Immunoreactive somatostatin in the rat ovary

Constitutive and follicle-stimulating hormone-induced action of somatostatin receptor-2 on regulation of apoptosis and steroidogenesis in bovine granulosa cells

In the present study, we employed primary bovine culture of granulosa cells (GCs) as a cellular model to study the potential involvement of somatostatin receptor 2 (SSTR2) in ovarian function. The results showed that bovine GCs expressed SST2 receptor and further found that SSTR2 was possibly regulated by follicle-stimulating hormone (FSH), as a significant increase in protein level of SSTR2 was observed in FSH-treated GCs. For further analysis, endogenous SSTR2 expression was disrupted using small inhibitory RNA (siRNA) and the efficacy of differential silencing of endogenous SSTR2 expression was measured both at transcriptional and translational levels. Transient blockage of SSTR2 evidenced its constitutive action on GCs, as it significantly increased level of cAMP (2.4-folds) and basal progesterone production (∼2-fold, P<0.05) with significant increase (P<0.05) in mRNA levels of StAR and P450ssc without altering estradiol concentration and aromatase mRNA expression. Furthermore, silencing of SSTR2 reduced GCs apoptosis (52.5%, P<0.05) and increased cell proliferation, which was further corroborated by up-regulation in protein expressions of B-cell leukemia/lymphoma 2 (Bcl-2), inhibition of caspase3 and mRNA level of bcl2-associated-X protein (Bax). These results provide evidence that SSTR2 subtype controls GCs apoptosis, proliferation and hormonal secretions through selective constitutive action, independently of somatostatin (SST). Given the local inhibitory actions of SSTR2 on the gonads, we further found that apoptosis in ssRNAi-2 transfected cells decreased (6.8% vs 1.9%, P<0.05) more strongly on FSH treatment. Apoptotic protein expressions and steroid hormone mRNA levels were correlated with a relative decrease in apoptosis and increase in progesterone production. Our results suggest that SSTR2 may play a crucial role as a local inhibitor of FSH action on GCs apoptosis and steroidogenesis.

Involvement of bone morphogenetic protein activity in somatostatin actions on ovarian steroidogenesis

Somatostatin is expressed in the hypothalamus, pancreas and gastrointestinal tracts and it inhibits the secretion of various hormones in vivo. In the rodent ovary, somatostatin receptor (SSTR) subtypes 2 and 5 are expressed in granulosa cells and oocytes. Somatostatin analogs have been clinically used for treatment of endocrine tumors. For this purpose, relatively high-dose or long-term treatments of somatostatin analogs are necessary; however, the direct and continuous impact of somatostatin analogs on gonadal functions has yet to be elucidated. In the present study, we investigated the effects of somatostatin analogs (octreotide and pasireotide) on ovarian steroidogenesis by rat primary granulosa cell culture. The expression levels of SSTR2 and SSTR5 in granulosa cells were upregulated by FSH treatment. Treatment with somatostatin analogs decreased FSH-induced estradiol production with reduction in aromatase mRNA expression, while the treatment also suppressed FSH-induced progesterone production with reduction of mRNAs levels of StAR, P450scc and 3βHSD2 in granulosa cells. This trend was also observed in a granulosa/oocyte co-culture condition. The effect of pasireotide was more potent than that of octreotide. FSH-induced synthesis of steroids and cAMP was also suppressed by somatostatin analog treatment. Notably, pretreatment with a BMP-binding protein, noggin reversed the suppressive effects of somatostatin analogs on progesterone and cAMP production, suggesting that the endogenous BMP system is functionally involved in the SSTR effects in granulosa cells. Treatment with BMP-2, -4, -6 and -7 decreased the mRNA expression of inhibitory Smads6 and 7, leading to enhancement of BMP actions detected by Id-1 transcription in granulosa cells. Collectively, the results revealed that SSTR activation modulates ovarian steroidogenesis by upregulating endogenous BMP activity in growing follicles.

Achievement of cardiovascular risk factor targets in young adults with diabetes mellitus

BACKGROUND

Many patients with diabetes mellitus fail to achieve treatment targets recommended in recognized guidelines. Little data is available in this area relating to young adults.

OBJECTIVE

To assess whether treatment goals for glycosylated hemoglobin (HbA(1c)), blood pressure, lipid-lowering, and process outcomes for microvascular screening are being achieved in young adults with diabetes mellitus.

METHODS

A retrospective clinical record audit of 202 consecutive patients with type 1 and type 2 diabetes, aged predominantly 18-45 years, attending a specialist diabetes center in Brisbane, Australia, was conducted. Assessment was made as to whether goals for HbA(1c), blood pressure, lipid lowering, and microvascular screening were being achieved. Descriptive statistics and comparison of continuous variables were produced.

RESULTS

Mean (SD) HbA(1c) was 8.30% (±1.5) with no statistical difference between patients with type 1 and type 2 diabetes (P = 0.44). Sixteen percent of patients (12% type 1, 31% type 2) had an HbA(1c) of < 7%. Eighty-three percent of patients had blood pressure ≤130/80 mmHg. Sixteen percent of patients with type 1 and 37% with type 2 diabetes were achieving combined lipid targets. Only 34% and 9% of patients who had an indication (and no documented contraindication) for lipid-lowering and antiplatelet therapy, respectively, were prescribed such agents. There was a significant difference in achievement of macrovascular treatment targets in patients with type 1 and type 2 diabetes, but no difference in screening or treatment outcomes in microvascular disease. Patients below the age of 25 years were less likely to achieve macrovascular treatment targets.

CONCLUSION

A large number of young adult patients with diabetes mellitus do not achieve recognized treatment targets. There appears to be less emphasis placed on macrovascular risk factor targets compared with previous audits in older patients, in patients with type 1 diabetes compared with type 2 diabetes and in patients younger than 25 years.

Kit ligand and the somatostatin receptor antagonist, BIM-23627, stimulate in vitro resting follicle growth in the neonatal mouse ovary

In the mammalian ovary, kit ligand (KL), coded by a cAMP-stimulatable gene, is a protein that promotes initiation of follicle growth. The neuropeptide somatostatin (SST) is a small peptide that inhibits cAMP generation in many cell types. Consequently, SST receptor agonists might alter KL production and subsequent follicle growth. The present study was undertaken to look for the existence of a functional SST system in the mouse ovary, to test the effects of the SST receptor 2 (SSTR-2) antagonist BIM-23627 on in vitro folliculogenesis, and to compare them with those of KL, which was demonstrated to stimulate follicle growth in the neonatal rat ovary. Pairs of ovaries from 5-d-old mice were incubated in vitro during 15 d in the presence of either KL or BIM-23627. For every mouse, one ovary was cultured in culture medium (control), and the other ovary was cultured in the presence of either KL or BIM-23627. After 5, 10, and 15 d culture, the ovaries were histologically assessed for the content of primordial, primary, and secondary follicles. The SSTR-2 and -5, but not SST, were identified at the transcriptional and translational (mainly in granulosa cells) levels. Both KL and BIM-23627 triggered a reduction of the percentages of primordial follicles and an increase of the percentages of primary and secondary follicles when compared with control ovaries from the same animal. In conclusion, extraovarian SST, acting through its receptors 2 and 5 present on granulosa cells, may be involved in mouse folliculogenesis by reducing recruitment of resting follicles.

Regulation of preprosomatostatin 1 (PSS1) gene expression by 17beta-estradiol and identification of the PSS1 promoter region in orange-spotted grouper (Epinephelus coioides)

In the present paper the effects of 17beta-estradiol on the expression of the preprosomatostatin 1 (PSS1) in the orange-spotted grouper hypothalamus and ovary were investigated. Results from in vivo of intraperitoneal injection and in vitro static cultures showed that estradiol increased the mRNA expression of PSS1 gene in both hypothalamus and ovary. To investigate the molecular basis of the estrogen regulation on PSS1 gene expression, we cloned the upstream region of 848bp from the translation initiation codon of the grouper PSS1 gene. The TATA-box and putative transcription factor binding sites were identified using computer analysis. Transient transfections with promoter-luciferase reporter constructs together with hER expression vector were carried out in MCF-7 cell line. The results suggest that the region from -848 to -373bp, containing five putative ERE half sites, may contribute to the promoter activity induced by estradiol. These results represent the first demonstration at the molecular level of the regulation of PSS1 gene by 17beta-estradiol in fish.

Effect of glutamate and somatostatin-14 on basal and cAMP-stimulated steroidogenesis by rainbow trout (Oncorhynchus mykiss) ovarian follicles, in vitro

The effects of glutamate and somatostatin-14 (SRIF) on the in vitro basal and cAMP-stimulated steroid production of mid-vitellogenic rainbow trout (Oncorhynchus mykiss) ovarian follicles were investigated. cAMP-stimulation was achieved by the addition of the adenylyl cyclase activator, forskolin (FS), or a membrane permeate cAMP agonist, 8-bromo-cAMP (BA), to the incubation medium. Testosterone (T) and 17beta-estradiol (E(2)) secretion was measured using radioimmunoassay. Solid phase extraction (SPE) was used to measure the relative formation of unconjugated and conjugated steroids, and high performance liquid chromatography (HPLC) was used to examine the steroid metabolites formed from the metabolism of a tritium labelled precursor, pregnenolone (P(5)). The accumulations of T and E(2) in the medium were suppressed in the presence of the glutamate agonists, N-methyl-d,l-aspartate (NMA) or l-glutamic acid (GA), and by the presence of SRIF. The suppression was evident for both basal and cAMP-stimulated steroidogenesis except for T concentrations of GA treatments following basal steroidogenesis, when there were no treatment effects. No significant effects of treatment on conjugated:unconjugated steroid ratios were found. For all treatments E(2) was the major end product steroid synthesized from P(5), and the steroid profiles were similar except for trace amounts of radiolabelled androgens in the medium following cAMP-stimulated steroidogenesis that were not present following basal steroidogenesis. The findings suggest that glutamate and SRIF reduce end point steroid production, possibly by reducing P(5) production. However, since the inhibitory affect was found for basal and cAMP-stimulated steroidogenesis, the response does not appear to be due to the inhibition of cAMP synthesis.

Chronic somatostatin treatment affects pituitary gonadotrophs, ovaries and onset of puberty in rats

The effects of chronic somatostatin (SRIH-14) treatment on the pituitary gonadotrophs (FSH and LH cells) and ovaries of female Wistar rats were examined. Females were given 20 microg/100 g b.w. twice per day from the immature (23rd day) till the adult period of life (71st day). The onset of puberty was determined by daily examination for vaginal opening. The peroxidase-antiperoxidase immunocytochemical procedure was used to study the gonadotrophs. Changes in the number per unit area (mm2), cell volume and volume densities of LH- and FSH-immunoreactive cells were evaluated by morphometry and stereology. Ovaries were analysed by simple point counting of follicles and corpora lutea (CL). Follicles were divided by size according to the classification of Gaytán and Osman. The mitotic indexes of granulosa and theca cells in the follicles were estimated at all stages of folliculogenesis. The number, volume and the volume density of FSH- and LH-immunoreactive cells decreased after chronic SRIH-14 treatment, particularly the latter. In the ovary, SRIH-14 treatment decreased the number of healthy follicles at all phases of folliculogenesis, lowered the mitotic indexes of granulosa and theca cells but increased the number of atretic follicles. Healthy CL were fewer in number, while regressive CL were increased. Vaginal opening occurred at a later age in treated females. It can be concluded that chronic SRIH-14 treatment markedly inhibited LH cells and to a lesser extent FSH cells. In the ovary SRIH-14 inhibited folliculogenesis, enhanced atretic processes and lowered proliferative activity of granulosa and theca cells. It also delayed puberty onset.

Effects of multiple somatostatin treatment on rat gonadotrophic cells and ovaries

The effect of multiple somatostatin (SRIH-14) treatment on the pituitary gonadotrophs, follicle stimulating harmone (FSH) and luteinizing harmone (LH), and ovaries of adult female Wistar rats was examined. Females received two 20 microg/100 g body wt. doses daily subcutaneously, for five consecutive days. FSH and LH cells were studied using a peroxidase-antiperoxidase immunocytochemical procedure. Morphometry and stereology were used to evaluate changes in the number per unit area (mm2), cell volume and volume densities of LH- and FSH-immunoreactive cells. Ovaries were analysed by simple point counting of follicles and corpora lutea. Follicles were divided by size according to the classification of Gaytán and Osman. Morphometric and stereological analysis of the pituitary showed that the number, volume and the volume density of FSH- and LH-immunoreactive cells were decreased after multiple SRIH-14 treatment, particularly in the latter. In the ovary, SRIH-14 induced decreases in the number of healthy follicles in all phases of folliculogenesis and corpora lutea, but the large antral follicle stage was most affected. The number of atretic follicles was increased. It can be concluded that multiple SRIH-14 treatment markedly inhibited LH cells, but affected FSH cells as well. In the ovary, SRIH- 14 acted by inhibiting folliculogenesis and enhancing atretic processes.

Growth hormone-releasing hormone and growth hormone secretagogue-receptor ligands: focus on reproductive system

Growth hormone-releasing hormone (GHRH) and somatostatin are the most important hypothalamic neurohormones controlling growth hormone (GH) secretion. Several neurotransmitters and neuropeptides also play an important role in the control of GH secretion, mainly acting via modulation of GHRH and somatostatin. In the past two decades, particular attention has been given to a new family of substances showing a strong GH-releasing effect: GH secretagogues (GHSs). GHSs increase GH secretion in a dose- and age-related manner after iv and even oral administration. The endocrine effects of GHSs, are not fully specific for GH; they show, in fact, prolactin- (PRL), adenocorticotropic hormone- and cortisol-releasing effects. Specific GHS receptors are present in both the central nervous system and peripheral tissues, where they mediate several extraendocrine effects of GHSs. The isolation of these "orphan" receptors suggested the existence of an endogenous GHS-like ligand that could be represented by a recently discovered gastric peptide, named ghrelin. The interaction between GHSs and GHRH at the central level and in the pituitary gland, but not at peripheral level, has clearly been shown. Because GHRH and GHS receptors share the same localization in some peripheral tissues, they may have some interactions even at this level.

Ovarian control of follicle development

A variety of ovarian autocrine and paracrine factors may modulate folliculogenesis and steroid production. The developmental program that leads to the production of a dominant follicle involves a precise quantitative and temporal pattern of expression of a large number of genes. Follicle-stimulating hormone plays an essential role in this process, and no other ligand by itself can serve in this regulatory capacity. It is clear that a variety of growth factors can modulate follicle-stimulating hormone action by autocrine and paracrine mechanisms. Advances in the understanding of the role of growth factors, particularly the family of insulin-like growth factor-related proteins, in regulating follicle-stimulating hormone action are discussed. It is likely that complex interactions exist between follicle-stimulating hormone and the growth factors. Significantly, growth factor regulation by pituitary gonadotropins is probably a central feature of their expression. With increased understanding of the ovarian control of follicle development, it is hoped that newer and more effective regimens for synchronous follicular and oocyte maturation can be realized.