Conversion from testosterone to oestradiol is required to modulate respiratory long-term facilitation in male rats

• Published in: The Journal of physiology Vol. 576; no. 3; pp. 903 - 912
• Main Authors: Zabka, A. G., Mitchell, G. S., Behan, M.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.11.2006; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Animals; Aromatase Inhibitors - pharmacology; Blood Pressure - physiology; Carbon Dioxide - metabolism; Dihydrotestosterone - pharmacology; Estradiol - metabolism; Hypoglossal Nerve - drug effects; Hypoglossal Nerve - physiology; Hypoxia - metabolism; Hypoxia - physiopathology; Male; Neuronal Plasticity - drug effects; Neuronal Plasticity - physiology; Orchiectomy; Phrenic Nerve - drug effects; Phrenic Nerve - physiology; Rats; Rats, Inbred F344; Respiratory; Respiratory System - drug effects; Respiratory System - innervation; Serotonin - physiology; Testosterone - metabolism; Testosterone - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2006.114850

Sex hormones modulate plasticity in the central nervous system, including respiratory long-term facilitation (LTF), a form of serotonin-dependent respiratory plasticity induced by intermittent hypoxia. Since gonadectomy (GDX) attenuates LTF in male rats, we tested the hypotheses that: (1) testosterone replenishment restores LTF in gonadectomized male rats, and (2) that the conversion of testosterone to oestradiol (under the influence of aromatase) is required for these effects. Intact and sham operated male F344 rats were compared to gonadectomized rats implanted with Silastic tubing containing testosterone (T), T plus an aromatase inhibitor (ADT), or 5α-dihydrotestosterone (DHT), a form of testosterone not converted to oestradiol. Seven days postsurgery, LTF was studied in anaesthetized, neuromuscularly blocked and ventilated rats while monitoring integrated phrenic and hypoglossal (XII) motor output. LTF was elicited by three 5 min hypoxic episodes ( P a,O 2 = 35 − 45 mmHg). Although significant phrenic and XII LTF were observed in all rat groups, GDX reduced both phrenic and XII LTF, an effect reversed by T. In contrast, LTF was not restored in T + ADT or DHT-treated gonadectomized rats. We conclude that the conversion of testosterone to oestradiol modulates phrenic and XII LTF in male F344 rats.