Gonadotropin secretion before and during acute and chronic dopamine-receptor blockade in insulin-dependent diabetic patients with amenorrhea

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.

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.

Evaluation of hypothalamic-pituitary-adrenal axis in amenorrhoeic women with insulin-dependent diabetes

Diabetes is associated with a higher incidence of secondary hypogonadotrophic amenorrhoea. In amenorrhoeic women with insulin-dependent diabetes a derangement in hypothalamic-pituitary-ovary axis has been proposed. No data exist on hypothalamic-pituitary-adrenal function in these women. Gonadotrophin releasing hormone (GnRH), corticotrophin releasing hormone (CRH), metoclopramide and thyroid releasing hormone (TRH) tests were performed in 15 diabetic women, eight amenorrhoeic (AD) and seven eumenorrhoeic (ED). Frequent blood samples were taken during 24 h to evaluate cortisol plasma concentrations. There were no differences between the groups in body mass index, duration of diabetes, insulin dose and metabolic control. The AD women had lower plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, oestradiol, androstenedione and 17-hydroxyprogesterone (17-OHP) than the ED women. The responses of pituitary gonadotrophins to GnRH, and of thyroid stimulating hormone (TSH) to TRH, were similar in both groups. The AD women had a lower prolactin response to TRH and metoclopramide, and lower ACTH and cortisol responses to CRH, than the ED women. Mean cortisol concentrations > 24 h were higher in the amenorrhoeic group. Significant differences in cortisol concentrations from 2400 to 1000 h were found between the two groups. Insulin-dependent diabetes may involve mild chronic hypercortisolism which may affect metabolic control. Stress-induced activation of the hypothalamic-pituitary-adrenal axis would increase hypothalamic secretion of CRH. This would lead directly and perhaps also indirectly by increasing dopaminergic tonus to inhibition of GnRH secretion and hence hypogonadotrophic amenorrhoea. Amenorrhoea associated with metabolically controlled insulin-dependent diabetes is a form of functional hypothalamic amenorrhoea that requires pharmacological and psychological management.

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.

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.

Luteinizing hormone responses to gonadotropin-releasing hormone and naloxone in menstruating women with type I diabetes of different duration

Luteinizing hormone (LH) responses to gonadotropin-releasing hormone (GnRH) (100 micrograms injected intravenously (IV)) or naloxone (4 mg injected plus 8 mg infused in 2 hours IV) were evaluated in 29 women with insulin-dependent diabetes mellitus (IDDM) (duration, group I (n = 15): less than 10 years, range 3 to 9 years; group II (n = 14): greater than 10 years, range 11 to 20 years) and in 15 normal controls, on the 22nd days of normal menstrual cycles. Both GnRH- and naloxone-induced LH responses were similar in group I diabetics and normal controls, whereas they were significantly lower in group II than in group I diabetics or normal controls. Positive correlations were found between LH responses to GnRH and naloxone, whereas negative correlations were observed between maximal LH peaks in response to GnRH or naloxone and duration of diabetes. These data indicate that a hypothalamic pituitary disorder affects LH secretion with time after the onset of IDDM.

The effect of residual beta cell activity on menstruation and the reproductive hormone profile of insulin-dependent diabetics

To investigate the cause of secondary amenorrhoea in insulin-dependent diabetes gonadotrophins, sex steroid hormone levels and residual beta cell activity (C-peptide index) were estimated in a group of 43 women with IDDM. Among 26 women with residual insulin secretion, the C-peptide positive (CpP) group, 5 had secondary amenorrhoea (CpP-Am); among 17 women without endogenous beta cell activity, the C-peptide negative (CpN) group 6 had secondary amenorrhoea (CpN-Am). In this study two different types of secondary amenorrhoea in insulin-dependent diabetics were observed. All CpP-Am women have the classical hormone profile of the polycystic ovary syndrome (increased (LH/FSH ratio, increased serum testosterone, decreased SHBG) together with a history of oligomenorrhoea and excess weight before the onset of diabetes. On the other hand, all CpN-Am women had decreased LH levels as well as low LH/FSH ratio and testosterone levels. These results strongly suggest that a lack of residual pancreatic beta cell activity influences hypothalamus-pituitary function in insulin-dependent diabetes. It might be concluded that PCOS is independent of diabetes while low LH amenorrhoea seems to be the consequence of diabetes and is strongly associated with a lack of residual insulin secretion.

Blunted prolactin response to metoclopramide in insulin-dependent diabetic patients with secondary amenorrhoea

In order to investigate the dopaminergic activity in diabetic women with secondary amenorrhoea we studied the response of prolactin to a dopamine receptor antagonist metoclopramide (MTC - 10 mg i.v.) in three groups of women: 5 insulin-dependent diabetic women with secondary amenorrhoea, 5 insulin-dependent diabetics with normal menstrual cycles and 6 non-diabetic women with regular cycles. Patients with diabetes and secondary amenorrhoea had significantly lower basal LH levels (P less than 0.001) and FSH levels (P less than 0.005) than normally cycling diabetic women. Basal and metoclopramide stimulated prolactin levels were lower in diabetic women with secondary amenorrhoea compared to normally cycling diabetics and control subjects. Evaluation of C-peptide levels in peripheral blood revealed that all amenorrheic diabetics had no endogenous beta cell function while diabetic women with normal cycles (except 1 patient) had preserved residual pancreatic beta cell secretion.