Facilitation of male sexual behavior in Syrian hamsters by the combined action of dihydrotestosterone and testosterone

Abstract

Background: Testosterone (T) controls male Syrian hamster sexual behavior, however, neither of T's primary metabolites, dihydrotestosterone (DHT) and estradiol (E(2)), even in highly supraphysiological doses, fully restores sexual behavior in castrated hamsters. DHT and T apparently interact with androgen receptors differentially to control male sexual behavior (MSB), but whether these two hormones act synergistically or antagonistically to control MSB has received scant experimental attention and is addressed in the present study.

Methodology/principal findings: Sexually experienced male Syrian hamsters were gonadectomized and monitored 5 weeks later to confirm elimination of the ejaculatory reflex (week 0), at which time they received subcutaneous DHT-filled or empty capsules that remained in situ for the duration of the experiment. Daily injections of a physiological dose of 25 µg T or vehicle commenced two weeks after capsule implantation. MSB was tested 2, 4 and 5 weeks after T treatment began. DHT capsules were no more effective than control treatment for long-term restoration of ejaculation. Combined DHT + T treatment, however, restored the ejaculatory reflex more effectively than T alone, as evidenced by more rapid recovery of ejaculatory behavior, shorter ejaculation latencies, and a greater number of ejaculations in 30 minute tests.

Conclusions/significance: DHT and T administered together restored sexual behavior to pre-castration levels more rapidly than did T alone, whereas DHT and vehicle were largely ineffective. The additive actions of DHT and T on MSB are discussed in relation to different effects of these androgens on androgen receptors in the male hamster brain mating circuit.

Figure 1. DHT and T synergize to accelerate restoration of ejaculatory behavior.

Percent of males displaying the ejaculatory reflex (A), number of ejaculations per 30 min test (B) and ejaculation latencies on the first ejaculatory series (C), during post-castration tests 2–5 wks after the onset of hormone or vehicle injections. * Significantly different from all other groups. “a” significantly different from the control group (p<0.05).

Figure 2. DHT + T treatment reduces the number of intromissions preceding ejaculation.

Number of intromissions (A) and intromission latencies (B), preceding the first ejaculation. * Significantly different from all other groups “a” significantly different from control group). “b” significantly different from DHT + T group.

Figure 3. T and DHT + T treatments do not affect number of mounts but reduce mount latencies.

Number of mounts (A) and mount latencies (B) preceding the first ejaculation. “a” significantly different from control group “b” significantly different from DHT + T group. Mount numbers did not differ significantly between groups over time.

Figure 4. DHT alone or in combination with T increases prostate and seminal vesicle but not penis weights.

Ventral prostate (A) seminal vesicle (B) and penis weights (C) (mg). Bars designated with different letters differ significantly from one another DHT increased prostate and seminal vesicle weights.

Figure 5. T and DHT + T elevate blood T concentrations; DHT + T increases E₂ concentrations.

Higher DHT concentrations are associated with increased ejaculatory behavior. (A) Testosterone, (B) estradiol, and (C) dihydrotestosterone concentrations. Bars designated with different letters differ significantly from one another N = 4–5 for each of the groups in panel A and 5–6 in panel B. C. N = 4 and 6 for hamsters that ejaculated or were non-ejaculators, respectively.