Altered hypothalamic-pituitary function in the adult female rat with streptozotocin-induced diabetes

Toxicological effects of the Curatella americana extract in embryo development of female pups from diabetic rats

Maternal diabetes can influence the development of offspring during fetal life and postnatally. Curatella americana is a plant used as a menstrual cycle regulator and to prevent diabetes. This study evaluates the effects of C. americana aqueous extract on the estrous cycle and preimplantation embryos of adult female pups from diabetic rats. Female Sprague Dawley newborn rats received Streptozotocin or vehicle (citrate buffer). At adulthood, were submitted to the Oral Glucose Tolerance Test, and mated. The female rats were obtained and were distributed into four experimental groups: OC and OC/T represent female pups of control mothers and received water or plant extract, respectively; OD and OD/T represent female pups of diabetic mothers and received water or plant extract, respectively. The estrous cycle was followed for 10 days, the rats were mated and on gestational day 4 was performed preimplantation embryo analysis. Phenolic composition and biogenic amines in the extract were analyzed about the influence of the thermal process. The female pups from diabetic dams exhibited glucose intolerance, irregular estral cycle and a higher percentage of pre-embryos in delayed development (morula stage). After C. americana treatment, OD/T group no present a regular estrous cycle. Furthermore, the infusion process increases phenolic compounds and biogenic amines levels, which can have anti-estrogenic effect, anticipates the early embryonic development, and impair pre-implantation embryos. Thus, the indiscriminate use of medicinal plants should be avoided in any life phases by women, especially during pregnancy.

Effects of high-fat diet-induced obesity and diabetes on Kiss1 and GPR54 expression in the hypothalamic-pituitary-gonadal (HPG) axis and peripheral organs (fat, pancreas and liver) in male rats

Recent data indicates that kisspeptin, encoded by the KISS1 gene, could play a role in transducing metabolic information into the hypothalamic-pituitary-gonadal (HPG) axis, the mechanism that controls reproductive functions. Numerous studies have shown that in a state of negative energy balance, the hypothalamic kisspeptin system is impaired. However, data concerning positive energy balance (e.g. diabetes and obesity) and the role of kisspeptin in the peripheral tissues is scant. We hypothesized that: 1) in diet-induced obese (DIO) male rats and/or rats with diabetes type 1 (DM1) and type 2 (DM2), altered reproductive functions are related to an imbalance in Kiss1 and GPR54 mRNA in the HPG axis; and 2) in DIO and/or DM1 and/or DM2 rats, Kiss1 and GPR 54 expression are altered in the peripheral tissues involved in metabolic functions (fat, pancreas and liver). Animals were fed a high-fat or control diets and STZ (streptozotocin - toxin, which destroys the pancreas) was injected in high or low doses to induce diabetes type 1 (DM1) or diabetes type 2 (DM2), respectively. RT-PCR and Western blot techniques were used to assess the expression of Kiss1 and GRP54 in tissues. At the level of mRNA, we found that diabetic but not obese rats have alterations in Kiss1 and/or GPR54 mRNA levels in the HPG axis as well as in peripheral tissues involved in metabolic functions (fat, pancreas and liver). The most severe changes were seen in DM1 rats. However, in the case of protein levels in the peripheral tissues (fat, pancreas and liver), changes in Kiss1/GPR54 expression were noticed in DIO, DM1 and DM2 animals and were tissue-specific. Our data support the hypothesis that alterations in Kiss1/GPR54 balance may account for both reproductive and metabolic abnormalities reported in obese and diabetic rats.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

The Deep Correlation between Energy Metabolism and Reproduction: A View on the Effects of Nutrition for Women Fertility

In female mammals, mechanisms have been developed, throughout evolution, to integrate environmental, nutritional and hormonal cues in order to guarantee reproduction in favorable energetic conditions and to inhibit it in case of food scarcity. This metabolic strategy could be an advantage in nutritionally poor environments, but nowadays is affecting women's health. The unlimited availability of nutrients, in association with reduced energy expenditure, leads to alterations in many metabolic pathways and to impairments in the finely tuned inter-relation between energy metabolism and reproduction, thereby affecting female fertility. Many energetic states could influence female reproductive health being under- and over-weight, obesity and strenuous physical activity are all conditions that alter the profiles of specific hormones, such as insulin and adipokines, thus impairing women fertility. Furthermore, specific classes of nutrients might affect female fertility by acting on particular signaling pathways. Dietary fatty acids, carbohydrates, proteins and food-associated components (such as endocrine disruptors) have per se physiological activities and their unbalanced intake, both in quantitative and qualitative terms, might impair metabolic homeostasis and fertility in premenopausal women. Even though we are far from identifying a "fertility diet", lifestyle and dietary interventions might represent a promising and invaluable strategy to manage infertility in premenopausal women.

Neuronal basis of reproductive dysfunctions associated with diet and alcohol: From the womb to adulthood

The theory that individuals are born as tabula rasa and that their knowledge comes from experience and perception is no longer true. Studies suggest that experience is gained as early as in the mother's womb. Moreover, environmental stressors like alcohol or inadequate diet can affect physiological systems such as the hypothalmic-pituitary-gonadal (HPG) axis. The effects of these stressors can manifest as alterations in sexual development and adult reproductive functions. In this review, we consider and compare evidence from animal models and human studies demonstrating the role of environmental stressors (alcohol and under- or overnutrition) on the HPG axis. We review the role of alcohol and inadequate diet in prenatal reproductive system programming and consider specific candidate neurons in the adult hypothalamus through which reproductive function is being regulated. Finally, we review evidence from animal studies on the role that alcohol and diet play in fertility and reproductive disorders. We conclude that in order to better understand reproductive failure in animals and humans we need to consider in utero development and pay more attention to early life experience when searching for the origins of reproductive diseases.

The involvement of gonadotropin inhibitory hormone and kisspeptin in the metabolic regulation of reproduction

Recently, kisspeptin (KP) and gonadotropin inhibitory hormone (GnIH), two counteracting neuropeptides, have been acknowledged as significant regulators of reproductive function. KP stimulates reproduction while GnIH inhibits it. These two neuropeptides seem to be pivotal for the modulation of reproductive activity in response to internal and external cues. It is well-documented that the current metabolic status of the body is closely linked to its reproductive output. However, how reproductive function is regulated by the body's energy status is less clear. Recent studies have suggested an active participation of hypothalamic KP and GnIH in the modulation of reproductive function according to available metabolic cues. Expression of KISS1, the KP encoding gene, is decreased while expression of RFRP (NPVF), the gene encoding GnIH, is increased in metabolic deficiency conditions. The lower levels of KP, as suggested by a decrease in KISS1 gene mRNA expression, during metabolic deficiency can be corrected by administration of exogenous KP, which leads to an increase in reproductive hormone levels. Likewise, administration of RF9, a GnIH receptor antagonist, can reverse the inhibitory effect of fasting on testosterone in monkeys. Together, it is likely that the integrated function of both these hypothalamic neuropeptides works as a reproductive output regulator in response to a change in metabolic status. In this review, we have summarized literature from nonprimate and primate studies that demonstrate the involvement of KP and GnIH in the metabolic regulation of reproduction.

Kisspeptin as a link between metabolism and reproduction: evidences from rodent and primate studies

Changes in metabolic status gate reproductive activity by still incompletely deciphered mechanisms. Many neuropeptides have been shown to be involved in restraining hypothalamic gonadotropin releasing hormone (GnRH) release under conditions of negative energy balance. Broadly, on the basis of their effect on feeding, these can be grouped as orexigenic and anorexigenic neuropeptides. Reciprocally correlated, in response to changes in systemic concentrations of metabolic hormones, the secretion of orexigenic neuropeptides increases while that of anorexigenic neuropeptides decreases during conditions of food restriction. Recently, kisspeptin signaling in hypothalamus has appeared as a pivotal regulator of the GnRH pulse generator. Kisspeptin apparently does not affect feeding, but in light of accumulating data, it has emerged as one of the major conduits in relaying body metabolic status information to GnRH neurons. The present review examines such data obtained from rodent and primate models, which suggest kisspeptin-Kiss1r signaling as a possible pathway providing a link between metabolism and reproduction.

Hypercytolipidemia-induced nuclear lipoapoptosis: cytochemical analysis and integrated review of hypogonadal, diabetes-obesity syndrome-induced female reproductive axis disruption

Expression of the diabetes (db/db) mutation (i.e., leptin receptor defect) in C57BL/KsJ mice results in the functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian lipocytoatrophy. The current studies define the cytostructural, metabolic and endocrine disturbances associated with hypercytolipidemia and coincident nuclear lipoapoptosis following expression of the db/db-mutation. Adult, female C57BL/KsJ control (+/+ and +/? genotypes) and db/db mutant littermates were monitored for systemic alterations in blood glucose, insulin, luteinizing hormone (LH) and 17-B-estradiol (E2) concentrations associated with db/db-enhanced cytolipid depositions and TUNEL-labeled 3'-DNA fragmentation indexed nuclear lipoapoptosis. Obesity, hyperglycemia and hyperinsulinemia, in addition to depressed LH and E2 concentrations, characterized all db/db-mutants relative to control indices. Structural and cytochemical analysis of basophilic gonadotroph cells, ovarian follicular granulosa cells and uterine endometrial epithelial layers indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to control cytoarchitecture profiles. Vasolipidemia and interstitial cytoadiposity were prominent in all db/db tissue compartments. In each affected cell type within the db/db pituitary-reproductive tract axis, hypercytolipidemia was localized with pronounced nuclear lipo-infiltration and 3'-DNA TUNEL-labeled fragmentation. These data indicate that coincident cytostructural, endocrine and metabolic disturbances associated with hypogonadal pituitary-reproductive tract hypercytolipidemia are functional manifestations of the expressed diabetes-obesity syndrome in db/db-mutants. The progressive vaso-, interstitial-, and cyto-lipidemic alterations in cytoarchitecture correlated with the coincident nuclear lipoapoptotic dissolution and pronounced organo-involution, alterations which contributed to the functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Neonatally induced mild diabetes in rats and its effect on maternal, placental, and fetal parameters

The aim of this study was to assess placental changes and reproductive outcomes in neonatally induced mild diabetic dams and fetal development in their offspring. At birth, female rats were assigned either to control or diabetic group (100 mg of streptozotocin/Kg, subcutaneously). At adulthood, the female rats were mated. During pregnancy, the blood glucose levels and glucose and insulin tolerance tests were performed. At term, maternal reproductive outcomes, fetal and placental weight, and placental morphology were analyzed. Diabetic rats had smaller number of living fetuses, implantations and corpora lutea, and increased rate of embryonic loss. Placenta showed morphometric alterations in decidua area. Our results showed that mild diabetes was sufficient to trigger alterations in maternal organism leading to impaired decidua development contributing to failure in embryonic implantation and early embryonic losses. Regardless placental decidua alteration, the labyrinth, which is responsible for the maternal-fetal exchanges, showed no morphometric changes contributing to an appropriate fetal development, which was able to maintain normal fetal weight at term in mild diabetic rats. Thus, this experimental model of diabetes induction at the day of birth was more effective to reproduce the reproductive alterations of diabetic women.

Female reproduction and type 1 diabetes: from mechanisms to clinical findings

BACKGROUND

The functional reproductive alterations seen in women with type 1 diabetes (T1D) have changed as therapy has improved. Historically, patients with T1D and insufficient metabolic control exhibited a high prevalence of amenorrhea, hypogonadism and infertility. This paper reviews the impact of diabetes on the reproductive axis of female T1D patients treated with modern insulin therapy, with special attention to the mechanisms by which diabetes disrupts hypothalamic-pituitary-ovarian function, as documented mainly by animal model studies.

METHODS

A comprehensive MEDLINE search of articles published from 1966 to 2012 was performed. Animal model studies on experimental diabetes and human studies on T1D were examined and cross-referenced with terms that referred to different aspects of the gonadotropic axis, gonadotrophins and gonadal steroids.

RESULTS

Recent studies have shown that women with T1D still display delayed puberty and menarche, menstrual irregularities (especially oligomenorrhoea), mild hyperandrogenism, polycystic ovarian syndrome, fewer live born children and possibly earlier menopause. Animal models have helped us to decipher the underlying basis of these conditions and have highlighted the variable contributions of defective leptin, insulin and kisspeptin signalling to the mechanisms of perturbed reproduction in T1D.

CONCLUSIONS

Despite improvements in insulin therapy, T1D patients still suffer many reproductive problems that warrant specific diagnoses and therapeutic management. Similar to other states of metabolic stress, T1D represents a challenge to the correct functioning of the reproductive axis.

Alterations in hypothalamic KiSS-1 system in experimental diabetes: early changes and functional consequences

Using long-term streptozotocin (STZ)-treated male rats, we recently proposed that defective function of hypothalamic KiSS-1 system is mechanistically relevant for central hypogonadotropism of uncontrolled diabetes. However, the temporal pattern of such defects and its potential contribution to disturbed gonadotropin secretion in the diabetic female remain so far unexplored. To cover these issues, expression analyses and hormonal tests were conducted in diabetic male (1 wk after STZ; short term) and female (4 wk after STZ; long term) rats. Short-term diabetic males had lower basal testosterone levels and decreased gonadotropin responses to orchidectomy (ORX), which associated with significantly attenuated post-ORX rises of hypothalamic KiSS-1 mRNA. Yet kisspeptin administration to diabetic males was able to acutely elicit supramaximal LH and testosterone responses and normalize post-ORX gonadotropin secretion. Long-term diabetic females showed persistent anestrus and significantly decreased basal gonadotropin levels as well as blunted LH responses to ovariectomy; changes that were linked to lowering of basal and postovariectomy expression of hypothalamic KiSS-1 mRNA. Moreover, despite prevailing gonadotropin suppression, LH responses to acute kisspeptin administration were fully preserved, and even enhanced after its repeated injection, in diabetic females. In sum, our present findings further define the temporal course and mechanistic relevance of altered hypothalamic KiSS-1 system in the hypogonadotropic state of uncontrolled diabetes. Furthermore, our data provide the basis for the potential therapeutic intervention of the KiSS-1 system as adjuvant in the management of disturbed gonadotropin secretion of type 1 diabetes in the female.

Kisspeptin and KISS1R: a critical pathway in the reproductive system

In 2003, three groups around the world simultaneously discovered that KISS1R (GPR54) is a key gatekeeper of sexual maturation in both mice and men. Developmental changes in the expression of the ligand for KISS1R, kisspeptin, support its critical role in the pubertal transition. In addition, kisspeptin, a powerful stimulus of GNRH-induced gonadotropin secretion and may modulate both positive and negative sex steroid feedback effects at the hypothalamic level. Genetic studies in humans have revealed both loss-of-function and gainof-function mutations in patients with idiopathic hypogonadotropic hypogonadism and precocious puberty respectively. This review examines the kisspeptin/KISS1R pathway in the reproductive system.

Expression of hypothalamic KiSS-1 system and rescue of defective gonadotropic responses by kisspeptin in streptozotocin-induced diabetic male rats

Hypogonadotropism is a common feature of uncontrolled diabetes, for which the ultimate mechanism remains to be elucidated. Kisspeptins, ligands of G protein-coupled receptor 54 (GPR54) encoded by the KiSS-1 gene, have recently emerged as major gatekeepers of the gonadotropic axis. Alteration in the hypothalamic KiSS-1 system has been reported in adverse metabolic conditions linked to suppressed gonadotropins, such as undernutrition. However, its potential contribution to defective gonadotropin secretion in diabetes has not been evaluated. We report herein analyses of luteinizing hormone (LH) responses to kisspeptin and hypothalamic expression of the KiSS-1 gene in streptozotocin (STZ)-induced diabetic male rats. In addition, functional studies involving kisspeptin replacement or continuous administration of leptin and insulin to diabetic male rats are presented. Kisspeptin administration evoked robust LH and testosterone bursts and enhanced postgonadectomy LH concentrations, despite prevailing attenuation of gonadotropic axis in diabetic animals. In addition, hypothalamic KiSS-1 mRNA levels were unambiguously decreased in diabetic male rats, and the postorchidectomy rise in KiSS-1 mRNA was severely blunted. Repeated administration of kisspeptin to diabetic rats evoked persistent LH and testosterone responses and partially rescued prostate and testis weights. In addition, central infusion of leptin, but not insulin, was sufficient to normalize hypothalamic KiSS-1 mRNA levels, as well as LH and testosterone concentrations. In summary, we provide evidence for altered expression of the hypothalamic KiSS-1 system in a model of uncontrolled diabetes. This observation, together with the ability of exogenous kisspeptin to rescue defective LH responses in diabetic rats, unravel the physiopathological implication, and potential therapeutic intervention, of the KiSS-1 system in altered gonadotropin secretion of type 1 diabetes.

Structural, metabolic and endocrine analysis of the diabetes (db/db) hypogonadal syndrome: relationship to hypophyseal hypercytolipidemia

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice results in functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian cytolipoatrophy. Cellular gluco- and lipo-metabolic disturbances promoted by the db/db systemic hyperglycemic-hyperinsulinemic state suppress pituitary gonadotropin release in response to gonadotropin-releasing hormone and gonadal steroid stimulation and results in a hypogonadal-infertility syndrome. Adult female C57BL/KsJ control (+/+ and +/? genotypes) and db/db littermates were monitored for associations in systemic and cellular alterations in luteinizing hormone (LH), follicle-stimulating hormone (FSH), gonadal steroid (binding) levels, and pituitary glucometabolic indices associated with db/db-enhanced lipid imbibition and cytostructural disruption. Obesity, hyperglycemia, and hyperinsulinemia characterized all db/db mutants relative to controls. Serum and pituitary progesterone and estradiol concentrations were suppressed in db/db mutants, in association with serum LH and FSH levels, but not with pituitary LH and FSH concentrations, which were comparable between groups. Pituitary insulin receptor binding and glucose utilization rates were suppressed in db/db groups relative to +/? indices. Structural and cytochemical analysis of anterior (AP), intermediate (IL), and neuro-(NP) hypophyseal lobes demonstrated prominent hypercytolipidemia in db/db mutants relative to controls. Prominent cytolipidemia was localized within well-granulated basophilic gonadotrophs and within IL and NP pituicytes. Vasolipidemia and interstitial cytoadiposity were prominent throughout all db/db pituitary lobes. Thus, disturbances associated with pituitary hypercytolipidemia are functional components of the expressed diabetes-associated hypogonadal syndrome in db/db mutants. Progressive alterations in hypophyseal cytoarchitecture are correlated with suppression of pituitary metabolic and endocrine indices, alterations that contribute to functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Hypophyseal lipoapoptosis: diabetes (db/db) mutation-associated cytolipidemia promotes pituitary cellular disruption and dysfunction

Expression of the diabetes (db/db) mutation in C57BL/KsJ mice suppresses the female pituitary-gonadal axis via progressive cytolipidemic disruption of hypophyseal gonadotropin release, culminating in premature involution of the reproductive tract and manifest infertility. The current studies define the systemic, endocrine, cytochemical and structural apoptotic changes that result from pituitary hypercytolipidemia induced by db/db mutation expression in this Type II diabetes-obesity syndrome (DOS) model. Adult female C57BL/KsJ control (+/? genotype) and db/db littermates were monitored for systemic and cellular alterations in LH-, FSH- and gonadal steroid-secretion, and coincident pituitary apoptosis, as indexed by TUNEL labeled 3' nuclear DNA-fragmentation, associated with cytolipid depositions. Obesity, hyperglycemia and hyperinsulinemia characterized all db/db-mutants relative to +/? groups. Serum progesterone (P) and estradiol (E2) concentrations were suppressed in db/db mutants coincident with decreased plasma LH and FSH concentrations relative to +/? values. Cytochemical analysis of anterior (AP) pituitary cell subtypes indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to +/? pituitary cytoarchitecture. Cytolipidemic vacuoles were localized within protein vesiculated db/db hypophyseal basophilic and acidophilic cell populations. Hypophyseal cytoadiposity in db/db AP cells was co-localized with prominent cellular apoptotic TUNEL labeling of nuclear 3'-DNA fragments in cells demonstrating vesicular depopulation and cytolytic vacuolization. These data represent the first demonstration of co-localized hypercytolipidemic and cytoapoptotic disruptive events occurring concurrently in a hypopituitary-hypogonadal syndrome model following expression of the Type II (NIDDM) diabetes-obesity syndrome in db/db-mutants. The coincident and progressive vascular-, interstitial- and cyto-lipidemic alterations in hypophyseal cytoarchitecture correlated with the concurrent apoptotic disruption of pituitary endocrine cytoarchitecture and supressed gonadal steroid synthesis, influences which collectively contribute to the premature involution of the pituitary-gonadal axis in C57BL/KsJ- db/db mice.

Impaired testicular function in rats with diet-induced hypercholesterolemia and/or streptozotocin-induced diabetes mellitus

Hypercholesterolemia and diabetes mellitus are known to be accompanied by reproductive dysfunction. In this study, we investigated the effects of hypercholesterolemia, hyperglycemia, and these conditions combined, on testosterone (T) and testicular luteinizing hormone/human chorionic gonadotropin (LH/hCG) binding. Sprague-Dawley rats (8 weeks old) were divided into four groups: Group 1 was the control, group 2 was fed standard chow containing 2% cholesterol (C-diet), group 3 was administered streptozotocin (STZ, 65 mg/kg, i.p.), group 4 was treated with both the C-diet and STZ. After 4 weeks, rats were sacrificed. Serum glucose was significantly higher in the STZ group (304% that of controls) and the C-diet plus STZ group (345%), but there was no difference between the C-diet group (89%) and the control group. Serum cholesterol was significantly higher in the C-diet group (206% that of controls), the STZ group (452%) and the C-diet plus STZ group (2042%). Serum T, testicular T, and LH/hCG binding were significantly lower in the C-diet group (49%, 52%, and 81% that of controls, respectively), the STZ group (15%, 32%, and 72%) and the C-diet plus STZ group (8%, 21%, and 57%). These results suggest that hypercholesterolemia is an independent risk factor for testicular dysfunction and that the reduction of serum and testicular T levels is due at least in part to a reduction in testicular LH/hCG binding in rats with hypercholesterolemia, hyperglycemia, and these conditions combined. It is further suggested that the reduction in LH/hCG binding is mainly related to a rise in serum cholesterol levels.

Cyproterone acetate and reversal of the impaired endometrial decidualization in streptozotocin-diabetic pseudopregnant rats

Reproductive dysfunction in the female diabetic rat is associated with impaired hypothalamic-hypophyseal system, anovulation, insufficiency of ovarian steroidogenesis and spontaneous failure of pregnancy. Formation of decidua, the highly modified endometrium of pregnancy and pseudopregnancy could only be achieved when the uterus was sensitized by a sequence of oestrogen and progesterone. In this study, we examined whether the impaired expression of endometrial decidualization in the pseudopregnant rat is linked with diabetes-associated hypersecretion of testosterone. Rats were made pseudopregnant by sterile mating. Diabetes was induced by streptozotocin on day 1 p.c. Deciduogenic stimulus was given on day 5 p.c. Treatment of cyproterone acetate (10 mg kg(-1)) was scheduled from day 5 through day 9 p.c. Animals were killed on day 10 p.c, and the degree of endometrial decidual growth, plasma levels of oestradiol, progesterone, ACTH and testosterone were determined. Results showed that compared to controls there was a concomitant drop in endometrial decidual growth concurrently with impaired levels of oestradiol and progesterone in diabetic pseudopregnant rats. ACTH and testosterone levels were, however, profoundly elevated. Cyproterone acetate treatment in the diabetic pseudopregnant rat resulted in a simultaneous elevation of oestradiol and progesterone, which eventually helped the endometrial differentiation to decidua in the diabetic pseudopregnant rat parallel to controls. Present experimental data suggest that diabetes-associated impaired endometrial decidualization in the pseudopregnant rat is possibly caused by testosterone-induced oestrogen deficiency.

Influence of residual insulin secretion and duration of diabetes mellitus on the control of luteinizing hormone secretion in women

BACKGROUND

The aim of the present study was to establish whether the persistence of residual beta-cell activity after long-term diabetes mellitus (DM) exerts a protective role on luteinizing hormone (LH) secretion.

METHODS

The LH responses to stimulation with gonadotropin-releasing hormone (Gn-RH) (100 microg in an i.v. bolus) or naloxone (4 mg injected in an i.v. bolus, followed by the constant infusion of 8 mg in 2 h) were measured in C-peptide-positive (CpP) and C-peptide-negative (CpN) normally menstruating women with short-term (group 1 < 3 years, CpP n = 11, CpN n = 11) or long-term (group 2 > 10 years, CpP n = 11, CpN n = 11) DM and in age-matched normal control subjects (n = 11).

RESULTS

Gn-RH induced significant increments in LH secretion in all groups. Significant LH responses to naloxone were observed in all groups, except in group 2 CpN patients. However, the LH response to either Gn-RH or naloxone was significantly lower in group 1 CpN, group 2 CpP and group 2 CpN patients than in the normal control subjects. Furthermore, the LH response was significantly lower in group 2 CpP than in group 1 CpP patients and in group 2 CpN than in group 1 CpN subjects.

CONCLUSIONS

These results indicate a role for both deficiency in residual endogenous insulin secretion and duration of diabetes in the derangement of LH secretory control. The data suggest that the protective role exerted by residual beta-cell activity on LH secretion during the early years of DM diminishes with time elapsed after the onset of diabetes mellitus.

The role of catecholamines in the etiology of infertility in diabetes mellitus

Patients suffering from diabetes mellitus often develop reproductive dysfunction including anovulation, infertility and disrupted pregnancy. The biochemical basis of these phenomena is yet to be provided. The current study utilizes a neuroendocrine paradigm involving an in vitro microdissection technique in conjunction with jugular catheterization to examined the proestrus dynamics of norepinephrine (NE) and the preovulatory luteinizing hormone (LH) surge in streptozotocin (STZ) treated female rats, an animal model for insulin dependent diabetes mellitus. Radioimmunoassays revealed that in control subjects LH was at basal level during the morning of proestrus (900-1200 h); the first significant increase in the level of this pituitary hormone occurred at 1400-1500 h. A maximum peak concentration of LH was attained at 1700 h. In contrast, plasma levels of LH in diabetic subjects showed the first significant increase at 1500 h and peaked at 2000 h. The peak of the LH curve in diabetic rats was reduced by about 65% with a 3 h shift to the right. Alpha-methyl-p-tyrosine-induced blockade of newly synthesized NE-based assay showed that NE turnover rates in several hypothalamic nuclei (e.g. medial preoptic nucleus, MPN; median eminence, ME; suprachiasmatic nucleus, SCN; arcuate nucleus, AN) of control subjects were at basal level during the morning of proestrus (0900-1100 h). However, they increased by the 1200-1400 h interval and remained elevated during the 1500-1700 h. This time dependent increase in hypothalamic NE turnover rates during proestrus was not observed in the STZ diabetic rats. Most of the above metabolic derangements were partially reversed following the institution of insulin replacement therapy. Overall, our data support the concept that the endocrine abnormalities (e.g. infertility, delayed preovulatory LH surge) in diabetes are due, at least in part, to a functional deficit in noradrenergic neurons within the hypothalamus.

Depressed luteinizing hormone response to estradiol in vivo and gonadotropin-releasing hormone in vitro in experimentally diabetic swine

The influence of the acute withdrawal of insulin therapy in streptozocin-diabetic female swine was examined for changes in 1) the in vivo pulsatile secretion of luteinizing hormone (LH), 2) the preovulatory-like gonadotropin patterns after exogenous estradiol, and 3) the in vitro LH secretion by cultured pituitary cells. In Experiment 1, ovariectomized diabetic pigs (n = 4) were maintained with insulin therapy until 4 d before estradiol benzoate (EB; 7 micrograms/kg body weight; subcutaneous) was administered. Four normal ovariectomized pigs, matched for age and weight, served as controls. The diabetic state was confirmed by the measurement of glucose and insulin concentrations during a glucose tolerance test. Pulsatile LH secretion was not influenced by experimental diabetes mellitus. However, the expected surge in LH was not induced by EB in diabetic gilts. In contrast, three of four normal gilts had a preovulatory-type surge in LH. Concentrations of follicle-stimulating hormone in serum were not affected by diabetes mellitus. Estradiol concentrations in serum after ER were influenced by diabetes mellitus (treatment by time interaction; P < 0.001). In individual estradiol profiles, maximum concentrations were similar (104 +/- 10.4 and 91 +/- 12.0 ng/ml for normal and diabetic pigs, respectively), but the interval to maximum concentration was delayed in diabetic pigs (27.5 vs. 9.0 h; SE = 3.0; P < 0.05). However, the duration of standing estrus (2.2 +/- .3 d) and the interval from EB to estrus (3.6 +/- 0.3 d) were not influenced by diabetes mellitus. In Experiment 2, LH secretion by cultured cells and residual cellular LH content were greater in the pituitaries of normal than diabetic pigs (P < 0.05), and only cells from normal pigs responded to gonadotropin-releasing hormone (GnRH), with increased production of LH (P < 0.05). In conclusion, diabetes mellitus did not affect pulsatile LH secretion but did lower the ability of exogenous estradiol to stimulate a surge in vivo and of GnRH to increase LH in vitro, suggesting that the pituitary response to estradiol and GnRH is more severely affected by diabetes than is the GnRH pulse generator.

Streptozotocin-induced diabetes blocks the positive feedback release of luteinizing hormone in the female rat

The effects of streptozotocin-induced (STZ) diabetes on the release of gonadotropins was studied in female rats. In the first experiment, rats were ovariectomized and 2 days later were injected with STZ. Three weeks later rats were treated with estrogen and progesterone and blood samples were taken via intraatrial cannulae for luteinizing hormone (LH) assay. Afternoon surges of LH were seen in 4/5 control but 0/8 STZ rats. Pituitary responses to LH-releasing hormone in vitro did not differ. In the 2nd experiment, ovariectomized estrogen-primed rats were killed prior to and during a progesterone-induced LH surge. As in Experiment 1, STZ-treatment inhibited the LH surge but did not effect the afternoon rise in median eminence norepinephrine turnover which has previously been shown to be important in stimulating LH release. Turnover of norepinephrine in the anterior hypothalamus was depressed in the diabetic rats both prior to and during the expected time of the LH surge. Dopamine turnover was depressed in all three brain regions studied. It can be concluded that the positive feedback control of LH release is severely attenuated in diabetic rats but the mechanism explaining the loss is not clear. Diabetes-induced alterations in hypothalamic catecholamine metabolism may be involved but further work is needed to more carefully define these relationships.

The psychoneuroendocrinology of diabetes mellitus in rodents

The metabolic-endocrine state of diabetes mellitus affects the brain and behavior of diabetic animals. Feeding, paradoxical sleep, analgesia, submissive behavior, and avoidance behavior, are generally increased in diabetic compared with nondiabetic rodents. In contrast, sexual behavior, aggressive behavior and sensitivity to the behavioral effects of amphetamine are decreased in diabetic rodents. This review examines behavioral changes in diabetes mellitus within the context of known disease-linked alterations in hypothalamo-pituitary relationships and brain monoamine metabolism.

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.

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.