Effects of Testosterone Replacement on Pain Sensitivity and Pain Perception

Naturally occurring opiates (endorphins) decrease testosterone levels by inhibiting the synthesis of gonadotropin releasing hormone (GnRH) and also inhibiting testosterone synthesis by the testes. Similarly, men with addiction to narcotics and those on exogenous opioids for pain control have decreased serum testosterone levels. Indeed, these men complain of decreased libido, erectile dysfunction and impaired quality of life. Animal studies have shown that gonadectomy results in a decrease in pain threshold in rats and repletion of testosterone elevates that threshold. These observations suggest that testosterone may possess analgesic properties. Hence, the investigators hypothesize that hypogonadism developing in men on opioids results in an increased sensitivity to pain and requirement of higher doses of opioids. In this study, the investigators plan to administer testosterone to men with opioid-induced hypogonadism and evaluate their pain perception, pain sensitivity in response to noxious stimuli and changes in the requirement of opioids in response to testosterone administration.

Hypothesis:

Testosterone replacement in men with opioid-induced hypogonadism will improve pain tolerance, pain perception and quality of life.

Specific aims:

1. To evaluate the effects of testosterone replacement on pain sensitivity, pain tolerance, and pain modulation in men with opioid-induced hypogonadism.
2. To determine the effects of testosterone replacement on health-related quality of life.
3. To determine whether testosterone replacement in hypogonadal men induces changes in the dosage requirements of opioid medications for pain control.

To accomplish our specific aims, the investigators propose a randomized, double blind, placebo-controlled, parallel arm study in which hypogonadal men with non-cancer chronic back pain syndrome on chronic opioids and low testosterone levels (\<300 ng/dl) will be randomized to exogenous testosterone replacement therapy vs placebo. Our primary outcome is change in pain tolerance using various external painful stimuli. Secondary outcomes are change in pain sensitivity and modulation, quality of life and opioid requirements.


Eligibility Criteria:
Inclusion Criteria:

* Men
* Age 18 years and older
* Non-cancer chronic pain
* Serum total testosterone level \<350 ng/dl
* Consumption of at least 20 mg of hydrocodone (or analgesic equivalent of another opioid) for at least 4 weeks
* Absence of hospitalization in the past 2 months
* No acute illness in the past 2 months
* No current anabolic therapy (growth hormone, DHEA, etc)
* No current use or consumption in the past 2 months of melatonin
* Normal prostate exam
* Normal PSA level

Exclusion Criteria:

* Cancer-related chronic pain
* Liver enzymes \> 3 times upper limit of normal
* Serum creatinine \> 2 times upper limit of normal
* Neurological disease
* Active psychiatric illness
* Any addictive drug use
* Alcoholism (\>3 drinks/day)
* Patients currently receiving melatonin or anabolic agents
* Hospitalization in the past 2 months
* Acute illness in the past 2 months
* Consumption of \< 20 mg of hydrocodone (or analgesic equivalent of another opioid)
* Severe BPH
* PSA \> 4.0 ng/ml
* Prostate cancer
* Breast cancer