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Bilateral ureteral ligation changes the blood urea nitrogen (BUN) concentration in pregnant and non-pregnant rats. Marked increases of the BUN concentration occurred in both pregnant and non-pregnant specimens after ligation. The BUN concentration in sham-ligated rats did not change from day 16 through 19 of pregnancy, but increased on day 20 of pregnancy and thereafter. There was no significant difference in BUN between ligated pregnant rats on days 16 and 17 of pregnancy and ligated non-pregnant rats. As pregnancy progressed from day 18 onward, the BUN in ligated pregnant rats decreased when compared with that of ligated non-pregnant rats, but did not reach the level in sham-ligated pregnant rats. The BUN of mothers and fetuses both in the ligated and the sham-ligated groups were similar. Amniotic fluid urea nitrogen levels were higher than in blood on late fetal days. In ligated mothers, a significant relationship between maternal BUN and the number of fetuses was noted on day 22 of pregnancy. These results suggest that the fetal kidney becomes functional for excreting urea in late fetal life.

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Sequential specular microscopy has shown that coalescence of endothelial cells occurs after thawing in cryopreserved rabbit corneas. Scanning electron microscopy of corneas studied in vitro by specular microscopy showed the same large, fused endothelial cells. As observed in the electron micrographs, these cells showed no evidence of the cell borders that had disappeared during the specular microscopic examination. These data support the reliability of our specular microscopic observations and provide additional evidence for the occurrence of fusion or coalescence of corneal endothelial cells.

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Acidic proline-rich proteins were localized histologically by means of the indirect immunoperoxidase technique in the acinar cells of parotid and submandibular gland sections of both man and Macaca fascicularis. These proteins were also identified as constituents of the long term in vivo-formed acquired pellicle on human tooth surfaces employing the same immunoperoxidase technique. Immunological quantitation of proline-rich proteins in whole and parotid saliva of 42 subjects indicates the presence of high concentrations in parotid secretions varying between 19-80 mg%, while their levels in whole saliva are significantly lower, ranging between 0-18 mg%. The concentrations of these proteins in whole saliva exhibited a negative correlation with plaque accumulation (r = -0.464) and gingival index scores (r = -0.576).

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Epithelia from the tongue dorsum of 14- to 21-day embryos, 21-day embryos, 3-week-old, and adult rats were separated from their connective tissues by incubation in balanced salt solution containing EDTA. Aliquots from total extracts of these tissues were electrophoresed on sodium dodecyl sulfate-polyacrylamide gels. Scans of gels stained with fast green (FG) revealed more than 20 peaks. Ten major peaks ranging from apparent molecular weights (MW) of 120,000 to 14,000 daltons comprised about 70% of the total protein on each gel. This report focuses primarily on two pairs of peaks, arbitrarily numbered 2 and 3 (MWs 71,000 and 69,000) and 9 and 10 (MWs 17,500 and 14,000). Peaks 9 and 10 predominated in the 15-day embryos where they comprised about 30% of the total protein. As development proceeded, there was a gradual shift in the protein profile in favor of peaks 2 and 3 until on the 20th day the relative amounts of these peaks reached a maximum and peaks 9 and 10 decreased in relative amounts. The protein profile on the 20th fetal day resembled that of the 3-week-old rats and the adults. The rise in the relative amounts of peaks 2 and 3 coincided with the morphologic appearance of large numbers of tonofilaments and the onset of cornification. When the gel was stained by a procedure specific for sulfhydryl groups, peaks 9 and 10 were especially reactive after the 18th day; plainmetric analysis revealed that these had twice the relative affinity for this stain than for FG whereas other peaks had equal or less affinity. The incorporation of [3H]cystine into peaks 9 and 10 was relatively greater than into the other proteins.

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A simple and disposable holder for electron microscope grids can be constructed from discs of silicon rubber. The discs (10 mm thick X 25 mm diameter) are scored 0.4 mm deep with a razor. Flexing the discs opens the scores for insertion of grids. Staining wells can be made from polyethylene snap-in vial tops by cutting away the nipple-like portion. After impaling the holders on the tips of a pair of forceps the grids can be washed by immersion. This holder is rigid, inert and inexpensive. It is of particular advantage for handling single-slotted grids.

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The morphogenesis of filiform papillae on rat tongue was investigated with the electron microscope. Tongue rudiments were first seen on the 12th day of gestation. At 15-17 days, dermal papillae had formed and were arranged in hexagonal array on the dorsal lingual surface. Capping each dermal papilla was a two-layered epithelium that protruded slightly above the lingual surface, thus forming the early filiform papilla. In the next stage of development, at 18-19 days of gestation, the epithelium lining the papilla had differentiated into two cell populations, one producing hard keratin, the other producing soft keratin. Some of the keratinized epithelial cells assumed a position at an acute angle to the tongue surface and extended deep into the epithelium. In the next stage, 20-21 days, a cleft appeared within these angularly oriented cells. This resulted in the division of the epithelium into keraatin-lined individual filiform papillae. Finally, the individual papillae increased in size to the adult form.

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