Growth hormone-releasing hormone messenger ribonucleic acid in the hypothalamus of the adult male rat is increased by testosterone

Since intact adult male rats have higher GH pulse amplitude than do castrated animals and since GH-releasing hormone (GHRH) secretion is predominantly responsible for the production of these GH pulses, we hypothesized that testosterone stimulates GHRH synthesis in neurons of the hypothalamus. To test this hypothesis, we compared GHRH mRNA content in individual neurons of the arcuate (ARC) and ventromedial (VMH) nuclei among groups of intact (n = 3), castrated (n = 5), and castrated testosterone-replaced (n = 5) adult male rats. Cellular GHRH mRNA content was measured by using semiquantitative in situ hybridization with an 35S-labeled cRNA probe complementary to the coding sequence of rat GHRH mRNA. Castration resulted in an approximately 35% decline in GHRH mRNA signal relative to that in intact animals in both the ARC (P less than 0.005) and VMH (P less than 0.005). Replacement with testosterone at the time of castration completely prevented the decline in both areas. Testosterone can exert effects either through activation of the androgen receptor directly or through aromatization to estradiol; therefore, we also examined the effects on GHRH mRNA of replacement with 17 beta-estradiol (n = 5) or dihydrotestosterone (DHT), a nonaromatizable androgen (n = 4). Estradiol had no effect on the castration-induced decline in GHRH mRNA in either the ARC or VMH. In contrast, DHT partially prevented the postcastration decline in GHRH in the ARC (P less than 0.005), while having no statistically significant effect on GHRH mRNA in the VMH. These results clearly indicate that testosterone stimulates expression of GHRH mRNA in neurons of the hypothalamus. Furthermore, the failure of estradiol to substitute for testosterone and the ability of DHT to substantially support GHRH mRNA suggest that testosterone exerts its effects on GHRH gene expression predominantly through direct activation of the androgen receptor.     

Valve-sparing root replacement after prior Starr-Edwards aortic valve replacement

Historically, patients with prior aortic valve replacements who subsequently present with an ascending aortic aneurysm require placement of a valve conduit. However, if the patient has a functional mechanical valve with proven long-term durability, an attempt can be made to preserve the intact valve and to graft the aneurysmal aortic root. The case is described of a patient with a previously placed Starr-Edwards aortic valve who subsequently developed a 6-cm ascending aortic aneurysm. By removing the valve ball and using the existing sewing ring, a proximal graft anastomosis was created with ease, eliminating valve excision.     

The effects of goitrogenesis, involution, and goitrogenic rechallenge on the clonogenic cell content of the rat thyroid.

A fraction of enzymatically monodispersed rat thyrocytes from untreated animals clonally proliferate into thyroid follicular units following transplantation into the subcutaneous fat pads of syngeneic recipients. During the induction of experimental goiters in rats either with 3-amino-1,2,4-triazole/iodine sufficient diet or KClO4/Remington low iodine diet, the clonogenic fractions of cells from aminotriazole goiters decreased to 1.9 x 10(-4) and KClO4 goiters to 9.8 x 10(-5) as compared to 5.8 x 10(-3) for cells from age-matched controls during the growth phase of goitrogenesis. With continued aminotriazole treatment after thyroid hyperplasia had ceased, the clonogenic fraction increased to 2.0 x 10(-3) while continued KClO4 treatment had little further effect. The changes in the clonogenic fraction induced by both regimens were reversed during involution; goitrogenic rechallenge of involuted glands led to changes in the clonogenic fraction similar to that noted during the initial challenge. The clonogenic fractions of cells from aminotriazole goiters were greater than that of cells from KClO4 goiters at all time points examined despite similar TSH levels in situ. We conclude that the rat thyroid contains a hierarchy of cells with different proliferative capacities and that the clonogenic thyrocytes possess many of the attributes of a stem-cell.     

Overnutrition induced decrease in insulin action for glucose storage: in vivo and in vitro in man

The effect of short-term overnutrition on insulin action for glucose disposal was assessed in 15 Southwest American Indians (mean wt = 74 +/- 6 kg). After two weeks of weight maintenance and again after two weeks of 62% greater caloric intake (constant ratio of fat:carbohydrate:protein), insulin action for glucose disposal was measured using the euglycemic clamp technique with plasma insulin concentrations of about 110 and 1800 uU/mL. Simultaneous indirect calorimetry was used to estimate carbohydrate oxidation and storage rates. Following overnutrition, mean weight gain was 3.0 +/- 0.2 kg, P less than 0.01. Overnutrition induced a decrease in glucose storage at the low and high insulin concentrations: 1.2 +/- 0.3 to 0.2 +/- 0.3, P less than 0.01, and 6.4 +/- 0.3 to 4.3 +/- 0.5, mg/kg FFM min, P less than 0.001. Carbohydrate oxidation was significantly increased at both insulin concentrations. The mean total insulin mediated glucose disposal rate decreased from 11.6 +/- 0.5 to 10.3 +/- 0.7, P less than 0.01, at the high insulin concentration. This decrease was due entirely to the reduction in carbohydrate storage and was correlated with increased fasting insulin concentration (r = 0.7, P less than 0.01). Overnutrition also induced a significant decrease in the percent muscle glycogen synthase active measured fasting and at the end of the high-dose insulin infusion. The results indicate that short-term overnutrition results in reduced insulin action for glucose storage and disposal which is correlated with increased fasting insulin concentrations. Reduced glycogen synthase activity may contribute to the effect of overnutrition on in vivo insulin-mediated glucose storage.     

Effect of calcium and dairy foods in high protein, energy-restricted diets on weight loss and metabolic parameters in overweight adults

OBJECTIVE: To compare the effects two high-protein (HP) diets that differ in dietary calcium and protein source on weight loss, body composition, glucose and lipid metabolism, markers of liver function, fibrinolysis and endothelial function and blood pressure. DESIGN: Randomized, parallel study (12 wk of energy restriction, 4 wk of energy balance) of high dairy protein/high-calcium (DP, 2400 mg Ca/d) and high mixed protein/moderate calcium (MP, 500 mg Ca/d) diets (5.5 MJ/d, 34% protein, 41% carbohydrate, 24% fat). SUBJECTS: In all, 50 healthy, overweight (age 25-64 y; body mass index 25-35 kg/m(2);) males (n=20) and females (n=30). RESULTS: Loss of total weight (-9.7+/-3.8 kg), fat mass (-8.3+/-0.4 kg) and lean mass (-1.6+/-0.3 kg) were independent of dietary group. Improvements in fasting insulin, lipids, systolic/diastolic blood pressure, and markers of liver function, fibrinolysis and endothelial function were independent of dietary intervention. CONCLUSIONS: Increased dietary calcium/dairy foods in an energy-restricted, HP diet does not affect weight loss or body composition. Weight reduction following increased protein diets is associated with beneficial metabolic outcomes that are not affected by protein source.     

Insulin-sensitive tyrosine kinase activity changes in parallel with plasma insulin and glucose concentrations in humans

Insulin receptor tyrosine kinase is an important step in insulin action. We examined the relationship between diet-induced changes in glucose metabolism and changes in skeletal muscle insulin-sensitive tyrosine kinase activity in 12 nondiabetic subjects. Subjects were fed a traditional, high carbohydrate Pima Indian diet and a modern, high fat western diet for 2 weeks in a randomized cross-over design. At the end of each dietary period, glucose tolerance was assessed, insulin sensitivity (SI) was estimated by Bergman's minimal model method, and insulin receptor concentration and tyrosine kinase activity were determined on lectin-purified extracts from quadriceps femoris muscle. Compared to the traditional diet, the modern diet was associated with a deterioration of glucose tolerance and an increase in glucose-induced plasma insulin levels. As expected, SI changes were associated with opposite changes in plasma insulin levels. However, the changes in maximal tyrosine kinase activity were negatively correlated with changes in SI (r = -0.69; P less than 0.01) and positively correlated with changes in plasma glucose (r = 0.70; P less than 0.01) and insulin response to glucose (r = 0.57; P less than 0.025). These results suggest that the site of diet-induced changes in insulin action is beyond the insulin-sensitive tyrosine kinase. The results further suggest that the kinase activity is modulated by prevailing plasma insulin levels.     

Borrelia burgdorferi bba66 Gene Inactivation Results in Attenuated Mouse Infection by Tick Transmission

The impact of the Borrelia burgdorferi surface-localized immunogenic lipoprotein BBA66 on vector and host infection was evaluated by inactivating the encoding gene, bba66, and characterizing the mutant phenotype throughout the natural mouse-tick-mouse cycle. The BBA66-deficient mutant isolate, Bb^ΔA66, remained infectious in mice by needle inoculation of cultured organisms, but differences in spirochete burden and pathology in the tibiotarsal joint were observed relative to the parental wild-type (WT) strain. Ixodes scapularis larvae successfully acquired Bb^ΔA66 following feeding on infected mice, and the organisms persisted in these ticks through the molt to nymphs. A series of tick transmission experiments (n = 7) demonstrated that the ability of Bb^ΔA66-infected nymphs to infect laboratory mice was significantly impaired compared to that of mice fed upon by WT-infected ticks. trans-complementation of Bb^ΔA66 with an intact copy of bba66 restored the WT infectious phenotype in mice via tick transmission. These results suggest a role for BBA66 in facilitating B. burgdorferi dissemination and transmission from the tick vector to the mammalian host as part of the disease process for Lyme borreliosis.