The influence of various neuromediators on pituitary TSH secretion in rats has been investigated. Noradrenaline 50 \g=m\g/rat,dopamine 50 \g=m\g/rat, serotonine-creatinine-sulphate 100 \g=m\g/rat,gamma-aminobutyric acid 100 \g=m\g/rat,pilocarpine 1 mg/rat, histamine 100 \g=m\/rat were administered into the lateral ventricle of the brain. All agents were dissolved in Parker's fluid. Two control groups of animals were given Parker's fluid and subjected to surgical manipulations, respectively. Plasma TSH level was estimated after 30 min by means of radioimmunoassay. The increase in the TSH level was observed after the injection of serotonine and noradrenaline (4.0 and 3.1 ng/ml, respectively) as compared with control group (0.7 ng/ml).The influence of various neuromediators on pituitary thyrotrophin (TSH) secre¬ tion has been investigated mainly in dopaminergic and noradrenergic system (Refetoff et al. 1972;Spaulding et al. 1972;Rapaport et al. 1973;Tuomisto et al. 1975) as well as the serotoninergic system (Grimm 8c Reichlin 1973;Mess 8c Peter 1974.The effect of various neuromediators on pituitary thyrotrophic function can be investigated in two ways. The indirect method consists in the intravenous injection of some drugs that influence either the neurohormone level or the functional condition of the appropriate receptor: they inhibit the synthesis or retard the disintegration of neuromediator, block or stimulate the receptor.

The effects of lithium on bone metabolism were determined using different organ culture models for the study of resorption and collagen synthesis. At concentrations of 3 X 10(-3)--10(-2) M, lithium blocked the stimulation of 45Ca and lysosomal enzyme release by parathyroid hormone (PTH) but did not affect bone resorption in control cultures in the absence of PTH. Lithium inhibition was observed in continuous culture with PTH or when bones were exposed to both agents for only 8 h. Lithium was less effective in inhibiting resorption of bones pretreated with PTH, and pretreatment with lithium did not prevent subsequent stimulation of bone resorption by PTH. Lithium did not inhibit the incorporation of labeled proline in collagen and noncollagen protein or of labelled thymidine into DNA.

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