Increased perinatal remodelling of the pancreas in somatostatin-deficient mice: potential role of transforming growth factor-beta signalling in regulating beta cell growth in early life

Early postnatal life is a critical period for development of the endocrine pancreas, involving remodelling of islet cells and maturation of secretory responses. Factors that regulate these processes are undefined. Somatostatin-secreting delta-cells are abundant in the developing pancreas and, because somatostatin inhibits growth, the hormone may regulate islet expansion in early life. The aim of this study was to investigate effects of somatostatin-deficiency on proliferation, apoptosis and pancreas expansion in the first 3 weeks of life in mice. Pancreases from control or somatostatin-knockout mice were analysed for beta cell, alpha cell and pancreatic volumes by morphometry, proliferation by BrdU incorporation and apoptosis by TUNEL labelling. Signalling pathways associated with proliferation and apoptosis were studied by immunohistochemistry and Western blotting. Knockout mice grew normally in the first 3 weeks of life, but had high circulating insulin that normalised by day 21. Beta cell, alpha cell and pancreatic volumes were decreased in knockout mice, accompanied by reduced proliferation and increased apoptosis in the pancreas. Decreased growth was not due to impaired Akt signalling, as Akt phosphorylation and nuclear cyclin-D2 increased in the knockout pancreas. Levels of TGF-β1, a factor implicated in tissue remodelling, together with SMAD phosphorylation through which TGF-β mediates its effects, were increased in the knockout pancreas. Beta cell expansion was impaired in knockout mice, potentially compensating for increased insulin secretion from islets lacking inhibitory effects of somatostatin, and was associated with increased TGF-β1 levels. TGF-β1 may represent an important regulator of beta cell mass in early life.

A linear hexapeptide somatostatin antagonist blocks somatostatin activity in vitro and influences growth hormone release in rats

Somatostatin (SRIF) is the main inhibitory peptide regulating growth hormone (GH) secretion. It has been difficult to establish the role of endogenous SRIF release in the absence of pure SRIF antagonists. Although several SRIF antagonists have recently been described, none have been shown to possess in vivo activity in the absence of added SRIF. Here, an SRIF antagonist with no detectable agonist activity has been identified from a synthetic combinatorial hexapeptide library containing 6.4 x 10(7) unique peptides. Each peptide in the library is amino-terminally acetylated and carboxyl-terminally amidated and consists entirely of D-amino acids. A SRIF-responsive yeast growth assay was used as a primary screening tool, and cAMP accumulation, competitive binding, and microphysiometry also were used to confirm and further characterize SRIF antagonist activity. The hexapeptide library was screened in stepwise iterative fashion to identify AC-178,335, a pure SRIF antagonist of the sequence Ac-hfirwf-NH2. This D-hexapeptide bound SRIF receptor type 2 with an affinity constant (Ki) of 172 +/- 12 nM, blocked SRIF inhibition of adenylate cyclase in vitro (IC50 = 5.1 +/- 1.4 microM), and induced GH release when given alone (50 micrograms intravenously) to anesthetized rats with or without pretreatment with a long-acting SRIF agonist.

The obese growth hormone (GH)-deficient dwarf rat: body fat responses to patterned delivery of GH and insulin-like growth factor-I

We describe a new animal model of obesity and GH deficiency and report the effects on body fat of administering (GH) and insulin-like growth factor (IGF-I) in the model. Female GH-deficient dwarf rats fed a high-fat diet became obese and insulin-resistant compared with chow-fed controls. They were treated with recombinant human GH (rhGH 100-500 micrograms/day, s.c. for 14 days) by daily injection or minipump infusion with or without rhIGF-I (200 micrograms/day, sc infusion). Injections of rhGH increased body weight; infusions of rhGH caused weight loss. RhIGF-I by itself, or rhIGF-I plus GH injections had little effect, whereas rhGH infusions plus rhIGF-I caused a weight loss equivalent to the weight gained during the high-fat feeding and a decrease in fat pad weight. For some responses (serum IGF-1 and GHBP), the obese rats were GH resistant. Fat was lost from the internal fat pads when obese rats were returned to a chow diet, and injections of rhGH surprisingly attenuated this loss of fat. In obese dwarf rats, the lipolytic effects of rhGH are dose-regime dependent. By itself IGF-I is not insulin-like, but in the presence of GH it has antiinsulin actions causing a powerful net lipolysis. If GH plus IGF-I have similar effects in humans they may be useful for reducing body fat.

Growth responses to patterned GH delivery

We have investigated the effects of different patterns of administration of recombinant human growth hormone (rhGH) on weight gain, organ growth, serum GH binding protein (GHBP) and insulin-like growth factor-l (IGF-1) levels in a series of studies using hypophysectomized (Hx) or GH-deficient dwarf (dw/dw) rats. Animals were given rhGH either by subcutaneous (s.c.) injections (1 or 2 per day) or s.c. infusions and rhlGF-1 (2 mg/kg/day) by s.c. infusion. In Hx rats, all rhGH regimes increased body weight, tibial epiphyseal plate width, and organ weights in a dose-related manner. Dwarf rats showed a smaller growth response to rhGH than Hx rats, whereas rhGH induced greater elevations in serum GHBP in drarf rats. Growth responses depended on the pattern of rhGH administration (twice daily injections > continuous infusions > daily injections). The shape of the body growth curves also differed; rhGH injections increased weight gain linearly, whereas infusions gave an initial rapid weight gain which slowed with time (a curvilinear response). For both regimens, tibial epiphyseal plate width increased linearly with rhGH dose but infusions were 5-fold more potent than daily injections. Spleen and thymus weights were markedly increased by rhGH and were also affected by the pattern of GH exposure. At 5 mg rhGH/kg/day, thymus weights were 390±35 mg for injectionsvs. 613 ± 34 mg for infusions (P<0.001) compared with 248 ± 16 mg in vehicle-treated Hx controls. Infusions of rhlGF-1 also stimulated specific organ growth but caused less weight gain. RhlGF-1 additively increased the weight gain caused by rhGH injections but not by rhGH infusions. Circulating IGF-1 and GHBP levels were increased in a dose-dependent manner by rhGH infusion, whereas daily injections were ineffective. Thus, differential organ growth could be related to the higher serum IGF-1 concentrations induced by continuous rhGH administration. These studies show that whole body growth is best maintained by intermittent rhGH exposure, whereas, paradoxically, differential organ growth is most pronounced with continuous rhGH administration.

Prolactin and the gut: a controversy

Previous reports suggest that prolactin could be one of the factors controlling intestinal mucosal growth. Therefore plasma levels of prolactin have been measured at the time of jejunal biopsy performed for suspicion of celiac disease. One hundred eighty-seven biopsies from 166 children have been reviewed according to histology, age, diagnosis, and plasma prolactin. No difference in the plasma prolactin could be detected among a group of 117 normal biopsies (9.4 +/- 0.4 ng/ml, mean +/- SEM), 31 biopsies with partial atrophy of various degree (9.0 +/- 0.9 ng/ml), and 39 biopsies with flat mucosa (9.1 +/- 0.7 ng/ml), nor could we demonstrate an increase in prolactin according to age and diagnosis (celiac disease before and after treatment, cow's milk protein intolerance, isolated postenteritic syndrome, selective sugar intolerance, and functional gut problems). Prolactinlike material has been detected by immunoperoxidase in the jejunal mucosa. The intracellular granules are located in the infranuclear portion of isolated epithelial cells mainly in the crypts. This material could not be correlated with the corresponding prolactinemias, whatever the histological appearance of the mucosa. These results would suggest that plasma prolactin is not a marker of jejunal regeneration in children. The nature and function(s) of this prolactinlike material remain to be established.

Hormonal changes during puberty. IV. Longitudinal study of acrenal androgen secretions

Longitudinal studies of plasma dehydroepiandrosterone sulfate (DHEA-S) and dehydroepiandrosterone (DHEA) were made in 13 girls aged 7 years and 14 aged 10 years, during 3 years, at 6-month intervals. Similarly, two groups of 12 boys aged 8 years and 11 years were followed. In addition, 3 girls with premature adrenarche and 4 male patients with Addison's disease were studied. In the normal girls a significant rise of plasma DHEA-S and DHEA occurred from 6 years of bone age (51.4 +/- 9.0 ng/ml and 50.5 +/-9.2 ng/100 ml, respectively) to 8 years (119. 7 +/- 19.1 ng/ml and 94.5 +/- 16.5 ng/100 ml). A further significant rise was apparent at 11 years (385.8 +/-60.9 ng/ml) and 329.0 +/- 78.4 ng/100 ml). In boys, a similar rise of DHEA-S and DHEA was observed between 6 years of bone age (75.8 %/- 12 ng/ml and 44.3 +/- 7.6 ng/100 ml) and 8 years (157.4 +/- 28.9 ng/ml and 76.1 +/- 8.9 ng/100 ml). Furhter significant rise of DHEA-S and DHEA were seen at 13 years of bone age (563.7 +/- 123.7 ng/ml and 267.9 +/- 50.0 ng/100 ml, respectively). Testosterone in both sexes rose 2-3 years later than DHEA-S and DHEA. In female patients with premature adrenarche, higher plasma levels of DHEA-S and DHEA were found when compared to normal levels at similar chronological and bone ages. Very low plasma concentrations of DHEA-S and DHEA were obsrved in the patients with Addison's disease.