Increased testicular blood flow maintains oxygen delivery and avoids testicular hypoxia in response to reduced oxygen content in inspired air

Abstract

Despite a long-standing assertion that mammalian testes operate near hypoxia and increased testicular temperature causes frank hypoxia, we have preliminary evidence that changes are due to hyperthermia per se. The objective was to determine how variations in inspired oxygen concentration affected testicular blood flow, oxygen delivery and extraction, testicular temperature and lactate production. Eight rams were maintained under general anesthesia, with successive decreases in oxygen concentration in inspired air (100, 21 and 13%, respectively). As oxygen concentration decreased from 100 to 13%, there were increases in testicular blood flow (9.6 ± 1.7 vs 12.9 ± 1.9 ml/min/100 g of testis, P < 0.05; mean ± SEM) and conductance (normalized flow; 0.46 ± 0.07 to 1.28 ± 0.19 ml/min/mm Hg/100 g testis (P < 0.05). Increased testicular blood flow maintained oxygen delivery and increased testicular temperature by ~1 °C; this increase was correlated to increased testicular blood flow (r = 0.35, P < 0.0001). Furthermore, oxygen utilization increased concomitantly and there were no significant differences among oxygen concentrations in blood pH, HCO3− or base excess, and no effects of venous-arterial differences in lactate production. In conclusion, under acute hypoxic conditions, testes maintained oxygen delivery and uptake by increasing blood flow and oxygen extraction, with no evidence of anaerobic metabolism. However, additional studies are needed to determine longer-term responses and potential evidence of anaerobic metabolism at the molecular level.

Testicular haemodynamics, plasma testosterone and oestradiol concentrations, and serum nitric oxide levels in the Egyptian buffalo bull after a single administration of human chorionic gonadotropin

“…Maintaining a consistent and stable supply of arterial vasculature through the supra‐main testicular artery is critical to testicular functionality (Abdelnaby et al., 2021b; Herwig et al., 2004). Several reports on humans (Battaglia et al., 2000; Rizzotto et al, 2018), stallions (Bollwein et al., 2008), donkeys (Abdelnaby et al., 2021b), camels (Kutzler et al., 2011) and Shiba bucks (Samir et al., 2015) have shown a link between plasma testosterone levels, semen quality and testicular haemodynamics. Elevation of the main testicular artery blood flow waveform pattern could result in a marked elevation in male fertility through a direct effect on the spermatogenesis process (Rizzoto et al., 2018; Velasco & Ruiz, 2021).…”

“…Several reports on humans (Battaglia et al., 2000; Rizzotto et al, 2018), stallions (Bollwein et al., 2008), donkeys (Abdelnaby et al., 2021b), camels (Kutzler et al., 2011) and Shiba bucks (Samir et al., 2015) have shown a link between plasma testosterone levels, semen quality and testicular haemodynamics. Elevation of the main testicular artery blood flow waveform pattern could result in a marked elevation in male fertility through a direct effect on the spermatogenesis process (Rizzoto et al., 2018; Velasco & Ruiz, 2021). Any declination in the main spectral wave of the testicular artery causes ischaemic changes that negatively affect the spermatogenesis process (Tarhan et al., 2003).…”

“…semen quality and testicular haemodynamics. Elevation of the main testicular artery blood flow waveform pattern could result in a marked elevation in male fertility through a direct effect on the spermatogenesis process (Rizzoto et al, 2018;Velasco & Ruiz, 2021). Any declination in the main spectral wave of the testicular artery causes ischaemic changes that negatively affect the spermatogenesis process (Tarhan et al, 2003).…”

Morphological and scanning electron microscopic study of the gonadal arterioles in the Tibetan sheep

“…This study showed that the basic structures of testicular and epididymal arteries and microarteries in Tibetan Sheep were similar to those in other mammals (Polguj et al., 2011; Polguj et al., 2015). Studies have shown that the differences in the morphology of the testicular artery protect sperm production and movement, with the coils facilitating vascular elongation or contraction, reduction of vascular pressure and regulation of blood flow (Chubb & Desjardins, 1982; Rizzoto et al., 2018). These studies found that the internal lobular artery, centripetal artery and centrifugal artery in the testicles were more abundant, indicating that the blood supply in the testicles was more abundant and conducive to spermatogenesis.…”

Melatonin improves testicular haemodynamics, echotexture and testosterone production in Ossimi rams during the breeding season

“…Due to relatively low oxygen concentrations in seminiferous tubules, physiological control of blood flow is pivotal for physiological testicular function. For example, exposing the testis to acute hypoxic conditions (13% oxygen in inspired air) increased testicular blood flow and oxygen uptake, with no indications of hypoxia (Rizzoto et al., 2018). Since testicular blood flow profoundly affects testicular function, maintaining an adequate arterial blood supply is critical.…”