Expression of leptin and long form of leptin receptor genes and proteins in pituitary of cyclic and pregnant pigs.

Leptin is a multifunctional regulator in numerous tissues, including the pituitary. It is not known, whether the porcine pituitary is a source of leptin synthesis and possesses the leptin receptor protein. It is also unknown, if a relationship exists between expression levels of these proteins in the pituitary and physiological status of sows. Therefore, the aim of the study was 1] to examine, by Western-blotting analysis, the expression levels of leptin and the long form of leptin receptor (OB-Rb) in the porcine anterior (AP) and posterior (NP) pituitary gland during mid- and late-luteal phases of the oestrous cycle (days 10 - 12 and 14 - 16) as well as during two stages of early pregnancy (days 14 - 16 and 30 - 32); and 2] to localise, using in situ hybridisation method (ISH), the expression of leptin and OB-Rb genes in the pituitary gland in the above mentioned stages of the cycle and pregnancy. Western-blotting analysis showed that leptin protein expression in AP was higher in the late-luteal phase than in the mid-luteal phase, while OB-Rb protein expression in both lobes was higher in the mid-luteal phase. In turn, during pregnancy leptin protein content in AP and OB-Rb protein content in NP were more pronounced on days 14 - 16 than on days 30 - 32. Comparison of leptin and OB-Rb protein expression levels in AP between the mid-luteal phase and two periods of pregnancy showed, respectively, stimulation of leptin protein and inhibition of OB-Rb protein expressions during both examined stages of pregnancy. Taking AP from late-luteal phase as the point of reference, it was revealed stimulation of leptin expression during earlier period of pregnancy, whereas on days 30 - 32 of pregnancy both the hormone and its receptor expressions were diminished. In turn, comparison of leptin and OB-Rb protein expression levels in NP between the late-luteal phase and days 14 - 16 or 30 - 32 of pregnancy showed inhibition of leptin protein expression and stimulation of OB-Rb protein expression during pregnancy. Moreover, ISH studies localised leptin and OB-Rb mRNAs expression in the cells of AP as well as NP tissue during the two stages of the cycle and pregnancy. In conclusion, our findings suggest that leptin is produced within the pituitary in the pig and may participate in auto/paracrine manner in the regulation of this gland function during the luteal phase of the oestrous cycle and early pregnancy.