Gail E. Richards

Insulin resistance with acanthosis nigricans: The roles of obesity and androgen excess☆

The roles of hyperandrogenemia and obesity in the syndrome of severe insulin resistance with acanthosis nigricans were evaluated in studies of 11 females with this condition. Our results in these subjects were compared to evaluations of control subjects matched for degree of androgen excess or obesity. Fasting insulin levels were 3-, 5-, and 15-fold higher in the obese (OB), hyperandrogenemic (HO), and acanthosis nigricans (AN) groups, respectively, when compared to normal females. Responsiveness to a standard bolus of exogenous insulin was 78% of normal in the OB group, 40% of normal in the HO group, and 30% of normal in the AN group. Insulin binding to monocytes from both the OB group, and the HO group was modestly diminished primarily due to decreased receptor number. As a group, AN subjects when compared to either normal or weight-matched controls, demonstrated a significant decrease in monocyte insulin binding predominantly due to a decrease in receptor number. However, two patients in the AN group had normal insulin binding suggesting a postreceptor mechanism for the insulin resistance in at least some of these subjects. In vivo glucose utilization insulin dose response curves were determined in 3 acanthotic subjects using the euglycemic clamp technique. All 3 of these subjects had a right shift of the curve and diminished maximal utilization, consistent with combined receptor and postreceptor defects in insulin action. In evaluating the relationship between hyperandrogenemia, insulin resistance, and acanthosis nigricans, significant correlations among basal levels of plasma insulin, and both testosterone and androstenedione were demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin circadian rhythm in childhood depression

Abstract The authors examined melatonin circadian rhythms in childhood depression by measuring integrated plasma melatonin concentrations in hourly blood samples, obtained by constant withdrawal during 24 hours, in nine depressed boys and 10 control boys similar in age and pubertal development. Mean 24-hour and mean overnight melatonin concentrations were significantly lower in the depressed boys. These preliminary results indicate that melatonin secretion is decreased in childhood depression, as in adult depression. Further studies are needed to examine the usefulness of melatonin as a marker for the trait of depression.

Somatostatin limits rise in glomerular filtration rate after a protein meal

To evaluate the glomerular filtration rate (GFR) response to a protein meal in patients with diabetes and to study the role of glucagon and growth hormone, we studied inulin clearance for three 30-minute periods before and 3 hours after an 80 g protein meal in seven healthy volunteers and 10 patients with diabetes. Patients with diabetes were chosen because their renal response to such a meal has been reported to be abnormal. All had an increase in GFR and plasma glucagon levels after the protein meal. The peak rise in GFR occurred from 1 to 2 1/2 hours after the meal (mean +/- SEM, delta 26 +/- 5 mL/min/m2, controls; delta 22 +/- 7 mL/min/m2, patients with diabetes), with the mean time to normal rise in GFR occurring at 2 hours after the meal. Similarly, plasma glucagon values peaked at different times in individual patients (delta 769 +/- 532 pg/mL, controls; delta 267 +/- 69 pg/mL, patients with diabetes), with the mean plasma glucagon rise occurring 1 hours after the meal. Premeal growth hormone levels tended to be higher in the patients with diabetes (7.6 +/- 1.4 vs 2.1 +/- 0.4 ng/mL), and did not change after the meal. To allow study of the contribution of the increased plasma glucagon to the rise in GFR, eight of these patients (five with diabetes) volunteered to undergo a second GFR response test with a simultaneous infusion of somatostatin. The glucagon response was significantly lowered at all time periods during the infusion (P less than 0.05); no significant change in growth hormone occurred. Without somatostatin in these eight patients, peak increase in postmeal GFR average 20.6 +/- 1.5 mL/min/m2; with the somatostatin, peak increase in GFR was 6.0 +/- 1.8 mL/min/m2 (P less than 0.01). Neither metabolic control nor degree of albuminuria was significantly different at the time of the two studies. Thus, as has been shown in animals, somatostatin infusion limits the rise in GFR after a protein meal in humans.

Evaluation of 5-hydroxytryptophan administration as a test of pineal function in humans

We tested the hypothesis that acute 5-hydroxytryptophan (5-HTP) administration would cause an increase in concentrations of plasma melatonin to levels observed during the spontaneous nocturnal melatonin surge. We administered 5-HTP orally (5-12 mg/kg) to 10 healthy children and 5 healthy adults, and measured melatonin concentrations in plasma samples obtained every 30 min for 3-6 h. There was no appreciable increase in melatonin after 5-HTP stimulation, even though a melatonin increase has been reported in sheep treated with 5-HTP.

Effect of Growth Hormone on the Glomerular Filtration Response to a Protein Meal

The role of dietary protein intake in the pathogenesis of progressive renal disease has been recently reexamined. Studies of both animal and humans with chronic renal disease have shown that restriction of dietary protein may slow the progression of the decline in renal function. This occurs because of a decrease in intraglomerular blood flow and pressure. The mechanism of this phenomenon is not known. The effect of protein intake on renal function is thought to be hormonally mediated. Since growth hormone can increase renal blood flow as well as GFR, we tested the hypothesis that the presence of growth hormone is necessary for the increase in glomerular filtration rate (GFR) seen after the ingestion of a protein meal. We evaluated the change in GFR after a standardized mixed protein meal in 13 patients with growth hormone deficiency. Neither basal creatinine clearance after an overnight fast (76 +/- 17 ml/min/m2; mean +/- SD) nor maximum increment after a 50 g/m2 protein meal (33 +/- 11 ml/min/m2) differed in these growth hormone-deficient patients from 16 normals controls (76 +/- 18 and 30 +/- 15 ml/min/m2, respectively). Twelve hours after an injection of exogenous growth hormone, 0.06 mg/kg up to a maximum of 5 mg, the GFR response to a protein meal did not differ from the pretreatment response (77 +/- 19 and 32 +/- 17 ml/min/m2, respectively). We conclude that the presence of physiologic amounts of growth hormone is not necessary for the GFR response to a standard protein meal.

Neurotransmitters and their metabolites in the brains of fetal and newborn lambs

We tested the hypothesis that there is an orderly progressive increase in neurotransmitters in the brains of fetal and neonatal sheep. The pregnant ewes or newborns were killed with an intravenous overdose of pentobarbitone. Brains were removed immediately and frozen at -80 degrees C for later dissection and measurement of norepinephrine (NE), dopamine (DA), serotonin (5HT), homovanillic acid (HVA) and hydroxyindole acetic acid (HIAA). Fetuses were studied at 130-135 days gestation (term gestation 147 days), 140-145 days gestation and 1-5 days after birth. The only compound that was significantly different at the three ages was HIAA. Significant regional differences for NE, DA, and HVA, but not for 5HT were demonstrated.

Effect of intravenous 5-hydroxytryptophan on hypothalamic concentration of norepinephrine, dopamine, serotonin and hydroxyindole acetic acid in the fetal lamb.

To investigate the neurochemical mechanism of the response of growth hormone to 5-hydroxytryptophan (5-HTP), we administered 5-HTP (20 mg/kg) to 10 ovine fetuses (110 or 130 days old; term gestation 147 days). Ninety minutes after 5-HTP administration, and following increases in plasma growth hormone concentrations, the fetus was delivered by hysterotomy. After local anesthesia of the fetus and sacrifice by cervical spinal cord transection the hypothalamus rapidly dissected, and stored at -80 degrees C for later analysis of norepinephrine, dopamine, serotonin and hydroxyindole acetic acid. Compared to the administration of saline, 5-HTP caused a significant increase in the hypothalamic content of serotonin, and norepinephrine, at both gestational ages. 5-hydroxyindole acetic acid increased significantly only in the older fetuses. These results indicate that serotonin may not be the only neurotransmitter active in the growth hormone response to 5-HTP.