Morphological changes in the hypothalamic-hypophyseal-gonadal axis of male rats after twelve months of streptozotocin-induced diabetes

Taurine Recovers Testicular Steroidogenesis and Spermatogenesis in Streptozotocin-Induced Diabetic Rats

A great deal of investigations have verified that diabetic male reproductive impairment is associated with the dysfunction of testicular steroidogenesis and spermatogenesis resulted from insulin deficiency and hyperglycaemia-induced oxidative stress. It has been identified taurine is profitable for diabetes mellitus and diabetic implications through its insulin-like and islet cells protective activity. Furthermore, our previous studies found that taurine could increase testicular antioxidative ability, stimulate the endocrine activity of hypothalamic-pituitary-testicular axis, elevate testosterone level, raise sperm quality, suppress the deterioration of testicular function. Accordingly, we hypothesized that taurine may have beneficial effects on testicular dysfunction under diabetic mellitus status. Here, we investigated the effects of taurine on testicular steroidogenesis and spermatogenesis in streptozotocin (STZ)-induced type I diabetic rats. We observed that taurine treatment can markedly increase the body and testis weights, testicular SDH and G6PDH activities, decrease the serum fasting glucose concentration of diabetic rats. Serum contents of GnRH, LH, FSH, T, and testicular StAR, 3β-HSD, 17β-HSD mRNA expression levels were also obviously raised by taurine administration, indicating that taurine can improve testicular steroidogenesis in diabetic animals. Finally, we found taurine supplementation effectively elevated the sperm count and motility, reduced sperm abnormality, suggesting that taurine can increase the testicular spermatogenesis function of diabetic rat. In summary, the present data indicated that taurine can rescue the function of testicular steroidogenesis and spermatogenesis in STZ-induced type I diabetic rats possibly by increasing the endocrine activity of hypothalamic-pituitary-testicular axis.

Insulin and growth hormone-releasing peptide-6 (GHRP-6) have differential beneficial effects on cell turnover in the pituitary, hypothalamus and cerebellum of streptozotocin (STZ)-induced diabetic rats

Poorly controlled type1 diabetes is associated with hormonal imbalances and increased cell death in different tissues, including the pituitary, hypothalamus and cerebellum. In the pituitary, lactotrophs are the cell population with the greatest increase in cell death, whereas in the hypothalamus and cerebellum astrocytes are most highly affected. Insulin treatment can delay, but does not prevent, diabetic complications. As ghrelin and growth hormone (GH) secretagogues are reported to prevent apoptosis in different tissues, and to modulate glucose homeostasis, a combined hormonal treatment may be beneficial. Hence, we analyzed the effect of insulin and GH-releasing peptide 6 (GHRP-6) on diabetes-induced apoptosis in the pituitary, hypothalamus and cerebellum of diabetic rats. Adult male Wistar rats were made diabetic by streptozotocin injection (65 mg/kg ip) and divided into four groups from diabetes onset: those receiving a daily sc injection of saline (1 ml/kg/day), GHRP-6 (150 μg/kg/day), insulin (1-8U/day) or insulin plus GHRP-6 for 8 weeks. Control non-diabetic rats received saline (1 ml/kg/day). Diabetes increased cell death in the pituitary, hypothalamus and cerebellum (P<0.05). In the pituitary, insulin treatment prevented diabetes-induced apoptosis (P<0.01), as well as the decline in prolactin and GH mRNA levels (P<0.05). In the hypothalamus, neither insulin nor GHRP-6 decreased diabetes-induced cell death. However, the combined treatment of insulin+GHRP-6 prevented the diabetes induced-decrease in glial fibrillary acidic protein (GFAP) levels (P<0.05). In the cerebellum, although insulin treatment increased GFAP levels (P<0.01), only the combined treatment of insulin+ GHRP-6 decreased diabetes-induced apoptosis (P<0.05). In conclusion, insulin and GHRP-6 exert tissue specific effects in STZ-diabetic rats and act synergistically on some processes. Indeed, insulin treatment does not seem to be effective on preventing some of the diabetes-induced alterations in the central nervous system.

Reproductive axis function and gonadotropin microheterogeneity in a male rat model of diet-induced obesity

Obesity causes complex metabolic and endocrine changes that may lead to adverse outcomes, including hypogonadism. We herein studied the reproductive axis function in male rats under a high-fat diet and analyzed the impact of changes in glycosylation of pituitary LH on the bioactivity of this gonadotropin. Rats were fed with a diet enriched in saturated fat (20% of total calories) and euthanized on days 90 or 180 of diet. Long-term (180 days), high-fat feeding rats exhibited a metabolic profile compatible with insulin resistance and metabolic syndrome; they concomitantly showed decreased intrapituitary and serum LH concentrations, low serum testosterone levels, and elevated serum 17beta-estradiol concentrations. A fall in biological to immunological ratio of intrapituitary LH was detected in 180 days control diet-treated rats but not in high-fat-fed animals, as assessed by a homologous in vitro bioassay. Chromatofocusing of pituitary extracts yielded multiple LH charge isoforms; a trend towards decreased abundance of more basic isoforms (pH 9.99-9.0) was apparent in rats fed with the control diet for 180 days but not in those that were fed the diet enriched in saturated fat. It is concluded that long-term high-fat feeding alters the function of the pituitary-testicular axis, resulting in hypogonadotropic hypogonadism. The alterations in LH function found in these animals might be subserved by changes in hypothalamic GnRH output and/or sustained gonadotrope exposure to an altered sex steroid hormone milieu, representing a distinctly different regulatory mechanism whereby the pituitary attempts to counterbalance the effects of long-term obesity on reproductive function.

Sex steroid hormones in diabetes-induced sexual dysfunction: focus on the female gender

INTRODUCTION

Diabetes is associated with gender-specific changes in sex steroid hormones. However, the mechanisms responsible for these associations as well as the link to sexual dysfunction are not well understood.

AIM

To discuss key clinical and laboratory findings linking diabetes, sex steroid hormones, and sexual dysfunction, with particular focus on the female gender.

METHODS

A comprehensive literature review was conducted using the PubMed database. Search terms were used in appropriate combinations, including diabetes, insulin, insulin sensitivity, androgen, estrogen, sexual function, women, men, estrogen receptor, and androgen receptor. Over 400 citations were selected, based on topical relevance, and examined for study methodology and major findings.

MAIN OUTCOME MEASURES

Data from peer-reviewed publications.

RESULTS

Imbalances in sex steroid hormone levels are strongly associated with diabetes and this may negatively impact upon sexual function. Although numerous factors are likely to contribute to the development of diabetes and its complications, the role of sex steroid hormones must be acknowledged.

CONCLUSIONS

Research related to diabetic women and sexual dysfunction is severely lacking. Identifying underlying causes for a given hormonal imbalance in diabetic patients, as well as determination of genetic and age-dependent factors, will become important in identifying the subpopulations in which hormonal replacement regimens will be most effective. Investigation into treating diabetic patients with adjunct hormonal therapies or steroid hormone receptor modulators holds much promise.

Pituitary-testicular axis function, biological to immunological ratio and charge isoform distribution of pituitary LH in male rats with experimental diabetes

Men with insulinopenic diabetes mellitus frequently present hypogonadism and exhibit circulating luteinizing hormone (LH) molecules with increased biological activity. To further study this latter issue, we analyzed the pattern of isoform distribution and the impact of changes in terminal glycosylation of pituitary LH on the bioactivity of this gonadotropin in experimental diabetes. Adult male rats were treated with streptozotocin or vehicle and euthanized on days 30, 60, or 90 posttreatment. All diabetic groups exhibited a significant decrease in serum insulin and testosterone levels as well as in sperm count; serum gonadotropins and 17beta-estradiol decreased only after 90 days of insulinopenia. Both the immunoreactive concentrations and the biological to immunological ratio of intrapituitary LH significantly increased in all experimental groups, as assessed by an in vitro homologous bioassay in HEK-293 cells expressing a recombinant LH receptor. Chromatofocusing of pituitary extracts revealed the presence of multiple LH charge isoforms; the pH distribution profile of LH in diabetic and control rats was indistinguishable on days 30 and 60 posttreatment. By contrast, the abundance of more basic isoforms (pH 9.99-9.0) decreased and that of isoforms with pH values 8.99-8.0 increased in rats with long-standing diabetes compared to controls. It is concluded that experimental diabetes alters the function of the pituitary-testicular axis, resulting in reduced sex steroids levels and hypogonadotropism. Long-standing insulinopenia leads to a paradoxical accumulation of intrapituitary LH molecules enriched in bioactivity with altered terminal glycosylation, which are apparently subserved by distinct mechanisms involving altered hypothalamic and/or gonadal inputs on the gonadotrope.

Enhanced muscarinic M1 receptor gene expression in the corpus striatum of streptozotocin-induced diabetic rats

Acetylcholine (ACh), the first neurotransmitter to be identified, regulate the activities of central and peripheral functions through interactions with muscarinic receptors. Changes in muscarinic acetylcholine receptor (mAChR) have been implicated in the pathophysiology of many major diseases of the central nervous system (CNS). Previous reports from our laboratory on streptozotocin (STZ) induced diabetic rats showed down regulation of muscarinic M1 receptors in the brainstem, hypothalamus, cerebral cortex and pancreatic islets. In this study, we have investigated the changes of acetylcholine esterase (AChE) enzyme activity, total muscarinic and muscarinic M1 receptor binding and gene expression in the corpus striatum of STZ--diabetic rats and the insulin treated diabetic rats. The striatum, a neuronal nucleus intimately involved in motor behaviour, is one of the brain regions with the highest acetylcholine content. ACh has complex and clinically important actions in the striatum that are mediated predominantly by muscarinic receptors. We observed that insulin treatment brought back the decreased maximal velocity (Vmax) of acetylcholine esterase in the corpus striatum during diabetes to near control state. In diabetic rats there was a decrease in maximal number (Bmax) and affinity (Kd) of total muscarinic receptors whereas muscarinic M1 receptors were increased with decrease in affinity in diabetic rats. We observed that, in all cases, the binding parameters were reversed to near control by the treatment of diabetic rats with insulin. Real-time PCR experiment confirmed the increase in muscarinic M1 receptor gene expression and a similar reversal with insulin treatment. These results suggest the diabetes-induced changes of the cholinergic activity in the corpus striatum and the regulatory role of insulin on binding parameters and gene expression of total and muscarinic M1 receptors.

A short-term diabetes induced changes of catecholamines and p38-MAPK in discrete areas of rat brain

Chronic diabetes is associated with the alteration of second messengers and CNS disorders. We have recently identified that protein kinases (CaMKII and PKC-alpha) and brain neurotransmitters are altered during diabetes as well as in hyperglycemic and acidotic conditions. In this study, we investigated the effects of acute diabetes on the levels of dopamine (DA), norepinephrine (NE), epinephrine (E) and p38-Mitogen-Activated Protein Kinase (p38-MAPK) in striatum (ST), hippocampus (HC), hypothalamus (HT), midbrain (MB), pons medulla (PM), cerebellum (CB) and cerebral cortex (CCX). Alloxan (45 mg/kg) diabetic untreated rats that showed hyperglycemia (>260 mg%), revealed significant increases of DA level in ST (1.5 fold), HC (2.2 fold) and PM (2.0 fold) and the E level also found to be increased significantly in HT (2.4 fold), whereas the NE level was decreased in CB (0.5 fold), after 7 days of diabetes. Immunoblotting study of p38-MAPK expression under identical conditions showed significant alterations in ST, HC, HT and PM (p<0.05) correlated with the changes of catecholamines (DA and E). On the other hand, the above changes were reversed in insulin-treated diabetic rats maintained under normal glucose level (80 -110 mg %). These results suggest that p38-MAPK may regulate the rate of either the synthesis or release of DA and E in corresponding brain areas, but not NE, under these conditions.

PKC-alpha mediated alterations of indoleamine contents in diabetic rat brain

We previously have reported that acute or chronic diabetes in animals resulted in altered neurotransmitter levels. In this study, we investigated the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in discrete areas of brain viz. striatum (ST), hippocampus (HC), hypothalamus (HT), midbrain (MB), pons medulla (PM), cerebellum (CB) and cerebral cortex (CCX) of control, untreated diabetic and insulin treated diabetic rats after 30 days. Alloxan (45 mg/kg) diabetic untreated rats, which showed hyperglycemia (>250 mg%), revealed significant increases of 5-HT level in ST, MB, PM, CB and CCX and the 5-HIAA level found to be increased significantly in ST, HC and MB. Whereas the insulin treated rats, which was maintained under normal glucose level (80-110 mg%), showed no significant changes in any of the areas studied. The expressions of PKC-alpha studied by immunoblotting also showed significant changes in ST, HC, MB, PM, CB and CCX that is identical to the changes of both 5-HT and 5-HIAA under similar condition, suggesting that the PKC-alpha may regulate the synthesis and release of indoleamines in diabetic animals.

Streptozotocin-induced diabetic effects on spermatogenesis with proliferative cell nuclear antigen immunostaining of adult rat testis

OBJECTIVE

To examine the histopathological effects of diabetes on spermatogenesis and to detect the proliferation of germ cells with proliferative cell nuclear antigen (PCNA).

DESIGN

Controlled experimental study.

SETTING

The animal laboratory of the Experimental Surgery Center of Ege University, Izmir, Turkey.

ANIMAL(S)

Ten nondiabetic (control) and 20 diabetic adult male albino rats.

INTERVENTION(S)

The rats were IP injected with 40 mg/kg streptozotocin for 5 days to create a diabetic condition that was confirmed by testing blood glucose levels 5-7 days after the first injection.

MAIN OUTCOME MEASURE(S)

Mean testicular diameter, mean semniferous tubuli diameter (MSTD), and PCNA index.

RESULT(S)

Six weeks after the streptozotocin injection, both the mean testicular and the seminiferous tubuli diameters were significantly decreased in diabetic rats compared with the control group.

CONCLUSION(S)

The effects of diabetes on spermatogenesis can be clearly detected as a decrease in testicular diameter, MSTD, and PCNA index.

Lifetime reproduction of giant transgenic mice: the energy stress paradigm

Lifetime reproduction of female transgenic rat growth hormone (TRrGH) mice and their normal siblings was evaluated on a high-protein (38%) diet, a standard diet (23% protein), and the standard diet supplemented with sucrose cubes. Compared with those on the standard diet, normal mice fed the high-protein diet showed significant increases in litter size, number of litters, and lifetime fecundity. Number of litters and lifetime fecundity were also enhanced in normal mice fed sucrose. TRrGH mice showed no significant improvements in reproduction on the high-protein diet, but they were significantly smaller. Sucrose dramatically improved reproduction of TRrGH mice, with no reduction in mature mass. The percentage of fertile TRrGH mice increased from 45% on standard chow to 71% with sucrose. The number and size of litters of TRrGH mice also significantly increased with sucrose, mean lifetime fecundity doubling from 9 pups on standard food to 18 pups on sucrose. However, TRrGH mice did not attain the reproductive success of normal mice on any diet. These results suggest that TRrGH mice are energetically stressed by enforced channelling of energy into growth. An immense literature addresses infertility due to energy limitation and stress generally. We synthesize these aspects with growth hormone transgenesis to derive an integrated view of neuroendocrine energy regulation relevant to restoring fertility of transgenic GH animals.

LHRH receptors and LHRH receptor-bearing cells in pituitaries of streptozocin diabetic male rats

Streptozocin (STZ)-diabetic rats have low hypothalamic luteotropic hormone-releasing hormone (LHRH) secretion and various alterations of gonadotrope cells, among which low luteotropic hormone (LH) secretion. Possible causes for the gonadotrope disorders may be low hypothalamic LHRH secretion alone or combined with reduced (a) number of LHRH receptor sites, or (b) receptor to ligand affinity, or (c) of LHRH receptor-bearing cells. To clarify this question we determined by saturation and competition binding Bmax, KD and KA of the LHRH receptor sites and counted the receptor-bearing cells in pituitary glands of control and STZ-diabetic adult male rats. We found a single receptor class, the Bmax was strongly reduced in diabetic animals whereas both KD and KA were similar in the two groups. The number of LHRH receptor-bearing cells in diabetic animals was increased. Therefore a reduced number of receptor sites per gonadotrope cell occurs in our model. Since in the STZ-diabetic male rats the number of gonadotropes is increased, a higher number of receptor-bearing cells was observed. We conclude that the reduced LH secretion from the diabetic pituitary gland might be due to a reduced number of LHRH receptor sites in the pituitary gland. The increased number of receptor-bearing cells might partially compensate for this change.

Tuberoinfundibular dopaminergic neurons and lactotropes in young and old female rats

Aging in female rats is accompanied by several endocrine dysfunctions, such as reproductive decline associated with characteristic hyperprolactinemia, lactotrope hyperplasia, and functional impairment of hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons. The aim of this morphometrical, immunocytochemical, and densitometrical study was to gain a better anatomical knowledge of TIDA neurons and axons as well as of lactotropes in old female rats with (A) or without (NA) pituitary adenomas, compared with young animals. At the hypothalamic level, we found that tyrosine hydroxylase (TH)-labeled neurons in the arcuate nucleus were comparable in young and old NA yet their size and TH-content were increased in A animals. Also the TH-labeled median eminence axons did not differ significantly between young and old NA but were more numerous in the old A rats. Independently from adenomas, both number of prolactin (PRL)-labeled structures and content of immunoreactive PRL were increased in pituitaries of old rats, the plasma PRL levels, however, were high only in A. Our findings support the documented lactotrope hypertrophy and hyperplasia in old female rats and suggest that TIDA-neuron changes only occur in hyperprolactinemic animals carrier of adenomas.

The age at onset of diabetes influences functional and structural changes in the pituitary-thyroid axis of streptozocin-diabetic male rats

Severe structural changes leading to marked alterations in secretory activity are known to occur in the pituitary-thyroid axis 1 month after induction of postpuberal streptozocin (SZ)-diabetes. However, SZ-diabetic rats of different age groups have not been compared, nor has the maturity of the pituitary and thyroid glands at the onset of diabetes been correlated with the type and evolution of functional and structural changes. We thus induced diabetes in 1-month (prepuberal of 3-month (postpuberal) old male rats and compared diabetic with control groups 4 and 8 months after SZ or saline injection. We determined: 1) pituitary and thyroid weights, 2) the basal plasma TSH, T3, and T4 concentrations, and 3) several morphometrical measurements in the pituitary and thyroid glands. After 4 months, 1) the pituitary and thyroid weights were decreased, 2) plasma TSH and T3 were unchanged, plasma T4 was reduced. and 3) the number of thyrotropes, degenerative changes of follicle cells, and colloid area were increased, the follicle cell height as well as the number of fused cold follicles decreased, and the follicle area was unchanged in diabetic compared with control rats. The lesions were more conspicuous in pre- than in postpuberal diabetic animals. After 8 months, plasma TSH, T3, and T4 were decreased in diabetic compared with control rats. Except for the increased colloid area, all other lesions were similar, though more severe in prepuberal diabetic rats after 8 than 4 months. Few changes were found in postpuberal diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Testicular alterations in the nonobese diabetic mouse

The nonobese diabetic (NOD) mouse was used as a model for evaluating alterations in testicutar structure. The NOD mouse exhibits diabetic manifestations on an apparently autoimmune basis and thus resembles human type 1 insulin-dependent diabetes mellitus. Testicular samples were obtained from animals with and without diabetic manifestations at various ages. The principal changes noted on histological examination were in the seminiferous tubules, including germ cell degeneration, disruption of spermatogenesis, tubular fibrosis, and intratubular calcification. These effects were diffuse and extensive in animals with severe hyperglycemia. In those with normal and borderline elevated glucose levels, focal tubular damage was found to occur in a patchy distribution. The changes included disorganization of maturation, malorientation of spermatids, and hypospermatogenesis. Electron microscopic studies also indicated effects on Sertoli cells and the peritubular tissue. There was no evidence of mononuclear cell infiltration or vascular abnormalities in any of the testicular specimens. The findings indicate that the NOD mouse may be a useful model for understanding the development of pathological changes in the testis in insulin-dependent diabetes.

Hypogonadotropic secondary amenorrhea in diabetes: effects of central opiate blockade and improved metabolic control

The effect of improving diabetic control on secondary hypogonadotropic amenorrhea was investigated in patients with insulin-dependent diabetes mellitus (IDDM). Second, the hypothesis that increased central (hypothalamic) opiate inhibition may have been responsible for the suppression of gonadotropin-releasing hormone (GnRH) was tested by observing the effect of a four-hour naloxone infusion (1.4 mg/hour) on serum gonadotropin levels. All known causes of secondary amenorrhea were excluded before patients were eligible for the study. The median duration of amenorrhea was six years, and median body weight was 101 percent of ideal. After six months of improved metabolic control (n = 5) using intensified conventional therapy or continuous subcutaneous insulin infusion, the level of glycosylated hemoglobin dropped from 11.8 +/- 0.9 percent to 8.5 +/- 0.5 percent (p less than 0.005), and body weight increased from 60.5 +/- 1.8 kg to 64.7 +/- 1.4 kg (p less than 0.02). Menses did not, however, return in any patient. There was no significant change in serum levels of estradiol, progesterone, dihydroxyepiandrosterone, testosterone, prolactin, basal or GnRH-stimulated luteinizing hormone, or follicle-stimulating hormone. There was no change in the levels of luteinizing hormone or follicle-stimulating hormone during the naloxone infusion either during poor metabolic control or after six months of improved metabolic control. In conclusion, a form of secondary hypogonadotropic amenorrhea was identified in patients with IDDM that did not remit with sustained improvements in metabolic control. It did not appear to be mediated through increased central opiate tone.

Thyroid and pituitary secretory disorders in streptozotocin-diabetic rats are associated with severe structural changes of these glands

Streptozotocin diabetes in rats is associated with reduced function of the hypothalamo-pituitary-thyroid axis. The structure and hormone secretion of the thyroid and pituitary glands were studied in adult male rats 1 month after streptozotocin injection. The thyroid of diabetic rats was characterized by decreased follicle area and epithelial thickness. By electron microscopy, thyroid epithelial cells were characterized by flattened and almost empty rough endoplasmic reticulum cisternae, scanty exocytotic apical and endocytotic vesicles as well as degenerate mitochondria and rough endoplasmic reticulum. By immunohistochemistry, intracolloidal thyroglobulin and T3 as well as intraepithelial thyroglobulin were reduced. Electron microscopic and immunohistochemical analysis of pituitary glands showed that in diabetic rats thyrotrophs were mostly of type II, and the number of thyrotrophs (type I + type II) was greater than in controls. By radioimmunoassay (RIA), plasma T3, T4, and TSH levels were markedly reduced, and the TSH response to TRH was deficient in diabetic animals. The pituitary TSH concentration was increased, as expected from the morphological data. This study demonstrates severe structural changes in the thyroid and pituitary glands of diabetic rats which are accompanied by marked alterations of their secretory activity.

Morphometry and cytochemistry of Leydig cells in experimental diabetes

Leydig cell ultrastructure and function in diabetic rats were studied by concurrent cytochemistry, morphometry, and testosterone assay. The streptozotocin (Stz) model was modified to include nondiabetic Stz-injected rats, an insulin-treated diabetic group, and semistarved animals in addition to controls and untreated diabetic rats. The separation of the effects of diabetes, Stz, semistarvation, and insulin treatments was achieved by application of orthogonal contrast statistics. After 3 months of treatments, testes were perfusion-fixed, incubated for delta 5,3 beta-hydroxysteroid dehydrogenase (HSD) activity, and processed for electron microscopy. Diabetes increased Leydig cell smooth endoplasmic reticulum (SER), increased mitochondrial and lipid content, decreased HSD staining, and decreased serum testosterone levels. Insulin treatment reduced SER and increased testosterone concentrations. Semistarvation also increased SER and reduced testosterone levels but did not alter HSD staining. Stz had no significant effect on these variables. The results suggested that the hypoandrogen state was due to a primary Leydig cell compromise and not solely to malnutrition and that it was correctable by insulin treatment.

The changes in the hypothalamo-pituitary-gonadal axis of streptozotocin-treated male rats depend from age at diabetes onset

The influence of age at diabetes onset and of capillary microangiopathy on the severity and evolution of hypothalamo-pituitary-gonadal changes was studied morphologically and morphometrically in male rats 4 and 8 months after streptozotocin injection. At each time period we studied 2 groups of rats, one made diabetic before (age 1 month), the other after puberty (age 3 months), and compared them with corresponding controls. The size of hypothalamic axons, numerical density and size of pituitary gonadotrophs, size of testicular tubules, and basement membrane thickness of retinal capillaries were measured. Major differences were found at 8 months. Changes of pituitary glands (i.e. small and numerous gonadotrophs) and testes (i.e. small tubular size) were more important in pre- than in postpubertal diabetic rats. This was a consequence of the aggravating prepubertal diabetes between 4 and 8 months. On the contrary, these changes partially regressed in postpubertal diabetic animals. Pituitary and testicular changes were correlated. Other lesions, such as swollen axonal processes in the hypothalamus, increased thickness of seminiferous epithelium and of capillary basement membranes, though very evident in diabetics, were independent from age at induction. Neither microangiopathy nor glycemia were correlated with any other change which confirmed their secondary role in diabetic neuroendocrine disorders. Thus, two types of diabetic disorders of the hypothalamo-pituitary-gonadal axis could be distinguished: 1) those with irreversible effects on immature yet partially reversible effects on mature structures; and 2) those independent from age at induction.

The effect of streptozotocin-induced diabetes on the neuroendocrine-male reproductive tract axis of the adult rat

Studies in the streptozotocin rat model for diabetes mellitus suggest that sexual dysfunction in these animals may result from diabetes-induced alterations of the neuroendocrine-reproductive tract axis. Our investigation was performed to better define the effects of diabetes on the neuroendocrine sex accessory organ axis in the male rat. Rats were rendered diabetic, and were either left untreated or treated with insulin, testosterone or both. Diabetes resulted in decreased body and reproductive organ weights, as well as diminished sperm counts and motility and prostatic acid phosphatase. Seminal fructose was increased. A significant decrease in serum LH, FSH and testosterone was noted. Insulin treatment of the diabetic rats restored serum gonadotropins, reproductive organ weight, sperm counts and motility, and seminal fructose to control levels. Prostatic weight and prostatic acid phosphatase levels remained abnormal. Testosterone restored the above mentioned parameters to control levels, with the exception of LH. Treatment with insulin and testosterone had a synergistic effect on spermatogenesis. A GnRH stimulation test demonstrated that pituitaries of diabetic animals had a blunted response, with diminished LH and FSH secretion. In the diabetic animal, there are both pituitary and testicular abnormalities which may be responsible for reproductive dysfunction.

Biochemical and histochemical studies on the pituitary-testicular axis in obese (C57Bl/6J-ob/ob) mice

Male C57Bl/6J-ob/ob mice (4 months old) and their homozygous lean controls were compared with respect to pituitary LH secretion and functional parameters of purified Leydig cells in vitro. Compared with controls, obese mice showed reductions in the following parameters: Plasma testosterone levels (reduced by 57%), hCG-stimulated testosterone formation in vitro (by 31%), conversion of progesterone to androgens by Leydig cells (by 39%), and GnRH-stimulated LH secretion (by 26%). Lipid accumulation and a 37% decrease in naphthylesterase activity in the Leydig cells as well as hyperplasia of pituitary gonadotrophs were observed histochemically in obese mice. The changes in testicular endocrine function in obese mice are interpreted as consequences of pituitary dysfunction.

Hypothalamic and cortical neurons of normotensive and spontaneously hypertensive rats are differently affected by streptozotocin diabetes

Diabetic encephalopathy is a relatively frequent late complication in human and experimental diabetes mellitus. Although it is generally assumed that microangiopathy plays a major role in its pathogenesis, many aspects of the latter are still poorly understood. To detect possible correlations between vascular and cellular changes, we examined in normotensive and spontaneously hypertensive streptozotocin diabetic rats the neurons of hypothalamic and cortical regions in which the capillary basement membrane thickness had been known from a previous study. Arcuate and ventromedial nucleus neurons of normotensive diabetic rats compared to those of corresponding controls showed a reduced cytoplasmic area after 4 but not after 8 months of experiment. No difference was found between hypertensive control and diabetic rats after either 4 or 8 months of experiment. After the 8th month cortical neurons of normotensive controls were smaller in an occipital than in a frontal region and within the same region in the following layer order: deep less than superficial less than intermediate. Neurons of hypertensive controls behaved comparably yet were generally smaller than those of normotensive controls in each corresponding region. Compared to those of control, cortical neurons of normotensive diabetic rats were smaller in superficial and deep layers of both regions and in the intermediate layer of the frontal region. Hypertension appeared to antagonize diabetes. Despite an arcuate nucleus microangiopathy found in rats from both strains after 4 and 8 months of diabetes, neuronal changes were seen only in normotensive animals after 4 months. In the intermediate cortical layer, where microangiopathy was most marked after 8 months of experiment, neurons were not or only slightly reduced in size.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in the prolactin secretion in streptozotocin-induced diabetic rats. Correlation with pituitary and hypothalamus estradiol receptors

The present study examined the effects of streptozotocin-induced diabetes on prolactin (Prl) secretion and its correlation with estrogen receptor levels in the anterior pituitary and hypothalamus. Prl was measured in adult ovariectomized rats and after estradiol treatment (10 micrograms estradiol benzoate (Eb) 48, 24 and 1 h before experiments) or acute TRH administration (4 micrograms/kg body weight). Substantial decreases in estradiol- and TRH-induced Prl release were observed in diabetic rats. Insulin therapy was able to restore this response. Measurement of nuclear estradiol receptors by exchange assay in the pituitary of Eb-treated rats revealed a significant reduction in receptor levels in the diabetic group and a restoration to normal values in insulin-treated diabetic rats. Similar results were obtained by measuring total pituitary receptor content (cytosolic plus nuclear receptors). No significant changes were observed in nuclear hypothalamic estradiol receptors. However, the number of total hypothalamic estradiol receptors was diminished in diabetic rats although the translocation was proportionally greater in these animals. These results indicate that the disrupted reproductive functions described in streptozotocin diabetic rats may be due, at least in part, to deficiencies in Prl secretion and pituitary estradiol action.

Effect of streptozotocin-induced diabetes on insulin binding parameters in adult rat testis

Insulin binding parameters have been measured in testicular membranes of streptozotocin diabetic male rats. Insulin binding decrease was ascribed to the well-known depressing effect of diabetes mellitus on circulating luteinizing hormone (LH). Because both LH and insulin receptors are modulated by pituitary LH and because of their reduction in testes of diabetic rats, we conclude that Leydig cell dysfunction is a secondary disorder associated with this complex metabolic condition.

Testicular function and glycemic control in diabetic men. A controlled study

We have investigated testicular function in 28 insulin-dependent diabetic men under the age of 50 years and 119 age-matched controls. Diabetics had reduced testicular volume, semen volume, total and total motile sperm output while plasma LH and FSH levels were elevated. Reduction in semen volume and impotence were more common in long-standing complicated diabetes. Glycosylated hemoglobin (GHb) levels were positively correlated with plasma LH levels (r = 0.46, p less than 0.02) but there was no direct correlation of glycemic control and spermatogenesis. The differences in testicular function were due to decreased spermatogenesis and could not be explained by other forms of testicular pathology or the presence of diabetic neurovascular complications. We conclude that the function of the hypothalamic pituitary testicular axis is impaired in diabetic men, that this impairment is at least partly related to the degree of preceding glycemic control and that multiple levels of the axis may be dysfunctional.

Effect of growth hormone-releasing stimuli in streptozotocin diabetic rats

The dynamics of growth hormone (GH) secretion in response to different GH secretagogues has been studied in adult freely moving male rats one month after induction of diabetes by single i.v. injection of streptozotocin (60 mg/kg). Baseline plasma GH concentrations and pituitary GH content were not different in streptozotocin-diabetic (St-D) rats and controls. Clonidine (0.15 mg/kg i.v.), an alpha 2-adrenergic agonist, failed to evoke GH release in St-D rats. Substitution therapy with insulin (1 IU/100 g b.wt.daily) delivered through subcutaneously implanted minipumps, allowed re-institution of a normal GH responsiveness to clonidine. At odds with clonidine, FK 33-824 (0.1 mg/kg i.v.), a potent analog of the opioid peptide Met-enkephalin, induced a similar rise in plasma GH levels in control and St-D rats. Finally, administration of a synthetic replicate of a GH-releasing hormone of human pancreatic origin, hpGRF-40 (2.5 micrograms/kg i.v.) elicited a higher GH response in St-D rats than in controls. These data indicate that in St-D rats: (1) an impaired function of noradrenergic pathways controlling GH release is present; (2) contrary to previous beliefs, an alpha 2-adrenergic mechanism is not involved in the GH-releasing effect of opioid peptides; and (3) pituitary GH responsiveness to hpGRF is increased.

Feedback effects of steroids and gonadotrophin control in adult rats with streptozotocin-induced diabetes mellitus

The effects of long-and short-term streptozotocin-induced diabetes mellitus on the control of gonadotrophin secretion have been investigated in adult intact rats. A high dose of streptozotocin (80 mg/kg), administered intraperitoneally 3 days before experimentation, inhibited ovulation and reduced the pituitary luteinizing hormone response to luteinizing hormone releasing hormone in proestrous rats. A lower dose (40 mg/kg) did not inhibit ovulation but abolished the luteinizing hormone releasing hormone-priming effect on the pituitary which normally occurs on proestrus, prior to ovulation. Oestrous cyclicity was lost when diabetes was induced for 14 or 56 days, but there was no effect on pituitary responsiveness to luteinizing hormone-releasing hormone compared with control animals. Similar observations were made with rats placed on a food-restricted diet. In all experiments there was no difference between diabetic and control animals in the pituitary luteinizing hormone content, the hypothalamic content of luteinizing hormone-releasing hormone or the ovarian weights. Ovariectomized rats treated with streptozotocin (40 mg/kg) were used to investigate the effects of diabetes on steroid feedback mechanisms. There was an attenuated luteinizing hormone response to ovariectomy in diabetic compared with control animals, and an impaired positive feedback effect of progesterone in oestrogen-primed animals. The results show that streptozotocin-induced diabetes mellitus inhibits feedback action of gonadal steroids and this could account for both the loss of oestrous cyclicity and the reduced pituitary sensitivity to luteinizing hormone-releasing hormone.

Basement membrane of hypothalamus and cortex capillaries from normotensive and spontaneously hypertensive rats with streptozotocin-induced diabetes

Basement membrane (BM) thickness of hypothalamic arcuate nucleus capillaries was measured in normotensive (WKY) and hypertensive (SHR) rats 4 and 8 months after streptozotocin or saline injection. Three groups were studied: controls (C), diabetics (D), and animals with impaired glucose tolerance (L). For comparison, BM thickness of cortical capillaries of an occipital and a frontal area was measured in three different layers starting from the pial surface. Independently from strain, hypothalamic capillary BM was thicker in older than in younger animals. At both 4 and 8 months, BM thickness was lowest in C, highest in D, and intermediate (between C and D) in L. Hypertension combined with diabetes did not further increase BM thickness. In both C and D no difference was found between the two cortical areas. The BM thickness of C increased from the superficial to the deep layer. In C hypertension induced BM thickening in the superficial frontal and the deep occipital layer. In the intermediate and the deep layer of the frontal area BM was thicker in WKY-D than in WKY-C. In every layer BM was thicker in SHR-D than in corresponding controls. Hypertension combined with diabetes enhanced BM thickening in the intermediate and the deep layer of the frontal and in the intermediate layer of the occipital area. Degenerative changes occurred in hypothalamic and cortical pericytes. These changes were more frequent in hypertensive than in normotensive animals. In conclusion, a microangiopathy characterized by BM thickening and pericytic degeneration occurs in the brain of diabetic animals. Its intensity and enhancement by a concomitant hypertension vary from hypothalamus to cortex.

Light microscopic histochemistry on plastic sections

As compared with conventional paraffin, celloidin, and frozen sections, semithin plastic sections offer a superior quality of the light microscopic image in terms of better resolution, absence of distortion and shrinkage artifacts, and suitability for calcified tissues. Application of histochemical methods to such sections often encounters, however, serious difficulties resulting from a considerably reduced reactivity of plastic-embedded biological material. Factors involved include a poor penetration of reagents into plastic embedding media due to a steric or hydrophobic hindrance, as well as a blockade of the reactive chemical groups in the sample due to interactions with fixatives and plastics. Embedding in polar (hydrophilic) plastics, such as glycol methacrylate, permits carrying out a large number of histochemical reactions, including the demonstration of enzymatic activities, directly on sections, but is less suitable for combined light/electron microscopic studies because of an imperfect ultrastructural preservation of tissues. Embedding in nonpolar epoxy resins, particularly if combined with a double aldehyde-osmium fixation, results in a high quality ultrastructure but almost fully inhibits the histochemical reactivity of the embedded material. In order to restore this reactivity, i.e. to unmask chemical groups bound by the polymerized resin, semithin epoxy sections require the removal of the embedding matrix by alkoxides prior to the histochemical procedure. Additional steps are also often necessary: treatment of osmium-fixed sections with oxidative agents, e.g., hydrogen peroxide or periodate which reoxidize the bound osmium and remove it from tissue, and a controlled proteolytic digestion, especially useful in immunocytochemical studies, which probably cleaves the bonds between the primary aldehyde fixative, and the reactive sites. This article reviews histochemical methods which have been successfully applied to plastic-embedded material. Using polar methacrylates and/or nonpolar epoxy resins as embedding media, it has been possible to demonstrate proteins and aminoacid residues, carbohydrates, lipids, nucleic acids, biogenic amines, inorganic ions, and some enzymes, although the spectrum of methods found as suitable for plastic-embedded material is far narrower than that available for paraffin or frozen sections.(ABSTRACT TRUNCATED AT 400 WORDS)

Circumventricular organs: receptors and mediators of direct peptide hormone action on brain

The concept of the brain as an endocrine target organ is not new, nor is it novel to consider the circumventricular organs as receptive regions of the brain for circulating substances. However, in this review we have emphasized the relatively novel concept that CVOs mediate exclusively the direct feedback actions of circulating peptide hormones on brain function. In addition we have presented speculations concerning the neural mechanisms by which signals arising from peptide hormone-receptor interaction might be relayed into the CNS, and indicated the possible involvement of CVO receptors in endocrine disorders. We hope that this analysis provides a conceptual framework for evaluating the functional relationship of circulating peptides to brain and inspires interest in this fascinating area of neuroendocrinology.