Mammotrophs or prolactin (PRL) cells were identifed in the adenohypophysis of adult golden
hamsters by immunocytochemical techniques with a
polyclonal anti-PRL, that was proved to be specific to
PRL by the dot immunoblotting test. Postembedding
immunostaining was performed on Araldite thin sections
by immunoperoxidase and immunogold methods. PRL
cells were classified into three types according to the
different size of the secretory granules. The Type A cells
were usually small and angular or oval in shape, and had
secretory granules ranging in diameter from 100-230 nm,
and showed poorly developed organelles. The Type B
and C cells were larger and round or ovoid in shape,
contained larger granules, 230-280 nm and 280-570 nm,
respectively, and displayed well developed organelles.
Immunoreactive PRL cells in the male pituitaries were
far less numerous than in the nonpregnant female glands,
and were mostly of the Type A and B, whereas in the
female the Type C and B cells predominated. In
pregnant females, Type C cells became activated and
increased in number, while the other two types
decreased in proportion. In lactating females, Type A
and B cells significantly increased in number at the
expense of the Type C cells; meanwhile, the exocytosis of
secretory granules was frequently found in all types of
PRL cells. The present findings suggest that Type C and
B PRL cells, especially the former, are potent in
producing and releasing PRL and highly responsive to
various physiological stimuli, while Type A cells are
probably relatively inert in synthetic activity