Somatostatin cells in human somatotropic adenomas

Effect of the slow-release formulation of somatuline (BIM 23014) on estrogen-induced hyperprolactinemia and lactotroph hyperplasia in the female rat

Somatuline, in common with other SRIH analogues, exerts antiproliferative and antisecretory activities on various tumors. Our purpose was to test the effectiveness of a slow-release formulation of somatuline on lactotroph hyperplasia and PRL hypersecretion induced by estrogens (17 beta E2) in rats. Female rats were primed with 17 beta E2 for 6 weeks before receiving somatuline (2 mg/kg) intramuscular injections every 10 days for one month. The mean anterior pituitary weight was 11.22 +/- 0.32 mg (mean +/- SEM) in non-estrogenized rats, 29.62 +/- 1.63 mg in 17 beta E2-primed rats and 23.58 +/- 1.26 mg in 17 beta E2-primed somatuline-treated rats. Mean plasma PRL level was 5.63 +/- 0.97 ng/ml, 182.37 +/- 27.55 ng/ml and 113.89 +/- 15.07 ng/ml in the same groups respectively. Thus, the 17 beta E2-induced pituitary enlargement and hyperprolactinemia were 20% and 38% lower respectively when animals were treated with somatuline during the last month of estrogenization. The 17 beta E2-induced increase in PRL cell density was also reduced by somatuline treatment. We conclude that the slow-release formulation of somatuline impedes 17 beta E2-induced hyperprolactinemia and pituitary enlargement concomittantly, at least in part by acting on lactotroph proliferation.

Evidence of tyrosine hydroxylase mRNA in the anterior and neurointermediate lobes of female rat pituitary

The anterior pituitary is thought to be unable to synthesize dopamine (DA) except under experimental conditions where a tyrosine hydroxylase (TH) activity, the rate-limiting step of its synthesis, has been demonstrated. In this work, we tested whether the enzyme described as active under particular conditions comes from de novo TH gene transcription or from a pre-existing TH mRNA poorly translated or untranslated under physiological conditions. Therefore, we searched for the presence of TH mRNA in normal female rat pituitary using the polymerase chain reaction following reverse transcription (RT/PCR) and in situ hybridization (ISH). The neurointermediate lobe (NIL) of the hypophysis was used as negative tissue, since it is thought to be unable to synthesize TH. As expected, no ISH labelling could be seen in the neural lobe (NL). However, scarce labelled cells were found in the intermediate lobe (IL) confirming the positive results observed in the NIL by RT/PCR. The anterior lobe (AL) also presented TH mRNA by PCR and ISH. The TH gene expression in sparse cells of the AL is discussed in regard to the ability of the AL to synthesize DA under particular conditions from a pre-existing mRNA.