Utilization of the convolution integral to calculate rates of melatonin secretion into blood and CSF of sheep

Due to the anatomical location of the pineal gland on the dorsal surface of the third ventricle, melatonin may be secreted either into the blood or into the cerebrospinal fluid (CSF). To determine the route of secretion in sheep, simultaneous samples of blood from the jugular vein and of CSF from the cisterna magna were obtained during an endogenous surge of melatonin secretion. Making the assumption that the distribution of melatonin in sheep could be modeled as a time-invariant linear system, two simultaneous equations were developed in which the only two unknowns, the input function into the blood and into the ventricles, were convolved with weighting functions derived from the concentration profiles obtained following the injection of known quantities of melatonin into the jugular vein and into the lateral ventricle. The respective input functions were evaluated following deconvolution in the frequency domain. The quantity of melatonin secreted into the blood was more than 100 times greater than that secreted into the CSF.