Investigation of the Neural Target Level of Hyperthyroidism in Premature Ejaculation in a Rat Model of Pharmacologically Induced Ejaculation Asif Cahangirov, MD,* Ahmet Cihan, MD,* Nergis Murat, PhD, † Omer Demir, MD,* Guven Aslan, MD,* Sedef Gidener, MD,* and Ahmet Adil Esen, MD* *Department of Urology, School of Medicine, Dokuz Eylul University, Izmir, Turkey; † Department of Pharmacology, School of Medicine, Dokuz Eylul University, Izmir, Turkey DOI: 10.1111/j.1743-6109.2010.02042.x ABSTRACT Introduction. Association between hyperthyroidism and premature ejaculation was demonstrated in clinical studies. Aim. The aim of this study is to determine the target level of changes on ejaculatory physiology under hyperthyroid states. Methods. p-Chloroamphetamine (PCA)-induced pharmacologic ejaculation model with 24 male Wistar rats was used in the study. Subcutaneous injection of L-thyroxine for 14 days was performed to induce hyperthyroidism. At the end of the injection period, thyroid hormone status was evaluated by serum thyroid-stimulating hormone measurements in all rats. At the beginning of the operations, complete spinal transections (tx) at the T8-T9 level were performed to half of the L-thyroxine-injected and control group rats. Thus, experimental groups were constructed as follows: Group 1—control-spinal intact (n = 6), group 2—control-spinal tx (n = 6), group 3—hyperthyroid-spinal intact (n = 6), and group 4—hyperthyroid-spinal tx (n = 6). Ejaculatory responses were recorded before and 30 minutes after intraperitoneal administration of 5 mg/kg PCA. Main Outcome Measures. During the operations, seminal vesicle (SV) catheterization and bulbospongiosus (BS) muscle dissections were performed in all rats to demonstrate SV pressure (SVP) BS electromyographic (EMG) activity changes. Results. Following PCA administration SVP tonic amplitude, SV phasic contraction (SVPC) frequency, SVPC maximal amplitude, and BS EMG area under curve values were higher in hyperthyroid intact rats than in control intact rats. The time interval between PCA administration and first ejaculation of hyperthyroid intact rats were significantly shorter than control intact rats (261  7.30 seconds vs. 426  49.6 seconds, P = 0.008). All of the changes in the ejaculatory parameters that were induced by hyperthyroidism were completely resolved after spinal transections at the T8-T9 level in group 4. Conclusion. In this study, we confirmed the recent data that hyperthyroidism affects both the emission and expulsion phases of ejaculation. The changes that were induced by hyperthyroidism on ejaculatory physiology probably take place in the supraspinal centers above T8 level. Cahangirov A, Cihan A, Murat N, Demir O, Aslan G, Gidener S, and Esen AA. Investigation of the neural target level of hyperthyroidism in premature ejaculation in a rat model of pharmacologically induced ejaculation. J Sex Med 2011;8:90–96. Key Words. Ejaculation; Hyperthyroidism; Neural Pathway; Thyroid; Ejaculatory Physiology Introduction P remature ejaculation (PE) is one of the most common male sexual problem in all countries with the prevalence of 20–30% [1]. Studies researching biological risk factors for PE sup- ported hyperthyroidism to be an etiological risk factor for acquired PE [2–4]. The relationship between hyperthyroidism and PE was demon- strated in clinical studies [2–4]. The effects of 90 J Sex Med 2011;8:90–96 © 2010 International Society for Sexual Medicine