) concentration of urea. Seminal plasma urea concentration showed a significant negative correlation with sperm motility, membrane integrity, and mitochondrial membrane potential (p < 0.05), but had a positive correlation with the ejaculate rejection rate (r = 0.69). Relative expression of the urea transporter genes revealed that UT-A was expressed only in the testis. In contrast, UT-B was expressed in both the testis and sperm, suggesting UT-B's role in regulating urea transport in sperm. At a supraphysiological level, urea adversely affected sperm functional attributes, osmoadaptation and may affect fertility.
•Supraphysiological level of urea affects sperm viability, kinematics, membrane integrity and acrosome reaction in 1 h.•Bovine sperm lose osmoadaptation ability after exposure to supraphysiological level of urea.•Seminal plasma urea showed a positive correlation with ejaculation rejection rate but negative relation with sperm function.•Of all the urea transporter (UT) genes, only UT-B transcript was expressed in the bovine sperm.