Elevated serum levels of cyclo (His-Pro), an endogenous inhibitor of pituitary prolactin secretion, in systemic lupus erythematosus patients

Abstract

Cyclo (His-Pro) or CHP is a cyclic dipeptide that is known to elicit many biologic activities including inhibition of pituitary prolactin (PRL) secretion. PRL stimulates humoral and cell mediated immune responses and hyperprolactinemia has been found in a subset of systemic lupus erythematosus (SLE) patients in association with active disease. To explore whether CHP may play a role in SLE patients, we measured, CHP and PRL levels in sera of 21 SLE patients and 11 normal controls. The results of this study show significantly ( P < 0.001) high levels of CHP in SLE compared to controls. However, there was no significant correlation between serum PRL and CHP levels in SLE patients ( r = 0.027, P = 0.29). The increase in serum levels of CHP may be in an attempt to increase hypothalamic content of dopamine which in turn would decrease pituitary PRL synthesis in hyperprolactinemic SLE patients.