Differentiation of Mammosomatotrophs in Swine Adenohypophysis

The existence and distribution of mammosomatotrophs (MS cells) containing growth hormone (GH) and prolactin (PRL) were detailed in swine adenohypophysis. MS cells were positively identified and were first recognized in the adenohypophysis of fetuses with 33.0 cm in body length, when GH cells existed earlier and PRL cells occurred. The proportion of MS cells transiently increased in the glands of three month-old females and were densely populated in the fore ventral (FV) and the hind ventral (HV) region except for the zona tuberalis (ZT). The distribution was similar to GH cells and PRL cells. MS cells were divided into three subtypes by the intracellular intensity of both GH and PRL stainings. Type I MS cells which were strongly stained with anti-GH antiserum, constituted 100% of MS cells in fetuses and the proportion decreased with age in females. Type II MS cells which were evenly stained with both anti-GH and PRL antisera were detected in all animals except for fetuses, and were proportioned moderately. Type III MS cells which contained more PRL than GH existed predominately in three and six month-old females, castrated males and aged males. The findings indicated that an amount of GH and PRL within MS cells was changeable in response to physiological conditions. The results suggest that GH cells may transform into PRL cells, with the MS cell acting as an intermediate cell in swine adenohypophysis, and that the GH and PRL in MS cells are synthesized synchronously or asynchronously according to the secretory activities.