Calcemic Responses To Photic And Pharmacological Manipulation Of Serum Melatonin

We have reported decreased serum calcium(CaS) in human infants(HI) and in newborn rats(NBR) during exposure to white light(Photo). In NBR, bone Ca uptake increased. At wavelengths below 600nM (orange to blue), cranial light penetration fell sharply and CaS was unaffected. Occipital shields prevented hypocalcemia in both HI and NBR. Pineal melatonin synthesis is increased by isoproterenol and decreased by propanolol and by light (PNAS 69: 2547, 1972). In NBR we found serum melatonin to be 27±8 pg/ml during Photo and 122±32 pg/ml in shaded littermates (n=24, p<.01). Exogenous melatonin (20ng/Gm IP) gave serum concentrations of 383 pg/ml at 1 hr and 83 pg/ml at 2 hrs and prevented the hypocalcemic response to Photo. Propanolol reduced CaS in shaded NBR from 9.5±.1 mg/dl to 7.9±.2 mg/dl; after propanolol + melatonin, CaS was 8.8±.2 mg/dl. Isoproterenol ameliorated hypocalcemia during Photo (Shade 9.7±.1 mg/dl, Photo 8.8±.1 mg/dl, Photo + isoproterenol 9.4±.1 mg/dl). These findings support the hypothesis that hypocalcemia during phototherapy results from transcranial photic inhibition of melatonin synthesis.