A novel diagnostic tool for the evaluation of hypothalamic-pituitary region and diagnosis of growth hormone deficiency: pons ratio.

Backgrounds Limitations in the evaluation of the pituitary size and changes according to pubertal status make its validity questionable. Recently, in a small-scale study, pons ratio (PR) has been suggested as a more sensitive tool for diagnosis and etiological evaluation of growth hormone deficiency (GHD). The aim of the study is to evaluate the diagnostic value of PR in the diagnosis of GHD. Methods We retrospectively evaluated the pituitary magnetic resonance imaging (MRI) of 133 patients with a diagnosis of GHD. Primary axis (PA) was assigned as a line crossing the mid-sagittal dorsum sella and fourth ventricle. PR was defined as the pons height above the PA divided by total pons height. The PR of patients with GHD was compared to subjects without GHD. Results Study included 133 patients with GHD and 47 controls. In total, 121 (91%) patients had isolated GHD and 12 (9%) patients had multiple pituitary hormone deficiency. The PR of the patient group (mean: 0.32 ± 0.89; range: 0.14-0.63) was significantly higher than controls (mean: 0.26 ± 0.067; range 0.19-0.44) (p: 0.000). The optimal cut-off value of PR for GHD diagnosis was 0.27 (sensitivity 71% specificity 56%). There was a negative correlation between anterior pituitary height (APH)-SDS and PR (p: 0.002; r: -0.27). APH was increased, but PR remained unchanged in pubertal patients (p: 0.089). Conclusions PR measurement is a noninvasive, practical method with a cost-benefit clinical value. As it is not affected by pubertal status, PR is potentially a more sensitive tool for evaluation of pituitary gland in GHD patients compared to APH.

Long-term, homologous prolactin, administered through ectopic pituitary grafts, induces hypothalamic dopamine neuron differentiation in adult Snell dwarf mice.

Pituitary prolactin (PRL) secretion is inhibited by dopamine (DA) released into the portal circulation from hypothalamic tuberoinfundibular DA (TIDA) neurons. Ames (df/df) and Snell (dw/dw) dwarf mice lack PRL, GH, and TSH, abrogating feedback and resulting in a reduced hypophysiotropic TIDA population. In Ames df/df, ovine PRL administration for 30 d during early postnatal development increases the TIDA neuron number to normal, but 30 d PRL treatment of adult df/df does not. The present study investigated the effects of homologous PRL, administered via renal capsule pituitary graft surgery for 4 or 6 months, on hypothalamic DA neurons in adult Snell dw/dw mice using catecholamine histofluorescence, tyrosine hydroxylase immunocytochemistry, and bromodeoxyuridine immunocytochemistry. PRL treatment did not affect TIDA neuron number in normal mice, but 4- and 6-month PRL-treated dw/dw had significantly increased (P < or = 0.01) TIDA (area A12) neurons compared with untreated dw/dw. Snell dwarfs treated with PRL for 6 months had more (P < or = 0.01) TIDA neurons than 4-month PRL-treated dw/dw, but lower (P < or = 0.01) numbers than normal mice. Periventricular nucleus (area A14) neuron number was lower in dwarfs than in normal mice, regardless of treatment. Zona incerta (area A13) neuron number was unchanged among phenotypes and treatments. Prolactin was unable to induce differentiation of a normal-sized A14 neuron population in dw/dw. Bromodeoxyuridine incorporation was lower (P < or = 0.01) in 6-month PRL-treated normal mice than in 6-month PRL-treated dwarfs in the subventricular zone of the lateral ventricle and in the dentate gyrus, and lower (P < or = 0.05) in 4-month untreated dwarfs than in 4-month untreated normal mice in the median eminence and the periventricular area surrounding the third ventricle. Thus, a PRL-sensitive TIDA neuron population exists in adult Snell dwarf mice when replacement uses homologous hormone and/or a longer duration. This finding indicates that there is potential for neuronal differentiation beyond early developmental periods and suggests plasticity within the mature hypothalamus.

Postnatal regression of hypothalamic dopaminergic neurons in prolactin-deficient Snell dwarf mice.

Both Snell (Pit-1(dw) or (dwj), dw/dw) and Ames (Prophet of Pit-1(df), df/df) dwarf mice fail to produce prolactin (PRL) as well as GH due to deficient transcription factor Pit-1 activity and have reduced numbers of hypothalamic PRL-inhibiting area A12 tuberoinfundibular dopaminergic (TIDA) neurons. It has been reported that the TIDA deficit in Ames dwarf mice develops postnatally as a reduction in number after an initial increase that is comparable to that of normal siblings. The present study was designed to characterize A12 TIDA neuronal development in the Snell dwarf (dw/dw) compared with littermate normal mice. Brains of normal (DW/?) and dw(j)/dw(j) mice were examined at 7, 14, 21, 30, and > or = 60 postnatal days (d) by catecholamine fluorescence and quantification of neuron number after tyrosine hydroxylase immunostaining in dopaminergic (DA) areas A12, A13 (medial zona incerta), and A14 (periventricular nucleus). Fluorescence was less in dw/dw than in DW/? A12 perikarya and median eminence but was not reduced in other DA areas, such as substantia nigra, at all ages; A12 fluorescence was virtually absent in Snell dwarf adults. Numbers of TIDA neurons were comparable in normal and Snell dwarf mice at 7 d. In normal (DW/?) mice, A12 neurons increased in number to adult levels at 14 d and were significantly higher than in Snell dwarf (dw/dw) mice at 14 d (P < 0.05) and at subsequent ages (P < 0.01). In Snell dwarf mice, numbers of A12 neurons did not differ at 7, 14, and 21 d, decreased at 30 d (P < 0.05), and reached, at 60 d, 23% of the population in normal sibling mice (P < 0.01 compared with earlier ages). Neuron numbers in nonhypophysiotropic DA area A13 did not vary with age or phenotype. In A14, cell number was higher in both phenotypes at 14 d (P < 0.05 for DW/?; P < 0.01 for dw/dw); neuron number was lower in dw/dw than in DW/? mice at 30 d (P < 0.05) and 60 d (P < 0.01). Thus, compared with normal mice of the same strain, the A12 deficit is more severe in Snell (dw/dw) than in Ames (df/df) dwarf hypothalamus (48% of DF/?), as previously reported, and develops as a decline from the population present at 7 d rather than first increasing. A reduction in A14 neuron number also occurs in the Snell dwarf. Treatment of DW/dw- and dw/dw-containing litters with ovine PRL (50 mug/d, ip), beginning at 12 or 7 d and continuing until 42 d, resulted in TIDA neuron numbers in Snell dwarfs that were lower than those in normal siblings (P < 0.01 for both) but were higher than in untreated adult dwarfs and comparable to the TIDA population size in dwarfs at 7 d, indicating that PRL maintained this maximal number and prevented TIDA neuron dedifferentiation, which occurs in dwarf postnatal development.

Reduced hypothalamic neuropeptide Y expression in growth hormone- and prolactin-deficient Ames and Snell dwarf mice.

Neuropeptide Y (NPY)-producing neurons in the hypothalamic arcuate nucleus (ARC) have been implicated in GH feedback in several studies in rats. Ames (df/df) and Snell (dw/dw) dwarf mice carry mutations in transcription factors Prop-1 and Pit-1, respectively, that abrogate detectable expression of GH, prolactin, and TSH. The present study was undertaken to determine whether and to what extent hypothalamic NPY neurons are affected by the lifelong absence of pituitary hormone feedback in hypopituitary Ames and Snell dwarf mice. Total ARC NPY mRNA levels were quantified using in situ hybridization, and numbers of ARC NPY-producing cells were quantified using immunocytochemistry. For in situ hybridization, dwarf and normal coronal brain sections were hybridized with 35S-labeled riboprobe complementary to rat NPY cDNA, and then analyzed for total signal intensity from the entire ARC for each animal as well as for mRNA per neuron. NPY-containing perikarya in ARC were counted in sections of colchicine-treated (intracerebroventricular) dwarf and normal mice. Total ARC NPY mRNA was reduced in df/df mice to 33.6% (P < 0.01) of that in normal littermates, and reduced in dw/dw mice to 46.3% (P < 0.05) of normals, but there was no difference in expression per neuron as determined by reduced silver-grain counting. The decrement in dwarf mice of total ARC NPY mRNA without reduction in mRNA per cell suggested a reduction in NPY-containing neuron number, which was the case as shown by immunocytochemistry. NPY neuronal number in adult Ames dwarf mice (1048 +/- 104) was significantly (P < 0.01) reduced to 68% of that in DF/df littermates (1536 +/- 73), and significantly (P < 0.05) reduced in Snell dwarf mice to 63% of normals (1138 +/- 137 vs. 1726 +/- 205). This study represents the first enumeration of NPY-producing neurons in mouse hypothalamus and the first demonstration of lower NPY neuron number in a hypopituitary model. The reduction in total NPY mRNA was greater than that reported in studies of GH-deficient rats, suggesting that NPY expression may be affected by the lifelong absence of prolactin or TSH or both, as well as GH.

Pattern-dependent suppression of growth hormone (GH) pulsatility by ghrelin and GH-releasing peptide-6 in moderately GH-deficient rats.

The peptide hormone ghrelin binds to the GH secretagogue receptor (GHS-R), stimulates GH secretion, and promotes adipogenesis. However, continuous GHS infusion does not stimulate skeletal growth and is associated with desensitization to further GH secretagogue treatment. In this study, 7-d intermittent (i.e. every 3 h) infusion of ghrelin, or the GH secretagogue, GH-releasing peptide-6, in the moderately GH- deficient transgenic growth-retarded rat, augmented GH secretion, leading to a sustained acceleration in skeletal growth. In contrast, continuous infusion of ghrelin, or GH-releasing peptide-6, suppressed the amplitude of spontaneous GH secretory episodes and produced only a transient increase in body weight gain. The reduction in GH secretion seen with continuous GHS-R activation was not associated with a desensitization of the pituitary to GH-releasing factor or to down-regulation of hypothalamic GHS-R mRNA expression. Continuous ghrelin treatment elicited an increase in somatostatin mRNA expression in the periventricular nuclei. Thus, exposure to continuously elevated circulating ghrelin may be responsible for the suppression of GH secretion reported in rats after prolonged starvation.

Autosomal dominant growth hormone deficiency disrupts secretory vesicles in vitro and in vivo in transgenic mice.

Autosomal dominant GH deficiency type II (IGHDII) is often associated with mutations in the human GH gene (GH1) that give rise to products lacking exon-3 ((Deltaexon3)hGH). In the heterozygous state, these act as dominant negative mutations that prevent the release of human pituitary GH (hGH). To determine the mechanisms of these dominant negative effects, we used a combination of transgenic and morphological approaches in both in vitro and in vivo models. Rat GC cell lines were generated expressing either wild-type GH1 (WT-hGH-GC) or a genomic GH1 sequence containing a G->A transition at the donor splice site of IVS3 ((Deltaexon3)hGH-GC). WT-hGH-GC cells grew normally and produced equivalent amounts of human and rGH packaged in dense-cored secretory vesicles (SVs). In contrast, (Deltaexon3)hGH-GC cells showed few SVs but accumulated secretory product in amorphous cytoplasmic aggregates. They produced much less rGH and grew more slowly than WT-hGH-GC cells. When cotransfected with an enhanced green fluorescent protein construct (GH-eGFP), which copackages with GH in SVs, WT-hGH-GC cells showed normal electron microscopy morphology and SV movements, tracked with total internal reflectance fluorescence microscopy. In contrast, coexpression of (Deltaexon3)hGH with GH-eGFP abolished the vesicular targeting of GH-eGFP, which instead accumulated in static aggregates. Transgenic mice expressing (Deltaexon3)hGH in somatotrophs showed an IGHD-II phenotype with mild to severe pituitary hypoplasia and dwarfism, evident at weaning in the most severely affected lines. Hypothalamic GHRH expression was up-regulated and somatostatin expression reduced in (Deltaexon3)hGH transgenic mice, consistent with their profound GHD. Few SVs were detectable in the residual pituitary somatotrophs in (Deltaexon3)hGH transgenic mice, and these cells showed grossly abnormal morphology. A low copy number transgenic line showed a mild effect relatively specific for GH, whereas two severely affected lines with higher transgene copy numbers showed early onset, widespread pituitary damage, macrophage invasion, and multiple hormone deficiencies. These new in vitro and in vivo models shed new light on the cellular mechanisms involved in IGHDII, as well as its phenotypic consequences in vivo.

Postnatal reduction in number of hypothalamic tuberoinfundibular dopaminergic neurons in prolactin-deficient dwarf mice.

Mice homozygous for the recessive 'Ames' dwarf mutation have undetectable serum or pituitary prolactin (PRL). Accompanying this pituitary deficiency is a marked reduction of dopamine (DA) and its rate-limiting synthetic enzyme tyrosine hydroxylase (TH) in PRL-regulating tuberoinfundibular hypothalamic neurons. In order to determine whether this deficit in adult Ames dwarf mice is congenital or arises postnatally, brains of dwarf (df/df) and normal (DF/?) littermate mice were assessed for TH immunoreactivity from 7 days through 2 months of age. Numbers of TH-positive neurons were counted in three hypothalamic DA areas: tuberoinfundibular A12, medial zona incerta A13, and anterior periventricular A14. There was an increase in the number of TH-positive neurons between 7 and 21 days of age in A12 and A14, but not in A13, for both DF/? and df/df mice. Between 21 days and 2 months of age, cell numbers were the same in all three areas in DF/? mice and in A13 and A14 in df/df mice. However, A12 TH-positive cell number in dwarfs decreased significantly (p < 0.01) between 21 days and 2 months, and was markedly lower (p < 0.001) in df/df than in DF/? mice at 2 months of age. The results emphasize the specificity of the dopaminergic neuron reduction in the Ames dwarf, which is restricted to the PRL-regulating tuberoinfundibular region. The data also indicate that the dwarf DA/TH deficit has an onset in late postnatal development, suggesting a response to absence of target PRL, rather than a primary hypothalamic effect of the dwarf mutation.

Evidence of a congenital midline brain anomaly in pituitary dwarfs: a magnetic resonance imaging study in 101 patients.

BACKGROUND: Magnetic resonance imaging (MRI) of the brain in pituitary dwarfs has revealed a previously unknown entity: ectopia of the posterior pituitary (PPE), absence or hypoplasia of the pituitary stalk and hypoplasia of the anterior pituitary. The pathogenesis of these findings was explained originally by a traumatic transection of the pituitary stalk during delivery. A high incidence of breech delivery has been reported in these groups, but the traumatic hypothesis cannot explain the findings in the relatively high percentage of patients with normal delivery, nor account for a different feature also found in other pituitary dwarfs consisting of pituitary hypoplasia with normal posterior pituitary. A second hypothesis could then been proposed, based on dysgenesis or abnormal embryonic development of both adenohypophysis and neurohypophysis. OBJECTIVE: To review the value and significance of these two different etiopathogenetic hypotheses by analyzing clinical, endocrinological, and MRI findings in a large population of pituitary dwarfs. METHODS: One hundred and one consecutive patients with congenital idiopathic growth hormone deficiency (CIGHD) were studied by MRI; they were compared with a control group of 46 healthy short children. A complete clinico-endocrinological evaluation was obtained in both patients and controls to assess the perinatal history, the pituitary-hypothalamic function, and the neurological status. MRI studies were evaluated both qualitatively and quantitatively and the pituitary volume (PV) was calculated in both patients and controls. Quantitative data were statistically analyzed to compare the mean PV of the patients with the mean PV of controls, the hormonal therapy, the single or multiple pituitary hormone deficiency, and the presence of breech delivery. RESULTS: MRI revealed PPE in 59 patients and a normal posterior pituitary (NPP) in 42. PV was extremely small in patients with PPE and in patients with NPP associated with a severely narrowed pituitary stalk; mean PV was significantly lower in CIGHD patients when compared with that of healthy short children. PV was not influenced by hormonal therapy and did not differ between patients with single and multiple pituitary hormone deficiency and between patients with normal and breech delivery. PPE patients differed from NPP patients for a higher male/female ratio (3:1 vs 1:1) and for a greater frequency of multiple pituitary hormone deficiency (49% vs 12%), breech delivery (32% vs 7%), and associated congenital brain anomalies (12% vs 7%). In PPE patients breech delivery was strongly associated with multiple pituitary hormone deficiency. CONCLUSION: On the basis of this study the traumatic hypothesis could theoretically explain the pathogenesis of PPE only in 32% of the patients with this condition. On the basis of modern understanding of embryogenesis of anterior and posterior pituitary, it is then justified to propose that a defective induction of mediobasal structure of the brain in the early embryo could account for both the complex morphological MRI abnormality and the clinico-endocrinological features encountered in all PPE patients. The close contiguity between the future pituitary and hypothalamus, the peculiar association with congenital midline brain anomalies, and the recent data about a possible role of Pit-1 gene, all support the hypothesis of a congenital defect. Finally, breech delivery can be considered not as a cause of PPE, but as an effect of the embryonic pituitary-hypothalamic abnormalities.