Differential effects of histamine on Leydig cell and testicular macrophage activities in wall lizards: precise role of H1/H2 receptor subtypes

The present study in the wall lizard, Hemidactylus flaviviridis, was aimed to understand the role of histamine (HA) in the regulation of Leydig cell and testicular macrophage activities, for the first time, in ectothermic vertebrates. Although HA did not affect the testosterone production from unstimulated Leydig cells, it had dual concentration-related effects, stimulatory at a low concentration of 10−10 M while inhibitory at a high concentration of 10−5 M, on FSH-induced testosterone production. This suggests that HA did not influence the basal Leydig cell steroidogenesis, but modulated the FSH-stimulated testosterone production in a biphasic manner depending upon its concentration. However, HA failed to affect the FSH-stimulated Leydig cell proliferation, indicating that HA modulated the testosterone production from Leydig cells without influencing their proliferation in wall lizards. HA, apart from Leydig cells, differentially regulated the testicular macrophage immune responses. It inhibited phagocytosis and superoxide production at high concentration (10−5 M), while stimulated superoxide production and could not affect phagocytosis at low concentration (10−10 M). Using selective H1 and H2 antagonists, pyrilamine and famotidine respectively, H1 receptor subtype was seen responsible for mediating the inhibitory effect of HA on Leydig cell steroidogenesis and testicular macrophage immune responses at high concentration, while H2 receptors were involved for the stimulation at low concentration.