Thymosin fraction 5 stimulates secretion of immunoreactive beta-endorphin in mouse corticotropic tumor cells

Neuroimmunopharmacologic effects of drugs of abuse

Direct studies linking drugs of abuse with changes in neurotransmitters and subsequent effects on the immune system are not abundant. One can, however, hypothesize that an indirect effect can occur since a variety of neurotransmitters known to be acted on by various drugs of abuse can, in turn, be correlated with changes in immunity. These changes most likely are mediated via alterations in the autonomic nervous system or the ratio of hormones regulated by the pituitary gland. In addition, there is sound evidence to suspect that the immune system might be capable of altering either the induction of tolerance or the severity of withdrawal symptoms. An increasing body of evidence indicates that IL-1, IFN-alpha, as well as C3a and C5a of the complement cascade, are capable of acting on central catecholamines within the brain. The possibility that immune system peptides are capable of regulating neurotransmitters is further suggested by the evidence of neuropsychiatric side effects during the course of clinical trials. Since a variety of drugs of abuse can directly alter immunocompetence as evidenced by the results of in vitro protocols described elsewhere in this volume, one could speculate that certain behavioral manifestations of drug addiction may be modulated, in part, by immunologic status.

Cytokine modulation of pituitary hormone secretion

A rapidly expanding body of evidence indicates that cytokines do indeed regulate pituitary hormone secretion. Recent studies with cytokines in vivo and in vitro support the idea that cytokines are the principal mediators of the neuroendocrine responses previously observed in infectious and inflammatory states. The dominant route of this modulation appears to be via the brain and hypothalamus, although a role for direct effects on the pituitary has not been excluded. These effects may be mediated by circulating cytokines, endogenously produced cytokines, or both. A number of receptor systems and second messengers may be involved, and a role for arachidonate metabolite pathways appears particularly likely. A final question: Of what use to the organism is the ability of immune activation to control pituitary hormone secretion? For some pituitary secretions there is a reasonable basis for speculation. Glucocorticoids serve to limit the severity of immune responses and recent studies argue that defects in this pathway permit the expression of autoimmune disease. Inhibition of thyroid function may limit the catabolic side effects of infectious illness. Stimulation of growth hormone could have the same effect, and growth hormone and prolactin may serve to enhance some immune responses.

Regulation of pituitary peptides by the immune system

It has long been thought that the central nervous system is able to influence the progression of disease. Furthermore, there is now overwhelming evidence that the communication pathways are bidirectional. A variety of immune system peptides are now known to be capable of transmitting information from the immune system to the central nervous system. These immunotransmitters include interleukins, interferons and thymosine peptides which have the capability of modulating slow-wave sleep as well as the release of neuro- and pituitary peptides. In some instances, release of these peptides during early development may have long lasting, if not permanent effects upon the normal development of neuroendocrine circuits. Collectively these various brain mediated events appear to contribute in various and diverse ways to defense against pathogens. It is becoming more and more apparent that certain abnormalities within the immune system may be the consequence of a neurological abnormality. The converse is also true.

Schistosomiasis: role of endogenous opioids in suppression of gonadal steroid secretion

1. Radioimmunoassay of the opiate, beta-endorphin, in mouse sera, indirect measurement of estrogen by examination of vaginal smears and indirect measurement of androgens by electrophoresis of major urinary proteins (MUP) revealed that beta-endorphin increases while estrogen and androgen levels decrease in mice with chronic Schistosoma mansoni infection. 2. Injections of the opiate antagonist, naltrexone, reversed the effects of schistosomiasis on estrogen and androgen levels. 3. Because opiates are known to inhibit the secretion of releasing hormones by the hypothalamus, the data suggest that the inhibition of hypothalamic-pituitary-gonadal function that occurs in chronically infected male and female mice results from excessive beta-endorphin. 4. It is also suggested that the excessive beta-endorphin may be secreted by T-lymphocytes and possibly macrophages involved in the cell-mediated immune response (CMIR) to the ova.