Quantification of cellular proliferation in experimental proliferative vitreoretinopathy.

Proliferation of host cells from around the optic nerve head has recently been implicated in the development of experimental proliferative vitreoretinopathy in rabbit eyes injected with homologous fibroblasts. We used liquid scintillation spectrometry to quantitate the tritiated thymidine incorporation into cells in the vitreous, retina, and optic nerve head following intravitreal injection of 250,000 homologous dermal fibroblasts. Cellular proliferation peaked three days after injection of the fibroblasts. The amount of tritiated thymidine incorporation that occurred three days following injection of irradiated homologous fibroblasts (incapable of cellular division) was not significantly different than that following injection of normal homologous fibroblasts, indicating that host cells were responsible for most of the cellular proliferation. Treatment with fluorouracil or triamcinolone acetonide completely arrested cellular proliferation following injection of normal fibroblasts.

Experimental diabetes in cats induced by partial pancreatectomy alone or combined with local injection of alloxan.

Experimental diabetes was produced in cats by partial pancreatectomy using a short and technically simple surgical procedure. Electrocautery was used to cauterize pancreatic blood vessels and seal free edges of remaining pancreatic tissue to prevent secretion of pancreatic enzymes into the peritoneal cavity. In a second group of animals, partial pancreatectomy was followed by local injection of alloxan into an arterial branch of the cranio-mesenteric artery. The combined procedure resulted in diabetes mellitus in 100% (8 of 8) animals as compared to only 70% (14 of 20) in those subjected to partial pancreatectomy alone. In addition, the alloxan-pancreatectomized cats had a reduced latency period prior to onset of chronic hyperglycemia (4.8 days compared to 19.3 days postoperatively in pancreatectomized cats). The diabetic cats were maintained in poor metabolic control (blood glucose approximately 300 mg/dl) by daily injections of low doses of long-acting insulin. Pancreatic enzyme supplementation was given by mouth. Weight changes and blood glucose levels were monitored carefully to maintain the health of the animals while keeping them in poor metabolic control.

A new method for vascular occlusion. Photochemical initiation of thrombosis.

A new photochemical method has been used to produce focal thrombosis and occlusion of the blood vessels on the surface of the myelin wings of rabbit retinas. Following intravenous injection of rose bengal, the vessels next to the disc on the nasal wing were exposed to filtered light (550 nm, the absorption maximum of rose bengal) for four minutes. As a control, the vessels on the temporal wing of each rabbit eye were exposed to filtered light for four minutes before the injection of rose bengal. Complete vascular occlusion was produced on the nasal wing in all eyes, with no visible alterations on the temporal wing. Progressive reopening of the arteries on the nasal wing was observed at three days, with reopening of the veins visible by seven days. Reperfusion of capillaries had occurred by 21 days. Light and electron microscopic examination of blood vessels on the nasal wing after light exposure with rose bengal showed disrupted endothelial cells in all exposed blood vessels and platelet aggregates in the arteries and arterioles. No morphologic abnormalities were observed in the temporal wings. This method should be useful in studying the effects of vascular occlusion in the retina and could lead to a new treatment modality for subretinal, iris, or corneal neovascularization.

The effect of perfluoropropane on the cornea in rabbits and cats.

The effects of perfluoropropane gas on the cornea were compared with those of sulfur hexafluoride gas following injection into the anterior chamber of rabbits and cats. Injection of 0.15 mL of gas produced a perfluoropropane bubble that lasted 22 days compared with a sulfur hexafluoride bubble that lasted seven days. The sulfur hexafluoride bubble produced corneal edema for as long as the gas was present. With perfluoropropane, corneal edema persisted even after the gas bubble disappeared. In another group of cats, multiple sequential injections of sulfur hexafluoride to maintain a gas bubble of duration comparable with the perfluoropropane bubble also produced edema as long as gas was present. Clinical corneal edema, endothelial fibrin deposition, endothelial opacities, and retrocorneal membrane were observed by slit-lamp and light, scanning, and transmission electron microscopic examinations of the corneas exposed to perfluoropropane but not of those exposed to sulfur hexafluoride. Prolonged corneal endothelial contact by perfluoropropane results in corneal edema due to endothelial dysfunction, which persists in cats probably because feline endothelium is less capable of regeneration than that of rabbit.

Fluctuation of serum concentration of 1,25-dihydroxyvitamin D3 during the menstrual cycle.

The serum concentrations of total calcium and 1,25-dihydroxyvitamin D3 were measured in seven women during a menstrual cycle. A rise in the serum level of 1,25-dihydroxyvitamin D3 was observed on day 15 of the cycle without a detectable change in the serum calcium level. The level of 1,25-dihydroxyvitamin D3 on day 15 was double the value at days 1 and 8 of the cycle. The peak of 1,25-dihydroxyvitamin D3 on day 15 was not observed in five women ingesting oral contraceptives, suggesting that ovulation or its hormonal control was involved in the peak on day 15. A small but significant fall in the serum calcium concentration occurred in the women ingesting oral contraceptives. In view of these findings the serum concentrations of 1,25-dihydroxyvitamin D in women with functioning ovaries must be interpreted in the context of the stage of the menstrual cycle when the blood sample was obtained.

A modified radioimmunoassay for 1,25-dihydroxycholecalciferol.

A radioimmunoassay for 1,25-dihydroxycholecalciferol which did not cross react with 1,25-dihydroxyergocalciferol is described. IgG fractions were prepared from the serum of rabbits that had been immunized with 1,25-dihydroxycholecalciferol-3-hemisuccinate coupled to bovine albumin. Radioligand binding by the IgG fractions was time-, temperature-, and pH-dependent. The IgG fractions had a high affinity for 1,25-dihydroxycholecalciferol but cross reacted with 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol. Vitamin D2 metabolites did not cross react in the assay when amounts up to 9 ng per tube were tested. The determination of 1,25-dihydroxycholecalciferol in human serum required an organic extraction and chromatographic isolation of the metabolite. Radioligand binding was influenced by the presence and concentration of the proteins in the phosphate buffer. The mean concentration of 1,25-dihydroxycholecalciferol in serum from normal adults was 56 (SEM 5.7) ng/L. 1,25-Dihydroxycholecalciferol was not detectable in serum from a nephrectomized subject and the concentration in serum was lower than normal in hypoparathyroid patients. Ingestion of 1,25-dihydroxycholecalciferol by nephrectomized or hypoparathyroid patients restored the concentration of 1,25-dihydroxycholecalciferol in serum to the normal range. The stability of the IgG fraction, the relatively short incubation interval, and the ability to measure 1,25-dihydroxycholecalciferol without interference from 1,25-dihydroxyergocalciferol are unique aspects of this radioimmunoassay.