Major element oxides and 40Ar/39Ar plateau and isochron ages of ODP Hole 165-1001A

40Ar-39Ar incremental heating experiments and electron microprobe analyses were performed on basaltic rocks recovered from Site 1001 during Ocean Drilling Program Leg 165. The lower Nicaraguan Rise, on which Site 1001 lies, appears to be part of a larger Caribbean oceanic plateau that makes up the core of the Caribbean plate. Our results indicate an eruption age of 81 ± 1 Ma. A single flow-rim glass is tholeiitic and almost identical to the shipboard X-ray fluorescence analyses of the whole rock. The slightly porphyritic basalts have at least two populations of plagioclase, groundmass, and glomerocrystic plagioclase laths that appear to be in equilibrium with the surrounding melt and corroded tabular phenocrysts that have a higher An content (An84-86).

Glomerular number and size in autopsy kidneys: The relationship to birth weight

Background. In the Southeast United States, African Americans have an estimated incidence of hypertension and end-stage renal disease (ESRD) that is five times greater than Caucasians. Higher rates of low birth weight (LBW) among African Americans is suggested to predispose African Americans to the higher risk, possibly by reducing the number of glomeruli that develop in the kidney. This study investigates the relationships between age, race, gender, total glomerular number (N-glom), mean glomerular volume (V-glom), body surface area (BSA), and birth weight. Methods. Stereologic estimates of N-glom and V-glom were obtained using the physical disector/fractionator combination for autopsy kidneys from 37 African Americans and 19 Caucasians. Results. N-glom was normally distributed and ranged from 227,327 to 1,825,380, an 8.0-fold difference. A direct linear relationship was observed between N-glom and birth weight (r=0.423, P=0.0012) with a regression coefficient that predicted an increase of 257,426 glomeruli per kilogram increase in birth weight (alpha=0.050:0.908). Among adults there was a 4.9-fold range in V-glom , and in adults, V-glom was strongly and inversely correlated with N-glom (r=-0.640, P=0.000002). Adult V-glom showed no significant correlation with BSA for males (r=-0.0150, P=0.936), although it did for females (r=0.606, P=0.022). No racial differences in average N-glom or V-glom were observed. Conclusion. Birth weight is a strong determinant of N-glom and thereby of glomerular size in the postnatal kidney. The findings support the hypothesis that LBW by impairing nephron development is a risk factor for hypertension and ESRD in adulthood.

Determinants of glomerular volume in different cortical zones of the human kidney

Enlarged glomerular size is a feature of focal segmental glomerulosclerosis, obesity-related glomerulopathy, diabetic nephropathy, and hypertension. The distribution of glomerular volumes within different cortical zones and glomerular volume alterations with age and obesity may contribute to understanding the evolution of these diseases. We analyzed the distributions of volumes of individual glomeruli in the superficial, middle, and juxtamedullary cortex of normal human kidneys using the disector/Cavalieri method. Volumes (V-glom) of 720 nonsclerotic glomeruli (30 per kidney, 10 per zone) were estimated in autopsy kidneys of 24 American men, 12 aged 20 to 30 yr and 12 aged 51 to 69 yr. Black and white individuals were represented equally. The range of individual V-glom within subjects varied from two- to eight-fold. There were no significant zonal differences in V-glom in the young or those with body surface area (BSA) <= 2.11 m(2). In contrast, superficial glomeruli in the older age group, in those with BSA > 2.11 m(2), and in white subjects were significantly larger than juxtamedullary glomeruli. Black subjects tended toward larger V-glom than white subjects, and this difference was significant and most marked in the juxtamedullary zone and independent of age, BSA, and glomerular number. There is a wide range in individual V-glom in adults. BSA, race, and age independently influence V-glom different zones of the renal cortex. These findings might reflect processes of aging and susceptibility factors to renal disease.

Hypertension, glomerular number, and birth weight in African Americans and white subjects in the southeastern United States

Low nephron number has been related to low birth weight and hypertension. In the southeastern United States, the estimated prevalence of chronic kidney disease due to hypertension is five times greater for African Americans than white subjects. This study investigates the relationships between total glomerular number (N-glom), blood pressure, and birth weight in southeastern African Americans and white subjects. Stereological estimates of N-glom were obtained using the physical disector/fractionator technique on autopsy kidneys from 62 African American and 60 white subjects 30-65 years of age. By medical history and recorded blood pressures, 41 African Americans, and 24 white subjects were identified as hypertensive and 21 African Americans and 36 white subjects as normotensive. Mean arterial blood pressure ( MAP) was obtained on 81 and birth weights on 63 subjects. For African Americans, relationships between MAP, N-glom, and birth weight were not significant. For white subjects, they were as follows: MAP and N-glom ( r = -0.4551, P = 0.0047); Nglom and birth weight ( r = 0.5730, P = 0.0022); MAP and birth weight ( r = -0.4228, P = 0.0377). For African Americans, average N-glom of 961 840 +/- 292 750 for normotensive and 867 358 +/- 341 958 for hypertensive patients were not significantly different ( P = 0.285). For white subjects, average N-glom of 923 377 +/- 256 391 for normotensive and 754 319 +/- 329 506 for hypertensive patients were significantly different ( P = 0.03). The data indicate that low nephron number and possibly low birth weight may play a role in the development of hypertension in white subjects but not African Americans.