Ultrastructural morphometric method for the measurement of prolactin release and synthesis in the rat pituitary induced by suckling stimulus
Nihon Sanka Fujinka Gakkai Zasshi 35(10): 1717-1726
The present ultrastructural morphometric study was performed to examine the mechanism of prolactin (PRL) secretion in lactating rats, compared with the alteration in serum and pituitary PRL as measured by radioimmunoassay. After 8 hours separation from pups, the pituitary PRL content double but serum PRL levels dropped markedly, whereas, in PRL cells, the granule content increased and dilated rough endoplasmic reticulum (RER) was observed. Until 30 min. after renewed suckling, a marked increase in the serum PRL was observed and the RER transformed frequently, ie. collapse (1, 30 min.) and dilation (5, 15 min.). However, the pituitary PRL and the granule content did not change noticeably. Between 60 and 240 min. after the renewed suckling, the serum PRL decreased gradually, and the pituitary PRL and the granule content showed a prominent decrease. However, the dilated RER and the well-developed Golgi apparatus were clearly observed. The results indicate that: The interrupted suckling stimulus does not suppress de novo synthesis of PRL. Renewed suckling immediately induces not only release but also de novo synthesis of PRL. Until 30 min. after renewed suckling, PRL is mainly released directly from RER, which mechanism is differently from the release by exocytosis of secretory granules that can be observed after 30 min. of renewed suckling.