Parotid gland tissue is able partially to assume pituitary functions underthe influence of hypothalamic factors: in vivo and in vitro studies

To test whether salivary tissue can secrete pituitary hormones, female Spra gue-Dawley rats were hypophysectomized (hypox) and the following were trans planted to the sella turcica: parotid gland (group 3, n=33), adrenal gland (group 4, n=30), muscle (group 5, n=24). Group 2 (n=21) had the sella turci ca filled with dentist's cement. In addition a group of rats (group 1, n=22 ) remained intact as controls. All groups were followed for 8 months. Daily vaginal smears showed normal cyclicity in controls and constant dioestrus in all hyper groups. Blood samples, taken once every 30 days before and aft er LHRH stimulation, showed significantly lower (P<0.001) plasma LH values in all hyper groups compared with controls. In group 3, a gradual and signi ficant increase (P<0.005) was observed in the LH response to LHRH in parall el with a partial recovery of oestrous smears. No LH modification was obser ved in the other hyper groups. Plasma prolactin (PRL) levels were also very low in all hyper groups and were unaltered throughout the study. At the en d of the experiments, half the animals were killed by decapitation and the hypothalamic-pituitary areas carefully dissected, homogenized and analysed for LH and PRL content. The remaining animals were perfused with 4% parafor maldehyde to obtain fixing of the whole body tissues. Hypothalamic and tran splant areas were carefully dissected, frozen, cut and submitted to immunoc hemical procedures. LH content in the graft of group 3 animals was markedly (P<0.001) lower than in the control pituitary, but significantly higher (P <0.05) than in the other hyper groups. Immunochemistry showed LH and PRL po sitive cells in the graft of group 3 animals, whereas neither positive cell s, nor LH content were observed in the parotid gland in situ. Experiments w ere completed with in vitro cultures of parotid glands in the presence or a bsence (controls) of synthetic hypothalamic hormones or rat hypothalamic ex tracts. After 1 5 weeks of culture, a significantly higher LH concentration (P<0.05) was observed in the wells treated with synthetic hypothalamic hor mones (216 +/- 46 pg/ml vs 41 +/- 6 pg/ml in controls). When hypothalamic e xtracts were used, the LH levels increased more markedly (1834 +/- 190 pg/m l vs 36 +/- 6 pg/ml in controls) and those values were maintained during 3 weeks of culture. Immunostaining of these cultures showed a positive LH rea ction in the epithelial cells found in the hypothalamic extract-treated wel ls. Both in vivo and in vitro studies confirm the transdifferentiation of p arotid gland tissue to pituitary hormone-producing cells under hypothalamic influence.