PROLACTIN SECRETION AND SYNTHESIS IN SHORT- AND LONG-TERM ORGAN CULTURE OF PITUITARY TUMOURS FROM ACROMEGALIC PATIENTS

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Abstract
To evaluate the in vitro PRL [prolactin] secretion and synthesis by pituitary tumors from acromegalic patients, 6 somatotropic and 2 somatomammotropic 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 long-term organ culture (7 and 14 days). Media were collected for GH [growth hormone] and PRL radioimmunoassay and fragments were studied by EM. In 2 experiments, fragments from a somatotropic adenoma and a somatomammotropic adenoma were cultured for 1-4 h and 9-16 days with [3H]leucine. The effect of somatostatin (2.5 nmol/ml) on PRL secretion was studied in short-term incubation. In long-term organ culture PRL concentrations increased in 8 of 16 media samples collected from 5 tumors and 1 normal pituitary cultured for 14 days, while GH concentrations decreased during the same time in all experiments. The [3H]PRL/[3H] protein 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 tumors, after 7 or 14 days of culture. In short-term incubation, PRL concentrations in media increased in most of the samples collected from the 3 tumors incubated for 1-4 h and the [3H]PRL/[3H]protein ratio was 10.6% after 1 h and 21% after 2 h of incubation. A decrease of PRL content [< 50%) was observed in 2 of the 3 tumors incubated with somatostatin. These data indicate that somatotropic adenomas, as well as somatomammotropic ones, can secrete and synthesize PRL in vitro. PRL synthesis from these adenomas increases during culture, as from normal pituitary, presumably because of the release of PRL-secreting cells from PRL inhibitory hypothalamic control (PIF). Somatostatin may reduce PRL release in vitro from somatotropic adenomas as reported in some cases in vivo.