Lithium and twenty-four hour rhythms of serum corticosterone, prolactin and growth hormone in pigmented eye rats

Lithium, a widely used substance for the treatment of manic-depressive illness, has been reported to alter the phase relationships of a variety of biological rhythms. We have previously found that lithium affects serum melatonin differently in albino compared to pigmented eye rats. The present study was undertaken to investigate the effect of lithium on pituitary rhythms in pigmented eye rats. Six point 24 hour maps were generated throughout a 12 hour light/12 hour dark lighting regime on separate groups of individually housed adult male Long Evans rats (with pigmented eyes), maintained for six weeks on ad lib water and either normal lab chow or lab chow supplemented with 50 mM/Kg of lithium chloride. Animals were sacrificed by rapid decapitation with care to ensure that blood samples were obtained from subjects in the resting, undisturbed state. Plasma lithium levels were 0.57 +/- 0.02 mEq/1. In comparison to normal controls, lithium treatment suppressed body weight by 19%, and increased water intake by 100%. Absolute corticosterone levels were not altered by lithium, but the 24-hour pattern was significantly changed. Growth hormone levels were significantly reduced by lithium treatment without alteration of the 24-hour pattern. Prolactin levels were significantly reduced by lithium and the normal 24-hour variation was attenuated. Comparison of these effects of lithium in pigmented eye rats with similar data from albino rats suggests that the effects on growth hormone, body weight and water intake were similar; however, the effects on prolactin and corticosterone differed.(ABSTRACT TRUNCATED AT 250 WORDS)