Oophorectomy improves pituitary activin inhibitory function preventing lactotroph hyperplasia development

Among pituitary adenomas, prolactinomas are the most frequently diagnosed (about 50%). Dopamine agonists are generally effective in the treatment of prolactinomas. However, a subset of about 25% of patients does not respond to these agents. The management of drug-resistant prolactinomas remains a challenge for endocrinologists and new inhibitory treatments are needed. Pituitary activins inhibit lactotroph function. Its expression and action were found reduced in animal models of lactotroph hyperplasia (female mice overexpressing the B subunit of the human chorionic gonadotrophin and female mice knockout for dopamine receptor type 2). In these models, an oophorectomy avoids prolactinoma development. Hormonal replacement with oestradiol and/or progesterone is not enough to reach the tumor size observed in transgenic females. We postulated that the loss of gonadal inhibins after an oophorectomy contributes to prevent hyperplasia development. Here, we demonstrated that an oophorectomy at 2 months age recovers the following in adulthood: (i) pituitary activin expression, (ii) activin receptor expression specifically in lactotroph population, (iii) activin biological activity in lactotrophs with a concomitant reduction of Pit-1 expression. To summarize, when an oophorectomy is performed, inhibins are lost and the inhibitory action of pituitary activins on lactotroph population is recovered, helping to prevent lactotroph hyperplasia development. These results emphasize the importance of the inhibitory action of activins on lactotroph function, positioning activins as a good therapeutic target for the treatment of resistant prolactinomas.

[Inhibins and Activin A in hypertensive Disorders of Pregnancy and HELLP-Syndrome]

OBJECTIVE

Are serum concentrations of the ovarian glycoproteins inhibin A, inhibin B, pro-alpha-C and activin A different in normotensive, chronical hypertensive or pregancies complicated by preeclampsia or HELLP-syndrome? What are the clinical consequences?

METHODS

Serum concentrations of inhibin A, inhibin B, pro-alpha-C, and activin A of 99 women (37 normotensive patients, 23 patients with chronical hypertension, 25 women with preeclampsia and 14 patients with HELLP-syndrome) at different stages of pregnancy were determined by high specific ELISAS.

RESULTS

During pregnancy serum levels of all parameters increased continually and fell rapidly within parturition. Activin A and inhibin B levels showed significant higher serum concentrations in patients with preeclampsia and - even more pronounced - in patients with HELLP-syndrome. Normotensive and chronically hypertensive patients were not different.

CONCLUSION

Activin A and inhibin A appear to be viable candidates as laboratory parameters for detection of pregnancy induced hypertension. Maybe furthermore both parameters will allow the discrimination between chronic hypertension and hypertension induced by pregnancy.

Administration of recombinant human Activin-A has powerful neurotrophic effects on select striatal phenotypes in the quinolinic acid lesion model of Huntington's disease

Huntington disease is characterized by the selective loss of striatal neurons, particularly of medium-sized spiny glutamate decarboxylase67 staining/GABAergic projection neurons which co-contain the calcium binding protein calbindin. Lesioning of the adult rat striatum by intrastriatal injection of the N-methyl-D-aspartate receptor agonist quinolinic acid (100 nmol) results in a pattern of striatal neuropathology seven days later that resembles that seen in the Huntington brain. Using this animal model of human Huntington's disease we investigated the effect of daily intrastriatal infusion of the nerve cell survival molecule ActivinA (single bolus dose of 0.73 microg daily for seven days) on the quinolinic acid-induced degeneration of various striatal neuronal phenotypes. By seven days, unilateral intrastriatal infusion of quinolinic acid produced a partial but significant loss (P < 0.01) in the number of striatal neurons immunoreactive for glutamate decarboxylase (to 51.0+/-5.8% of unlesioned levels), calbindin (to 58.7+/-5.1%), choline acetyltransferase (to 68.6+/-6.1%), NADPH-diaphorase (to 47.4+/-5.4%), parvalbumin (to 58.8+/-4.1%) and calretinin (to 60.6+/-8.6%) in adult rats that were administered intrastriatal phosphate-buffered saline for seven days following quinolinic acid. In contrast, in rats that received intrastriatal recombinant human ActivinA once daily for seven days following quinolinic acid, phenotypic degeneration was significantly attenuated in several populations of striatal neurons. Treatment with ActivinA had the most potent protective effect on the striatal cholinergic interneuron population almost completely preventing the lesion induced decline in choline acetyltransferase expression (to 95.1+/-5.8% of unlesioned levels, P < 0.01). ActivinA also conferred a significant protective effect on parvalbumin (to 87.5+/-7.7%, P < 0.01) and NADPH-diaphorase (to 77.5+/-7.5%, P < 0.01) interneuron populations but failed to prevent the phenotypic degeneration of calretinin neurons (to 56.6+/-5.5%). Glutamate decarboxylase67 and calbindin-staining nerve cells represent largely overlapping populations and both identify striatal GABAergic projection neurons. We found that ActivinA significantly attenuated the loss in the numbers of neurons staining for calbindin (to 79.7+/-6.6%, P < 0.05) but not glutamate decarboxylase67 (to 61.1+/-5.9%) at seven days following quinolinic acid lesioning. Taken together these results suggest that exogenous administration of ActivinA can rescue both striatal interneurons (labelled with choline acetyltransferase, parvalbumin, NADPH-diaphorase) and striatal projection neurons (labelled by calbindin) from excitotoxic lesioning with quinolinic acid. Longer-term studies will be required to determine whether these surviving calbindin-expressing projection neurons recover their ability to express the glutamate decarboxylase67/GABAergic phenotype. These results therefore suggest that treatment with ActivinA may help to prevent the degeneration of vulnerable striatal neuronal populations in Huntington's disease.

Oestradiol feedback stimulation of androgen biosynthesis by human theca cells

This study analysed the effect of oestradiol on basal and LH-stimulated production of androstenedione and progesterone by human theca cells in monolayer culture. Incubations were carried out for either 2 days (seven experiments) or 4 days (four experiments), in the presence or absence of luteinizing hormone (LH), oestradiol (10(-9)-10(-6) M) or inhibin. Medium collected at 48 and 96 h was stored until radioimmunoassay for steroid content. Theca pooled from small follicles (<10 mm) was used in all but two experiments; in these, ovaries were obtained from ovulatory women in the mid-follicular phase of their cycle and theca from small and large follicles was pooled. Oestradiol inhibited progesterone production in a dose-dependent manner in all experiments, irrespective of follicle size, ovulatory status and ovarian morphology, with maximum effect at 10(-6) M. At this dose, oestradiol had no effect on androstenedione production by theca from four anovulatory women with polycystic ovaries but produced a significant augmentation of both basal and LH-stimulated androstenedione production in theca from five of the seven ovulatory women, with maximal response in theca from the two pre-ovulatory subjects. During the 48-96 h period of incubation, oestradiol augmented androstenedione production in all four experiments and had a greater stimulatory effect than the physiological dose of inhibin (10 ng/ml). This is the first report of oestradiol regulating human theca cell steroidogenesis in a dose-dependent manner.

Human prostatic inhibin suppresses tumor growth and inhibits clonogenic cell survival of a model prostatic adenocarcinoma, the Dunning R3327G rat tumor

Prostatic inhibin (PI) is a M(r) 10,700 protein found in human seminal plasma and is secreted by the prostate. Recognition of alteration of PI levels in prostatic diseases prompted us to investigate its effect on an animal prostatic adenocarcinoma model, the Dunning R3327G rat tumor. PI not only inhibited in vitro growth of tumor cells but also suppressed tumor growth in vivo. A dose-dependent inhibition of both the clonogenic cell growth and rate of proliferation (DNA synthesis) was observed in tumor cell cultures incubated with purified PI. These inhibitory activities were similar in both androgen-dependent and androgen-independent Dunning tumor cell lines. A functional decapeptide of PI was also found to inhibit Dunning tumor cell colonies in a dose-dependent manner. Daily injection of purified PI into tumor-bearing rats suppressed the tumor growth. A 58% reduction in tumor weight and a 2-fold reduction in tumor growth rate were observed over a 15-day treatment period. Continued treatment with PI significantly suppressed the tumor growth rate by nearly 3-fold. These findings clearly demonstrate a potential application of PI for treating human prostatic adenocarcinoma.

Effect of prostatic inhibin peptide (PIP) on prostate cancer cell growth in vitro and in vivo

Prostatic inhibin peptide (PIP), is a 94 amino acid protein which is secreted by the prostate gland in an androgen-independent manner. Previously, it has been demonstrated that PIP appears to inhibit follicle-stimulating-hormone (FSH) secretion by the pituitary and prostate glands. In vitro, the Dunning R3327 rat prostate cancer cell line MAT-LyLu (MLL) cells and the human prostate cancer cell line PC-3, are stimulated to grow in response to exogenous FSH and these effects are blocked by PIP. In vivo, PIP inhibits the growth of the highly metastatic MLL prostate cancer cell line. A comparison of hormone levels in control and PIP-treated rats demonstrates a significant inhibition of FSH in treated animals. It appears that, in vivo, PIP may inhibit prostate cancer growth by inhibiting FSH. PIP may represent a novel hormonal treatment for prostate cancer.