Effects of long-term treatment with testosterone enanthate in rhesus monkeys: I. Pharmacokinetics of testosterone, testicular volume and liver metabolism of testosterone

The effects of orchidectomy and supraphysiological testosterone administration on trabecular bone structure and gene expression in rats

OBJECTIVE

This study aimed to determine the effects of orchidectomy and supraphysiological testosterone replacement on trabecular structure and gene expression in the bone.

METHODS

Twenty-four 3-month old male rats were randomized into sham (SH), orchidectomized (ORX) and testosterone-treated (TE) groups. Orchidectomy was performed on the ORX and TE group. Weekly testosterone enanthate intramuscular injection at 7 mg/kg body weight was administered to the TE group for 8 weeks while the other groups received peanut oil as vehicle. Blood was collected before and after treatment for serum testosterone analysis. The femora and tibiae were harvested after the treatment period for trabecular structure and gene expression analysis.

RESULTS

The trabecular bone volume decreased significantly and the porosity increased significantly in the ORX group compared to the SH group (p < 0.05). Testosterone treatment prevented all these changes (p < 0.05). The expression of osteogenic genes decreased significantly in the ORX group compared to the SH group (p < 0.05). Testosterone treatment decreased the expressions of RANKL and OPG genes significantly (p < 0.05).

CONCLUSION

Orchidectomy-induced degeneration in trabecular structure is caused by a decrease in the expressions of osteogenic genes. Supraphysiological testosterone replacement is able to prevent these degenerative changes in the bone despite the modest changes in gene expression.

Short-term testosterone manipulations do not affect cognition or motor function but differentially modulate emotions in young and older male rhesus monkeys

Human aging is characterized by declines in cognition and fine motor function as well as improved emotional regulation. In men, declining levels of testosterone (T) with age have been implicated in the development of these age-related changes. However, studies examining the effects of T replacement on cognition, emotion and fine motor function in older men have not provided consistent results. Rhesus monkeys (Macaca mulatta) are excellent models for human cognitive aging and may provide novel insights on this issue. We tested 10 aged intact male rhesus monkeys (mean age=19, range 15-25) on a battery of cognitive, motor and emotional tasks at baseline and under low or high T experimental conditions. Their performance was compared to that of 6 young males previously tested in the same paradigm (Lacreuse et al., 2009; Lacreuse et al., 2010). Following a 4-week baseline testing period, monkeys were treated with a gonadotropin releasing hormone agonist (Depot Lupron, 200 μg/kg) to suppress endogenous T and were tested on the task battery under a 4-week high T condition (injection of Lupron+T enanthate, 20 mg/kg, n=8) or 4-week low T condition (injection of Lupron+oil vehicle, n=8) before crossing over to the opposite treatment. The cognitive tasks consisted of the Delayed Non-Matching-to-Sample (DNMS), the Delayed Response (DR), and the Delayed Recognition Span Test (spatial-DRST). The emotional tasks included an object Approach-Avoidance task and a task in which monkeys were played videos of unfamiliar conspecifics in different emotional context (Social Playbacks). The fine motor task was the Lifesaver task that required monkeys to remove a Lifesaver candy from rods of different complexity. T manipulations did not significantly affect visual recognition memory, working memory, reference memory or fine motor function at any age. In the Approach-Avoidance task, older monkeys, but not younger monkeys, spent more time in proximity of novel objects in the high T condition relative to the low T condition. In both age groups, high T increased watching time of threatening social stimuli in the Social Playbacks. These results suggest that T affects some aspects of emotional processing but has no effect on fine motor function or cognition in young or older male macaques. It is possible that the duration of T treatment was not long enough to affect cognition or fine motor function or that T levels were too high to improve these outcomes. An alternative explanation for the discrepancies of our findings with some of the cognitive and emotional effects of T reported in rodents and humans may be the use of a chemical castration, which reduced circulating gonadotropins in addition to T. Further studies will investigate whether the luteinizing hormone LH mediates the effects of T on brain function in male primates.

Testosterone modulation of anxiety in gonadally-suppressed male rhesus monkeys: a role for gonadotropins?

Testosterone (T) has repeatedly been shown to have anxiolytic properties in rodents, but findings in primates are more mixed. To examine the effects of exogenous T on anxiety, we tested pharmacologically-castrated adult male rhesus monkeys in a modified version of the Human Intruder Paradigm, which measured defensive responses to an unfamiliar human staring directly at them for 2 min. Monkeys were tested at 2 week intervals during 4 experimental conditions lasting 4 weeks each: at baseline, during treatment with the gonadotropin releasing hormone (GnRH) agonist leuprolide acetate (200 μg/kg; Lupron phase), during treatment with Lupron+T enanthate (TE, 5 mg/kg; TE phase) and during treatment with Lupron+oil vehicle (oil phase). We found that the number of anxious behaviors was lower during periods of low T (Lupron only and Lupron+oil phases) than during the Lupron+TE phase. No change in pacing or watching behavior was observed. Thus, in contrast to rodent data, we found no evidence for anxiolytic properties of T in male rhesus monkeys. Rather, T supplementation restored baseline levels of anxiety in Lupron-treated monkeys. These discrepant findings may be best explained by the low levels of gonadotropins achieved by the GnRH agonist. We suggest that Lupron-induced luteinizing hormone (LH) suppression reduced anxiety and that this effect was abolished by T administration. This interpretation is consistent with the view that T increases emotional reactivity to a potential threat and facilitates adaptive arousal response in face of immediate social challenge.

The efficacy of ultrasound treatment as a reversible male contraceptive in the rhesus monkey

BACKGROUND

The use of therapeutic ultrasound as a contraceptive approach has involved nonhuman primates as well as rats and dogs. The current study was undertaken to determine whether this treatment could be a method for reversible contraception, using a model with testes size similar to adult humans.

METHODS

Two methods of ultrasound exposure were used, either the transducer probe at the bottom of a cup filled with saline (Cup) or direct application to the surface of the scrotum (Direct). Four adult rhesus (Macaca mulatta) males with normal semen parameters were treated with therapeutic ultrasound at 2.5 W/cm(2) for 30 min. Treatment was given 3 times, one every other day on a Monday-Wednesday-Friday schedule. For each male, semen quality was evaluated a minimum of three times over several months prior to ultrasound exposure and weekly for two months following ultrasound treatment.

RESULTS

Semen samples from all males, regardless of exposure method, exhibited a decrease in the percentage of motile sperm following ultrasound treatment. There was an average reduction in motility of 40% the week following treatment. Similarly, curvilinear velocity and the percentage of sperm with a normally shaped flagellum were also reduced in all males following ultrasound treatment. A significant reduction in the total number of sperm in an ejaculate (total sperm count) was only observed in males that received ultrasound via the cup method. Following treatment via the cup method, males exhibited up to a 91.7% decrease in average total sperm count (n = 2). Sperm count did not approach pre-treatment levels until 8 weeks following ultrasound exposure.

CONCLUSIONS

The sustained reduction in sperm count, percent motility, normal morphology, and sperm vigor with the cup exposure method provides proof of principle that testicular treatment with ultrasound can be an effective contraceptive approach in humans.

Effects of testosterone on attention and memory for emotional stimuli in male rhesus monkeys

Increasing evidence in humans and other animals suggests that testosterone (T) plays an important role in modulating emotion. We previously reported that T treatment in rhesus monkeys undergoing chemically induced hypogonadism results in increased watching time of videos depicting fights between unfamiliar conspecifics (Lacreuse et al., 2010). In the current study, we aimed to further investigate the effect of T manipulations on attention and memory for emotional stimuli in male rhesus monkeys. Six males (7 years old) were administered Depot Lupron to suppress endogenous T levels and treated with either testosterone enanthate (TE, 5 mg/kg) or oil, before crossing over to the alternate treatment. Animals were tested for 16 weeks on two computerized touchscreen tasks with both social and nonsocial emotional and neutral stimuli. The Dot-Probe task was used to measure attention, and the Delayed-Non-Matching-to-Sample task with a 1s delay (DNMS) was used to measure recognition memory for these stimuli. Performance on the two tasks was examined during each of four month-long phases: Baseline, Lupron alone, Lupron+TE and Lupron+oil. It was predicted that T administration would lead to increased attention to negative social stimuli (i.e., negative facial expressions of unfamiliar conspecifics) and would improve memory for such stimuli. We found no evidence to support these predictions. In the Dot-Probe task, an attentional bias towards negative social stimuli was observed at baseline, but T treatment did not enhance this bias. Instead, monkeys had faster response times when treated with T compared to oil, independently of the emotional valence or social relevance of stimuli, perhaps reflecting an enhancing effect of T on reward sensitivity or general arousal. In the DNMS, animals had better memory for nonsocial compared to social stimuli and showed the poorest performance in the recognition of positive facial expressions. However, T did not affect performance on the task. Thus, even though monkeys were sensitive to the social relevance and emotional valence of the stimuli in the two tasks, T manipulations had no effect on attention or memory for these stimuli. Because habituation to the stimuli may have mitigated the effect of treatment in the attentional task, we suggest that T may increase attentional biases to negative social stimuli only during early exposure to the stimuli with acute treatment or when stimuli are highly arousing (i.e., dynamically presented) with chronic treatment. In addition, the data suggest that T does not enhance working memory for emotional stimuli in young male macaques.

Short-term testosterone manipulations modulate visual recognition memory and some aspects of emotional reactivity in male rhesus monkeys

The role of testosterone (T) in modulating cognitive function and emotion in men remains unclear. The paucity of animal studies has likely contributed to the slow progress in this area. In particular, studies in nonhuman primates have been lacking. Our laboratory has begun to address this issue by pharmacologically manipulating T levels in intact male rhesus monkeys, using blind, placebo-controlled, crossover designs. We previously found that T-suppressed monkeys receiving supraphysiological T for 4 weeks had lower visual recognition memory for long delays and enhanced attention to videos of negative social stimuli (Lacreuse et al., 2009, 2010) compared to when treated with oil. To further delineate the conditions under which T affects cognition and emotion, the present study focused on the short-term effects of physiological T. Six intact males were treated with the gonadotropin-releasing hormone antagonist degarelix (3 mg/kg) for 7 days and received one injection of T enanthate (5 mg/kg) followed by one injection of oil vehicle 7 days later (n=3), or the reverse treatment (n=3). Performance on two computerized tasks, the Delayed-non-matching-to-sample (DNMS) with random delays and the object-Delayed Recognition Span test (object-DRST) and one task of emotional reactivity, an approach/avoidance task of negative, familiar and novel objects, was examined at baseline and 3-5 days after treatment. DNMS performance was significantly better when monkeys were treated with T compared to oil, independently of the delay duration or the nature (emotional or neutral) of the stimuli. Performance on the object-DRST was unaffected. Interestingly, subtle changes in emotional reactivity were also observed: T administration was associated with fewer object contacts, especially on negative objects, without overt changes in anxious behaviors. These results may reflect increased vigilance and alertness with high T. Altogether, the data suggest that changes in general arousal may underlie the beneficial effects of T on DNMS performance. This hypothesis will require further study with objective measures of physiological arousal.

Current status of fertility control methods in India

Approximately 48.2% of couples of 15 to 49 years of age practice family planning methods in India. Female sterilization accounts for 34.2%, with male sterilization declining from 3.4% in 1992-93 to 1.9% in 1998-99. Use of the condom increased to 3.1% from 2.4%. There is an urgent need for research to develop new contraceptive modalities especially for men and also for women and to make existing methods more safe, affordable and acceptable. Current efforts in India to develop a male contraceptive are mainly directed towards (i) development of antispermatogenic agents to suppress sperm production, (ii) prevention of sperm maturation, (iii) prevention of sperm transport through vas deferens or rendering these sperm infertile and (iv) prevention of sperm deposition. Research work in the field of prevention of sperm transport through vas deferens has made significant advances. Styrene maleic anhydride (SMA) disturbed the electrical charge of spermatozoa leading to acrosome rupture and consequent loss in fertilizing ability of sperm. A multicentre phase-III clinical trial using SMA is continuing and it is hoped that the SMA approach would be available in the near future as an indigenously developed injectable intra-vasal male contraceptive. The safety and efficacy of available oral contraceptives were evaluated. An indigenously developed oral contraceptive 'Centchorman', which is a nonsteroidal, weakly estrogenic but potently antiestrogenic, was found to be safe and effective and is now being marketed in India since 1991 as a 'once a week' pill. Cyclofem and Mesigyna have been recommended as injectable contraceptives with proper counselling and service delivery by Indian studies. It has been recommended that these injectable contraceptives be added to the existing range of contraceptive methods available in the National Family Planning Programme. Based on the Indian studies CuT 200 was also recommended. Studies have indicated the advantage of intrauterine devices (IUD); they are long acting, relatively easily removed and fertility returns rapidly after their removal. Recent studies have recommended CuT 200 for use up to 5 years. The combination of some plant products i.e. Embelia ribes, Borax and Piper longum has been found to be safe and effective as a female contraceptive and the results of phase-I clinical trials are encouraging. Research work is going on in the country in various areas with special reference to hormonal contraceptive - a three monthly injectable contraceptive, immuno-contraceptives, antiprogestins, etc.