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Chronic diseases are often accompanied by inflammatory and degenerative processes. Estrogens have repeatedly been found to be involved in these processes. Testosterone (T) is the main precursor of estrogen in the brain and T replacement in chronic diseases has become important in recent years, prompting research on new T-conjugated molecules. We recently synthesized three new molecules including unsaturated fatty acid esters: T-linoleate (TL), T-oleate (TO) and T-eicosapentanoate (TEPA). These substances were s.c. administered for 7 days to intact male rats subjected to the formalin test (FT). Three other groups were included as comparisons: NAIVE, receiving no substance, OIL, treated with almond oil (vehicle), and TN, treated with T-undecanoate, a saturated fatty acid. Spontaneous behaviors and pain-induced responses were determined during the FT, hormones (T and dihydrotestosterone, DHT) were determined in blood, while estrogen receptors (ERα and β) were detected at the genomic and proteomic levels in the hippocampus, hypothalamus and spinal cord. In the hippocampus, ERα and ERβ mRNA levels were increased respectively by TN and TL treatments with respect to OIL, whereas the hypothalamus TO and TL caused a decrease of ERα mRNA levels. At the proteomic level, TO, TL and TEPA decreased the levels of ERα in the hypothalamus, whereas TEPA decreased ERβ in the spinal cord, hippocampus and hypothalamus. There was no effect of treatment on the spontaneous behaviors, while the TO and TL groups showed lower pain-induced behaviors (paw jerk frequency and licking duration) than the OIL group. TN increased paw jerk frequency and decreased licking duration with respect to OIL. The treatments had no effect on T and DHT plasma levels. These results clearly indicate the possibility of pain and ER modulation by T-esters.

An excessive food supply has resulted in an increasing prevalence of overweight and obesity, conditions accompanied by serious health problems. Several studies have confirmed the significant inverse correlation between testosterone and obesity. Indeed after decades of intense controversy, a consensus has emerged that androgens are important regulators of fat mass and distribution in mammals and that androgen status affects cellularity in vivo. The high correlation of testosterone levels with body composition and its contribution to the balance of lipid metabolism are also suggested by the fact that testosterone lowering is associated with important clinical disorders such as dyslipidemia, atherosclerosis, cardiovascular diseases, metabolic syndrome and diabetes. In contrast, testosterone supplementation therapy in hypogonadic men has been shown to improve the lipid profile by lowering cholesterol, blood sugar and insulin resistance. Leptin, ghrelin and adiponectin are some of the substances related to feeding as well as androgen regulation. Thus, complex and delicate mechanisms appear to link androgens with various tissues (liver, adipose tissue, muscles, coronary arteries and heart) and the subtle alteration of some of these interactions might be the cause of correlated diseases. This review underlines some aspects regarding the high correlations between testosterone physiology and body fat composition.

Chronic pain has to be considered in all respects a debilitating disease and 10–20% of the world's adult population is affected by this disease. In the most general terms, pain is symptomatic of some form of dysfunction and (often) the resulting inflammatory processes in the body. In the study of pain, great attention has been paid to the possible involvement of gonadal hormones, especially in recent years. In particular, testosterone, the main androgen, is thought to play a beneficial, protective role in the body. Other important elements to be related to pain, inflammation, and hormones are lipids, heterogenic molecules whose altered metabolism is often accompanied by the release of interleukins, and lipid-derived proinflammatory mediators. Here we report data on interactions often not considered in chronic pain mechanisms.

The results of several studies strongly indicate a bidirectional relationship among gonadal hormones and pain. While gonadal hormones play a key role in pain modulation, they have been found to be affected by pain therapies in different experimental and clinical conditions. However, the effects of pain and pain therapy on the gonads are still not clear. In this study, we determined the long-lasting (72 h) effects of inflammatory pain (formalin test) and/or morphine on estrogen receptor (ER), androgen receptor (AR) and TRPV1 gene expression in the rat testis and ovary. The animals were divided into groups: animals receiving no treatment, animals exposed only to the experimental procedure (control group), animals receiving no pain but morphine (sham/morphine), animals receiving pain and morphine (formalin/morphine), and animals receiving only formalin (formalin/saline). Testosterone (T) and estradiol (E) were determined in the plasma at the end of the testing. In the sham/morphine rats, there were increases of ERα, ERβ, AR and TRPV1 mRNA expression in the ovary; in the testis, ERα and ERβ mRNA expression were reduced while AR and TRPV1 expression were unaffected by treatment. T and E plasma levels were increased in morphine-treated female rats, while T levels were greatly reduced in morphine-treated and formalin-treated males. In conclusion, both testicular and ovarian ER (ERα and ERβ) and ovarian AR and TRPV1 gene expression appear to be affected by morphine treatment, suggesting long-lasting interactions among opioids and gonads.

The role of endocrine systems in chronic pain mechanisms is slowly getting increasing experimental and clinical consideration. Many painful conditions appear to be directly and/or indirectly induced, reduced or, in some cases, modulated by hormones. We have done much work in trying to understand the relationship between hormones and pain, with particular attention to the hypothalamus-pituitary-gonadal axis. To expand our knowledge of this field, we have directed our attention to another axis, the hypothalamus-pituitary-thyroid (HPT). The literature on thyroid functions is vast but very few studies have focused on the HPT axis and pain. The few available data are considered in the present review to stimulate interest in the possible interactions between the HPT axis and pain.