Localization and ultrastructural maturation of prolactin (PRI) and growth hormone (GH) cells were studied in pituitaries from neonatal, immature (4-6 weeks old), and adult rats (2-3 months old) by light and electron microscopic immunocytochemistry. The distribution pattern of these cells did not change with age. Both cell types were concentrated laterodorsally, with PRL cells adjacent to the intermediate lobe and GH cells nearer the center of the pars distalis. Labeling density of the immunogold reaction was highest for both hormones in immature rats. In neonatal

Prolactin (PRL) cells were purified from nulliparous normal female adult Wistar rat pituitary cell suspensions by linear Percoll density gradient centrifugation, a procedure yielding single cells. Lactotrophs were found in two different layers, the first containing 70% PRL cells in the density range 1.055 to 1.065 g/ml, the second with 28% PRL cells in the range 1.070 to 1.080 g/ml. Both cell fractions contained more than 90% viable cells with an intact ultrastructure. The physiological integrity of the 70% enriched PRL cells was assessed by their basal PRL secretion, their secretory response to TRH and dopamine, and their cAMP production in a basal situation and after incubation with dopamine.

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.

Abstract. Immunoreactive calcitonin (I-CT) was assayed in rat thyroid glands from foetuses with a gestational age of 15.5–22 days. The mean content of the hormone was 455.0 ± 35.8 ng/gland. A positive linear correlation was found between the I-CT content in the thyroid glands and the gestational age of the foetuses. I-CT was also present in rat placentae from 10.5–21.5 days old pregnancies. A mean placental concentration of 4.5 ± 1.2 ng I-CT/mg wet tissue was found. The highest hormone concentrations were observed in placentae from 10.5 day old foetuses, displaying a progressive fall during the further course of pregnancy. It is concluded that the rat foetal thyroid gland produces I-CT beginning from a gestational age of 15.5 days'. The need for further investigations into a possible role of CT in transplacental calcium transport is also indicated.

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