Effect of obesity on the hypothalamo-pituitary-gonadal function in childhood

Perspectives in Pediatric Pathology, Chapter 22. Testicular Involvement in Systemic Diseases

Normal testicular physiology requires appropriate function of endocrine glands and other tissues. Testicular lesions have been described in disorders involving the hypothalamus-hypophysis, thyroid glands, adrenal glands, pancreas, liver, kidney, and gastrointestinal tract. Testicular abnormalities can also associate with chronic anemia, obesity, and neoplasia. Although many of the disorders that affect the above-mentioned glands and tissues are congenital, acquired lesions may result in hypogonadism in children and adolescents.

Leptin and androgens in male obesity: evidence for leptin contribution to reduced androgen levels

Leptin circulates in plasma at concentrations that parallel the amount of fat reserves. In obese males, androgen levels decline in proportion to the degree of obesity. Recently, we have shown that in rodent Leydig cells leptin inhibits hCG-stimulated testosterone (T) production via a functional leptin receptor isoform; others have found that leptin inhibits basal and hCG-induced T secretion by testis from adult rats. In this study, we further investigated the relationship linking leptin and androgens in men. Basal and hCG-stimulated leptin and sex hormone levels were studied in a large group of men ranging from normal weight to very obese (body mass index, 21.8-55.7). Initial cross-sectional studies showed that circulating leptin and fat mass (FM) were inversely related with total and free T (r = -0.51 and r = -0.38, P < 0.01 and P < 0.05, respectively). Multiple regression analysis indicated that the correlation between leptin or FM and T was not lost after controlling for SHBG and/or LH and/or estradiol (E2) levels and that leptin was the best hormonal predictor of the lower androgen levels in obesity. Dynamic studies showed that in obese men the area under the curve of T and free T to LH/hCG stimulation (5000 IU i.m.) was 30-40% lower than in controls and inversely correlated with leptin levels (r = -0.45 and r = -0.40, P < 0.01 and P < 0.05, respectively). Also, LH/hCG-stimulation caused higher increases in 17-OH-progesterone to T ratio in obese men than in controls, whereas no differences were observed between groups either in stimulated E2 levels or in the E2/T ratio. In all subjects, the percentage increases from baseline in the 17-OH-progesterone to T ratio were directly correlated with leptin levels or FM (r = 0.40 and r = 0.45, P < 0.01), but not with E2 or other hormonal variables. In conclusion, our studies, together with previous in vitro findings, indicate that excess of circulating leptin may be an important contributor to the development of reduced androgens in male obesity.

Childhood obesity, adipose tissue distribution, and the pediatric practitioner

The prevalence of pediatric obesity is increasing in the United States. Sequelae from pediatric obesity are increasingly being seen, and long-term complications can be anticipated. Obesity is the most common cause of abnormal growth acceleration in childhood. Obesity in females is associated with an early onset of puberty and early menarche. Puberty is now occurring earlier in females than in the past, and this is probably related either directly or indirectly to the population increase in body weight. The effect of obesity on male pubertal maturation is more variable, and obesity can lead to both early and delayed puberty. Pubertal gynecomastia is a common problem in the obese male. Many of the complications of obesity seen in adults appear to be related to increased accumulation of visceral fat. It has been proposed that subcutaneous fat may be protective against the adverse effects of visceral fat. Males typically accumulate fat in the upper segment of the body, both subcutaneously and intraabdominally. In females, adiposity is usually subcutaneous and is found particularly over the thighs, although visceral fat deposition also occurs. Gender-related patterns of fat deposition become established during puberty and show significant familial associations. There are no reliable means for assessing childhood and adolescent visceral fat other than radiologically. Noninsulin-dependent diabetes is being seen more commonly in the pediatric population. Diabetes and impaired glucose tolerance are noted particularly in obese children with a family history of diabetes. In this situation, a glucose tolerance test may be indicated, even in the presence of fasting normoglycemia. Hypertriglyceridemia and low high-density lipoprotein-cholesterol levels are the primary lipid abnormalities of obesity and are related primarily to the amount of visceral fat. Low-density lipoprotein-cholesterol levels are not typically elevated in simple obesity. The offspring of parents with early coronary disease tend to be obese. Very low-density lipoprotein and intermediate-density lipoprotein particles, which are small in size, may be important in atherogenesis but they cannot be identified in a fasting lipid panel. The propensity to atherogenesis cannot be interpreted readily from a fasting lipid panel, which therefore should be interpreted in conjunction with a family history for coronary risk factors. Hypertriglyceridemia may be indicative of increased visceral fat, familial combined hyperlipidemia, familial dyslipidemic hypertension, impaired glucose tolerance, or diabetes. Almost half of adult females with polycystic ovary syndrome are obese and many have a central distribution of body fat. This condition frequently has its origins in adolescence. It is associated with increased androgen secretion, hirsutism, menstrual abnormalities, and infertility, although these may not be present in every case. Adults with polycystic ovary syndrome adults are hyperlipidemic, have a high incidence of impaired glucose tolerance and noninsulin-dependent diabetes, and are at increased risk for coronary artery disease. Weight reduction and lipid lowering therefore are an important part of therapy. Obstructive sleep apnea with daytime somnolence is a common problem in obese adults. Pediatric studies suggest that obstructive sleep apnea occurs in approximately 17% of obese children and adolescents. Sleep disorders in the obese may be a major cause of learning disability and school failure, although this remains to be confirmed. Symptoms suggestive of a sleep disorder include snoring, restlessness at night with difficulty breathing, arousals and sweating, nocturnal enuresis, and daytime somnolence. Questions to exclude obstructive sleep apnea should be part of the history of all obese children, particularly for the morbidly obese. For many children and adolescents with mild obesity, and particularly for females, one can speculate that obesity may not be a great health risk

Endocrine aspects of obesity

As is obvious from the previous discussions, obesity is associated with a wide variety of changes in endocrine parameters (Table 1). Some of these changes, such as the reduction in SHBG without change in serum free testosterone levels, reflect merely laboratory abnormalities that may influence interpretation of diagnostic tests but have no important physiologic relevance. Other abnormalities have major clinical impact, such as hyperestrogenemia-endometrial carcinoma and hyperlipidemia-coronary artery disease. In some cases, endocrine changes in obesity are beneficial--that is, hyperestrogenemia leading to lower incidence of osteoporosis. In other cases, such as the profound suppression of growth hormone output in obesity, the physiologic relevance is unknown. Several endocrine changes in obesity, such as the impaired response of many hormones (growth hormone, prolactin, vasopressin, corticotropin) to insulin-induced hypoglycemia and elevated endorphin levels, suggest hypothalamic dysfunction. Furthermore, the failure of all of these abnormalities to be normalized after weight reduction raises the possibility of an underlying disorder leading to both endocrine dysfunction and obesity, rather than the endocrine dysfunction being simply a consequence of the obesity. Successful elucidation of the pathogenesis of obesity, which might then lead to much needed specific treatment modalities, may be advanced if we can solve some of these puzzles.

Haemorheologic and fibrinolytic evaluation in obese children and adolescents

The haemorheologic condition was evaluated in 43 obese children and 35 controls. In 18 of the obese children and in 21 controls the euglobulin lysis time (ELT) was also studied. Blood viscosity at 94.5 and at 0.204 s-1 shear rates, plasma viscosity, fibrinogen and erythrocyte filtration time were significantly higher in obese than in control children. No significant differences were observed in haematocrit levels. Triglycerides, non-esterified fatty acids (NEFA), pre-beta-lipoprotein and insulin rates were all significantly higher in obese than in control children. There were no significant differences in glycaemia and in haemoglobin A1 values. ELT, both basal and after stimulation with 1-deamino-8-D-arginine-vasopressin (DDAVP), was significantly higher in the obese than in control children. The haemorheologic disturbances together with alterations of the haemostatic balance and fibrinolysis may be an important risk factor for the development of vascular changes at paediatric age.

Growth and development in simple obesity

It is well known that fat children tend to be taller than their peers and to present a slight acceleration of skeletal and pubertal maturation. To verify this tendency and to examine some of the points that are still controversial, auxological data were studied concerning 303 subjects (141 males and 162 females, aged 6-16 years) affected by simple obesity. Subjects were seen to be taller than average by about 1 SD from 6 to 9 years of age, becoming close to or shorter than average at later ages. Height below the 10th percentile was common in 17% of males and 8% of females, due to hereditary shortness, growth delay or late puberty. Girls had early puberty and menarche; the rate of sexual maturation was variable in boys.

Hemostatic balance alterations in obese children

Fibrinolytic response to venous occlusion and other clotting parameters were studied in 34 obese children and 16 controls. The obese children (mean age 9 2/12 years) had a mean overweight of 51.8% +/- 15.6, higher blood glucose and cholesterol levels, and increased baseline and glucose-induced insulinemia. However, baseline ELT did not differ significantly; ELT after 5 min venous occlusion was 203.2 +/- 110.9 min in the obese children and 114.7 +/- 67.9 min in the control group (p less than 0.01) with a mean percent decrease respectively of 14.9% and 29.2%. Poor fibrinolytic responders did not correlate with age, overweight, or metabolic indices. Lower levels of ATIII (p less than 0.01) and no changes in F VIII: C and F VIII: R Ag were also found in the obese. Furthermore, in a larger group of 84 prepubertal obese children (mean age 10 years; mean overweight 48.2%) and in 39 normal prepubertal children (mean age 10 4/12 years) we also studied platelet aggregation capacity according to Breddin. This parameter was altered in a high proportion of the obese children (p less than 0.05). The obese children were also poor fibrinolytic responders, similarly to obese adults, and exhibited early alteration of the clotting balance.

Disordered prolactin secretion in the obese child and adolescent

Thirty-eight obese (13 prepubertal, 25 pubertal) boys, and 17 obese (16 prepubertal, 11 pubertal) girls underwent a thyroid-releasing hormone test with assay of prolactin. Obese pre-pubertal boys had prolactin levels that were significantly below those of the control group both under basal conditions and after stimulus. In the obese pubertal boys the difference was significant only after stimulus. The pituitary prolactin reserve in obese pubertal girls was lower than that of the control group. We conclude that in children and adolescents obesity may induce a hypothalamo-pituitary disorder that affects prolactin secretion.

Diagnosis of gonadotropin deficiency in adolescents: limited usefulness of a standard gonadotropin-releasing hormone test in obese boys

The pubertal maturation of five boys (Group A) who were initially thought to be gonadotropin deficient was studied over 10 to 58 months (mean 36 months) by serial physical examinatons and standard GnRH tests. Four were seen because of obesity, delayed sexual maturation, depression, and poor school performance. The other boy had acquired hypothalamic hypopituitarism at 13 years of age. Gonadotropin responses during the initial GnRH test were either absent or abnormally low as related to the degree of skeletal maturation. Subsequent responses showed progressive maturation into the normal range for adult males. These boys had normal olfaction and moderate-to-marked obesity, but initial assessment of testicular size, basal gonadotropins, and testosterone or gonadotropin responses to GnRH did not distinguish these boys from seven patients with isolated gonadotropin deficiency (Group B). Contrary to previous reports and expectations, these studies indicate that an absent or markedly blunted response to synthetic GnRH is not diagnostic of gonadotropin deficiency, even when skeletal age is 12 years or greater. Furthermore, unless a patient is hyposomic or anosmic, or has an associated anomaly such as cleft palate, isolated gonadotropin deficiency cannot be diagnosed reliably until late adolescence or early adulthood.