Additive effects of orchiectomy and intermittent hypoxia on lung mechanics and inflammation in C57BL/6J male mice

Abstract

New Findings What is the central question of this study?Does endogenous testosterone modulate the consequences of intermittent hypoxia (IH) in the lungs of male mice? What is the main finding and its importance?Orchiectomized mice exposed to IH develop a pattern that is similar to emphysema or obstructive lung disease with elevated lung volumes, low pulmonary elastance during a methacholine challenge test and high counts of lymphocytes in bronchoalveolar lavages. Since low testosterone levels and other respiratory diseases are common in sleep apnoea, there is a clear clinical relevance to these results. Abstract We tested the hypothesis that low testosterone levels modulate the pulmonary responses to intermittent hypoxia (IH; used as a model of sleep apnoea (SA)) in male mice. We used intact (SHAM) or orchiectomized (ORX) mice exposed to IH for 14 days (12 h/day, 10 cycles/h, 6% oxygen) or to normoxia (Nx). We first measured ventilation and metabolic rates in freely behaving mice (whole‐body plethysmography) and then respiratory mechanics in tracheotomized mice (flexiVent). We assessed the respiratory system resistance and elastance (Ers), Newtonian resistance (resistance of the large airways), tissue damping and tissue elastance (H) under baseline conditions and during a methacholine challenge test. We also measured the quasi‐static compliance and inspiratory capacity with partial pressure‐volume loops. Finally, inflammatory cells were counted in the broncho‐alveolar lavage (BAL) and we measured lung volume by water displacement. ORX‐IH mice had higher tidal volume, inspiratory capacity and lung volume compared to the other groups, but showed signs of low efficiency of O2 exchange rate relative to minute ventilation. During the methacholine challenge, orchiectomy decreased the values of most mechanical parameters and IH reduced Ers and H leading to very low values in ORX‐IH mice. Finally, the total number of cells and the number of lymphocytes in BAL were both increased by IH in ORX mice. Since reduced lung elasticity, low O2 extraction, increased lung volumes and inflammation are signs of emphysematous lung disease, we conclude that testosterone might prevent lung emphysema during IH exposures.

Loss of testosterone induces postprandial insulin resistance and increases the expression of the hepatic antioxidant flavin‐containing monooxygenases in mice exposed to intermittent hypoxia

“…Plasma testosterone levels and the mass of the seminal vesicles at the end of the IH or Nx exposures are presented in Table 1 (including ANOVA p values). As previously reported, 15,16 ORX successfully reduced testosterone levels and seminal vesicle mass.…”

“…10 weeks old), mice were housed in standard cages (4 mice/cage) connected to an oxycycler (Biospherix, Redfield, NY, USA). Oxygen dropped from 21% to 6% in 90 s, remained at 6% for 30 s, then returned to 21% in 70 s, and remained at normoxia for 120 s. There were 12 cycles/h for 12 consecutive hours between 6:00 am and 6:00 pm for 14 consecutive days, as described previously 15,16,20 . Following the last day of exposure to IH or Nx, the mice were either fasted for 6 h or overnight for 12 h (9 pm–9 am), then allowed to feed ad‐libitum for 2 h.…”

“…All surgeries were performed as previously described. 15,16 Each mice received a dorsal injection of meloxicam (1 mg/ kg), buprenorphine (0.05 mg/kg), and Ringer's lactate (10 mL/kg/h) before being anesthetized with isoflurane (4% for induction, 2% thereafter, in 30% O 2 ). The level of anesthesia was assessed by the lack of reflex responses to pinches of toes.…”

“…Oxygen dropped from 21% to 6% in 90 s, remained at 6% for 30 s, then returned to 21% in 70 s, and remained at normoxia for 120 s. There were 12 cycles/h for 12 consecutive hours between 6:00 am and 6:00 pm for 14 consecutive days, as described previously. 15,16,20 Following the last day of exposure to IH or Nx, the mice were either fasted for 6 h or overnight for 12 h (9 pm-9 am), then allowed to feed ad-libitum for 2 h. The mice fasted for 6 h were used for the insulin and glucose tolerance tests (ITT and GTT), then sacrificed with an anesthetic overdose. Body composition was measured non-invasively in restrained, non-anesthetized mice before and after the exposures to IH in the mice under fasting conditions with a MiniSpec LF90 body composition analyzer (Bruker, Billerica, MA, USA) following the instructions of the manufacturer.…”

Malat1 deficiency prevents hypoxia-induced lung dysfunction by protecting the access to alveoli

“…The temperature of the plethysmograph chamber was recorded Frontiers in Physiology frontiersin.org with a thermocouple. Rectal temperature was measured at the end of the recording session (Ganouna-Cohen et al, 2022). All signals were digitized (Micro 1401 data acquisition system; Cambridge Electronic Design, Cambridge, England), stored and analyzed on a computer using the Spike 2 software (version 7.06-CED).…”