An Experimental Approach to the Interrelationship Between Hyperthyroidism and Ejaculation Latency Time in Male Rats

Purpose: We investigated the effects of experimentally induced hyperthyroidism on seminal vesicle pressure measurements and bulbospongiosus muscle contractile activity in a para-chloroamphetamine (Sigma-Aldrich (R)) induced ejaculation model in rats. Materials and Methods: Male Wistar rats were used in the study. Daily injection of 25 mu g/100 gm body weight L-thyroxine (T4, Sigma-Aldrich) for 14 days was performed in 14 rats to induce hyperthyroidism. Seven L-thyroxine injected rats were in the hyperthyroid group. The remaining 7 rats (recovery group) underwent operation after a 28-day washout period to determine spontaneous recovery from hyperthyroidism. At each operation seminal vesicle catheterization was done to measure intraluminal pressure and bulbospongiosus muscle dissection was performed for electromyography. After intraperitoneal administration of 5 mg/kg para-chloroamphetamine physiological parameters related to the ejaculatory process were measured. Results: The interval between para-chloroamphetamine administration and first ejaculation was significantly decreased in the hyperthyroid rat group compared with that in the control group (mean SD +/- 202.8 +/- 22.3 vs 465.4 +/- 104.6 seconds, p = 0.001). Seminal vesicle phasic contraction frequency was significantly higher than control group values in hyperthyroid rats (for 30 minutes 32.3 +/- 13.9, p = 0.047). The mean AUC of bulbospongiosus muscle electromyography activity was also significantly increased in this group (11.1 +/- 4.1 V per second x 10(-4), p = 0.0001). All parameters in recovery and control group rats were not significantly differed from each other. Conclusions: Hyperthyroidism leads to enhanced seminal vesicle contraction frequency and bulbospongiosus muscle contractile activity in rats. Hyperthyroidism affects the emission and expulsion phases of ejaculation in reversible fashion.