ABSTRACT
To evaluate the in vitro PRL secretion and synthesis by pituitary tumours from acromegalic patients, six somatotrophic and two somatomammotrophic adenomas were collected after surgery and divided into fragments 1 mm3 in size. Fragments were cultured in short-term (1–2–3–4 h) and in long-term organ culture (7 and 14 days). Media were collected for GH and PRL radioimmunoassay and fragments studied by electron microscopy. In two experiments, fragments from a somatotrophic adenoma and from a somatomammotrophic adenoma were cultured for 1 to 4 h and 9 to 16 days with [3H]leucine. In addition the effect of somatostatin (2.5 nmole/ml) upon PRL secretion was studied in short-term incubation. In long-term organ culture PRL concentrations increased in 8 out of 16 media samples collected from the five tumours and one normal pituitary cultured for 14 days, while GH concentrations decreased during the same time in all the experiments. The [3H]PRL/[3H] proteins ratios were 9.7 % on the 9th day of culture and 20.8 % on the 16th day while for GH, the ratios were respectively 40 and 34.7 %. Ultrastructural studies showed, besides GH cells, the presence of PRL secreting cells in the different tumours, after 7 or 14 days of culture. In short-term incubation, PRL concentrations in media increased in most of the samples collected from the three tumours incubated for 1 to 4 h and the [3H]PRL/[3H]proteins ratio was 10.6 % after 1 h and 21 % after 2 h of incubation. A decrease of PRL content (< 50 %) was observed in two of the three tumours incubated with somatostatin.
These data indicate that 1) somatotrophic adenomas, as well as somatomammotrophic ones, are able to secrete and synthesize PRL in vitro, 2) PRL synthesis from these adenomas increases during culture, as from normal pituitary, presumably because of the release of PRL-secreting cells from the PRL inhibitory hypothalamic control (PIF), 3) somatostatin may reduce PRL release in vitro from somatotrophic adenomas as reported in some cases in vivo.