Absent or delayed preovulatory luteinizing hormone surge in experimental diabetes mellitus

Kisspeptin as a test of hypothalamic dysfunction in pubertal and reproductive disorders

The hypothalamic-pituitary-gonadal axis is regulated by the gonadotropin-releasing hormone pulse generator in the hypothalamus. This is comprised of neurons that secrete kisspeptin in a pulsatile manner to stimulate the release of GnRH, and, in turn, downstream gonadotropins from the pituitary gland, and subsequently sex steroids and gametogenesis from the gonads. Many reproductive disorders in both males and females are characterized by hypothalamic dysfunction, including functional disorders (such as age-related hypogonadism, obesity-related secondary hypogonadism, hyperprolactinemia, functional hypothalamic amenorrhea and polycystic ovary syndrome), structural pathologies (such as craniopharyngiomas or radiation or surgery-related hypothalamic dysfunction), and pubertal disorders (constitutional delay of growth and puberty and congenital hypogonadotropic hypogonadism). However, in many of these conditions, the relative contribution of hypothalamic dysfunction to the observed hypogonadism is unclear; as to date, there is no direct method of evaluating hypothalamic reproductive function in humans. Indeed, it is not possible to directly measure gonadotropin-releasing hormone levels in the hypothalamo-pituitary portal vessels, such that secondary (i.e., pituitary dysfunction) and tertiary (i.e., hypothalamic dysfunction) hypogonadism are often conflated as one entity. In this review, we examine the evidence for the use of kisspeptin as a method of directly evaluating hypothalamic reproductive dysfunction, and deliberate its potential future role in the evaluation of pubertal and reproductive disorders.

Obesity-Related Hypogonadism in Women

Obesity-related hypogonadotropic hypogonadism is a well-characterized condition in men (termed male obesity-related secondary hypogonadism; MOSH); however, an equivalent condition has not been as clearly described in women. The prevalence of polycystic ovary syndrome (PCOS) is known to increase with obesity, but PCOS is more typically characterized by increased gonadotropin-releasing hormone (GnRH) (and by proxy luteinizing hormone; LH) pulsatility, rather than by the reduced gonadotropin levels observed in MOSH. Notably, LH levels and LH pulse amplitude are reduced with obesity, both in women with and without PCOS, suggesting that an obesity-related secondary hypogonadism may also exist in women akin to MOSH in men. Herein, we examine the evidence for the existence of a putative non-PCOS "female obesity-related secondary hypogonadism" (FOSH). We précis possible underlying mechanisms for the occurrence of hypogonadism in this context and consider how such mechanisms differ from MOSH in men, and from PCOS in women without obesity. In this review, we consider relevant etiological factors that are altered in obesity and that could impact on GnRH pulsatility to ascertain whether they could contribute to obesity-related secondary hypogonadism including: anti-Müllerian hormone, androgen, insulin, fatty acid, adiponectin, and leptin. More precise phenotyping of hypogonadism in women with obesity could provide further validation for non-PCOS FOSH and preface the ability to define/investigate such a condition.

Accelerated Ovarian Aging Among Type 2 Diabetes Patients and Its Association With Adverse Lipid Profile

BACKGROUND

The impact of diabetes on reproductive function is still not clearly defined. This study aimed to evaluate accelerated ovarian aging in women with type 2 diabetes mellitus (T2DM) and its association with adverse lipid profile.

METHODS

Female patients with T2DM (n=964) and non-T2DM controls (n=263) aging from 18-80 years were included. Levels of circulating sex hormones were measured at the follicular phase in menstruating women. We analyzed the age-specific trends in the levels of sex hormones between T2DM and controls. The correlations of sex hormones with the lipid profile, including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC) and triglycerides (TG) were also evaluated.

RESULTS

In the temporal trends analysis, LH and FSH both started to increase obviously approximately from the age of 45 years among patients with T2DM, and displayed peaks of LH and FSH among patients with T2DM aged between 61 and 65, both of which were obviously earlier than that in non-T2DM controls and proved the accelerated ovarian aging among patients with T2DM. E2 of patients with T2DM was continuous lower than that of non-T2DM controls from approximately 45 years old, and LH and FSH of patients with T2DM were higher than those of non-T2DM controls between the age of 55 to 65 years. Multiple linear regression analyses revealed that LH was positively correlated with LDL-C (Coefficient=0.156, P=0.001) and TC (Coefficient=0.134, P=0.025), and was negatively correlated with HDL-C (Coefficient =-0.065, P=0.001) in patients with T2DM aged between 51 and 60, which was independent of age, T2DM duration, body mass index (BMI), glycosylated hemoglobin (HbA1c), FSH, E2 and other potential confounders. Higher E2 level was significantly and independently correlated with lower LDL-C (Coefficient= -0.064, P=0.033) in patients with T2DM aged between 51 and 60.

CONCLUSIONS

This study suggests that patients with T2DM have accelerated ovarian aging, and it is correlated with the occurrence of disturbed lipid profile in patients with T2DM. With an ever increasing number of female patients with T2DM diagnosed at younger ages, the accelerated ovarian aging and its adverse impacts in T2DM need to be carefully managed.

High-Fat, High-Sugar Diet Disrupts the Preovulatory Hormone Surge and Induces Cystic Ovaries in Cycling Female Rats

Diet-induced obesity has been associated with various metabolic and reproductive disorders, including polycystic ovary syndrome. However, the mechanisms by which obesity influences the reproductive system are still not fully known. Studies have suggested that impairments in hormone signaling are associated with the development of symptoms such as acyclicity and ovarian cysts. However, these studies have often failed to address how these hormonal changes arise and how they might contribute to the progression of reproductive diseases. In the present study, we used a high-fat, high-sugar (HFHS) diet to induce obesity in a female rodent model to determine the changes in critical reproductive hormones that might contribute to the development of irregular estrous cycling and reproductive cycle termination. The HFHS animals exhibited impaired estradiol, progesterone (P4), and luteinizing hormone (LH) surges before ovulation. The HFHS diet also resulted in altered basal levels of testosterone (T) and LH. Furthermore, alterations in the basal P4/T ratio correlated strongly with ovarian cyst formation in HFHS rats. Thus, this model provides a method to assess the underlying etiology of obesity-related reproductive dysfunction and to examine an acyclic reproductive phenotype as it develops.

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.

Insulin: its role in the central control of reproduction

Insulin has long been recognized as a key regulator of energy homeostasis via its actions at the level of the brain, but in addition, plays a role in regulating neural control of reproduction. In this review, we consider and compare evidence from animal models demonstrating a role for insulin for physiological control of reproduction by effects on GnRH/LH secretion. We also review the role that insulin plays in prenatal programming of adult reproduction, and consider specific candidate neurons in the adult hypothalamus by which insulin may act to regulate reproductive function. Finally, we review clinical evidence of the role that insulin may play in adult human fertility and reproductive disorders. Overall, while insulin appears to have a significant impact on reproductive neuroendocrine function, there are many unanswered questions regarding its precise sites and mechanisms of action, and their impact on developing and adult reproductive neuroendocrine function.

Maternal diabetes causes alterations of DNA methylation statuses of some imprinted genes in murine oocytes

Maternal diabetes has adverse effects not only on oocyte quality but also on embryo development. However, it is still unknown whether the DNA imprinting in oocytes is altered by diabetes. By using streptozotocin (STZ)-induced and nonobese diabetic (NOD) mouse models we investigated the effect of maternal diabetes on DNA methylation of imprinted genes in oocytes. Mice which were judged as being diabetic 4 days after STZ injection were used for experiments. In superovulated oocytes of diabetic mice, the methylation pattern of Peg3 differential methylation regions (DMR) was affected in a time-dependent manner, and evident demethylation was observed on Day 35 after STZ injection. The expression level of DNA methyltransferases (DNMTs) was also decreased in a time-dependent manner in diabetic oocytes. However, the methylation patterns of H19 and Snrpn DMRs were not significantly altered by maternal diabetes, although there were some changes in Snrpn. In NOD mice, the methylation pattern of Peg3 was similar to that of STZ-induced mice. Embryo development was adversely affected by maternal diabetes; however, no evident imprinting abnormality was observed in oocytes from female offspring derived from a diabetic mother. These results indicate that maternal diabetes has adverse effects on DNA methylation of maternally imprinted gene Peg3 in oocytes of a diabetic female in a time-dependent manner, but methylation in offspring's oocytes is normal.

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.

Effects of long-term diabetes on the structure and cell proliferation of the myometrium in the early pregnancy of mice

It is known that the development of diabetic complications in human pregnancy is directly related to the severity and the duration of this pathology. In this study, we developed a model of long-term type 1 diabetes to investigate its effects on the cytoarchitecture, extracellular matrix and cell proliferation during the first adaptation phase of the myometrium for pregnancy. A single dose of alloxan was used to induce diabetes in mice prior to pregnancy. To identify the temporal effects of diabetes the mice were divided into two groups: Group D1 (females that became pregnant 90-100 days after alloxan); Group D2 (females that became pregnant 100-110 days after alloxan). Uterine samples were collected after 168 h of pregnancy and processed for light and electron microscopy. In both groups the histomorphometric evaluation showed that diabetes promoted narrowing of the myometrial muscle layers which was correlated with decreased cell proliferation demonstrated by PCNA immunodetection. In D1, diabetes increased the distance between muscle layers and promoted oedema. Contrarily, in D2 the distance between muscle layers decreased and, instead of oedema, there was a markedly deposition of collagen in the myometrium. Ultrastructural analysis showed that diabetes affects the organization of the smooth muscle cells and their myofilaments. Consistently, the immunoreaction for smooth muscle α-actin revealed clear disorganization of the contractile apparatus in both diabetic groups. In conclusion, the present model demonstrated that long-term diabetes promotes significant alterations in the myometrium in a time-sensitive manner. Together, these alterations indicate that diabetes impairs the first phenotypic adaptation phase of the pregnant myometrium.

Functional state of the hypothalamic-pituitary-gonadal axis in diabetes mellitus

Diabetic patients present with a wide variety of reproductive disorders supposed to be underlain by changes in the functional activity of the hypothalamic-pituitary-gonadal axis (HPGA) and sensitivity of the reproductive system tissues to the regulatory hormonal action. The objective of the present review is to analyse the literature data and the results of original studies pertinent to the biosynthesis and secretion of hypothalamic LH releasing factor, pituitary gonadotropic hormones, steroid hormones, and susceptibility of their target tissues in patients with types 1 and 2 diabetes mellitus. It is concluded that the improvement of control over blood glucose levels constitutes a most efficacious approach to the correction and normalization of reproductive function in diabetic patients.

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.

Caloric restriction: impact upon pituitary function and reproduction

Reduced energy intake, or caloric restriction (CR), is known to extend life span and to retard age-related health decline in a number of different species, including worms, flies, fish, mice and rats. CR has been shown to reduce oxidative stress, improve insulin sensitivity, and alter neuroendocrine responses and central nervous system (CNS) function in animals. CR has particularly profound and complex actions upon reproductive health. At the reductionist level the most crucial physiological function of any organism is its capacity to reproduce. For a successful species to thrive, the balance between available energy (food) and the energy expenditure required for reproduction must be tightly linked. An ability to coordinate energy balance and fecundity involves complex interactions of hormones from both the periphery and the CNS and primarily centers upon the master endocrine gland, the anterior pituitary. In this review article we review the effects of CR on pituitary gonadotrope function and on the male and female reproductive axes. A better understanding of how dietary energy intake affects reproductive axis function and endocrine pulsatility could provide novel strategies for the prevention and management of reproductive dysfunction and its associated comorbidities.

Tungstate administration improves the sexual and reproductive function in female rats with streptozotocin-induced diabetes

BACKGROUND

Diabetes induces great alterations in female reproductive function. We analyzed the effects of tungstate, an anti-diabetic agent, on the reproductive function of healthy and diabetic female rats.

METHODS

Healthy and streptozotocin-induced diabetic rats were treated with sodium tungstate (2 mg/ml in their drinking water) for 12 weeks. Markers of reproductive function and diabetes were measured in serum, and in uterus and ovaries by Western blot or RT-PCR. Reproductive function was also assessed by mating.

RESULTS

Diabetic rats showed great impairment of libido, which was accompanied by a total loss of fertility (P < 0.05) and a decrease in the serum levels of FSH (P < 0.05) and LH (P < 0.05) compared with healthy rats. Tungstate treatment of diabetic rats partially recovered libido while fertility rate increased to 66.6%. This improvement was accompanied by a recovery of serum FSH (to a level higher than healthy rats) and LH. Moreover, tungstate treatment normalized ovarian expression of GLUT 3 hexose transporter, and estrogen, progesterone and FSH receptors, whereas only GLUT 3 and FSH receptors were normalized in the uterus.

CONCLUSIONS

Our results indicate that the alterations in female reproduction in diabetes were partially reversed after tungstate treatment by a mechanism(s) involving the normalization of serum FSH and LH levels, and ovarian and uterine expression of FSH receptors and GLUT3.

Neuropeptide signaling in the integration of metabolism and reproduction

Fertility is gated by nutrition and the availability of stored energy reserves, but the cellular and molecular mechanisms that link energy stores and reproduction are not well understood. Neuropeptides including galanin-like peptide (GALP), neuropeptide Y (NPY), products of the proopiomelanocortin (POMC; e.g., alpha-MSH and beta-endorphin), and kisspeptin are thought to be involved in this process for several reasons. First, the neurons that express these neuropeptides all reside in the hypothalamic arcuate nucleus, a critical site for the regulation of both metabolism and reproduction. Second, these neuropeptides are all targets for regulation by metabolic hormones, such as leptin and insulin. And third, these neuropeptides have either direct or indirect effects on feeding and metabolism, as well as on the secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). As the target for the action of metabolic hormones and sex steroids, these neuropeptides serve as molecular motifs integrating the control of metabolism and reproduction.

The hypothalamus–pituitary–ovary axis and type 1 diabetes mellitus: a mini review

A high prevalence of menstrual cycle and fertility disturbances has long been associated with diabetes mellitus. However, rationalization of the intrinsic mechanisms of these alterations is controversial and even contradictory. This review considers (i) the relationship between diabetes mellitus, especially type 1 diabetes mellitus (T1DM), and the hypothalamus-pituitary-ovary (HPO) axis, (ii) the state of our knowledge concerning neuroendocrine control and its relationship with dopaminergic and opioid tonus, and (iii) the influence of the hypothalamus-pituitary-adrenal axis on ovarian function. Functional disturbances that occur as a consequence of diabetes are also discussed, but some T1DM-related diseases of autoimmune origin, such as oophoritis, are not further analysed. Although there are clear indications of a relationship between menstrual and fertility alterations and glycaemic control, in many instances the improvement of the latter is not sufficient to reverse such alterations. It appears that the oligoamenorrhoea and amenorrhoea associated with T1DM is mainly of hypothalamic origin (i.e. failure of the GnRH pulse generator) and may be reversible. The importance of the evaluation of the HPO axis in T1DM women with menstrual irregularities, even in the presence of adequate metabolic control, is emphasized.

Altered meiotic regulation in oocytes from diabetic mice

In the present study, we have utilized a streptozotocin-induced diabetic mouse model to examine how the diabetic condition and different glucose concentrations affect several parameters of reproductive physiology. We report that oocyte maturation is altered under all experimental conditions examined. In cumulus cell-enclosed oocytes (CEO) from diabetic mice, spontaneous maturation was accelerated but the FSH-mediated delay of spontaneous maturation was suppressed. Higher glucose levels in the culture medium suppressed spontaneous maturation but did not influence the transient arrest mediated by FSH. Meiotic arrest in CEO by hypoxanthine and dibutyryl cAMP (dbcAMP) was less effective at higher glucose concentrations. In addition, both FSH-induced maturation in vitro and hCG-induced maturation in vivo were reduced by the diabetic condition. The ovulation rate was lowered by about 50% in diabetic mice and fewer ovulated ova had reached metaphase II. Despite the decreased number of ova at metaphase II, in vitro cultures showed the oocytes were capable of completing meiotic maturation at control levels. Insulin treatment reversed the detrimental effects of diabetes on meiotic induction, ovulation, and completion of meiotic maturation. Cultures of pronuclear-staged embryos confirmed a negative effect of diabetes and hyperglycemia on development to the blastocyst stage. These data suggest that defects in meiotic regulation brought about by the diabetic condition are due to decreased communication between the somatic and germ cell compartments, and it is concluded that such conditions may contribute to postfertilization developmental abnormalities.

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.

The effect of diabetes on alpha2-adrenergic receptor activity in the reproductive centers of the female rat brain

OBJECTIVE

We hypothesized that known diabetes-induced deficits in female rat reproduction may result in part from decreased central alpha(2)-noradrenergic receptor density or affinity.

STUDY DESIGN

Female rats were oophorectomized and divided into 2 groups; one group received streptozocin during the operation to induce diabetes, and the other served as a nondiabetic control group. Random blood glucose levels were measured. Half the rats in each group were killed on postoperative day 10, and half were killed on postoperative day 14. Direct radioligand binding assays were performed on tissue prepared from the hypothalamus, preoptic area, and cortex of each rat. Analysis of variance was used to evaluate intergroup differences in receptor concentration or equilibrium constant.

RESULTS

We detected no significant difference in the mean receptor concentration or equilibrium constant between the groups with and without diabetes in the hypothalamus, the preoptic area, and the cortex on postoperative day 10 or 14.

CONCLUSION

Diabetes-induced impairments in female rat reproduction do not involve alterations in alpha(2)-receptor density or affinity in the hypothalamus, preoptic area, or cortex.

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.

Neuroendocrine control of the gonadotropic function of the hypophysis in experimental diabetes

The stability of the function of the reproductive system depends on a multitude of factors of the internal and external milieux. Serious disturbances in its function, with alterations in carbohydrate homeostasis, underlie such diseases as diabetes mellitus. Disturbances to the functional activity of the reproductive system in laboratory animals with diabetes are known to be associated not only with destructive changes in the gonads, but also with dysfunction of the hypothalamo-hypophyseal complex [9, 11]. Published data show that these lesions have different severities in male and female individuals [7, 8]. The question of the extent to which lesions due to the diabetic state depend on the level of sex steroids and insulin in the body thus far remains unanswered. Unlike the situation in males, females are characterized by cyclic changes in the activity of the reproductive system. Thus, it is possible that differences in the regulation of gonadotropic function in male and female rats, observed in normal animals, could explain their different sensitivities to diabetes. Thus, we elected to carry out various studies of the functional activity of the hypothalamo-hypophyseal-gonadal system in male and female rats with experimental diabetes induced by administration of streptozotocin (STZ).

Insulin-dependent diabetes mellitus and menstrual dysfunction

Disordered reproductive function has long been recognized as a prevalent problem among women of reproductive age who suffer from insulin-dependent diabetes mellitus (IDDM). Delay in menarchial age is frequently seen if IDDM develops in the peripubertal years and some form of menstrual dysfunction is found in nearly one-third of all women of reproductive age with IDDM. This review summarizes some of the prevailing views regarding the mechanisms through which uncontrolled IDDM is thought to disrupt normal hypothalamic-pituitary-gonadal function. Although animal studies have suggested that poorly controlled IDDM may adversely affect the uterovaginal outflow tract and/or ovarian function, no clinical studies have suggested that abnormal uterine or ovarian function underlies the menstrual dysfunction observed in young diabetic women. Similarly, pituitary function as assessed by basal gonadotrophins and gonadotrophin-releasing hormone (GnRH)-stimulated gonadotrophin release appears to be normal in young women with IDDM. Moreover, although there has been some suggestion that pituitary function may decline with increasing duration of diabetes, this issue has not been thoroughly investigated. It appears that the oligo/amenorrhea noted in IDDM is principally hypothalamic in origin and may represent intermittent (and perhaps reversible) failure of the GnRH pulse generator, similar to the situation observed in women who engage in endurance training or who suffer from anorexia nervosa. Although the exact pathophysiological mechanisms that subserve dysfunction of the GnRH neuronal system are not well understood, attention has focused on increased central opioidergic activity, increased central dopaminergic activity, and central glucose deprivation. In this era of emphasis on tight glycaemic control and its impact in preventing diabetes complications, the consequences of IDDM on reproductive potential appear to be important and must be included in future investigative efforts.

Diabetes prevents the normal responses of the ovary to FSH

FSH in vitro stimulates increased oxygen uptake by isolated follicular granulosa cells from immature rats treated with diethylstilbestrol (DES) when substrates are present (glucose, glutamate, pyruvate or fumerate) or are completely absent. However, when glucose is the only substrate or when any single substrate is omitted from the buffer, FSH has no effect. FSH in vitro also increases the uptake of glucose and the formation of 14CO2 from [1-6 14C]-glucose. Granulosa cells from diabetic immature rats treated with DES did not show increased oxygen uptake with in vitro FSH. Diabetic cells had similar receptor binding of FSH to that of control non-diabetic cells. The addition of both insulin and FSH in vitro to buffer with diabetic granulosa cells gave increased oxygen uptake over that of control cells from diabetic rats. The insulin stimulation of oxygen uptake by FSH in cells from diabetic rats was not duplicated by either epidermal growth factor (EGF) or insulin-like growth factor I (IGF-1). Follicle counts of ovaries from diabetic and control immature rats treated with DES showed increased atresia in the diabetic ovaries after only 44 hr. of diabetes. Follicle counts of ovaries from adult diabetic rats showed increased atresia in 24 hours after induction of diabetes at proestrus. Follicle counts of pseudopregnant rats showed increased atresia by 3 days after diabetes was induced. We conclude that diabetes prevents normal follicle growth stimulated either by exogenous DES or by endogenous hormones secreted during proestrus.

Soluble and particulate phenylethanolamine N-methyltransferase in hypothalamus of diabetic rats

Experimental diabetes increases total phenylethanolamine N-methyltransferase (PNMT) activity in the medulla-pons but not in the hypothalamus. In this study diabetes was induced with streptozotocin (65 mg/kg) in male Sprague-Dawley rats. Twenty-eight days after treatment there were no differences in soluble PNMT activity in the hypothalamus of diabetics and controls, but PNMT activity in a membrane-associated (particulate) fraction of hypothalamus was evaluated approximately twofold in tissues of diabetic animals compared with controls. A specific PNMT inhibitor, incubated with tissue extracts of control rats, abolished greater than 90% of particulate PNMT activity in the hypothalamus but reduced soluble PNMT activity in the hypothalamus by only 47%. These findings indicate that membrane-associated PNMT activity in rat hypothalamus differs from soluble hypothalamic PNMT in the in vitro response to an inhibitor and the in vivo response to diabetes and suggest the importance of separating subcellular hypothalamic fractions prior to assay of PNMT.

Effects of short and long-lasting diabetes mellitus on mouse brain monoamines

Concentrations of monoamines and their metabolites were investigated in various brain regions of 3, 50, and 100 days diabetic mice. An increase in the content of norepinephrine was observed in the pons-medulla and striatum in short-term (3 days) diabetic mice, and could be sustained for 100 days and 50 days, respectively. In the hypothalamus and cortex, the increase of norepinephrine was observed in both 50 and 100 day diabetic mice, but that of cerebellum was only observed in the 100 day diabetic mice. The concentration of dopamine was increased in the striatum both in short-term and long-term (50 and 100 days) diabetic mice, that of pons-medulla and cortex was increased in the long-term diabetic mice. Concentrations of the acidic metabolites of dopamine, dihydroxyphenylacetic acid and homovanillic acid were decreased in the hypothalamus, hippocampus and striatum, while increased in the pons-medulla and cortex. 5-Hydroxytryptamine concentration was increased in the hypothalamus, hippocampus, pons-medulla and cortex progressively from short-term to long-term diabetic mice. However, the concentration of its acidic metabolite, 5-hydroxyindoleacetic acid, was decreased in the hypothalamus, hippocampus, striatum, pons-medulla and cortex. These data suggest that diabetes is associated with a significant disturbance of brain monoamine metabolism. This disturbance was not generalized but related to some specific areas of the brain and some of these alterations were progressive from short term to long term diabetes.

Elevated neuropeptide Y concentrations in the central hypothalamus of the spontaneously diabetic BB/E Wistar rat

Insulin-deficient diabetes causes hypothalamic and pituitary dysfunction. The possible role of hypothalamic regulatory peptides in mediating these disturbances was investigated in spontaneously diabetic BB/E Wistar rats. Concentrations of 10 regulatory peptides were measured in the central (nucleus-rich) and lateral parts of the hypothalamus in 18 diabetic and 5 non-diabetic BB/E rats. Diabetic rats were treated with either intensified or low-dose insulin schedules to achieve moderate or severe hyperglycaemia (mean blood glucose concentrations, 8 and 20 mmol l-1 respectively). Neuropeptide Y concentration and content in the central hypothalamus were increased by 30-40% in both moderately and severely hyperglycaemic diabetic groups (p less than 0.01). Lateral hypothalamic neuropeptide Y levels did not differ significantly between the groups. The only other peptide to show any significant difference between diabetic and control rats was calcitonin gene-related peptide, whose central hypothalamic concentrations were significantly increased in the severely hyperglycaemic animals. Alterations of hypothalamic neuropeptide Y, which has potent experimental effects on hypothalamo-pituitary function, may contribute to certain neuroendocrine disturbances in insulin-deficient diabetes.

Behavioral and neurochemical profile of the spontaneously diabetic Wistar BB rat

The overall objective of the present investigation was to examine the behavioral and neurochemical profile of long-term diabetes (2-4 months), in the spontaneously diabetic Wistar BB rat (SDR). This animal model mimics the salient symptomatology of Type-I diabetes in man and circumvents confounds attributed to non-specific effects encountered in the chemically-induced models of diabetes. The first set of experiments were designed to investigate the effects of dopamine (DA) agonists and circadian cycle on the following spontaneous behaviors: locomotion, floor activity, rearing frequency and rearing duration. The results demonstrated that the SDR manifests (1) a blunted response to D-amphetamine (0.5-3.0 mg/kg; i.p.), and (2) lower levels of spontaneous locomotor and rearing activity in the latter part of the dark cycle, particularly at the transition of the cycle from dark to light. The next set of experiments assessed the status of brain catecholamine and metabolite levels in the insulin maintained and deprived SDR. The regional catecholamine and metabolite levels of the insulin-maintained SDR were not significantly different from those of the non-diabetic or the genetically distinct controls. However, the cessation of insulin administration to the SDR for 4 days resulted in significant increases in the levels of norepinephrine in the cortex and the hypothalamus, DA in the hippocampus, and homovanillic acid in the striatum.

Decreased serum testosterone response to gonadotropin-releasing hormone in male offspring of diabetic female rats

A study was designed to examine the testicular function of male offspring rats produced by diabetic dams. A marked decrease in testosterone response to exogenous administration of gonadotropin-releasing hormone (GnRH) was found in male offspring of female rats made diabetic by administration of streptozotocin during early pregnancy. Control rats responded to GnRH with a marked increase in serum testosterone within 4-h postinjection. Male offspring of diabetic female rats demonstrated an unexpected decrease in serum testosterone in response to GnRH when compared with saline-injected rats. The results suggest that a defect in Leydig cell function may occur in the male offspring of diabetic female rats. However, a decreased release of pituitary LH in response to exogenous GnRH stimulation cannot be excluded as a cause of the lower testosterone values.

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.

Diabetes-induced changes in monoamine concentrations of rat hypothalamic nuclei

Streptozotocin-induced diabetes produced marked alterations of monoamine concentrations in several hypothalamic nuclei of male and female rats. Norepinephrine (NE) concentrations were significantly elevated in the median eminence (ME), supraoptic nucleus (SON) and periventricular nucleus (PEVN) in both sexes of diabetic rats. NE concentrations in the suprachiasmatic nucleus (SCN) and ventromedial nucleus (VMN) of male and female diabetic animals remained unaltered. Serotonin (5-HT) concentrations were increased in PEVN of male and female diabetic rats. No significant changes in hypothalamic dopamine (DA) concentrations were observed. Insulin treatment reversed the diabetes-related changes in monoamine concentrations in most of the nuclei. The significance of these biochemical changes relative to the endocrine and behavioral abnormalities in diabetes is discussed.

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.