The expression of the sodium/iodide symporter is up-regulated in the thyroid of fetuses of iodine-deficient rats.

Is the fetal thyroid already capable to increase its iodide uptake in response to iodine deficiency? To answer this question, we analyzed the expression of the Na(+)/I(-) symporter and several other genes in the thyroid of rat fetuses at 21 d of gestation from control mothers presenting a mild or more severe iodine deficiency. Female rats were placed on a low iodine diet, not supplemented, or supplemented with iodide or perchlorate for 3 months. The maternal and fetal thyroidal iodide uptake was measured 24 h after injection of 10 microCi Na (125)I into the dams. The absolute iodide uptake of the maternal thyroid was unchanged in a low iodine diet, not supplemented, compared with one supplemented with iodide. In contrast, the fetal thyroid absolute iodide uptake of a low iodine diet, not supplemented, and one supplemented with perchlorate was decreased by 70% and 95% compared with that supplemented with iodide. Na(+)/I(-) symporter mRNA was detected in the fetal thyroid of supplemented with iodide and increased about 2- and 4- fold in the thyroid of fetuses from a low iodine diet, not supplemented, and one supplemented with perchlorate, respectively. Na(+)/I(-) symporter expression was induced in the fetal side of the placenta in both a low iodine diet, not supplemented, and one supplemented with perchlorate; in contrast, Na(+)/I(-) symporter mRNA was never detected in the maternal side of the placenta. Fetal thyroid thyroglobulin and type I deiodinase mRNA contents were only significantly increased with a diet supplemented with perchlorate. Glucose transporter 4 mRNA was decreased in the fetal thyroid of both a low iodine diet, not supplemented, and one supplemented with perchlorate compared with one supplemented with iodide. In conclusion, although the up-regulation of Na(+)/I(-) symporter expression in fetal thyroid and placenta in the low iodine diet, not supplemented group did not lead to restoration of a normal absolute iodide uptake, our data show that all adaptive and/or defending mechanisms against iodine deficiency are already present in the fetus.

Electrophysiological evidence for a key control function of the medial preoptic area in the regulation of prolactin secretion in cycling, pregnant and lactating rats.

Female rats were chronically fitted with stainless steel electrodes in the medial preoptic area (MPOA), together with a chronic atrial blood sampling/blood transfusion catheter. The surgery did not affect cyclicity, pregnancy or lactation. Twenty-five minutes of bilateral electrical stimulation (100-Hz voltage pulses, 0.2 ms width, 10 s on/5 s off) of the MPOA significantly reduced the magnitude of the proestrous and estrous afternoon levels of prolactin (Prl) in cycling rats, the nocturnal and diurnal levels of Prl in pregnant rats as well as Prl secretion during suckling in lactating rats. These data demonstrate that the MPO exerts dominant inhibitory control over all known surges of Prl secretion in female rats and may be considered as 'antisurge key control center' for Prl secretion. A functional role of the sexually dimorphic nucleus in the control of Prl secretion is suggested.

Effects of red dim illumination and surgery on prolactin secretion during the estrous cycle and early pseudopregnancy in the rat: different regulatory mechanisms for prolactin secretion.

The effects of surgery and red light on prolactin (Prl) secretion were investigated in cycling and in pseudopregnant (PSP) rats. Secretion patterns of Prl were determined at hourly intervals from 07.00 to 22.00 h. Different regulatory mechanisms for Prl secretion were hypothesized for three time periods: a nocturnal (07.00-11.00 h), a prediurnal (14.00-17.00 h), and a diurnal (19.00-22.00 h) period. The results demonstrate that red light can affect significantly Prl secretion, in particular nocturnal and prediurnal Prl secretion in estrous, diestrous day 1 and PSP rats. The effect of surgery varied with the time of the day and was dependent upon whether the animals, during the dark period, were maintained under full darkness or constant red dim illumination. In PSP rats the regulation of Prl secretion was different for the three time periods. In PSP day 0 rats there was a prediurnal surge of Prl secretion, comparable in timing and regulation to a prediurnal surge in estrous rats. This prediurnal surge was not evident on the other days of PSP. The regulation of nocturnal as well as diurnal Prl secretion was similar in PSP rats, but differed from cycling rats. The afternoon surge of Prl secretion on proestrus lasted the full afternoon and was basically one surge, distinct from all other surges. In diestrous rats Prl levels were low but showed a circadian variation. In summary, the effects of red light and surgery on Prl secretion varied with the physiological state and with the time of the day, indicating that the regulation of Prl secretion is complex and multimodal in nature.

No evidence for an autoregulatory mechanism for the proestrous afternoon surge of prolactin secretion in rats.

The temporal effects of intracerebroventricular (icv) infusion of prolactin (PRL) on endogenous PRL secretion was investigated in intact, freely moving, cycling rats. An icv infusion of 10 ng or 100 ng rat-PRL/min from 13.00 to 17.00 h during the proestrous afternoon did not affect endogenous PRL secretion; infusion from 09.00 to 13.00 h showed a tendency to delay the time of onset of the PRL proestrous afternoon surge. The results do not indicate the involvement of an autoregulatory mechanism in the expression or the termination of the proestrous afternoon surge of PRL secretion.

Haematological, immunological and endocrinological aspects of chronic high frequency blood sampling in rats with replacement by fresh or preserved donor blood.

Haematological, immunological and endocrinological aspects of blood transfusions with either freshly collected or preserved donor blood were investigated in chronically cannulated unrestrained rats. Three anticoagulant preservatives were tested: citrate, citrate-dextrose and citrate-phosphate-dextrose-adenine (CPDA-1). Prolactin was used as an indicator of stress in endocrine studies. The repeated collection of 4 ml blood at 2-week intervals did not affect normal blood composition. Whole blood of rats could be stored in citrate, citrate-dextrose or CPDA-1 for 8, 22 or 35 days, respectively. Blood transfusions with fresh or preserved donor blood of F1 (R X U) rats did not affect normal blood composition nor did it induce immunological responses in F1 rats. Frequent blood sampling for several hours at highest rates of 1 sample/min did not affect prolactin secretion when blood volume reduction was replaced by blood transfusions with fresh donor blood. However, compensation with preserved blood affected prolactin secretion significantly. Blood transfusions did not affect health, behaviour, cyclicity or pseudopregnancy. The application of blood transfusion in chronically cannulated rats appeared to be quite simple. Its advantages are the possibility of following individual secretion patterns of blood-bound substances, the repeated use of animals and the reduction of the number of animals.

A chronic technique for high frequency blood sampling/transfusion in the freely behaving rat which does not affect prolactin and corticosterone secretion.

A blood sampling/blood transfusion technique is described for chronically cannulated freely behaving rats. The procedure permits high frequency sampling for several hours at a maximum rate of one blood sample per min. Prolactin and corticosterone were used as indicators of stress. In male rats the prolactin concentration in blood obtained by rapid decapitation was not significantly different from that obtained through a cannula. A blood volume reduction of 1 or 2 ml did not affect prolactin or corticosterone secretion; however, a reduction of 3 ml or more increased corticosterone secretion but did not consistently increase prolactin secretion. When blood volume reduction was compensated for by blood transfusion, frequent blood sampling did not affect prolactin or corticosterone secretion in dioestrous rats. The surges of prolactin secretion during the afternoon of pro-oestrus and pseudopregnancy were also unaffected by high frequency blood sampling. It is therefore concluded that the blood sampling/transfusion procedure described does not stress the animals. Its advantages include not only the possibility of following individual hormone profiles, but also the economic and ethical aspects of reducing the number of animals needed for experimentation.